Enamel microcracks in the form of tooth damage during orthodontic debonding: a systematic review and meta-analysis of in vitro studies

Enamel microcracks in the form of tooth damage during orthodontic debonding: a systematic review... Abstract Objectives To evaluate and compare the enamel microcracks (EMCs) characteristics (qualitative and quantitative) in the form of tooth damage before and after debonding from human teeth of in vitro studies. Eligibility criteria Laboratorial studies evaluating EMCs characteristics before and after debonding metal and ceramic brackets from human teeth with intact buccal enamel. Information sources An electronic search of four databases (all databases of the Cochrane Library, CA Web of Science, MEDLINE via PubMed, and Google Scholar) and additional manual searches were carried out, without language restrictions. Studies published between 2000 and 2017 years were selected. Reference lists of the included articles were screened, and authors were contacted when necessary. Risk of bias The following six parameters were analyzed: blinding of examiner and outcome assessment, incomplete outcome data before bonding and after debonding, selective outcome reporting, and incomplete reporting of EMCs assessment. Included studies Out of 430 potentially eligible studies, 259 were screened by title and abstract, 180 were selected for full-text analysis, 14 were included in the systematic review. Seven studies were selected for the meta-analysis. Synthesis of results The results for EMCs characteristics were expressed as mean differences (MDs) with their 95 per cent confidence intervals (CIs), and calculated from random-effects meta-analyses. Debonding was associated with the increase in number (three studies, MD = 3.50, 95% CI, 2.13 to 4.87, P < 0.00001), length (seven studies, MD = 3.09 mm, 95% CI, 0.75–5.43, P < 0.00001), and width (three studies, MD = 0.39 µm, 95% CI, −0.01 to 0.79, P = 0.06) of EMCs. Considerable statistical heterogeneity was found for two forest plots evaluating the changes of number and length characteristics during debonding. Conclusions There is weak evidence indicating length and width of EMCs increase following bracket removal and the scientific evidence concerning quantitative evaluation of the number parameter before and after debonding is insufficient. However, there is a strong evidence that after debonding the number of EMCs is likely to increase. Registration No registration was performed. Introduction Rationale Several studies have shown that the bracket removal procedure leads to irreversible changes in the enamel structure despite the debonding techniques and residual adhesive removal methods used (1, 2). Due to the forces generated during debonding enamel microcracks (EMCs), a form of teeth damage, may develop and appear morphological changes of their characteristics (3–6). EMCs, quite often visible by the naked eye both by the patients and the dentists, may jeopardize the integrity of the enamel, cause stain, and plaque accumulation on the rough fractured surface, thus increasing susceptibility to carious lesions and compromising the appearance of the teeth (7, 8). Furthermore, the question about the effect of EMCs on the sensitivity of the teeth during the removal of brackets has been already raised (9). As orthodontic treatment is on the margins of pathology alleviation and esthetic improvement, it is important due to the principles of ethical provision of medical care that a clear benefit-to-harm relationship exists. Understanding this basic principle have led to a necessity of publishing scientific reports dealing with the effect of the debonding procedure on EMCs. Over the last two decades extending amount of investigations have been presented analyzing from distribution of frequency of cracks (3, 10) and increased crack numbers and lengths (11), or changes in frequency and severity of EMCs (12) to the evaluation of EMCs characteristics both qualitatively and quantitatively (4–6, 13–18). Progress in laboratory techniques introduced with methods for EMCs detection, such as transillumination, staining, ultrasound, or optical coherence tomography (10, 12, 19, 20). However, several techniques (scanning electron microscopy, stereomicroscopy, confocal optical profilometry, and optical coherence tomography, ultrasound) have been proved to be appropriate not only for visualization of EMCs, but also for measuring volumetric enamel loss, actual depth of enamel removed, or performing spot or line measurements of EMCs parameters (1, 4, 5, 11, 13–21). A variety of metal and ceramic brackets introduced in the market can meet the needs of every patient and orthodontist in respect to esthetics, comfortability, and manipulation. The effect of debonding of both types of brackets on the enamel damage and EMCs have been assessed in the orthodontic literature (3–6, 10–18, 22). Due to the physical properties of ceramics such as hardness, high bond strength, and low fracture toughness or brittleness even more attention has been paid on the removal of ceramic brackets (12, 23). However, although various EMCs parameters have been analyzed extensively before and after brackets removal in laboratorial studies, the evaluation of the changes of the EMCs characteristics in the context of a systematic review has been not undertaken. Furthermore, there is no strong evidence showing the EMCs increase following debonding, nor greater extent of enamel damage after ceramic brackets removal in comparison with metal ones. Objectives The aim of this investigation was to systematically review the literature based on in vitro studies that evaluated and compared the EMCs characteristics (both qualitative and quantitative) before and after debonding metal and ceramic brackets (with and without residual adhesive removal) using human teeth. Materials and methods Protocol and registration The protocol for the systematic review was constructed a priori based on Cochrane Handbook for Systematic Reviews of Interventions 5.1.0 (24), no registration was performed. The systematic review is reported according to the PRISMA statement (i.e., Preferred Reporting Items for Systematic Reviews and Meta-analyses) and its extension for abstracts (25, 26). Eligibility criteria Inclusion and exclusion criteria were determined for study selection before starting a systematic review (Table 1). Table 1. Eligibility criteria used for the study selection. Category  Inclusion criteria  Exclusion criteria  Sample size (participants)  Human teeth with intact buccal enamel, with no white spots; no pretreatment with any chemical agents (such as H2O2); no previous orthodontic, endodontic, or restorative treatment  Animal teeth (non-human studies) or enamel blocks (sections)  Intervention  Bonding and debonding procedures of metal and ceramic brackets Buccal brackets bonding with light-cured adhesives  Lingual brackets bonding Laser-assisted debonding Rebonding    Conventional debonding, i.e. with the use of pliers and mechanical debonding, i.e. with a universal testing machine, with or without residual adhesive removal    Comparison  Enamel surface analysis before and after debonding  Enamel surface analysis only after the removal of brackets  Outcome  Enamel microcracks (EMCs) characteristics evaluation (qualitatively and quantitatively) Direct analysis of EMCs, i.e. not through replication procedure  Various types of enamel damage evaluation, such as fracture, loss, defects, etc., except for EMCs Studies that cannot extract the available data: quantitative data on the changes of EMCs parameters following debonding  Study design  Original in vitro studies  Case reports and case series (n < 10) Reviews Abstracts Author debates Editorials Letters Commentaries Conference proceedings  Category  Inclusion criteria  Exclusion criteria  Sample size (participants)  Human teeth with intact buccal enamel, with no white spots; no pretreatment with any chemical agents (such as H2O2); no previous orthodontic, endodontic, or restorative treatment  Animal teeth (non-human studies) or enamel blocks (sections)  Intervention  Bonding and debonding procedures of metal and ceramic brackets Buccal brackets bonding with light-cured adhesives  Lingual brackets bonding Laser-assisted debonding Rebonding    Conventional debonding, i.e. with the use of pliers and mechanical debonding, i.e. with a universal testing machine, with or without residual adhesive removal    Comparison  Enamel surface analysis before and after debonding  Enamel surface analysis only after the removal of brackets  Outcome  Enamel microcracks (EMCs) characteristics evaluation (qualitatively and quantitatively) Direct analysis of EMCs, i.e. not through replication procedure  Various types of enamel damage evaluation, such as fracture, loss, defects, etc., except for EMCs Studies that cannot extract the available data: quantitative data on the changes of EMCs parameters following debonding  Study design  Original in vitro studies  Case reports and case series (n < 10) Reviews Abstracts Author debates Editorials Letters Commentaries Conference proceedings  View Large Table 1. Eligibility criteria used for the study selection. Category  Inclusion criteria  Exclusion criteria  Sample size (participants)  Human teeth with intact buccal enamel, with no white spots; no pretreatment with any chemical agents (such as H2O2); no previous orthodontic, endodontic, or restorative treatment  Animal teeth (non-human studies) or enamel blocks (sections)  Intervention  Bonding and debonding procedures of metal and ceramic brackets Buccal brackets bonding with light-cured adhesives  Lingual brackets bonding Laser-assisted debonding Rebonding    Conventional debonding, i.e. with the use of pliers and mechanical debonding, i.e. with a universal testing machine, with or without residual adhesive removal    Comparison  Enamel surface analysis before and after debonding  Enamel surface analysis only after the removal of brackets  Outcome  Enamel microcracks (EMCs) characteristics evaluation (qualitatively and quantitatively) Direct analysis of EMCs, i.e. not through replication procedure  Various types of enamel damage evaluation, such as fracture, loss, defects, etc., except for EMCs Studies that cannot extract the available data: quantitative data on the changes of EMCs parameters following debonding  Study design  Original in vitro studies  Case reports and case series (n < 10) Reviews Abstracts Author debates Editorials Letters Commentaries Conference proceedings  Category  Inclusion criteria  Exclusion criteria  Sample size (participants)  Human teeth with intact buccal enamel, with no white spots; no pretreatment with any chemical agents (such as H2O2); no previous orthodontic, endodontic, or restorative treatment  Animal teeth (non-human studies) or enamel blocks (sections)  Intervention  Bonding and debonding procedures of metal and ceramic brackets Buccal brackets bonding with light-cured adhesives  Lingual brackets bonding Laser-assisted debonding Rebonding    Conventional debonding, i.e. with the use of pliers and mechanical debonding, i.e. with a universal testing machine, with or without residual adhesive removal    Comparison  Enamel surface analysis before and after debonding  Enamel surface analysis only after the removal of brackets  Outcome  Enamel microcracks (EMCs) characteristics evaluation (qualitatively and quantitatively) Direct analysis of EMCs, i.e. not through replication procedure  Various types of enamel damage evaluation, such as fracture, loss, defects, etc., except for EMCs Studies that cannot extract the available data: quantitative data on the changes of EMCs parameters following debonding  Study design  Original in vitro studies  Case reports and case series (n < 10) Reviews Abstracts Author debates Editorials Letters Commentaries Conference proceedings  View Large Information sources, search, and study selection All databases of the Cochrane Library, CA Web of Science, MEDLINE via PubMed, and Google Scholar electronic databases were searched to identify studies that could be considered. The search terms and search strategy presented in Table 2. No limitations were applied regarding publication type, status, or language. The search was undertaken to identify literature published between January 2000 and July 2017 (inclusive). Abstracts and conference proceedings were also accessed. Reference lists of the included studies were reviewed. Authors were contacted to clarify data by e-mail when necessary. If no information was provided (no response from the corresponding author received), the investigation was excluded from the systematic review. Table 2. Databases and search terms. Database  Key Words  All databases of the Cochrane Library http://onlinelibrary.wiley.com/cochranelibrary/search  TITLE, ABSTRACT, KEYWORDS: (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Sort by relevance; dates: between 2000 and 2017  MEDLINE via PubMed http://www.ncbi.nln.nih.gov/pubmed  (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Sort by best match (relevance); publication dates: 2000/01 to 2017/07 (inclusive)  CA Web of Science http://apps.webofknowledge.com  TOPIC: (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Refined by: Research Domains: (Science Technology) AND Research areas: (Dentistry Oral Surgery Medicine); search language = Auto; sort by relevance; time span: 2000–2017  Google Scholar scholar.google.lt  With all of the words: ‘enamel’, ‘orthodontic’, ‘debonding’, ‘bracket’, ‘removal’ in anywhere in the article; at least one of the words: ‘damage’, OR ‘fracture’, OR ‘defect’, OR ‘crack’, OR ‘microcrack’, OR ‘micro-crack’; any language; without patents and citations; sort by relevance; custom range: 2000–2017; 100 most relevant articles  Database  Key Words  All databases of the Cochrane Library http://onlinelibrary.wiley.com/cochranelibrary/search  TITLE, ABSTRACT, KEYWORDS: (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Sort by relevance; dates: between 2000 and 2017  MEDLINE via PubMed http://www.ncbi.nln.nih.gov/pubmed  (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Sort by best match (relevance); publication dates: 2000/01 to 2017/07 (inclusive)  CA Web of Science http://apps.webofknowledge.com  TOPIC: (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Refined by: Research Domains: (Science Technology) AND Research areas: (Dentistry Oral Surgery Medicine); search language = Auto; sort by relevance; time span: 2000–2017  Google Scholar scholar.google.lt  With all of the words: ‘enamel’, ‘orthodontic’, ‘debonding’, ‘bracket’, ‘removal’ in anywhere in the article; at least one of the words: ‘damage’, OR ‘fracture’, OR ‘defect’, OR ‘crack’, OR ‘microcrack’, OR ‘micro-crack’; any language; without patents and citations; sort by relevance; custom range: 2000–2017; 100 most relevant articles  View Large Table 2. Databases and search terms. Database  Key Words  All databases of the Cochrane Library http://onlinelibrary.wiley.com/cochranelibrary/search  TITLE, ABSTRACT, KEYWORDS: (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Sort by relevance; dates: between 2000 and 2017  MEDLINE via PubMed http://www.ncbi.nln.nih.gov/pubmed  (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Sort by best match (relevance); publication dates: 2000/01 to 2017/07 (inclusive)  CA Web of Science http://apps.webofknowledge.com  TOPIC: (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Refined by: Research Domains: (Science Technology) AND Research areas: (Dentistry Oral Surgery Medicine); search language = Auto; sort by relevance; time span: 2000–2017  Google Scholar scholar.google.lt  With all of the words: ‘enamel’, ‘orthodontic’, ‘debonding’, ‘bracket’, ‘removal’ in anywhere in the article; at least one of the words: ‘damage’, OR ‘fracture’, OR ‘defect’, OR ‘crack’, OR ‘microcrack’, OR ‘micro-crack’; any language; without patents and citations; sort by relevance; custom range: 2000–2017; 100 most relevant articles  Database  Key Words  All databases of the Cochrane Library http://onlinelibrary.wiley.com/cochranelibrary/search  TITLE, ABSTRACT, KEYWORDS: (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Sort by relevance; dates: between 2000 and 2017  MEDLINE via PubMed http://www.ncbi.nln.nih.gov/pubmed  (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Sort by best match (relevance); publication dates: 2000/01 to 2017/07 (inclusive)  CA Web of Science http://apps.webofknowledge.com  TOPIC: (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Refined by: Research Domains: (Science Technology) AND Research areas: (Dentistry Oral Surgery Medicine); search language = Auto; sort by relevance; time span: 2000–2017  Google Scholar scholar.google.lt  With all of the words: ‘enamel’, ‘orthodontic’, ‘debonding’, ‘bracket’, ‘removal’ in anywhere in the article; at least one of the words: ‘damage’, OR ‘fracture’, OR ‘defect’, OR ‘crack’, OR ‘microcrack’, OR ‘micro-crack’; any language; without patents and citations; sort by relevance; custom range: 2000–2017; 100 most relevant articles  View Large Studies selection, extraction of data, and risk of bias assessment were performed independently and in duplicate by two investigators (I.D. and J.V.) who were not blinded to the authors and results of the study. Disagreement were resolved through discussion with conflict resolution by the third reviewer (L.L.). Data collection process and data items A data extraction form was developed to summarize the following study characteristics: type of human tooth, number of teeth per group, brackets and bonding materials, type of debonding, method for enamel surface examination, and evaluated EMCs parameters (qualitative and quantitative). At least in three studies analyzed and measured EMCs characteristics before and after brackets removal (mean values before, after debonding, and differences in mean with standard deviations, SD, and standard errors, SE) were presented in separate tables, and a meta-analysis was performed. Risk of bias in individual studies Two authors (I.D. and J.V.) independently evaluated the risk of bias inherent in each included study. The following six parameters were analyzed: blinding of examiner (performance bias), blinding of outcome assessment (detection bias), incomplete outcome data before bonding (attrition bias), incomplete outcome data after debonding (attrition bias), selective outcome reporting (reporting bias), and incomplete reporting of EMCs assessment (other bias). An assessment of risk of bias (high, unclear, low) was made for each included trial by using the Cochrane risk of bias tool that was adapted to the current systematic review (24). Summary measures and synthesis of results For the meta-analyses, the pooled effect estimates were obtained by comparing mean values of EMCs characteristics (number, length, and width) before and after debonding, irrespective of the bracket type (metal or ceramic), and residual adhesive removal (with or without it). For studies that presented results of several subgroups having one or more intervention groups in common, the results were combined by a formula according to the Cochrane Statistical Guidelines (Part 2: 7.7.3.8 Combining groups, Figure 7.7.a: Formule for combining groups; 24), and a single sample size, mean and SD values before and after debonding were obtained. In the selected investigations, only the data of interest were extracted to be analyzed in the meta-analysis. If the same sample size was used to measure number of EMCs and number of pronounced EMCs, only the data for number of cracks were selected (number of pronounced EMCs was not included in further analysis) (13, 16). In cases, where the same sample size was utilized to calculate number of EMCs after debonding without and with residual adhesive removal, only the data obtained following debonding with residual adhesive removal was extracted for meta-analysis (16). The statistical differences between groups were calculated using Review Manager (RevMan version 5.3 software, Cochrane Collaboration, Copenhagen, Denmark, 2014; 27). A random-effects model was utilized to estimate all pooled estimates, since measured values of EMCs varied across studies likely due to differences in the sample (i.e. age group of the included teeth, tooth group to which the specimens belonged) and implementation (i.e. selected bracket type, debonding instrument utilized, microscope used for enamel surface evaluation, other various operators, and settings). This model takes into account existing heterogeneity and can be considered more conservative than the fixed-effect model in the presence of heterogeneity (28, 29). Since the studies included in the meta-analysis measured the same continuous outcomes (number, length, and width of EMCs) and used the same measurement scales (millimeter scale for the length and micrometer scale for the width parameters), the results for EMCs characteristics were expressed as mean differences (MDs) with 95 per cent confidence intervals (95% CIs; 28, 29). A positive difference (after data – before data) indicated that parameters values were greater after the debonding procedure, whereas a negative difference referred to higher number, length, and width values before bonding. Significance for all statistical tests was predetermined to be P ≤ 0.05 (Z test). Results of the analyses were presented graphically with forest plots after comparisons of study designs, sample sizes, and methodologies to judge the clinical heterogeneity of the studies. The extent and impact of between-study statistical heterogeneity was evaluated by inspecting the forests plots and by calculating the Tau2 and the I2 statistic. The 95 per cent CIs around I2 were calculated (30). I2 values of more than 75 per cent would indicate considerable heterogeneity (31). Risk of bias across studies If a sufficient number of trials were identified (n > 10), standard funnel plots and contoured funnel plots would be drawn to identify publication bias. Additional analyses Sensitivity analysis was performed to define the influence of specific studies on the total calculated effect. Sensitivity analysis was expanded by: 1. including trials width adequate sample size and methodological quality, 2. excluding studies at high risk of bias. Results Study selection and study characteristics Four hundred twenty-seven records were identified through database searching and three articles were determined through additional sources (Figure 1). Following removal of duplicates, 259 records were reviewed by title and abstract. If there was any doubt, the full text of the article was read. During the screening process, 79 records were excluded as not relevant to the subject, and 180 articles were selected for full-text analysis. One hundred sixty-six studies were excluded since they did not meet the eligibility criteria due to the following reasons: case reports (2 studies), reviews, abstracts, editorials, commentaries, conference proceedings (22 studies), investigations with animal teeth or on enamel blocks (27 studies), studies dealing with various forms of enamel damage, except for EMCs (98 studies), lingual brackets (2 studies), rebonding (2 studies), the available data could not be extracted: quantitative data of the EMCs parameters (13 studies). Finally, 14 studies were selected for the systematic review (Table 3). Figure 1. View largeDownload slide PRISMA flow diagram for the selection of studies. Figure 1. View largeDownload slide PRISMA flow diagram for the selection of studies. Table 3. Summary of study characteristics of included articles. Author, Year  Type of human tooth  Number of teeth per group  Brackets and bonding  Debonding  Enamel surface evaluation  Enamel microcracks (EMCs) characteristics  Ahrari et al. (5)  Premolars  20  Ceramic brackets • Chemical retention (Fascination; Dentaurum, Ispringen, Germany) • Mechanical retention (Inspire Ice; Ormco, Orange, California, USA) Bonding with Transbond XT primer (3M Unitek; Monrovia, California, USA) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of pliers: for chemical retention brackets—Weingart pliers; for mechanical retention brackets—plastic debonding pliers • Laser-assisted debonding, i.e. by the aid of laser light (for chemical and mechanical retention brackets)  Stereomicroscope (23.5×) with a colour digital video camera Before bonding After debonding (residual adhesive removed)  Number Number of pronounced EMCs Direction Length Absolute value for number characteristic is not provided  Baherimoghadam et al. (18)  Premolars  15  Metal brackets (Dyna-Lock; 3M Unitek) Bonding with • Light Bond primer (Reliance, Itasca, Illinois, USA) and adhesive (Reliance) • Adhesion promoter Enhance LC (Reliance), Light Bond primer and adhesive  Mechanical debonding, i.e. with a universal testing machine (Zwick roll, Germany) at a crosshead speed of 0.5 mm/min (shear force)  Digital camera connected to a stereomicroscope (38×) Before bonding After debonding (residual adhesive removed)  Number Length  Bishara et al. (12)  Premolars  15  Ceramic brackets (mechanical retention; APC Plus Clarity; 3M Unitek) Bonding with Transbond Plus Self-Etching Primer (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers • With new Debonding instrument  Magnifying lens (10×) and transillumination with a fiber optic light head Before bonding After debonding (residual adhesive removed)  Number Severity (pronounced or weak) Direction Absolute values are not provided  Dumbryte et al. (6)  Incisors, canines and premolars  15  Metal brackets (Discovery; Dentaurum) Bonding with Contex Primer (Dentaurum) and Contex Lc adhesive (Dentaurum)  Conventional debonding, i.e. with the use of Utility/Weingart pliers  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Dumbryte et al. (17)  Premolars  15  Brackets • Metal (Discovery; Dentaurum) • Ceramic (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers (for metal brackets) • With Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Dumbryte et al. (15)  Premolars  30  Brackets • Metal (Discovery; Dentaurum) • Ceramic (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers (for metal brackets) • With Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Visibility Direction Location Length Absolute values are not provided  Dumbryte et al. (21)  Premolars  60  Ceramic brackets (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding with Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–00×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Habibi et al. (11)  Premolars  12  Brackets • Metal (Rocky Mountain Orthodontics; Denver, Colorado, USA) • Ceramic with chemical retention (Signature II; Rocky Mountain Orthodontics) • Ceramic with mechanical retention (Signature III; Rocky Mountain Orthodontics) Bonding with light-activated adhesive luting Mono Lok2 (Rocky Mountain Orthodontics)  Mechanical debonding, i.e. sharp-edged debonding pliers in a universal testing machine at a crosshead speed of 1 mm/min (squeezing force)  Stereomicroscope (10×) Before bonding After debonding (residual adhesive removed)  Number Length Absolute values are not provided  Heravi et al. (13)  Premolars  25  Metal brackets (Dentaurum, Pforzheim, Germany) Bonding with a no-mix orthodontic composite adhesive (Dent Zar Inc., USA)  Debonding with • Medium ligature cutter (Dentaurum, Pforzheim, Germany) • Single-blade bracket remover (Dentaurum) • Two-blade bracket remover (Dentaurum)  Stereomicroscope (23.9×) and colour digital video camera Before bonding After debonding (residual adhesive not removed)  Number Number of pronounced EMCs Direction Length  Heravi et al. (16)  Incisors  30  Metal brackets (Dentaurum, Pforzheim) Bonding with • Transbond XT adhesive (3M Unitek) • Self-adhesive composite cement Maxcem Elite (Kerr, Orange, California, USA)  Mechanical debonding, i.e. RMO i-546 remover pliers in a Zwick Z250 testing machine at a speed of 0.5 mm/min (squeezing force)  Stereomicroscope (23.9×) and digital camera Before bonding After debonding (evaluation before and after residual adhesive removal)  Number Number of pronounced EMCs Direction Length  Kitahara-Ceia et al. (3)  Premolars  15  Ceramic brackets • Mechanical retention (Clarity; 3M Unitek) • Mechanical retention with a polymer base (InVu; TP Orthodontics, LaPorte, Indiana, USA) • Chemical retention (Fascination 2; Dentaurum, Ispringen, Germany) Bonding with adhesive resin Concise (3M Unitek)  Debonding with • Howes pliers (for mechanical retention) • Orthodontic wire cutter (for polymer base) • Weingart pliers (for chemical retention)  Magnifying loupe (60×) in an optical stereomicroscope with a digital camera Before bonding After debonding (residual adhesive removed)  Distribution of frequency of cracks Absolute values are not provided  Rix et al. (10)  Premolars  40  Metal brackets (Ormco “A” company, San Diego, California, USA) Bonding with • Transbond XT primer and Transbond XT composite resin (3M Unitek, St Paul, Minnesota, USA) • Resin-modified glass ionomer cement Fuji Ortho LC (GC America Corp, Alsip, Illinois, USA) • Polyacid-modified composite resin Assure (Reliance Orthodontic Products Inc, Itasca, Illinois, USA) under dry and saliva-contaminated conditions  Mechanical debonding, i.e. shear-peel load by means of a Universal Instron testing machine with a 50-kg load cell and a crosshead speed of 2 mm/min (shear-peeling force)  Transillumination with a fiber-optic light head under 16× magnification Before bonding After debonding (residual adhesive not removed)  Frequency distribution of the extent of enamel cracking Absolute values are not provided  Salehi et al. (14)  Premolars  30  Metal brackets (Dyna-Lock; 3M Unitek) Bonding with • Light-cured composite Transbond XT (3M Unitek, Monrovia, California, USA) • No-Mix self-cured composite Unite (3M Unitek, Monrovia, California, USA)  Debonding with • Lift Off Debonding Instrument (LODI; 3M Unitek) • Bracket removing pliers (Dentaurum)  Stereomicroscope (38x) with a connected digital camera Before bonding After deboning (residual adhesive not removed)  Number Length  Shahabi et al. (4)  Premolars  25  Metal brackets (Dentarum, Inspringen, Germany) Bonding with • One layer of enamel bonding agent (EBA) • Two layers of EBA • No EBA and no-mix self-cured polymerizing composite resin (3M Unitek, Monrovia, California, USA)  Mechanical debonding, i.e. shear loading with a universal testing machine at a crosshead speed of 5 mm/min (shear force)  Stereomicroscope (20x) equipped with a camera Before bonding After debonding (residual adhesive not removed)  Number Direction Length Depth (shallow or deep) Absolute values are not provided  Author, Year  Type of human tooth  Number of teeth per group  Brackets and bonding  Debonding  Enamel surface evaluation  Enamel microcracks (EMCs) characteristics  Ahrari et al. (5)  Premolars  20  Ceramic brackets • Chemical retention (Fascination; Dentaurum, Ispringen, Germany) • Mechanical retention (Inspire Ice; Ormco, Orange, California, USA) Bonding with Transbond XT primer (3M Unitek; Monrovia, California, USA) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of pliers: for chemical retention brackets—Weingart pliers; for mechanical retention brackets—plastic debonding pliers • Laser-assisted debonding, i.e. by the aid of laser light (for chemical and mechanical retention brackets)  Stereomicroscope (23.5×) with a colour digital video camera Before bonding After debonding (residual adhesive removed)  Number Number of pronounced EMCs Direction Length Absolute value for number characteristic is not provided  Baherimoghadam et al. (18)  Premolars  15  Metal brackets (Dyna-Lock; 3M Unitek) Bonding with • Light Bond primer (Reliance, Itasca, Illinois, USA) and adhesive (Reliance) • Adhesion promoter Enhance LC (Reliance), Light Bond primer and adhesive  Mechanical debonding, i.e. with a universal testing machine (Zwick roll, Germany) at a crosshead speed of 0.5 mm/min (shear force)  Digital camera connected to a stereomicroscope (38×) Before bonding After debonding (residual adhesive removed)  Number Length  Bishara et al. (12)  Premolars  15  Ceramic brackets (mechanical retention; APC Plus Clarity; 3M Unitek) Bonding with Transbond Plus Self-Etching Primer (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers • With new Debonding instrument  Magnifying lens (10×) and transillumination with a fiber optic light head Before bonding After debonding (residual adhesive removed)  Number Severity (pronounced or weak) Direction Absolute values are not provided  Dumbryte et al. (6)  Incisors, canines and premolars  15  Metal brackets (Discovery; Dentaurum) Bonding with Contex Primer (Dentaurum) and Contex Lc adhesive (Dentaurum)  Conventional debonding, i.e. with the use of Utility/Weingart pliers  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Dumbryte et al. (17)  Premolars  15  Brackets • Metal (Discovery; Dentaurum) • Ceramic (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers (for metal brackets) • With Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Dumbryte et al. (15)  Premolars  30  Brackets • Metal (Discovery; Dentaurum) • Ceramic (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers (for metal brackets) • With Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Visibility Direction Location Length Absolute values are not provided  Dumbryte et al. (21)  Premolars  60  Ceramic brackets (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding with Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–00×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Habibi et al. (11)  Premolars  12  Brackets • Metal (Rocky Mountain Orthodontics; Denver, Colorado, USA) • Ceramic with chemical retention (Signature II; Rocky Mountain Orthodontics) • Ceramic with mechanical retention (Signature III; Rocky Mountain Orthodontics) Bonding with light-activated adhesive luting Mono Lok2 (Rocky Mountain Orthodontics)  Mechanical debonding, i.e. sharp-edged debonding pliers in a universal testing machine at a crosshead speed of 1 mm/min (squeezing force)  Stereomicroscope (10×) Before bonding After debonding (residual adhesive removed)  Number Length Absolute values are not provided  Heravi et al. (13)  Premolars  25  Metal brackets (Dentaurum, Pforzheim, Germany) Bonding with a no-mix orthodontic composite adhesive (Dent Zar Inc., USA)  Debonding with • Medium ligature cutter (Dentaurum, Pforzheim, Germany) • Single-blade bracket remover (Dentaurum) • Two-blade bracket remover (Dentaurum)  Stereomicroscope (23.9×) and colour digital video camera Before bonding After debonding (residual adhesive not removed)  Number Number of pronounced EMCs Direction Length  Heravi et al. (16)  Incisors  30  Metal brackets (Dentaurum, Pforzheim) Bonding with • Transbond XT adhesive (3M Unitek) • Self-adhesive composite cement Maxcem Elite (Kerr, Orange, California, USA)  Mechanical debonding, i.e. RMO i-546 remover pliers in a Zwick Z250 testing machine at a speed of 0.5 mm/min (squeezing force)  Stereomicroscope (23.9×) and digital camera Before bonding After debonding (evaluation before and after residual adhesive removal)  Number Number of pronounced EMCs Direction Length  Kitahara-Ceia et al. (3)  Premolars  15  Ceramic brackets • Mechanical retention (Clarity; 3M Unitek) • Mechanical retention with a polymer base (InVu; TP Orthodontics, LaPorte, Indiana, USA) • Chemical retention (Fascination 2; Dentaurum, Ispringen, Germany) Bonding with adhesive resin Concise (3M Unitek)  Debonding with • Howes pliers (for mechanical retention) • Orthodontic wire cutter (for polymer base) • Weingart pliers (for chemical retention)  Magnifying loupe (60×) in an optical stereomicroscope with a digital camera Before bonding After debonding (residual adhesive removed)  Distribution of frequency of cracks Absolute values are not provided  Rix et al. (10)  Premolars  40  Metal brackets (Ormco “A” company, San Diego, California, USA) Bonding with • Transbond XT primer and Transbond XT composite resin (3M Unitek, St Paul, Minnesota, USA) • Resin-modified glass ionomer cement Fuji Ortho LC (GC America Corp, Alsip, Illinois, USA) • Polyacid-modified composite resin Assure (Reliance Orthodontic Products Inc, Itasca, Illinois, USA) under dry and saliva-contaminated conditions  Mechanical debonding, i.e. shear-peel load by means of a Universal Instron testing machine with a 50-kg load cell and a crosshead speed of 2 mm/min (shear-peeling force)  Transillumination with a fiber-optic light head under 16× magnification Before bonding After debonding (residual adhesive not removed)  Frequency distribution of the extent of enamel cracking Absolute values are not provided  Salehi et al. (14)  Premolars  30  Metal brackets (Dyna-Lock; 3M Unitek) Bonding with • Light-cured composite Transbond XT (3M Unitek, Monrovia, California, USA) • No-Mix self-cured composite Unite (3M Unitek, Monrovia, California, USA)  Debonding with • Lift Off Debonding Instrument (LODI; 3M Unitek) • Bracket removing pliers (Dentaurum)  Stereomicroscope (38x) with a connected digital camera Before bonding After deboning (residual adhesive not removed)  Number Length  Shahabi et al. (4)  Premolars  25  Metal brackets (Dentarum, Inspringen, Germany) Bonding with • One layer of enamel bonding agent (EBA) • Two layers of EBA • No EBA and no-mix self-cured polymerizing composite resin (3M Unitek, Monrovia, California, USA)  Mechanical debonding, i.e. shear loading with a universal testing machine at a crosshead speed of 5 mm/min (shear force)  Stereomicroscope (20x) equipped with a camera Before bonding After debonding (residual adhesive not removed)  Number Direction Length Depth (shallow or deep) Absolute values are not provided  View Large Table 3. Summary of study characteristics of included articles. Author, Year  Type of human tooth  Number of teeth per group  Brackets and bonding  Debonding  Enamel surface evaluation  Enamel microcracks (EMCs) characteristics  Ahrari et al. (5)  Premolars  20  Ceramic brackets • Chemical retention (Fascination; Dentaurum, Ispringen, Germany) • Mechanical retention (Inspire Ice; Ormco, Orange, California, USA) Bonding with Transbond XT primer (3M Unitek; Monrovia, California, USA) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of pliers: for chemical retention brackets—Weingart pliers; for mechanical retention brackets—plastic debonding pliers • Laser-assisted debonding, i.e. by the aid of laser light (for chemical and mechanical retention brackets)  Stereomicroscope (23.5×) with a colour digital video camera Before bonding After debonding (residual adhesive removed)  Number Number of pronounced EMCs Direction Length Absolute value for number characteristic is not provided  Baherimoghadam et al. (18)  Premolars  15  Metal brackets (Dyna-Lock; 3M Unitek) Bonding with • Light Bond primer (Reliance, Itasca, Illinois, USA) and adhesive (Reliance) • Adhesion promoter Enhance LC (Reliance), Light Bond primer and adhesive  Mechanical debonding, i.e. with a universal testing machine (Zwick roll, Germany) at a crosshead speed of 0.5 mm/min (shear force)  Digital camera connected to a stereomicroscope (38×) Before bonding After debonding (residual adhesive removed)  Number Length  Bishara et al. (12)  Premolars  15  Ceramic brackets (mechanical retention; APC Plus Clarity; 3M Unitek) Bonding with Transbond Plus Self-Etching Primer (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers • With new Debonding instrument  Magnifying lens (10×) and transillumination with a fiber optic light head Before bonding After debonding (residual adhesive removed)  Number Severity (pronounced or weak) Direction Absolute values are not provided  Dumbryte et al. (6)  Incisors, canines and premolars  15  Metal brackets (Discovery; Dentaurum) Bonding with Contex Primer (Dentaurum) and Contex Lc adhesive (Dentaurum)  Conventional debonding, i.e. with the use of Utility/Weingart pliers  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Dumbryte et al. (17)  Premolars  15  Brackets • Metal (Discovery; Dentaurum) • Ceramic (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers (for metal brackets) • With Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Dumbryte et al. (15)  Premolars  30  Brackets • Metal (Discovery; Dentaurum) • Ceramic (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers (for metal brackets) • With Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Visibility Direction Location Length Absolute values are not provided  Dumbryte et al. (21)  Premolars  60  Ceramic brackets (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding with Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–00×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Habibi et al. (11)  Premolars  12  Brackets • Metal (Rocky Mountain Orthodontics; Denver, Colorado, USA) • Ceramic with chemical retention (Signature II; Rocky Mountain Orthodontics) • Ceramic with mechanical retention (Signature III; Rocky Mountain Orthodontics) Bonding with light-activated adhesive luting Mono Lok2 (Rocky Mountain Orthodontics)  Mechanical debonding, i.e. sharp-edged debonding pliers in a universal testing machine at a crosshead speed of 1 mm/min (squeezing force)  Stereomicroscope (10×) Before bonding After debonding (residual adhesive removed)  Number Length Absolute values are not provided  Heravi et al. (13)  Premolars  25  Metal brackets (Dentaurum, Pforzheim, Germany) Bonding with a no-mix orthodontic composite adhesive (Dent Zar Inc., USA)  Debonding with • Medium ligature cutter (Dentaurum, Pforzheim, Germany) • Single-blade bracket remover (Dentaurum) • Two-blade bracket remover (Dentaurum)  Stereomicroscope (23.9×) and colour digital video camera Before bonding After debonding (residual adhesive not removed)  Number Number of pronounced EMCs Direction Length  Heravi et al. (16)  Incisors  30  Metal brackets (Dentaurum, Pforzheim) Bonding with • Transbond XT adhesive (3M Unitek) • Self-adhesive composite cement Maxcem Elite (Kerr, Orange, California, USA)  Mechanical debonding, i.e. RMO i-546 remover pliers in a Zwick Z250 testing machine at a speed of 0.5 mm/min (squeezing force)  Stereomicroscope (23.9×) and digital camera Before bonding After debonding (evaluation before and after residual adhesive removal)  Number Number of pronounced EMCs Direction Length  Kitahara-Ceia et al. (3)  Premolars  15  Ceramic brackets • Mechanical retention (Clarity; 3M Unitek) • Mechanical retention with a polymer base (InVu; TP Orthodontics, LaPorte, Indiana, USA) • Chemical retention (Fascination 2; Dentaurum, Ispringen, Germany) Bonding with adhesive resin Concise (3M Unitek)  Debonding with • Howes pliers (for mechanical retention) • Orthodontic wire cutter (for polymer base) • Weingart pliers (for chemical retention)  Magnifying loupe (60×) in an optical stereomicroscope with a digital camera Before bonding After debonding (residual adhesive removed)  Distribution of frequency of cracks Absolute values are not provided  Rix et al. (10)  Premolars  40  Metal brackets (Ormco “A” company, San Diego, California, USA) Bonding with • Transbond XT primer and Transbond XT composite resin (3M Unitek, St Paul, Minnesota, USA) • Resin-modified glass ionomer cement Fuji Ortho LC (GC America Corp, Alsip, Illinois, USA) • Polyacid-modified composite resin Assure (Reliance Orthodontic Products Inc, Itasca, Illinois, USA) under dry and saliva-contaminated conditions  Mechanical debonding, i.e. shear-peel load by means of a Universal Instron testing machine with a 50-kg load cell and a crosshead speed of 2 mm/min (shear-peeling force)  Transillumination with a fiber-optic light head under 16× magnification Before bonding After debonding (residual adhesive not removed)  Frequency distribution of the extent of enamel cracking Absolute values are not provided  Salehi et al. (14)  Premolars  30  Metal brackets (Dyna-Lock; 3M Unitek) Bonding with • Light-cured composite Transbond XT (3M Unitek, Monrovia, California, USA) • No-Mix self-cured composite Unite (3M Unitek, Monrovia, California, USA)  Debonding with • Lift Off Debonding Instrument (LODI; 3M Unitek) • Bracket removing pliers (Dentaurum)  Stereomicroscope (38x) with a connected digital camera Before bonding After deboning (residual adhesive not removed)  Number Length  Shahabi et al. (4)  Premolars  25  Metal brackets (Dentarum, Inspringen, Germany) Bonding with • One layer of enamel bonding agent (EBA) • Two layers of EBA • No EBA and no-mix self-cured polymerizing composite resin (3M Unitek, Monrovia, California, USA)  Mechanical debonding, i.e. shear loading with a universal testing machine at a crosshead speed of 5 mm/min (shear force)  Stereomicroscope (20x) equipped with a camera Before bonding After debonding (residual adhesive not removed)  Number Direction Length Depth (shallow or deep) Absolute values are not provided  Author, Year  Type of human tooth  Number of teeth per group  Brackets and bonding  Debonding  Enamel surface evaluation  Enamel microcracks (EMCs) characteristics  Ahrari et al. (5)  Premolars  20  Ceramic brackets • Chemical retention (Fascination; Dentaurum, Ispringen, Germany) • Mechanical retention (Inspire Ice; Ormco, Orange, California, USA) Bonding with Transbond XT primer (3M Unitek; Monrovia, California, USA) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of pliers: for chemical retention brackets—Weingart pliers; for mechanical retention brackets—plastic debonding pliers • Laser-assisted debonding, i.e. by the aid of laser light (for chemical and mechanical retention brackets)  Stereomicroscope (23.5×) with a colour digital video camera Before bonding After debonding (residual adhesive removed)  Number Number of pronounced EMCs Direction Length Absolute value for number characteristic is not provided  Baherimoghadam et al. (18)  Premolars  15  Metal brackets (Dyna-Lock; 3M Unitek) Bonding with • Light Bond primer (Reliance, Itasca, Illinois, USA) and adhesive (Reliance) • Adhesion promoter Enhance LC (Reliance), Light Bond primer and adhesive  Mechanical debonding, i.e. with a universal testing machine (Zwick roll, Germany) at a crosshead speed of 0.5 mm/min (shear force)  Digital camera connected to a stereomicroscope (38×) Before bonding After debonding (residual adhesive removed)  Number Length  Bishara et al. (12)  Premolars  15  Ceramic brackets (mechanical retention; APC Plus Clarity; 3M Unitek) Bonding with Transbond Plus Self-Etching Primer (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers • With new Debonding instrument  Magnifying lens (10×) and transillumination with a fiber optic light head Before bonding After debonding (residual adhesive removed)  Number Severity (pronounced or weak) Direction Absolute values are not provided  Dumbryte et al. (6)  Incisors, canines and premolars  15  Metal brackets (Discovery; Dentaurum) Bonding with Contex Primer (Dentaurum) and Contex Lc adhesive (Dentaurum)  Conventional debonding, i.e. with the use of Utility/Weingart pliers  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Dumbryte et al. (17)  Premolars  15  Brackets • Metal (Discovery; Dentaurum) • Ceramic (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers (for metal brackets) • With Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Dumbryte et al. (15)  Premolars  30  Brackets • Metal (Discovery; Dentaurum) • Ceramic (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers (for metal brackets) • With Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Visibility Direction Location Length Absolute values are not provided  Dumbryte et al. (21)  Premolars  60  Ceramic brackets (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding with Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–00×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Habibi et al. (11)  Premolars  12  Brackets • Metal (Rocky Mountain Orthodontics; Denver, Colorado, USA) • Ceramic with chemical retention (Signature II; Rocky Mountain Orthodontics) • Ceramic with mechanical retention (Signature III; Rocky Mountain Orthodontics) Bonding with light-activated adhesive luting Mono Lok2 (Rocky Mountain Orthodontics)  Mechanical debonding, i.e. sharp-edged debonding pliers in a universal testing machine at a crosshead speed of 1 mm/min (squeezing force)  Stereomicroscope (10×) Before bonding After debonding (residual adhesive removed)  Number Length Absolute values are not provided  Heravi et al. (13)  Premolars  25  Metal brackets (Dentaurum, Pforzheim, Germany) Bonding with a no-mix orthodontic composite adhesive (Dent Zar Inc., USA)  Debonding with • Medium ligature cutter (Dentaurum, Pforzheim, Germany) • Single-blade bracket remover (Dentaurum) • Two-blade bracket remover (Dentaurum)  Stereomicroscope (23.9×) and colour digital video camera Before bonding After debonding (residual adhesive not removed)  Number Number of pronounced EMCs Direction Length  Heravi et al. (16)  Incisors  30  Metal brackets (Dentaurum, Pforzheim) Bonding with • Transbond XT adhesive (3M Unitek) • Self-adhesive composite cement Maxcem Elite (Kerr, Orange, California, USA)  Mechanical debonding, i.e. RMO i-546 remover pliers in a Zwick Z250 testing machine at a speed of 0.5 mm/min (squeezing force)  Stereomicroscope (23.9×) and digital camera Before bonding After debonding (evaluation before and after residual adhesive removal)  Number Number of pronounced EMCs Direction Length  Kitahara-Ceia et al. (3)  Premolars  15  Ceramic brackets • Mechanical retention (Clarity; 3M Unitek) • Mechanical retention with a polymer base (InVu; TP Orthodontics, LaPorte, Indiana, USA) • Chemical retention (Fascination 2; Dentaurum, Ispringen, Germany) Bonding with adhesive resin Concise (3M Unitek)  Debonding with • Howes pliers (for mechanical retention) • Orthodontic wire cutter (for polymer base) • Weingart pliers (for chemical retention)  Magnifying loupe (60×) in an optical stereomicroscope with a digital camera Before bonding After debonding (residual adhesive removed)  Distribution of frequency of cracks Absolute values are not provided  Rix et al. (10)  Premolars  40  Metal brackets (Ormco “A” company, San Diego, California, USA) Bonding with • Transbond XT primer and Transbond XT composite resin (3M Unitek, St Paul, Minnesota, USA) • Resin-modified glass ionomer cement Fuji Ortho LC (GC America Corp, Alsip, Illinois, USA) • Polyacid-modified composite resin Assure (Reliance Orthodontic Products Inc, Itasca, Illinois, USA) under dry and saliva-contaminated conditions  Mechanical debonding, i.e. shear-peel load by means of a Universal Instron testing machine with a 50-kg load cell and a crosshead speed of 2 mm/min (shear-peeling force)  Transillumination with a fiber-optic light head under 16× magnification Before bonding After debonding (residual adhesive not removed)  Frequency distribution of the extent of enamel cracking Absolute values are not provided  Salehi et al. (14)  Premolars  30  Metal brackets (Dyna-Lock; 3M Unitek) Bonding with • Light-cured composite Transbond XT (3M Unitek, Monrovia, California, USA) • No-Mix self-cured composite Unite (3M Unitek, Monrovia, California, USA)  Debonding with • Lift Off Debonding Instrument (LODI; 3M Unitek) • Bracket removing pliers (Dentaurum)  Stereomicroscope (38x) with a connected digital camera Before bonding After deboning (residual adhesive not removed)  Number Length  Shahabi et al. (4)  Premolars  25  Metal brackets (Dentarum, Inspringen, Germany) Bonding with • One layer of enamel bonding agent (EBA) • Two layers of EBA • No EBA and no-mix self-cured polymerizing composite resin (3M Unitek, Monrovia, California, USA)  Mechanical debonding, i.e. shear loading with a universal testing machine at a crosshead speed of 5 mm/min (shear force)  Stereomicroscope (20x) equipped with a camera Before bonding After debonding (residual adhesive not removed)  Number Direction Length Depth (shallow or deep) Absolute values are not provided  View Large Risk of bias within studies The risk of bias for the fourteen studies included is summarized in Table 4 and Figure 2 (3–6, 10–18, 21). Seven trials were considered as being in high risk of bias, with the most problematic parameter being selective outcome reporting (in seven studies, 4–6, 12, 14, 16, 18). The rest seven trials were judged as being in unclear risk of bias (3, 10, 11, 13, 15, 17, 21). Table 4. Risk of bias assessment. Study  Blinding of examiner  Blinding of outcome assessment  Incomplete outcome data before bonding  Incomplete outcome data after debonding  Selective outcome reporting  Incomplete reporting of enamel microcracks assessment  Ahrari et al. (5)  Unclear  Unclear  Unclear  High  High  Low  Baherimoghadam et al. (18)  Unclear  Unclear  Unclear  Unclear  High  Low  Bishara et al. (12)  Unclear  Unclear  Low  Low  High  Low  Dumbryte et al. (6)  Unclear  Unclear  Low  Low  High  Low  Dumbryte et al. (17)  Unclear  Unclear  Unclear  Unclear  Unclear  Low  Dumbryte et al. (15)  Unclear  Unclear  Low  Low  Low  Low  Dumbryte et al. (21)  Unclear  Unclear  Low  Low  Low  Low  Habibi et al. (11)  Unclear  Unclear  Low  Low  Low  Low  Heravi et al. (13)  Unclear  Unclear  Unclear  Unclear  Low  Low  Heravi et al. (16)  Unclear  Unclear  Unclear  Unclear  High  Low  Kitahara-Ceia et al. (3)  Unclear  Low  Unclear  Unclear  Low  Low  Rix et al. (10)  Unclear  Unclear  Low  Low  Low  Low  Salehi et al. (14)  Unclear  Unclear  Unclear  Unclear  High  Low  Shahabi et al. (4)  Unclear  Unclear  Unclear  Unclear  High  High  Study  Blinding of examiner  Blinding of outcome assessment  Incomplete outcome data before bonding  Incomplete outcome data after debonding  Selective outcome reporting  Incomplete reporting of enamel microcracks assessment  Ahrari et al. (5)  Unclear  Unclear  Unclear  High  High  Low  Baherimoghadam et al. (18)  Unclear  Unclear  Unclear  Unclear  High  Low  Bishara et al. (12)  Unclear  Unclear  Low  Low  High  Low  Dumbryte et al. (6)  Unclear  Unclear  Low  Low  High  Low  Dumbryte et al. (17)  Unclear  Unclear  Unclear  Unclear  Unclear  Low  Dumbryte et al. (15)  Unclear  Unclear  Low  Low  Low  Low  Dumbryte et al. (21)  Unclear  Unclear  Low  Low  Low  Low  Habibi et al. (11)  Unclear  Unclear  Low  Low  Low  Low  Heravi et al. (13)  Unclear  Unclear  Unclear  Unclear  Low  Low  Heravi et al. (16)  Unclear  Unclear  Unclear  Unclear  High  Low  Kitahara-Ceia et al. (3)  Unclear  Low  Unclear  Unclear  Low  Low  Rix et al. (10)  Unclear  Unclear  Low  Low  Low  Low  Salehi et al. (14)  Unclear  Unclear  Unclear  Unclear  High  Low  Shahabi et al. (4)  Unclear  Unclear  Unclear  Unclear  High  High  View Large Table 4. Risk of bias assessment. Study  Blinding of examiner  Blinding of outcome assessment  Incomplete outcome data before bonding  Incomplete outcome data after debonding  Selective outcome reporting  Incomplete reporting of enamel microcracks assessment  Ahrari et al. (5)  Unclear  Unclear  Unclear  High  High  Low  Baherimoghadam et al. (18)  Unclear  Unclear  Unclear  Unclear  High  Low  Bishara et al. (12)  Unclear  Unclear  Low  Low  High  Low  Dumbryte et al. (6)  Unclear  Unclear  Low  Low  High  Low  Dumbryte et al. (17)  Unclear  Unclear  Unclear  Unclear  Unclear  Low  Dumbryte et al. (15)  Unclear  Unclear  Low  Low  Low  Low  Dumbryte et al. (21)  Unclear  Unclear  Low  Low  Low  Low  Habibi et al. (11)  Unclear  Unclear  Low  Low  Low  Low  Heravi et al. (13)  Unclear  Unclear  Unclear  Unclear  Low  Low  Heravi et al. (16)  Unclear  Unclear  Unclear  Unclear  High  Low  Kitahara-Ceia et al. (3)  Unclear  Low  Unclear  Unclear  Low  Low  Rix et al. (10)  Unclear  Unclear  Low  Low  Low  Low  Salehi et al. (14)  Unclear  Unclear  Unclear  Unclear  High  Low  Shahabi et al. (4)  Unclear  Unclear  Unclear  Unclear  High  High  Study  Blinding of examiner  Blinding of outcome assessment  Incomplete outcome data before bonding  Incomplete outcome data after debonding  Selective outcome reporting  Incomplete reporting of enamel microcracks assessment  Ahrari et al. (5)  Unclear  Unclear  Unclear  High  High  Low  Baherimoghadam et al. (18)  Unclear  Unclear  Unclear  Unclear  High  Low  Bishara et al. (12)  Unclear  Unclear  Low  Low  High  Low  Dumbryte et al. (6)  Unclear  Unclear  Low  Low  High  Low  Dumbryte et al. (17)  Unclear  Unclear  Unclear  Unclear  Unclear  Low  Dumbryte et al. (15)  Unclear  Unclear  Low  Low  Low  Low  Dumbryte et al. (21)  Unclear  Unclear  Low  Low  Low  Low  Habibi et al. (11)  Unclear  Unclear  Low  Low  Low  Low  Heravi et al. (13)  Unclear  Unclear  Unclear  Unclear  Low  Low  Heravi et al. (16)  Unclear  Unclear  Unclear  Unclear  High  Low  Kitahara-Ceia et al. (3)  Unclear  Low  Unclear  Unclear  Low  Low  Rix et al. (10)  Unclear  Unclear  Low  Low  Low  Low  Salehi et al. (14)  Unclear  Unclear  Unclear  Unclear  High  Low  Shahabi et al. (4)  Unclear  Unclear  Unclear  Unclear  High  High  View Large Figure 2. View largeDownload slide Risk of bias summary. Figure 2. View largeDownload slide Risk of bias summary. Results of individual studies and synthesis of results Characteristics of the 14 studies included in the systematic review are presented in Table 3. All investigations were published between 2001 and 2017. Twelve trials were performed on human premolar teeth (3–5, 10–15, 17, 18, 21), one study used incisors for its’ sample size (16) and in one investigation teeth from various tooth groups were selected (6). The distribution of metal and ceramic brackets among the studies was as follows: metal brackets were chosen in seven studies (4, 6, 10, 13, 14, 16, 18), ceramic brackets were used in four trials (3, 5, 12, 21), both metal and ceramic brackets were selected in three investigations (11, 15, 17). For the debonding procedure, either conventional bracket removal method, i.e. with the use of appropriate pliers by hand (3, 5, 6, 12–15, 17, 21) or mechanical debonding, i.e. with the help of testing machine was chosen (4, 10, 11, 16, 18). After debonding residual adhesive was removed in nine studies (3, 5, 6, 11, 12, 15, 17, 18, 21), while four investigations evaluated EMCs with left adhesive remnants on the enamel surface (4, 10, 13, 14). In one trial EMCs characteristics were measured before and following residual adhesive removal (16). In the majority of studies stereomicroscopy technique was utilized for the EMCs visualization and analysis (3–5, 11, 13, 14, 16, 18), followed by scanning electron microscopy (6, 15, 17, 21) and transillumination methods (10, 12). Length of EMCs was the most frequently examined parameter (4–6, 11, 13–18, 21), followed by number (4, 5, 11–14, 16, 18), direction (4, 5, 12, 13, 15, 16), location (6, 15, 17, 21), and width (6, 17, 21) evaluation. However, six trials did not provide absolute values for measured EMCs and were not included in the meta-analysis (3, 4, 10–12, 15). One study was excluded from further quantitative synthesis due to inadequate statistical analysis (high standard deviations for not described reasons) (18). Seven studies were included in the meta-analysis: four investigations evaluated number of EMCs (5, 13, 14, 16), seven studies measured length (5, 6, 13, 14, 16, 17, 21), and three trials examined width parameter (6, 17, 21). One study did not provide absolute values for number of EMCs, thus these results were not included in further analysis (5). Changes in the number of EMCs were calculated only during debonding metal brackets (13, 14, 16), while length and width characteristics were evaluated following metal (length—five investigations (6, 13, 14, 16, 17), width—two studies, 6, 17) and ceramic brackets removal (length—three trials (5, 17, 21), width—two studies, 17, 21). In four trials enamel surface analysis was performed after debonding followed by residual adhesive removal (5, 6, 17, 21), in two investigations EMCs were evaluated without adhesive remnants elimination after brackets removal (13, 14), and in one trial EMCs characteristics were measured before and following residual adhesive removal (16). Recorded number, length, and width values of EMCs before and after debonding are presented in Table 5. Table 5. Mean number, length, and width values of enamel microcracks before and after debonding, and difference in means. Study  Number of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (6)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (17)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (21)  —  —  —  —  —  —  —  —  —  Heravi et al. (13)  75  4.70  2.43  75  7.63  2.96  2.93  2.71  0.44  Heravi et al. (16)  60  2.35  0.93  60  7.04  1.29  4.69  1.13  0.21  Salehi et al. (14)  120  2.20  1.26  120  5.02  2.61  2.82  2.05  0.26    Length of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  40  6.50  3.27  36  12.30  3.67  5.80  3.49  0.78  Dumbryte et al. (6)  15  5.94  3.09  15  5.80  3.07  −0.14  3.08  1.12  Dumbryte et al. (17)  60  2.67  1.71  60  2.49  1.80  −0.18  1.76  0.32  Dumbryte et al. (21)  30  4.02  2.20  30  4.14  2.33  0.12  2.27  0.59  Heravi et al. (13)  75  8.67  4.0175  75  11.97  4.48  3.30  4.26  0.69  Heravi et al. (16)  60  5.40  1.50  60  9.65  1.71  4.25  1.61  0.29  Salehi et al. (14)  120  4.08  2.55  120  12.42  6.64  8.34  5.03  0.65    Width of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (6)  15  9.22  5.31  15  13.04  10.91  3.82  8.58  3.13  Dumbryte et al. (17)  60  1.81  1.06  60  2.18  1.23  0.37  1.15  0.21  Dumbryte et al. (21)  30  3.22  3.71  30  3.77  3.91  0.55  3.81  0.98  Heravi et al. (13)  —  —  —  —  —  —  —  —  —  Heravi et al. (16)  —  —  —  —  —  —  —  —  —  Salehi et al. (14)  —  —  —  —  —  —  —  —  —  Study  Number of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (6)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (17)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (21)  —  —  —  —  —  —  —  —  —  Heravi et al. (13)  75  4.70  2.43  75  7.63  2.96  2.93  2.71  0.44  Heravi et al. (16)  60  2.35  0.93  60  7.04  1.29  4.69  1.13  0.21  Salehi et al. (14)  120  2.20  1.26  120  5.02  2.61  2.82  2.05  0.26    Length of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  40  6.50  3.27  36  12.30  3.67  5.80  3.49  0.78  Dumbryte et al. (6)  15  5.94  3.09  15  5.80  3.07  −0.14  3.08  1.12  Dumbryte et al. (17)  60  2.67  1.71  60  2.49  1.80  −0.18  1.76  0.32  Dumbryte et al. (21)  30  4.02  2.20  30  4.14  2.33  0.12  2.27  0.59  Heravi et al. (13)  75  8.67  4.0175  75  11.97  4.48  3.30  4.26  0.69  Heravi et al. (16)  60  5.40  1.50  60  9.65  1.71  4.25  1.61  0.29  Salehi et al. (14)  120  4.08  2.55  120  12.42  6.64  8.34  5.03  0.65    Width of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (6)  15  9.22  5.31  15  13.04  10.91  3.82  8.58  3.13  Dumbryte et al. (17)  60  1.81  1.06  60  2.18  1.23  0.37  1.15  0.21  Dumbryte et al. (21)  30  3.22  3.71  30  3.77  3.91  0.55  3.81  0.98  Heravi et al. (13)  —  —  —  —  —  —  —  —  —  Heravi et al. (16)  —  —  —  —  —  —  —  —  —  Salehi et al. (14)  —  —  —  —  —  —  —  —  —  Number of enamel microcracks was not evaluated in the following studies: Ahrari et al. (examined number parameter, but did not provide absolute value for this characteristic; 5), Dumbryte et al. (6), Dumbryte et al. (17), and Dumbryte et al. (21). Width of enamel microcracks was not evaluated in the following studies: Ahrari et al. (5), Heravi et al. (13), Heravi et al. (16), Salehi et al. (14). SD, Standard deviation; SE, Standard error. View Large Table 5. Mean number, length, and width values of enamel microcracks before and after debonding, and difference in means. Study  Number of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (6)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (17)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (21)  —  —  —  —  —  —  —  —  —  Heravi et al. (13)  75  4.70  2.43  75  7.63  2.96  2.93  2.71  0.44  Heravi et al. (16)  60  2.35  0.93  60  7.04  1.29  4.69  1.13  0.21  Salehi et al. (14)  120  2.20  1.26  120  5.02  2.61  2.82  2.05  0.26    Length of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  40  6.50  3.27  36  12.30  3.67  5.80  3.49  0.78  Dumbryte et al. (6)  15  5.94  3.09  15  5.80  3.07  −0.14  3.08  1.12  Dumbryte et al. (17)  60  2.67  1.71  60  2.49  1.80  −0.18  1.76  0.32  Dumbryte et al. (21)  30  4.02  2.20  30  4.14  2.33  0.12  2.27  0.59  Heravi et al. (13)  75  8.67  4.0175  75  11.97  4.48  3.30  4.26  0.69  Heravi et al. (16)  60  5.40  1.50  60  9.65  1.71  4.25  1.61  0.29  Salehi et al. (14)  120  4.08  2.55  120  12.42  6.64  8.34  5.03  0.65    Width of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (6)  15  9.22  5.31  15  13.04  10.91  3.82  8.58  3.13  Dumbryte et al. (17)  60  1.81  1.06  60  2.18  1.23  0.37  1.15  0.21  Dumbryte et al. (21)  30  3.22  3.71  30  3.77  3.91  0.55  3.81  0.98  Heravi et al. (13)  —  —  —  —  —  —  —  —  —  Heravi et al. (16)  —  —  —  —  —  —  —  —  —  Salehi et al. (14)  —  —  —  —  —  —  —  —  —  Study  Number of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (6)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (17)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (21)  —  —  —  —  —  —  —  —  —  Heravi et al. (13)  75  4.70  2.43  75  7.63  2.96  2.93  2.71  0.44  Heravi et al. (16)  60  2.35  0.93  60  7.04  1.29  4.69  1.13  0.21  Salehi et al. (14)  120  2.20  1.26  120  5.02  2.61  2.82  2.05  0.26    Length of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  40  6.50  3.27  36  12.30  3.67  5.80  3.49  0.78  Dumbryte et al. (6)  15  5.94  3.09  15  5.80  3.07  −0.14  3.08  1.12  Dumbryte et al. (17)  60  2.67  1.71  60  2.49  1.80  −0.18  1.76  0.32  Dumbryte et al. (21)  30  4.02  2.20  30  4.14  2.33  0.12  2.27  0.59  Heravi et al. (13)  75  8.67  4.0175  75  11.97  4.48  3.30  4.26  0.69  Heravi et al. (16)  60  5.40  1.50  60  9.65  1.71  4.25  1.61  0.29  Salehi et al. (14)  120  4.08  2.55  120  12.42  6.64  8.34  5.03  0.65    Width of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (6)  15  9.22  5.31  15  13.04  10.91  3.82  8.58  3.13  Dumbryte et al. (17)  60  1.81  1.06  60  2.18  1.23  0.37  1.15  0.21  Dumbryte et al. (21)  30  3.22  3.71  30  3.77  3.91  0.55  3.81  0.98  Heravi et al. (13)  —  —  —  —  —  —  —  —  —  Heravi et al. (16)  —  —  —  —  —  —  —  —  —  Salehi et al. (14)  —  —  —  —  —  —  —  —  —  Number of enamel microcracks was not evaluated in the following studies: Ahrari et al. (examined number parameter, but did not provide absolute value for this characteristic; 5), Dumbryte et al. (6), Dumbryte et al. (17), and Dumbryte et al. (21). Width of enamel microcracks was not evaluated in the following studies: Ahrari et al. (5), Heravi et al. (13), Heravi et al. (16), Salehi et al. (14). SD, Standard deviation; SE, Standard error. View Large The meta-analysis was performed considering the overall analysis for number, length, and width parameters. Due to the limited number of studies, no subgroup analyses could be performed with respect to the bracket type and residual adhesive removal. As far as changes in number of EMCs are concerned, following bracket removal number of EMCs increased (MD = 3.50, 95% CI, 2.13–4.87, P < 0.00001) compared to the values before the bonding procedure (Figure 3; Table 6). Figure 3. View largeDownload slide Forest plot of the mean difference (after debonding data – before bonding data) of the number parameter based on the random-effects model together with the 95 per cent confidence interval (CI). Figure 3. View largeDownload slide Forest plot of the mean difference (after debonding data – before bonding data) of the number parameter based on the random-effects model together with the 95 per cent confidence interval (CI). With regard to the changes in the length characteristic, debonding effect was also evident. The length of EMCs was on average 3.09 mm greater than before bracket removal (Figure 4; Table 6). Figure 4. View largeDownload slide Forest plot of the mean difference (after debonding data – before bonding data) of the length parameter based on the random-effects model together with the 95 per cent confidence interval (CI). Figure 4. View largeDownload slide Forest plot of the mean difference (after debonding data – before bonding data) of the length parameter based on the random-effects model together with the 95 per cent confidence interval (CI). Table 6. Details of the performed meta-analyses with tests on heterogeneity. No.  Variable  Studies  Effect size  Heterogeneity  MD  95% CIs  P  Tau2  I2 (%)  95% CIs  P  1.  Number  3  3.50  2.13, 4.87  <0.00001  1.37  94  87.2, 97.6  <0.00001  2.  Length  7  3.09  0.75, 5.43  0.010  9.52  97  96.1, 98.2  <0.00001  3.  Width  3  0.39  −0.01, 0.79  0.06  0.00  0  0.0, 89.6  0.54  No.  Variable  Studies  Effect size  Heterogeneity  MD  95% CIs  P  Tau2  I2 (%)  95% CIs  P  1.  Number  3  3.50  2.13, 4.87  <0.00001  1.37  94  87.2, 97.6  <0.00001  2.  Length  7  3.09  0.75, 5.43  0.010  9.52  97  96.1, 98.2  <0.00001  3.  Width  3  0.39  −0.01, 0.79  0.06  0.00  0  0.0, 89.6  0.54  CIs, confidence intervals; MD, mean difference. View Large Table 6. Details of the performed meta-analyses with tests on heterogeneity. No.  Variable  Studies  Effect size  Heterogeneity  MD  95% CIs  P  Tau2  I2 (%)  95% CIs  P  1.  Number  3  3.50  2.13, 4.87  <0.00001  1.37  94  87.2, 97.6  <0.00001  2.  Length  7  3.09  0.75, 5.43  0.010  9.52  97  96.1, 98.2  <0.00001  3.  Width  3  0.39  −0.01, 0.79  0.06  0.00  0  0.0, 89.6  0.54  No.  Variable  Studies  Effect size  Heterogeneity  MD  95% CIs  P  Tau2  I2 (%)  95% CIs  P  1.  Number  3  3.50  2.13, 4.87  <0.00001  1.37  94  87.2, 97.6  <0.00001  2.  Length  7  3.09  0.75, 5.43  0.010  9.52  97  96.1, 98.2  <0.00001  3.  Width  3  0.39  −0.01, 0.79  0.06  0.00  0  0.0, 89.6  0.54  CIs, confidence intervals; MD, mean difference. View Large Finally, for the width parameter the increase was observed following debonding, however the change was statistically insignificant (MD = 0.39 µm, 95% CI, −0.01 to 0.79, P = 0.06, Figure 5; Table 6). Figure 5. View largeDownload slide Forest plot of the mean difference (after debonding data – before bonding data) of the width parameter based on the random-effects model together with the 95 per cent confidence interval (CI). Figure 5. View largeDownload slide Forest plot of the mean difference (after debonding data – before bonding data) of the width parameter based on the random-effects model together with the 95 per cent confidence interval (CI). Risk of bias across studies Risk of bias across studies could not be performed due to limited number of trials. Additional analyses Sensitivity analysis showed that the included investigations dealing with the length and width parameters had a balanced impact on the calculated MD. With regard to the number of EMCs, further analysis was undertaken to gauge the exclusion of the study by Heravi et al. (16). The results did not change significantly (MD = 2.85, 95% CI, 2.41–3.29, P < 0.00001), however no statistical heterogeneity was found (Tau2 = 0, I2 = 0%, P = 0.83). Further sensitivity analysis revealed that if the study by Baherimoghadam et al. (18) was included in the meta-analysis, there would be only slight changes in the number and length values of EMCs (on average, the number of EMCs would increase by 2.98 and the length by 3.21 mm) with slight changes in the heterogeneity level following debonding compared to the original analysis (on average, the number increased by 3.50 and the length by 3.09 mm, Supplementary materials 1 and 2). Finally, sensitivity analysis showed that if studies with high risk of bias (5, 6, 14, 16) were excluded from the meta-analysis, the increase in length of EMCs would be, on average, 1.01 mm, i.e.~ 3 times lower compared to the original analysis (Supplementary material 3). Due to the limited number of studies no further sensitivity analysis (with exclusion of trials at high risk of bias) could be performed for the evaluation of the changes in number and width parameters following debonding. Discussion Summary of evidence This review included data from seven in vitro studies which assessed changes of EMCs characteristics (both qualitative and quantitative) following bracket removal from human teeth. Four investigations dealt with the number of EMCs (5, 13, 14, 16), seven studies measured length (5, 6, 13, 14, 16, 17, 21) and three trials examined width parameter (6, 17, 21). One study did not provide absolute values for number of EMCs, thus these results were not included in meta-analysis (5). As far as the number characteristic was concerned, results of the random-effects meta-analysis showed that following debonding there were significant changes of this parameter (on average, number of EMCs increased by 3.50 after bracket removal compared with the values before bonding). Since upper (4.87) and lower (2.13) limits of the 95 per cent CI do not cross zero line (line at 0) in the forest plot, the result can be considered as clinically significant (Figure 3). During further analysis of the forest plot, considerable between-study statistical heterogeneity was found (Tau2 = 1.37, I2 = 94%, 95% CI, 87.2–97.6, P < 0.00001, Figure 3). However, all identified trials dealing with number of EMCs lie to the right of the non-effect line (line at 0) in the forest plot, meaning that they all favor increase group. In this case, existing heterogeneity might have influence on the accurate calculation of the effect, i.e. what is the amount of the increase, but would not influence our decision, i.e. whether debonding leads to an increase in number of EMCs (31)? If the study by Heravi et al. (16) was excluded from the analysis, on average, the number would increase by 2.85 following removal of brackets and there would be no statistical heterogeneity (Tau2 = 0, I2 = 0%, P = 0.83). According to the methodology of this investigation (16), number of EMCs was calculated after debonding followed by residual adhesive removal, while in the rest two studies enamel surface analysis was performed without adhesive remnants elimination (13, 14). Better visibility of the buccal tooth surface and EMCs could lead to different results among the studies. However, considerable statistical heterogeneity should be interpreted with caution, because it is related to lack of investigations and the artificially narrow confidence intervals (28). All three studies evaluated number parameter following metal brackets removal. As for the adults’ esthetic brackets are usually the first choice appliance, additional future investigations analyzing ceramic brackets effect on EMCs would be desirable to produce more robust conclusions. The debonding procedure effect was also evident for the length characteristic. Although the effect of bracket removal varied among the included studies, the average of the various effects was an increase in length of EMCs by 3.09 mm compared to the values before bonding. Although 95 per cent CI of the overall effect (95% CI, 0.75–5.43) does not include zero value, however broad limits of the 95 per cent CI lead to doubtful clinical significance of the result. With regard to the heterogeneity evaluation, considerable between-study inconsistency was found (Tau2 = 9.52, I2 = 97%, 95% CI, 96.1–98.2, P < 0.00001, Figure 4). It is important to admit that the identified inconsistency could affect our decision, i.e. whether debonding leads to an increase in length of EMCs, because two trials (6, 17) are located on the left side and five studies (5, 13, 14, 16, 21) on the right side of the forest plot (31). Three investigations (6, 17, 21) where upper and lower limits of the 95 per cent CI cross the non-effect line, used the same device and methodology for the measurement of the length parameter. The rest four trials (5, 13, 14, 16) located on the right side of the forest plot utilized different techniques for EMCs analysis and did not present detailed description how the length was measured. The aforementioned differences might explain between-study inconsistency. Four out of seven investigations that calculated length of EMCs were judged as being in high risk of bias (5, 6, 14, 16) with the most problematic parameter being selective outcome reporting (5, 6, 14, 16). If studies with high risk of bias (5, 6, 14, 16) were excluded from further analysis, on average, length of EMCs would increase by 1.01 mm (95% CI, −0.91 to 2.93, P = 0.30, Supplementary material 3).The overall effect is ~ 3 times smaller compared to the original analysis. Upper and lower limits of the 95 per cent CI cross zero line in the forest plot, indicating that result is not significant (both clinically and statistically). Finally, there were no significant changes, neither clinically or statistically, in the width parameter after debonding (Figure 5). The average of the various effects was an increase in width of 0.39 µm (95% CI, −0.01 to 0.79, P = 0.06). Thus, additional future studies evaluating width of EMCs are needed to produce more robust conclusions. Based on the results of the systematic review, we summarized data about the changes of EMCs characteristics during orthodontic debonding. Since at the moment no method is invented and applied for direct measurement of EMCs parameters intraorally, precise examination of enamel damage under laboratory conditions remains the most important source of information about the changes of EMCs characteristics during orthodontic treatment. The summarized data could be important for clinicians in patient education as it is important to know which patients will benefit from traditional fixed appliances as well as which individuals possessing EMCs before the bonding procedure may require different appliances (e.g. lingual brackets, aligners) or debonding methods. Furthermore, results of the review might lead to the idea that EMCs increase following bracket removal could be regarded as an unavoidable consequence of debonding rather than orthodontic treatment failure. Such message is of particular importance clinically—patients should be fully informed of this issue before initiating orthodontic treatment as they are notified for e.g. of possible root resorption. Limitations Although no serious methodological limitations were found in the included investigations, their quality was moderate. For example, selective outcome reporting was observed in seven out of fourteen studies, complete outcome data before and after debonding was not presented clearly in eight trials (Figure 2). Moreover, due to the limited number of studies evaluating EMCs characteristics, especially number and width, the effect of debonding was analyzed without considering bracket type or residual adhesive removal. Therefore, additional future high-quality investigations that examine EMCs following debonding are necessary to draw more robust conclusions. Conclusions There is weak evidence indicating length and width of EMCs increase following bracket removal and the scientific evidence concerning quantitative evaluation of the number parameter before and after debonding is insufficient. However, there is a strong evidence that after debonding the number of EMCs is likely to increase. Supplementary Material Supplementary material is available at European Journal of Orthodontics online. Conflict of Interest None to declare. Acknowledgements European Commissions’s Seventh Framework Programme Laserlab-Europe IV JRA support BIOAPP (EC-GA 654148) is acknowledged. Authors are thankful to Dr. Vytautas Kazakevicius (Institute of Applied Mathematics at Vilnius University, Vilnius) for helping with the statistical analysis. References 1. Ryf, S., Flury, S., Palaniappan, S., Lussi, A., van Meerbeek, B. and Zimmerli, B. ( 2012) Enamel loss and adhesive remnants following bracket removal and various clean-up procedures in vitro. 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All rights reserved. For permissions, please email: journals.permissions@oup.com http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The European Journal of Orthodontics Oxford University Press

Enamel microcracks in the form of tooth damage during orthodontic debonding: a systematic review and meta-analysis of in vitro studies

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© The Author(s) 2018. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: journals.permissions@oup.com
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0141-5387
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1460-2210
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10.1093/ejo/cjx102
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Abstract

Abstract Objectives To evaluate and compare the enamel microcracks (EMCs) characteristics (qualitative and quantitative) in the form of tooth damage before and after debonding from human teeth of in vitro studies. Eligibility criteria Laboratorial studies evaluating EMCs characteristics before and after debonding metal and ceramic brackets from human teeth with intact buccal enamel. Information sources An electronic search of four databases (all databases of the Cochrane Library, CA Web of Science, MEDLINE via PubMed, and Google Scholar) and additional manual searches were carried out, without language restrictions. Studies published between 2000 and 2017 years were selected. Reference lists of the included articles were screened, and authors were contacted when necessary. Risk of bias The following six parameters were analyzed: blinding of examiner and outcome assessment, incomplete outcome data before bonding and after debonding, selective outcome reporting, and incomplete reporting of EMCs assessment. Included studies Out of 430 potentially eligible studies, 259 were screened by title and abstract, 180 were selected for full-text analysis, 14 were included in the systematic review. Seven studies were selected for the meta-analysis. Synthesis of results The results for EMCs characteristics were expressed as mean differences (MDs) with their 95 per cent confidence intervals (CIs), and calculated from random-effects meta-analyses. Debonding was associated with the increase in number (three studies, MD = 3.50, 95% CI, 2.13 to 4.87, P < 0.00001), length (seven studies, MD = 3.09 mm, 95% CI, 0.75–5.43, P < 0.00001), and width (three studies, MD = 0.39 µm, 95% CI, −0.01 to 0.79, P = 0.06) of EMCs. Considerable statistical heterogeneity was found for two forest plots evaluating the changes of number and length characteristics during debonding. Conclusions There is weak evidence indicating length and width of EMCs increase following bracket removal and the scientific evidence concerning quantitative evaluation of the number parameter before and after debonding is insufficient. However, there is a strong evidence that after debonding the number of EMCs is likely to increase. Registration No registration was performed. Introduction Rationale Several studies have shown that the bracket removal procedure leads to irreversible changes in the enamel structure despite the debonding techniques and residual adhesive removal methods used (1, 2). Due to the forces generated during debonding enamel microcracks (EMCs), a form of teeth damage, may develop and appear morphological changes of their characteristics (3–6). EMCs, quite often visible by the naked eye both by the patients and the dentists, may jeopardize the integrity of the enamel, cause stain, and plaque accumulation on the rough fractured surface, thus increasing susceptibility to carious lesions and compromising the appearance of the teeth (7, 8). Furthermore, the question about the effect of EMCs on the sensitivity of the teeth during the removal of brackets has been already raised (9). As orthodontic treatment is on the margins of pathology alleviation and esthetic improvement, it is important due to the principles of ethical provision of medical care that a clear benefit-to-harm relationship exists. Understanding this basic principle have led to a necessity of publishing scientific reports dealing with the effect of the debonding procedure on EMCs. Over the last two decades extending amount of investigations have been presented analyzing from distribution of frequency of cracks (3, 10) and increased crack numbers and lengths (11), or changes in frequency and severity of EMCs (12) to the evaluation of EMCs characteristics both qualitatively and quantitatively (4–6, 13–18). Progress in laboratory techniques introduced with methods for EMCs detection, such as transillumination, staining, ultrasound, or optical coherence tomography (10, 12, 19, 20). However, several techniques (scanning electron microscopy, stereomicroscopy, confocal optical profilometry, and optical coherence tomography, ultrasound) have been proved to be appropriate not only for visualization of EMCs, but also for measuring volumetric enamel loss, actual depth of enamel removed, or performing spot or line measurements of EMCs parameters (1, 4, 5, 11, 13–21). A variety of metal and ceramic brackets introduced in the market can meet the needs of every patient and orthodontist in respect to esthetics, comfortability, and manipulation. The effect of debonding of both types of brackets on the enamel damage and EMCs have been assessed in the orthodontic literature (3–6, 10–18, 22). Due to the physical properties of ceramics such as hardness, high bond strength, and low fracture toughness or brittleness even more attention has been paid on the removal of ceramic brackets (12, 23). However, although various EMCs parameters have been analyzed extensively before and after brackets removal in laboratorial studies, the evaluation of the changes of the EMCs characteristics in the context of a systematic review has been not undertaken. Furthermore, there is no strong evidence showing the EMCs increase following debonding, nor greater extent of enamel damage after ceramic brackets removal in comparison with metal ones. Objectives The aim of this investigation was to systematically review the literature based on in vitro studies that evaluated and compared the EMCs characteristics (both qualitative and quantitative) before and after debonding metal and ceramic brackets (with and without residual adhesive removal) using human teeth. Materials and methods Protocol and registration The protocol for the systematic review was constructed a priori based on Cochrane Handbook for Systematic Reviews of Interventions 5.1.0 (24), no registration was performed. The systematic review is reported according to the PRISMA statement (i.e., Preferred Reporting Items for Systematic Reviews and Meta-analyses) and its extension for abstracts (25, 26). Eligibility criteria Inclusion and exclusion criteria were determined for study selection before starting a systematic review (Table 1). Table 1. Eligibility criteria used for the study selection. Category  Inclusion criteria  Exclusion criteria  Sample size (participants)  Human teeth with intact buccal enamel, with no white spots; no pretreatment with any chemical agents (such as H2O2); no previous orthodontic, endodontic, or restorative treatment  Animal teeth (non-human studies) or enamel blocks (sections)  Intervention  Bonding and debonding procedures of metal and ceramic brackets Buccal brackets bonding with light-cured adhesives  Lingual brackets bonding Laser-assisted debonding Rebonding    Conventional debonding, i.e. with the use of pliers and mechanical debonding, i.e. with a universal testing machine, with or without residual adhesive removal    Comparison  Enamel surface analysis before and after debonding  Enamel surface analysis only after the removal of brackets  Outcome  Enamel microcracks (EMCs) characteristics evaluation (qualitatively and quantitatively) Direct analysis of EMCs, i.e. not through replication procedure  Various types of enamel damage evaluation, such as fracture, loss, defects, etc., except for EMCs Studies that cannot extract the available data: quantitative data on the changes of EMCs parameters following debonding  Study design  Original in vitro studies  Case reports and case series (n < 10) Reviews Abstracts Author debates Editorials Letters Commentaries Conference proceedings  Category  Inclusion criteria  Exclusion criteria  Sample size (participants)  Human teeth with intact buccal enamel, with no white spots; no pretreatment with any chemical agents (such as H2O2); no previous orthodontic, endodontic, or restorative treatment  Animal teeth (non-human studies) or enamel blocks (sections)  Intervention  Bonding and debonding procedures of metal and ceramic brackets Buccal brackets bonding with light-cured adhesives  Lingual brackets bonding Laser-assisted debonding Rebonding    Conventional debonding, i.e. with the use of pliers and mechanical debonding, i.e. with a universal testing machine, with or without residual adhesive removal    Comparison  Enamel surface analysis before and after debonding  Enamel surface analysis only after the removal of brackets  Outcome  Enamel microcracks (EMCs) characteristics evaluation (qualitatively and quantitatively) Direct analysis of EMCs, i.e. not through replication procedure  Various types of enamel damage evaluation, such as fracture, loss, defects, etc., except for EMCs Studies that cannot extract the available data: quantitative data on the changes of EMCs parameters following debonding  Study design  Original in vitro studies  Case reports and case series (n < 10) Reviews Abstracts Author debates Editorials Letters Commentaries Conference proceedings  View Large Table 1. Eligibility criteria used for the study selection. Category  Inclusion criteria  Exclusion criteria  Sample size (participants)  Human teeth with intact buccal enamel, with no white spots; no pretreatment with any chemical agents (such as H2O2); no previous orthodontic, endodontic, or restorative treatment  Animal teeth (non-human studies) or enamel blocks (sections)  Intervention  Bonding and debonding procedures of metal and ceramic brackets Buccal brackets bonding with light-cured adhesives  Lingual brackets bonding Laser-assisted debonding Rebonding    Conventional debonding, i.e. with the use of pliers and mechanical debonding, i.e. with a universal testing machine, with or without residual adhesive removal    Comparison  Enamel surface analysis before and after debonding  Enamel surface analysis only after the removal of brackets  Outcome  Enamel microcracks (EMCs) characteristics evaluation (qualitatively and quantitatively) Direct analysis of EMCs, i.e. not through replication procedure  Various types of enamel damage evaluation, such as fracture, loss, defects, etc., except for EMCs Studies that cannot extract the available data: quantitative data on the changes of EMCs parameters following debonding  Study design  Original in vitro studies  Case reports and case series (n < 10) Reviews Abstracts Author debates Editorials Letters Commentaries Conference proceedings  Category  Inclusion criteria  Exclusion criteria  Sample size (participants)  Human teeth with intact buccal enamel, with no white spots; no pretreatment with any chemical agents (such as H2O2); no previous orthodontic, endodontic, or restorative treatment  Animal teeth (non-human studies) or enamel blocks (sections)  Intervention  Bonding and debonding procedures of metal and ceramic brackets Buccal brackets bonding with light-cured adhesives  Lingual brackets bonding Laser-assisted debonding Rebonding    Conventional debonding, i.e. with the use of pliers and mechanical debonding, i.e. with a universal testing machine, with or without residual adhesive removal    Comparison  Enamel surface analysis before and after debonding  Enamel surface analysis only after the removal of brackets  Outcome  Enamel microcracks (EMCs) characteristics evaluation (qualitatively and quantitatively) Direct analysis of EMCs, i.e. not through replication procedure  Various types of enamel damage evaluation, such as fracture, loss, defects, etc., except for EMCs Studies that cannot extract the available data: quantitative data on the changes of EMCs parameters following debonding  Study design  Original in vitro studies  Case reports and case series (n < 10) Reviews Abstracts Author debates Editorials Letters Commentaries Conference proceedings  View Large Information sources, search, and study selection All databases of the Cochrane Library, CA Web of Science, MEDLINE via PubMed, and Google Scholar electronic databases were searched to identify studies that could be considered. The search terms and search strategy presented in Table 2. No limitations were applied regarding publication type, status, or language. The search was undertaken to identify literature published between January 2000 and July 2017 (inclusive). Abstracts and conference proceedings were also accessed. Reference lists of the included studies were reviewed. Authors were contacted to clarify data by e-mail when necessary. If no information was provided (no response from the corresponding author received), the investigation was excluded from the systematic review. Table 2. Databases and search terms. Database  Key Words  All databases of the Cochrane Library http://onlinelibrary.wiley.com/cochranelibrary/search  TITLE, ABSTRACT, KEYWORDS: (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Sort by relevance; dates: between 2000 and 2017  MEDLINE via PubMed http://www.ncbi.nln.nih.gov/pubmed  (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Sort by best match (relevance); publication dates: 2000/01 to 2017/07 (inclusive)  CA Web of Science http://apps.webofknowledge.com  TOPIC: (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Refined by: Research Domains: (Science Technology) AND Research areas: (Dentistry Oral Surgery Medicine); search language = Auto; sort by relevance; time span: 2000–2017  Google Scholar scholar.google.lt  With all of the words: ‘enamel’, ‘orthodontic’, ‘debonding’, ‘bracket’, ‘removal’ in anywhere in the article; at least one of the words: ‘damage’, OR ‘fracture’, OR ‘defect’, OR ‘crack’, OR ‘microcrack’, OR ‘micro-crack’; any language; without patents and citations; sort by relevance; custom range: 2000–2017; 100 most relevant articles  Database  Key Words  All databases of the Cochrane Library http://onlinelibrary.wiley.com/cochranelibrary/search  TITLE, ABSTRACT, KEYWORDS: (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Sort by relevance; dates: between 2000 and 2017  MEDLINE via PubMed http://www.ncbi.nln.nih.gov/pubmed  (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Sort by best match (relevance); publication dates: 2000/01 to 2017/07 (inclusive)  CA Web of Science http://apps.webofknowledge.com  TOPIC: (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Refined by: Research Domains: (Science Technology) AND Research areas: (Dentistry Oral Surgery Medicine); search language = Auto; sort by relevance; time span: 2000–2017  Google Scholar scholar.google.lt  With all of the words: ‘enamel’, ‘orthodontic’, ‘debonding’, ‘bracket’, ‘removal’ in anywhere in the article; at least one of the words: ‘damage’, OR ‘fracture’, OR ‘defect’, OR ‘crack’, OR ‘microcrack’, OR ‘micro-crack’; any language; without patents and citations; sort by relevance; custom range: 2000–2017; 100 most relevant articles  View Large Table 2. Databases and search terms. Database  Key Words  All databases of the Cochrane Library http://onlinelibrary.wiley.com/cochranelibrary/search  TITLE, ABSTRACT, KEYWORDS: (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Sort by relevance; dates: between 2000 and 2017  MEDLINE via PubMed http://www.ncbi.nln.nih.gov/pubmed  (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Sort by best match (relevance); publication dates: 2000/01 to 2017/07 (inclusive)  CA Web of Science http://apps.webofknowledge.com  TOPIC: (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Refined by: Research Domains: (Science Technology) AND Research areas: (Dentistry Oral Surgery Medicine); search language = Auto; sort by relevance; time span: 2000–2017  Google Scholar scholar.google.lt  With all of the words: ‘enamel’, ‘orthodontic’, ‘debonding’, ‘bracket’, ‘removal’ in anywhere in the article; at least one of the words: ‘damage’, OR ‘fracture’, OR ‘defect’, OR ‘crack’, OR ‘microcrack’, OR ‘micro-crack’; any language; without patents and citations; sort by relevance; custom range: 2000–2017; 100 most relevant articles  Database  Key Words  All databases of the Cochrane Library http://onlinelibrary.wiley.com/cochranelibrary/search  TITLE, ABSTRACT, KEYWORDS: (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Sort by relevance; dates: between 2000 and 2017  MEDLINE via PubMed http://www.ncbi.nln.nih.gov/pubmed  (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Sort by best match (relevance); publication dates: 2000/01 to 2017/07 (inclusive)  CA Web of Science http://apps.webofknowledge.com  TOPIC: (enamel damage OR enamel fracture* OR enamel defect* OR enamel crack* OR enamel microcrack* OR enamel micro-crack*) AND (debonding OR orthodontic debonding OR removal) AND (bracket* OR metal bracket* OR ceramic bracket* OR metal and ceramic bracket*) Refined by: Research Domains: (Science Technology) AND Research areas: (Dentistry Oral Surgery Medicine); search language = Auto; sort by relevance; time span: 2000–2017  Google Scholar scholar.google.lt  With all of the words: ‘enamel’, ‘orthodontic’, ‘debonding’, ‘bracket’, ‘removal’ in anywhere in the article; at least one of the words: ‘damage’, OR ‘fracture’, OR ‘defect’, OR ‘crack’, OR ‘microcrack’, OR ‘micro-crack’; any language; without patents and citations; sort by relevance; custom range: 2000–2017; 100 most relevant articles  View Large Studies selection, extraction of data, and risk of bias assessment were performed independently and in duplicate by two investigators (I.D. and J.V.) who were not blinded to the authors and results of the study. Disagreement were resolved through discussion with conflict resolution by the third reviewer (L.L.). Data collection process and data items A data extraction form was developed to summarize the following study characteristics: type of human tooth, number of teeth per group, brackets and bonding materials, type of debonding, method for enamel surface examination, and evaluated EMCs parameters (qualitative and quantitative). At least in three studies analyzed and measured EMCs characteristics before and after brackets removal (mean values before, after debonding, and differences in mean with standard deviations, SD, and standard errors, SE) were presented in separate tables, and a meta-analysis was performed. Risk of bias in individual studies Two authors (I.D. and J.V.) independently evaluated the risk of bias inherent in each included study. The following six parameters were analyzed: blinding of examiner (performance bias), blinding of outcome assessment (detection bias), incomplete outcome data before bonding (attrition bias), incomplete outcome data after debonding (attrition bias), selective outcome reporting (reporting bias), and incomplete reporting of EMCs assessment (other bias). An assessment of risk of bias (high, unclear, low) was made for each included trial by using the Cochrane risk of bias tool that was adapted to the current systematic review (24). Summary measures and synthesis of results For the meta-analyses, the pooled effect estimates were obtained by comparing mean values of EMCs characteristics (number, length, and width) before and after debonding, irrespective of the bracket type (metal or ceramic), and residual adhesive removal (with or without it). For studies that presented results of several subgroups having one or more intervention groups in common, the results were combined by a formula according to the Cochrane Statistical Guidelines (Part 2: 7.7.3.8 Combining groups, Figure 7.7.a: Formule for combining groups; 24), and a single sample size, mean and SD values before and after debonding were obtained. In the selected investigations, only the data of interest were extracted to be analyzed in the meta-analysis. If the same sample size was used to measure number of EMCs and number of pronounced EMCs, only the data for number of cracks were selected (number of pronounced EMCs was not included in further analysis) (13, 16). In cases, where the same sample size was utilized to calculate number of EMCs after debonding without and with residual adhesive removal, only the data obtained following debonding with residual adhesive removal was extracted for meta-analysis (16). The statistical differences between groups were calculated using Review Manager (RevMan version 5.3 software, Cochrane Collaboration, Copenhagen, Denmark, 2014; 27). A random-effects model was utilized to estimate all pooled estimates, since measured values of EMCs varied across studies likely due to differences in the sample (i.e. age group of the included teeth, tooth group to which the specimens belonged) and implementation (i.e. selected bracket type, debonding instrument utilized, microscope used for enamel surface evaluation, other various operators, and settings). This model takes into account existing heterogeneity and can be considered more conservative than the fixed-effect model in the presence of heterogeneity (28, 29). Since the studies included in the meta-analysis measured the same continuous outcomes (number, length, and width of EMCs) and used the same measurement scales (millimeter scale for the length and micrometer scale for the width parameters), the results for EMCs characteristics were expressed as mean differences (MDs) with 95 per cent confidence intervals (95% CIs; 28, 29). A positive difference (after data – before data) indicated that parameters values were greater after the debonding procedure, whereas a negative difference referred to higher number, length, and width values before bonding. Significance for all statistical tests was predetermined to be P ≤ 0.05 (Z test). Results of the analyses were presented graphically with forest plots after comparisons of study designs, sample sizes, and methodologies to judge the clinical heterogeneity of the studies. The extent and impact of between-study statistical heterogeneity was evaluated by inspecting the forests plots and by calculating the Tau2 and the I2 statistic. The 95 per cent CIs around I2 were calculated (30). I2 values of more than 75 per cent would indicate considerable heterogeneity (31). Risk of bias across studies If a sufficient number of trials were identified (n > 10), standard funnel plots and contoured funnel plots would be drawn to identify publication bias. Additional analyses Sensitivity analysis was performed to define the influence of specific studies on the total calculated effect. Sensitivity analysis was expanded by: 1. including trials width adequate sample size and methodological quality, 2. excluding studies at high risk of bias. Results Study selection and study characteristics Four hundred twenty-seven records were identified through database searching and three articles were determined through additional sources (Figure 1). Following removal of duplicates, 259 records were reviewed by title and abstract. If there was any doubt, the full text of the article was read. During the screening process, 79 records were excluded as not relevant to the subject, and 180 articles were selected for full-text analysis. One hundred sixty-six studies were excluded since they did not meet the eligibility criteria due to the following reasons: case reports (2 studies), reviews, abstracts, editorials, commentaries, conference proceedings (22 studies), investigations with animal teeth or on enamel blocks (27 studies), studies dealing with various forms of enamel damage, except for EMCs (98 studies), lingual brackets (2 studies), rebonding (2 studies), the available data could not be extracted: quantitative data of the EMCs parameters (13 studies). Finally, 14 studies were selected for the systematic review (Table 3). Figure 1. View largeDownload slide PRISMA flow diagram for the selection of studies. Figure 1. View largeDownload slide PRISMA flow diagram for the selection of studies. Table 3. Summary of study characteristics of included articles. Author, Year  Type of human tooth  Number of teeth per group  Brackets and bonding  Debonding  Enamel surface evaluation  Enamel microcracks (EMCs) characteristics  Ahrari et al. (5)  Premolars  20  Ceramic brackets • Chemical retention (Fascination; Dentaurum, Ispringen, Germany) • Mechanical retention (Inspire Ice; Ormco, Orange, California, USA) Bonding with Transbond XT primer (3M Unitek; Monrovia, California, USA) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of pliers: for chemical retention brackets—Weingart pliers; for mechanical retention brackets—plastic debonding pliers • Laser-assisted debonding, i.e. by the aid of laser light (for chemical and mechanical retention brackets)  Stereomicroscope (23.5×) with a colour digital video camera Before bonding After debonding (residual adhesive removed)  Number Number of pronounced EMCs Direction Length Absolute value for number characteristic is not provided  Baherimoghadam et al. (18)  Premolars  15  Metal brackets (Dyna-Lock; 3M Unitek) Bonding with • Light Bond primer (Reliance, Itasca, Illinois, USA) and adhesive (Reliance) • Adhesion promoter Enhance LC (Reliance), Light Bond primer and adhesive  Mechanical debonding, i.e. with a universal testing machine (Zwick roll, Germany) at a crosshead speed of 0.5 mm/min (shear force)  Digital camera connected to a stereomicroscope (38×) Before bonding After debonding (residual adhesive removed)  Number Length  Bishara et al. (12)  Premolars  15  Ceramic brackets (mechanical retention; APC Plus Clarity; 3M Unitek) Bonding with Transbond Plus Self-Etching Primer (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers • With new Debonding instrument  Magnifying lens (10×) and transillumination with a fiber optic light head Before bonding After debonding (residual adhesive removed)  Number Severity (pronounced or weak) Direction Absolute values are not provided  Dumbryte et al. (6)  Incisors, canines and premolars  15  Metal brackets (Discovery; Dentaurum) Bonding with Contex Primer (Dentaurum) and Contex Lc adhesive (Dentaurum)  Conventional debonding, i.e. with the use of Utility/Weingart pliers  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Dumbryte et al. (17)  Premolars  15  Brackets • Metal (Discovery; Dentaurum) • Ceramic (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers (for metal brackets) • With Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Dumbryte et al. (15)  Premolars  30  Brackets • Metal (Discovery; Dentaurum) • Ceramic (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers (for metal brackets) • With Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Visibility Direction Location Length Absolute values are not provided  Dumbryte et al. (21)  Premolars  60  Ceramic brackets (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding with Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–00×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Habibi et al. (11)  Premolars  12  Brackets • Metal (Rocky Mountain Orthodontics; Denver, Colorado, USA) • Ceramic with chemical retention (Signature II; Rocky Mountain Orthodontics) • Ceramic with mechanical retention (Signature III; Rocky Mountain Orthodontics) Bonding with light-activated adhesive luting Mono Lok2 (Rocky Mountain Orthodontics)  Mechanical debonding, i.e. sharp-edged debonding pliers in a universal testing machine at a crosshead speed of 1 mm/min (squeezing force)  Stereomicroscope (10×) Before bonding After debonding (residual adhesive removed)  Number Length Absolute values are not provided  Heravi et al. (13)  Premolars  25  Metal brackets (Dentaurum, Pforzheim, Germany) Bonding with a no-mix orthodontic composite adhesive (Dent Zar Inc., USA)  Debonding with • Medium ligature cutter (Dentaurum, Pforzheim, Germany) • Single-blade bracket remover (Dentaurum) • Two-blade bracket remover (Dentaurum)  Stereomicroscope (23.9×) and colour digital video camera Before bonding After debonding (residual adhesive not removed)  Number Number of pronounced EMCs Direction Length  Heravi et al. (16)  Incisors  30  Metal brackets (Dentaurum, Pforzheim) Bonding with • Transbond XT adhesive (3M Unitek) • Self-adhesive composite cement Maxcem Elite (Kerr, Orange, California, USA)  Mechanical debonding, i.e. RMO i-546 remover pliers in a Zwick Z250 testing machine at a speed of 0.5 mm/min (squeezing force)  Stereomicroscope (23.9×) and digital camera Before bonding After debonding (evaluation before and after residual adhesive removal)  Number Number of pronounced EMCs Direction Length  Kitahara-Ceia et al. (3)  Premolars  15  Ceramic brackets • Mechanical retention (Clarity; 3M Unitek) • Mechanical retention with a polymer base (InVu; TP Orthodontics, LaPorte, Indiana, USA) • Chemical retention (Fascination 2; Dentaurum, Ispringen, Germany) Bonding with adhesive resin Concise (3M Unitek)  Debonding with • Howes pliers (for mechanical retention) • Orthodontic wire cutter (for polymer base) • Weingart pliers (for chemical retention)  Magnifying loupe (60×) in an optical stereomicroscope with a digital camera Before bonding After debonding (residual adhesive removed)  Distribution of frequency of cracks Absolute values are not provided  Rix et al. (10)  Premolars  40  Metal brackets (Ormco “A” company, San Diego, California, USA) Bonding with • Transbond XT primer and Transbond XT composite resin (3M Unitek, St Paul, Minnesota, USA) • Resin-modified glass ionomer cement Fuji Ortho LC (GC America Corp, Alsip, Illinois, USA) • Polyacid-modified composite resin Assure (Reliance Orthodontic Products Inc, Itasca, Illinois, USA) under dry and saliva-contaminated conditions  Mechanical debonding, i.e. shear-peel load by means of a Universal Instron testing machine with a 50-kg load cell and a crosshead speed of 2 mm/min (shear-peeling force)  Transillumination with a fiber-optic light head under 16× magnification Before bonding After debonding (residual adhesive not removed)  Frequency distribution of the extent of enamel cracking Absolute values are not provided  Salehi et al. (14)  Premolars  30  Metal brackets (Dyna-Lock; 3M Unitek) Bonding with • Light-cured composite Transbond XT (3M Unitek, Monrovia, California, USA) • No-Mix self-cured composite Unite (3M Unitek, Monrovia, California, USA)  Debonding with • Lift Off Debonding Instrument (LODI; 3M Unitek) • Bracket removing pliers (Dentaurum)  Stereomicroscope (38x) with a connected digital camera Before bonding After deboning (residual adhesive not removed)  Number Length  Shahabi et al. (4)  Premolars  25  Metal brackets (Dentarum, Inspringen, Germany) Bonding with • One layer of enamel bonding agent (EBA) • Two layers of EBA • No EBA and no-mix self-cured polymerizing composite resin (3M Unitek, Monrovia, California, USA)  Mechanical debonding, i.e. shear loading with a universal testing machine at a crosshead speed of 5 mm/min (shear force)  Stereomicroscope (20x) equipped with a camera Before bonding After debonding (residual adhesive not removed)  Number Direction Length Depth (shallow or deep) Absolute values are not provided  Author, Year  Type of human tooth  Number of teeth per group  Brackets and bonding  Debonding  Enamel surface evaluation  Enamel microcracks (EMCs) characteristics  Ahrari et al. (5)  Premolars  20  Ceramic brackets • Chemical retention (Fascination; Dentaurum, Ispringen, Germany) • Mechanical retention (Inspire Ice; Ormco, Orange, California, USA) Bonding with Transbond XT primer (3M Unitek; Monrovia, California, USA) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of pliers: for chemical retention brackets—Weingart pliers; for mechanical retention brackets—plastic debonding pliers • Laser-assisted debonding, i.e. by the aid of laser light (for chemical and mechanical retention brackets)  Stereomicroscope (23.5×) with a colour digital video camera Before bonding After debonding (residual adhesive removed)  Number Number of pronounced EMCs Direction Length Absolute value for number characteristic is not provided  Baherimoghadam et al. (18)  Premolars  15  Metal brackets (Dyna-Lock; 3M Unitek) Bonding with • Light Bond primer (Reliance, Itasca, Illinois, USA) and adhesive (Reliance) • Adhesion promoter Enhance LC (Reliance), Light Bond primer and adhesive  Mechanical debonding, i.e. with a universal testing machine (Zwick roll, Germany) at a crosshead speed of 0.5 mm/min (shear force)  Digital camera connected to a stereomicroscope (38×) Before bonding After debonding (residual adhesive removed)  Number Length  Bishara et al. (12)  Premolars  15  Ceramic brackets (mechanical retention; APC Plus Clarity; 3M Unitek) Bonding with Transbond Plus Self-Etching Primer (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers • With new Debonding instrument  Magnifying lens (10×) and transillumination with a fiber optic light head Before bonding After debonding (residual adhesive removed)  Number Severity (pronounced or weak) Direction Absolute values are not provided  Dumbryte et al. (6)  Incisors, canines and premolars  15  Metal brackets (Discovery; Dentaurum) Bonding with Contex Primer (Dentaurum) and Contex Lc adhesive (Dentaurum)  Conventional debonding, i.e. with the use of Utility/Weingart pliers  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Dumbryte et al. (17)  Premolars  15  Brackets • Metal (Discovery; Dentaurum) • Ceramic (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers (for metal brackets) • With Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Dumbryte et al. (15)  Premolars  30  Brackets • Metal (Discovery; Dentaurum) • Ceramic (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers (for metal brackets) • With Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Visibility Direction Location Length Absolute values are not provided  Dumbryte et al. (21)  Premolars  60  Ceramic brackets (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding with Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–00×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Habibi et al. (11)  Premolars  12  Brackets • Metal (Rocky Mountain Orthodontics; Denver, Colorado, USA) • Ceramic with chemical retention (Signature II; Rocky Mountain Orthodontics) • Ceramic with mechanical retention (Signature III; Rocky Mountain Orthodontics) Bonding with light-activated adhesive luting Mono Lok2 (Rocky Mountain Orthodontics)  Mechanical debonding, i.e. sharp-edged debonding pliers in a universal testing machine at a crosshead speed of 1 mm/min (squeezing force)  Stereomicroscope (10×) Before bonding After debonding (residual adhesive removed)  Number Length Absolute values are not provided  Heravi et al. (13)  Premolars  25  Metal brackets (Dentaurum, Pforzheim, Germany) Bonding with a no-mix orthodontic composite adhesive (Dent Zar Inc., USA)  Debonding with • Medium ligature cutter (Dentaurum, Pforzheim, Germany) • Single-blade bracket remover (Dentaurum) • Two-blade bracket remover (Dentaurum)  Stereomicroscope (23.9×) and colour digital video camera Before bonding After debonding (residual adhesive not removed)  Number Number of pronounced EMCs Direction Length  Heravi et al. (16)  Incisors  30  Metal brackets (Dentaurum, Pforzheim) Bonding with • Transbond XT adhesive (3M Unitek) • Self-adhesive composite cement Maxcem Elite (Kerr, Orange, California, USA)  Mechanical debonding, i.e. RMO i-546 remover pliers in a Zwick Z250 testing machine at a speed of 0.5 mm/min (squeezing force)  Stereomicroscope (23.9×) and digital camera Before bonding After debonding (evaluation before and after residual adhesive removal)  Number Number of pronounced EMCs Direction Length  Kitahara-Ceia et al. (3)  Premolars  15  Ceramic brackets • Mechanical retention (Clarity; 3M Unitek) • Mechanical retention with a polymer base (InVu; TP Orthodontics, LaPorte, Indiana, USA) • Chemical retention (Fascination 2; Dentaurum, Ispringen, Germany) Bonding with adhesive resin Concise (3M Unitek)  Debonding with • Howes pliers (for mechanical retention) • Orthodontic wire cutter (for polymer base) • Weingart pliers (for chemical retention)  Magnifying loupe (60×) in an optical stereomicroscope with a digital camera Before bonding After debonding (residual adhesive removed)  Distribution of frequency of cracks Absolute values are not provided  Rix et al. (10)  Premolars  40  Metal brackets (Ormco “A” company, San Diego, California, USA) Bonding with • Transbond XT primer and Transbond XT composite resin (3M Unitek, St Paul, Minnesota, USA) • Resin-modified glass ionomer cement Fuji Ortho LC (GC America Corp, Alsip, Illinois, USA) • Polyacid-modified composite resin Assure (Reliance Orthodontic Products Inc, Itasca, Illinois, USA) under dry and saliva-contaminated conditions  Mechanical debonding, i.e. shear-peel load by means of a Universal Instron testing machine with a 50-kg load cell and a crosshead speed of 2 mm/min (shear-peeling force)  Transillumination with a fiber-optic light head under 16× magnification Before bonding After debonding (residual adhesive not removed)  Frequency distribution of the extent of enamel cracking Absolute values are not provided  Salehi et al. (14)  Premolars  30  Metal brackets (Dyna-Lock; 3M Unitek) Bonding with • Light-cured composite Transbond XT (3M Unitek, Monrovia, California, USA) • No-Mix self-cured composite Unite (3M Unitek, Monrovia, California, USA)  Debonding with • Lift Off Debonding Instrument (LODI; 3M Unitek) • Bracket removing pliers (Dentaurum)  Stereomicroscope (38x) with a connected digital camera Before bonding After deboning (residual adhesive not removed)  Number Length  Shahabi et al. (4)  Premolars  25  Metal brackets (Dentarum, Inspringen, Germany) Bonding with • One layer of enamel bonding agent (EBA) • Two layers of EBA • No EBA and no-mix self-cured polymerizing composite resin (3M Unitek, Monrovia, California, USA)  Mechanical debonding, i.e. shear loading with a universal testing machine at a crosshead speed of 5 mm/min (shear force)  Stereomicroscope (20x) equipped with a camera Before bonding After debonding (residual adhesive not removed)  Number Direction Length Depth (shallow or deep) Absolute values are not provided  View Large Table 3. Summary of study characteristics of included articles. Author, Year  Type of human tooth  Number of teeth per group  Brackets and bonding  Debonding  Enamel surface evaluation  Enamel microcracks (EMCs) characteristics  Ahrari et al. (5)  Premolars  20  Ceramic brackets • Chemical retention (Fascination; Dentaurum, Ispringen, Germany) • Mechanical retention (Inspire Ice; Ormco, Orange, California, USA) Bonding with Transbond XT primer (3M Unitek; Monrovia, California, USA) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of pliers: for chemical retention brackets—Weingart pliers; for mechanical retention brackets—plastic debonding pliers • Laser-assisted debonding, i.e. by the aid of laser light (for chemical and mechanical retention brackets)  Stereomicroscope (23.5×) with a colour digital video camera Before bonding After debonding (residual adhesive removed)  Number Number of pronounced EMCs Direction Length Absolute value for number characteristic is not provided  Baherimoghadam et al. (18)  Premolars  15  Metal brackets (Dyna-Lock; 3M Unitek) Bonding with • Light Bond primer (Reliance, Itasca, Illinois, USA) and adhesive (Reliance) • Adhesion promoter Enhance LC (Reliance), Light Bond primer and adhesive  Mechanical debonding, i.e. with a universal testing machine (Zwick roll, Germany) at a crosshead speed of 0.5 mm/min (shear force)  Digital camera connected to a stereomicroscope (38×) Before bonding After debonding (residual adhesive removed)  Number Length  Bishara et al. (12)  Premolars  15  Ceramic brackets (mechanical retention; APC Plus Clarity; 3M Unitek) Bonding with Transbond Plus Self-Etching Primer (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers • With new Debonding instrument  Magnifying lens (10×) and transillumination with a fiber optic light head Before bonding After debonding (residual adhesive removed)  Number Severity (pronounced or weak) Direction Absolute values are not provided  Dumbryte et al. (6)  Incisors, canines and premolars  15  Metal brackets (Discovery; Dentaurum) Bonding with Contex Primer (Dentaurum) and Contex Lc adhesive (Dentaurum)  Conventional debonding, i.e. with the use of Utility/Weingart pliers  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Dumbryte et al. (17)  Premolars  15  Brackets • Metal (Discovery; Dentaurum) • Ceramic (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers (for metal brackets) • With Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Dumbryte et al. (15)  Premolars  30  Brackets • Metal (Discovery; Dentaurum) • Ceramic (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers (for metal brackets) • With Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Visibility Direction Location Length Absolute values are not provided  Dumbryte et al. (21)  Premolars  60  Ceramic brackets (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding with Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–00×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Habibi et al. (11)  Premolars  12  Brackets • Metal (Rocky Mountain Orthodontics; Denver, Colorado, USA) • Ceramic with chemical retention (Signature II; Rocky Mountain Orthodontics) • Ceramic with mechanical retention (Signature III; Rocky Mountain Orthodontics) Bonding with light-activated adhesive luting Mono Lok2 (Rocky Mountain Orthodontics)  Mechanical debonding, i.e. sharp-edged debonding pliers in a universal testing machine at a crosshead speed of 1 mm/min (squeezing force)  Stereomicroscope (10×) Before bonding After debonding (residual adhesive removed)  Number Length Absolute values are not provided  Heravi et al. (13)  Premolars  25  Metal brackets (Dentaurum, Pforzheim, Germany) Bonding with a no-mix orthodontic composite adhesive (Dent Zar Inc., USA)  Debonding with • Medium ligature cutter (Dentaurum, Pforzheim, Germany) • Single-blade bracket remover (Dentaurum) • Two-blade bracket remover (Dentaurum)  Stereomicroscope (23.9×) and colour digital video camera Before bonding After debonding (residual adhesive not removed)  Number Number of pronounced EMCs Direction Length  Heravi et al. (16)  Incisors  30  Metal brackets (Dentaurum, Pforzheim) Bonding with • Transbond XT adhesive (3M Unitek) • Self-adhesive composite cement Maxcem Elite (Kerr, Orange, California, USA)  Mechanical debonding, i.e. RMO i-546 remover pliers in a Zwick Z250 testing machine at a speed of 0.5 mm/min (squeezing force)  Stereomicroscope (23.9×) and digital camera Before bonding After debonding (evaluation before and after residual adhesive removal)  Number Number of pronounced EMCs Direction Length  Kitahara-Ceia et al. (3)  Premolars  15  Ceramic brackets • Mechanical retention (Clarity; 3M Unitek) • Mechanical retention with a polymer base (InVu; TP Orthodontics, LaPorte, Indiana, USA) • Chemical retention (Fascination 2; Dentaurum, Ispringen, Germany) Bonding with adhesive resin Concise (3M Unitek)  Debonding with • Howes pliers (for mechanical retention) • Orthodontic wire cutter (for polymer base) • Weingart pliers (for chemical retention)  Magnifying loupe (60×) in an optical stereomicroscope with a digital camera Before bonding After debonding (residual adhesive removed)  Distribution of frequency of cracks Absolute values are not provided  Rix et al. (10)  Premolars  40  Metal brackets (Ormco “A” company, San Diego, California, USA) Bonding with • Transbond XT primer and Transbond XT composite resin (3M Unitek, St Paul, Minnesota, USA) • Resin-modified glass ionomer cement Fuji Ortho LC (GC America Corp, Alsip, Illinois, USA) • Polyacid-modified composite resin Assure (Reliance Orthodontic Products Inc, Itasca, Illinois, USA) under dry and saliva-contaminated conditions  Mechanical debonding, i.e. shear-peel load by means of a Universal Instron testing machine with a 50-kg load cell and a crosshead speed of 2 mm/min (shear-peeling force)  Transillumination with a fiber-optic light head under 16× magnification Before bonding After debonding (residual adhesive not removed)  Frequency distribution of the extent of enamel cracking Absolute values are not provided  Salehi et al. (14)  Premolars  30  Metal brackets (Dyna-Lock; 3M Unitek) Bonding with • Light-cured composite Transbond XT (3M Unitek, Monrovia, California, USA) • No-Mix self-cured composite Unite (3M Unitek, Monrovia, California, USA)  Debonding with • Lift Off Debonding Instrument (LODI; 3M Unitek) • Bracket removing pliers (Dentaurum)  Stereomicroscope (38x) with a connected digital camera Before bonding After deboning (residual adhesive not removed)  Number Length  Shahabi et al. (4)  Premolars  25  Metal brackets (Dentarum, Inspringen, Germany) Bonding with • One layer of enamel bonding agent (EBA) • Two layers of EBA • No EBA and no-mix self-cured polymerizing composite resin (3M Unitek, Monrovia, California, USA)  Mechanical debonding, i.e. shear loading with a universal testing machine at a crosshead speed of 5 mm/min (shear force)  Stereomicroscope (20x) equipped with a camera Before bonding After debonding (residual adhesive not removed)  Number Direction Length Depth (shallow or deep) Absolute values are not provided  Author, Year  Type of human tooth  Number of teeth per group  Brackets and bonding  Debonding  Enamel surface evaluation  Enamel microcracks (EMCs) characteristics  Ahrari et al. (5)  Premolars  20  Ceramic brackets • Chemical retention (Fascination; Dentaurum, Ispringen, Germany) • Mechanical retention (Inspire Ice; Ormco, Orange, California, USA) Bonding with Transbond XT primer (3M Unitek; Monrovia, California, USA) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of pliers: for chemical retention brackets—Weingart pliers; for mechanical retention brackets—plastic debonding pliers • Laser-assisted debonding, i.e. by the aid of laser light (for chemical and mechanical retention brackets)  Stereomicroscope (23.5×) with a colour digital video camera Before bonding After debonding (residual adhesive removed)  Number Number of pronounced EMCs Direction Length Absolute value for number characteristic is not provided  Baherimoghadam et al. (18)  Premolars  15  Metal brackets (Dyna-Lock; 3M Unitek) Bonding with • Light Bond primer (Reliance, Itasca, Illinois, USA) and adhesive (Reliance) • Adhesion promoter Enhance LC (Reliance), Light Bond primer and adhesive  Mechanical debonding, i.e. with a universal testing machine (Zwick roll, Germany) at a crosshead speed of 0.5 mm/min (shear force)  Digital camera connected to a stereomicroscope (38×) Before bonding After debonding (residual adhesive removed)  Number Length  Bishara et al. (12)  Premolars  15  Ceramic brackets (mechanical retention; APC Plus Clarity; 3M Unitek) Bonding with Transbond Plus Self-Etching Primer (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers • With new Debonding instrument  Magnifying lens (10×) and transillumination with a fiber optic light head Before bonding After debonding (residual adhesive removed)  Number Severity (pronounced or weak) Direction Absolute values are not provided  Dumbryte et al. (6)  Incisors, canines and premolars  15  Metal brackets (Discovery; Dentaurum) Bonding with Contex Primer (Dentaurum) and Contex Lc adhesive (Dentaurum)  Conventional debonding, i.e. with the use of Utility/Weingart pliers  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Dumbryte et al. (17)  Premolars  15  Brackets • Metal (Discovery; Dentaurum) • Ceramic (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers (for metal brackets) • With Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Dumbryte et al. (15)  Premolars  30  Brackets • Metal (Discovery; Dentaurum) • Ceramic (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding • Conventional, i.e. with the use of Utility/Weingart pliers (for metal brackets) • With Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–100×) Before bonding After debonding (residual adhesive removed)  Visibility Direction Location Length Absolute values are not provided  Dumbryte et al. (21)  Premolars  60  Ceramic brackets (mechanical retention; Clarity; 3M Unitek) Bonding with Contex Primer (Dentaurum) and Transbond XT adhesive (3M Unitek)  Debonding with Debonding instrument (for ceramic brackets)  Scanning electron microscope (50–00×) Before bonding After debonding (residual adhesive removed)  Location Length Width  Habibi et al. (11)  Premolars  12  Brackets • Metal (Rocky Mountain Orthodontics; Denver, Colorado, USA) • Ceramic with chemical retention (Signature II; Rocky Mountain Orthodontics) • Ceramic with mechanical retention (Signature III; Rocky Mountain Orthodontics) Bonding with light-activated adhesive luting Mono Lok2 (Rocky Mountain Orthodontics)  Mechanical debonding, i.e. sharp-edged debonding pliers in a universal testing machine at a crosshead speed of 1 mm/min (squeezing force)  Stereomicroscope (10×) Before bonding After debonding (residual adhesive removed)  Number Length Absolute values are not provided  Heravi et al. (13)  Premolars  25  Metal brackets (Dentaurum, Pforzheim, Germany) Bonding with a no-mix orthodontic composite adhesive (Dent Zar Inc., USA)  Debonding with • Medium ligature cutter (Dentaurum, Pforzheim, Germany) • Single-blade bracket remover (Dentaurum) • Two-blade bracket remover (Dentaurum)  Stereomicroscope (23.9×) and colour digital video camera Before bonding After debonding (residual adhesive not removed)  Number Number of pronounced EMCs Direction Length  Heravi et al. (16)  Incisors  30  Metal brackets (Dentaurum, Pforzheim) Bonding with • Transbond XT adhesive (3M Unitek) • Self-adhesive composite cement Maxcem Elite (Kerr, Orange, California, USA)  Mechanical debonding, i.e. RMO i-546 remover pliers in a Zwick Z250 testing machine at a speed of 0.5 mm/min (squeezing force)  Stereomicroscope (23.9×) and digital camera Before bonding After debonding (evaluation before and after residual adhesive removal)  Number Number of pronounced EMCs Direction Length  Kitahara-Ceia et al. (3)  Premolars  15  Ceramic brackets • Mechanical retention (Clarity; 3M Unitek) • Mechanical retention with a polymer base (InVu; TP Orthodontics, LaPorte, Indiana, USA) • Chemical retention (Fascination 2; Dentaurum, Ispringen, Germany) Bonding with adhesive resin Concise (3M Unitek)  Debonding with • Howes pliers (for mechanical retention) • Orthodontic wire cutter (for polymer base) • Weingart pliers (for chemical retention)  Magnifying loupe (60×) in an optical stereomicroscope with a digital camera Before bonding After debonding (residual adhesive removed)  Distribution of frequency of cracks Absolute values are not provided  Rix et al. (10)  Premolars  40  Metal brackets (Ormco “A” company, San Diego, California, USA) Bonding with • Transbond XT primer and Transbond XT composite resin (3M Unitek, St Paul, Minnesota, USA) • Resin-modified glass ionomer cement Fuji Ortho LC (GC America Corp, Alsip, Illinois, USA) • Polyacid-modified composite resin Assure (Reliance Orthodontic Products Inc, Itasca, Illinois, USA) under dry and saliva-contaminated conditions  Mechanical debonding, i.e. shear-peel load by means of a Universal Instron testing machine with a 50-kg load cell and a crosshead speed of 2 mm/min (shear-peeling force)  Transillumination with a fiber-optic light head under 16× magnification Before bonding After debonding (residual adhesive not removed)  Frequency distribution of the extent of enamel cracking Absolute values are not provided  Salehi et al. (14)  Premolars  30  Metal brackets (Dyna-Lock; 3M Unitek) Bonding with • Light-cured composite Transbond XT (3M Unitek, Monrovia, California, USA) • No-Mix self-cured composite Unite (3M Unitek, Monrovia, California, USA)  Debonding with • Lift Off Debonding Instrument (LODI; 3M Unitek) • Bracket removing pliers (Dentaurum)  Stereomicroscope (38x) with a connected digital camera Before bonding After deboning (residual adhesive not removed)  Number Length  Shahabi et al. (4)  Premolars  25  Metal brackets (Dentarum, Inspringen, Germany) Bonding with • One layer of enamel bonding agent (EBA) • Two layers of EBA • No EBA and no-mix self-cured polymerizing composite resin (3M Unitek, Monrovia, California, USA)  Mechanical debonding, i.e. shear loading with a universal testing machine at a crosshead speed of 5 mm/min (shear force)  Stereomicroscope (20x) equipped with a camera Before bonding After debonding (residual adhesive not removed)  Number Direction Length Depth (shallow or deep) Absolute values are not provided  View Large Risk of bias within studies The risk of bias for the fourteen studies included is summarized in Table 4 and Figure 2 (3–6, 10–18, 21). Seven trials were considered as being in high risk of bias, with the most problematic parameter being selective outcome reporting (in seven studies, 4–6, 12, 14, 16, 18). The rest seven trials were judged as being in unclear risk of bias (3, 10, 11, 13, 15, 17, 21). Table 4. Risk of bias assessment. Study  Blinding of examiner  Blinding of outcome assessment  Incomplete outcome data before bonding  Incomplete outcome data after debonding  Selective outcome reporting  Incomplete reporting of enamel microcracks assessment  Ahrari et al. (5)  Unclear  Unclear  Unclear  High  High  Low  Baherimoghadam et al. (18)  Unclear  Unclear  Unclear  Unclear  High  Low  Bishara et al. (12)  Unclear  Unclear  Low  Low  High  Low  Dumbryte et al. (6)  Unclear  Unclear  Low  Low  High  Low  Dumbryte et al. (17)  Unclear  Unclear  Unclear  Unclear  Unclear  Low  Dumbryte et al. (15)  Unclear  Unclear  Low  Low  Low  Low  Dumbryte et al. (21)  Unclear  Unclear  Low  Low  Low  Low  Habibi et al. (11)  Unclear  Unclear  Low  Low  Low  Low  Heravi et al. (13)  Unclear  Unclear  Unclear  Unclear  Low  Low  Heravi et al. (16)  Unclear  Unclear  Unclear  Unclear  High  Low  Kitahara-Ceia et al. (3)  Unclear  Low  Unclear  Unclear  Low  Low  Rix et al. (10)  Unclear  Unclear  Low  Low  Low  Low  Salehi et al. (14)  Unclear  Unclear  Unclear  Unclear  High  Low  Shahabi et al. (4)  Unclear  Unclear  Unclear  Unclear  High  High  Study  Blinding of examiner  Blinding of outcome assessment  Incomplete outcome data before bonding  Incomplete outcome data after debonding  Selective outcome reporting  Incomplete reporting of enamel microcracks assessment  Ahrari et al. (5)  Unclear  Unclear  Unclear  High  High  Low  Baherimoghadam et al. (18)  Unclear  Unclear  Unclear  Unclear  High  Low  Bishara et al. (12)  Unclear  Unclear  Low  Low  High  Low  Dumbryte et al. (6)  Unclear  Unclear  Low  Low  High  Low  Dumbryte et al. (17)  Unclear  Unclear  Unclear  Unclear  Unclear  Low  Dumbryte et al. (15)  Unclear  Unclear  Low  Low  Low  Low  Dumbryte et al. (21)  Unclear  Unclear  Low  Low  Low  Low  Habibi et al. (11)  Unclear  Unclear  Low  Low  Low  Low  Heravi et al. (13)  Unclear  Unclear  Unclear  Unclear  Low  Low  Heravi et al. (16)  Unclear  Unclear  Unclear  Unclear  High  Low  Kitahara-Ceia et al. (3)  Unclear  Low  Unclear  Unclear  Low  Low  Rix et al. (10)  Unclear  Unclear  Low  Low  Low  Low  Salehi et al. (14)  Unclear  Unclear  Unclear  Unclear  High  Low  Shahabi et al. (4)  Unclear  Unclear  Unclear  Unclear  High  High  View Large Table 4. Risk of bias assessment. Study  Blinding of examiner  Blinding of outcome assessment  Incomplete outcome data before bonding  Incomplete outcome data after debonding  Selective outcome reporting  Incomplete reporting of enamel microcracks assessment  Ahrari et al. (5)  Unclear  Unclear  Unclear  High  High  Low  Baherimoghadam et al. (18)  Unclear  Unclear  Unclear  Unclear  High  Low  Bishara et al. (12)  Unclear  Unclear  Low  Low  High  Low  Dumbryte et al. (6)  Unclear  Unclear  Low  Low  High  Low  Dumbryte et al. (17)  Unclear  Unclear  Unclear  Unclear  Unclear  Low  Dumbryte et al. (15)  Unclear  Unclear  Low  Low  Low  Low  Dumbryte et al. (21)  Unclear  Unclear  Low  Low  Low  Low  Habibi et al. (11)  Unclear  Unclear  Low  Low  Low  Low  Heravi et al. (13)  Unclear  Unclear  Unclear  Unclear  Low  Low  Heravi et al. (16)  Unclear  Unclear  Unclear  Unclear  High  Low  Kitahara-Ceia et al. (3)  Unclear  Low  Unclear  Unclear  Low  Low  Rix et al. (10)  Unclear  Unclear  Low  Low  Low  Low  Salehi et al. (14)  Unclear  Unclear  Unclear  Unclear  High  Low  Shahabi et al. (4)  Unclear  Unclear  Unclear  Unclear  High  High  Study  Blinding of examiner  Blinding of outcome assessment  Incomplete outcome data before bonding  Incomplete outcome data after debonding  Selective outcome reporting  Incomplete reporting of enamel microcracks assessment  Ahrari et al. (5)  Unclear  Unclear  Unclear  High  High  Low  Baherimoghadam et al. (18)  Unclear  Unclear  Unclear  Unclear  High  Low  Bishara et al. (12)  Unclear  Unclear  Low  Low  High  Low  Dumbryte et al. (6)  Unclear  Unclear  Low  Low  High  Low  Dumbryte et al. (17)  Unclear  Unclear  Unclear  Unclear  Unclear  Low  Dumbryte et al. (15)  Unclear  Unclear  Low  Low  Low  Low  Dumbryte et al. (21)  Unclear  Unclear  Low  Low  Low  Low  Habibi et al. (11)  Unclear  Unclear  Low  Low  Low  Low  Heravi et al. (13)  Unclear  Unclear  Unclear  Unclear  Low  Low  Heravi et al. (16)  Unclear  Unclear  Unclear  Unclear  High  Low  Kitahara-Ceia et al. (3)  Unclear  Low  Unclear  Unclear  Low  Low  Rix et al. (10)  Unclear  Unclear  Low  Low  Low  Low  Salehi et al. (14)  Unclear  Unclear  Unclear  Unclear  High  Low  Shahabi et al. (4)  Unclear  Unclear  Unclear  Unclear  High  High  View Large Figure 2. View largeDownload slide Risk of bias summary. Figure 2. View largeDownload slide Risk of bias summary. Results of individual studies and synthesis of results Characteristics of the 14 studies included in the systematic review are presented in Table 3. All investigations were published between 2001 and 2017. Twelve trials were performed on human premolar teeth (3–5, 10–15, 17, 18, 21), one study used incisors for its’ sample size (16) and in one investigation teeth from various tooth groups were selected (6). The distribution of metal and ceramic brackets among the studies was as follows: metal brackets were chosen in seven studies (4, 6, 10, 13, 14, 16, 18), ceramic brackets were used in four trials (3, 5, 12, 21), both metal and ceramic brackets were selected in three investigations (11, 15, 17). For the debonding procedure, either conventional bracket removal method, i.e. with the use of appropriate pliers by hand (3, 5, 6, 12–15, 17, 21) or mechanical debonding, i.e. with the help of testing machine was chosen (4, 10, 11, 16, 18). After debonding residual adhesive was removed in nine studies (3, 5, 6, 11, 12, 15, 17, 18, 21), while four investigations evaluated EMCs with left adhesive remnants on the enamel surface (4, 10, 13, 14). In one trial EMCs characteristics were measured before and following residual adhesive removal (16). In the majority of studies stereomicroscopy technique was utilized for the EMCs visualization and analysis (3–5, 11, 13, 14, 16, 18), followed by scanning electron microscopy (6, 15, 17, 21) and transillumination methods (10, 12). Length of EMCs was the most frequently examined parameter (4–6, 11, 13–18, 21), followed by number (4, 5, 11–14, 16, 18), direction (4, 5, 12, 13, 15, 16), location (6, 15, 17, 21), and width (6, 17, 21) evaluation. However, six trials did not provide absolute values for measured EMCs and were not included in the meta-analysis (3, 4, 10–12, 15). One study was excluded from further quantitative synthesis due to inadequate statistical analysis (high standard deviations for not described reasons) (18). Seven studies were included in the meta-analysis: four investigations evaluated number of EMCs (5, 13, 14, 16), seven studies measured length (5, 6, 13, 14, 16, 17, 21), and three trials examined width parameter (6, 17, 21). One study did not provide absolute values for number of EMCs, thus these results were not included in further analysis (5). Changes in the number of EMCs were calculated only during debonding metal brackets (13, 14, 16), while length and width characteristics were evaluated following metal (length—five investigations (6, 13, 14, 16, 17), width—two studies, 6, 17) and ceramic brackets removal (length—three trials (5, 17, 21), width—two studies, 17, 21). In four trials enamel surface analysis was performed after debonding followed by residual adhesive removal (5, 6, 17, 21), in two investigations EMCs were evaluated without adhesive remnants elimination after brackets removal (13, 14), and in one trial EMCs characteristics were measured before and following residual adhesive removal (16). Recorded number, length, and width values of EMCs before and after debonding are presented in Table 5. Table 5. Mean number, length, and width values of enamel microcracks before and after debonding, and difference in means. Study  Number of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (6)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (17)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (21)  —  —  —  —  —  —  —  —  —  Heravi et al. (13)  75  4.70  2.43  75  7.63  2.96  2.93  2.71  0.44  Heravi et al. (16)  60  2.35  0.93  60  7.04  1.29  4.69  1.13  0.21  Salehi et al. (14)  120  2.20  1.26  120  5.02  2.61  2.82  2.05  0.26    Length of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  40  6.50  3.27  36  12.30  3.67  5.80  3.49  0.78  Dumbryte et al. (6)  15  5.94  3.09  15  5.80  3.07  −0.14  3.08  1.12  Dumbryte et al. (17)  60  2.67  1.71  60  2.49  1.80  −0.18  1.76  0.32  Dumbryte et al. (21)  30  4.02  2.20  30  4.14  2.33  0.12  2.27  0.59  Heravi et al. (13)  75  8.67  4.0175  75  11.97  4.48  3.30  4.26  0.69  Heravi et al. (16)  60  5.40  1.50  60  9.65  1.71  4.25  1.61  0.29  Salehi et al. (14)  120  4.08  2.55  120  12.42  6.64  8.34  5.03  0.65    Width of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (6)  15  9.22  5.31  15  13.04  10.91  3.82  8.58  3.13  Dumbryte et al. (17)  60  1.81  1.06  60  2.18  1.23  0.37  1.15  0.21  Dumbryte et al. (21)  30  3.22  3.71  30  3.77  3.91  0.55  3.81  0.98  Heravi et al. (13)  —  —  —  —  —  —  —  —  —  Heravi et al. (16)  —  —  —  —  —  —  —  —  —  Salehi et al. (14)  —  —  —  —  —  —  —  —  —  Study  Number of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (6)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (17)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (21)  —  —  —  —  —  —  —  —  —  Heravi et al. (13)  75  4.70  2.43  75  7.63  2.96  2.93  2.71  0.44  Heravi et al. (16)  60  2.35  0.93  60  7.04  1.29  4.69  1.13  0.21  Salehi et al. (14)  120  2.20  1.26  120  5.02  2.61  2.82  2.05  0.26    Length of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  40  6.50  3.27  36  12.30  3.67  5.80  3.49  0.78  Dumbryte et al. (6)  15  5.94  3.09  15  5.80  3.07  −0.14  3.08  1.12  Dumbryte et al. (17)  60  2.67  1.71  60  2.49  1.80  −0.18  1.76  0.32  Dumbryte et al. (21)  30  4.02  2.20  30  4.14  2.33  0.12  2.27  0.59  Heravi et al. (13)  75  8.67  4.0175  75  11.97  4.48  3.30  4.26  0.69  Heravi et al. (16)  60  5.40  1.50  60  9.65  1.71  4.25  1.61  0.29  Salehi et al. (14)  120  4.08  2.55  120  12.42  6.64  8.34  5.03  0.65    Width of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (6)  15  9.22  5.31  15  13.04  10.91  3.82  8.58  3.13  Dumbryte et al. (17)  60  1.81  1.06  60  2.18  1.23  0.37  1.15  0.21  Dumbryte et al. (21)  30  3.22  3.71  30  3.77  3.91  0.55  3.81  0.98  Heravi et al. (13)  —  —  —  —  —  —  —  —  —  Heravi et al. (16)  —  —  —  —  —  —  —  —  —  Salehi et al. (14)  —  —  —  —  —  —  —  —  —  Number of enamel microcracks was not evaluated in the following studies: Ahrari et al. (examined number parameter, but did not provide absolute value for this characteristic; 5), Dumbryte et al. (6), Dumbryte et al. (17), and Dumbryte et al. (21). Width of enamel microcracks was not evaluated in the following studies: Ahrari et al. (5), Heravi et al. (13), Heravi et al. (16), Salehi et al. (14). SD, Standard deviation; SE, Standard error. View Large Table 5. Mean number, length, and width values of enamel microcracks before and after debonding, and difference in means. Study  Number of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (6)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (17)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (21)  —  —  —  —  —  —  —  —  —  Heravi et al. (13)  75  4.70  2.43  75  7.63  2.96  2.93  2.71  0.44  Heravi et al. (16)  60  2.35  0.93  60  7.04  1.29  4.69  1.13  0.21  Salehi et al. (14)  120  2.20  1.26  120  5.02  2.61  2.82  2.05  0.26    Length of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  40  6.50  3.27  36  12.30  3.67  5.80  3.49  0.78  Dumbryte et al. (6)  15  5.94  3.09  15  5.80  3.07  −0.14  3.08  1.12  Dumbryte et al. (17)  60  2.67  1.71  60  2.49  1.80  −0.18  1.76  0.32  Dumbryte et al. (21)  30  4.02  2.20  30  4.14  2.33  0.12  2.27  0.59  Heravi et al. (13)  75  8.67  4.0175  75  11.97  4.48  3.30  4.26  0.69  Heravi et al. (16)  60  5.40  1.50  60  9.65  1.71  4.25  1.61  0.29  Salehi et al. (14)  120  4.08  2.55  120  12.42  6.64  8.34  5.03  0.65    Width of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (6)  15  9.22  5.31  15  13.04  10.91  3.82  8.58  3.13  Dumbryte et al. (17)  60  1.81  1.06  60  2.18  1.23  0.37  1.15  0.21  Dumbryte et al. (21)  30  3.22  3.71  30  3.77  3.91  0.55  3.81  0.98  Heravi et al. (13)  —  —  —  —  —  —  —  —  —  Heravi et al. (16)  —  —  —  —  —  —  —  —  —  Salehi et al. (14)  —  —  —  —  —  —  —  —  —  Study  Number of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (6)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (17)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (21)  —  —  —  —  —  —  —  —  —  Heravi et al. (13)  75  4.70  2.43  75  7.63  2.96  2.93  2.71  0.44  Heravi et al. (16)  60  2.35  0.93  60  7.04  1.29  4.69  1.13  0.21  Salehi et al. (14)  120  2.20  1.26  120  5.02  2.61  2.82  2.05  0.26    Length of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  40  6.50  3.27  36  12.30  3.67  5.80  3.49  0.78  Dumbryte et al. (6)  15  5.94  3.09  15  5.80  3.07  −0.14  3.08  1.12  Dumbryte et al. (17)  60  2.67  1.71  60  2.49  1.80  −0.18  1.76  0.32  Dumbryte et al. (21)  30  4.02  2.20  30  4.14  2.33  0.12  2.27  0.59  Heravi et al. (13)  75  8.67  4.0175  75  11.97  4.48  3.30  4.26  0.69  Heravi et al. (16)  60  5.40  1.50  60  9.65  1.71  4.25  1.61  0.29  Salehi et al. (14)  120  4.08  2.55  120  12.42  6.64  8.34  5.03  0.65    Width of enamel microcracks before bonding  After debonding  Difference (after data – before data)  N  Mean  SD  N  Mean  SD  Mean  SD  SE  Ahrari et al. (5)  —  —  —  —  —  —  —  —  —  Dumbryte et al. (6)  15  9.22  5.31  15  13.04  10.91  3.82  8.58  3.13  Dumbryte et al. (17)  60  1.81  1.06  60  2.18  1.23  0.37  1.15  0.21  Dumbryte et al. (21)  30  3.22  3.71  30  3.77  3.91  0.55  3.81  0.98  Heravi et al. (13)  —  —  —  —  —  —  —  —  —  Heravi et al. (16)  —  —  —  —  —  —  —  —  —  Salehi et al. (14)  —  —  —  —  —  —  —  —  —  Number of enamel microcracks was not evaluated in the following studies: Ahrari et al. (examined number parameter, but did not provide absolute value for this characteristic; 5), Dumbryte et al. (6), Dumbryte et al. (17), and Dumbryte et al. (21). Width of enamel microcracks was not evaluated in the following studies: Ahrari et al. (5), Heravi et al. (13), Heravi et al. (16), Salehi et al. (14). SD, Standard deviation; SE, Standard error. View Large The meta-analysis was performed considering the overall analysis for number, length, and width parameters. Due to the limited number of studies, no subgroup analyses could be performed with respect to the bracket type and residual adhesive removal. As far as changes in number of EMCs are concerned, following bracket removal number of EMCs increased (MD = 3.50, 95% CI, 2.13–4.87, P < 0.00001) compared to the values before the bonding procedure (Figure 3; Table 6). Figure 3. View largeDownload slide Forest plot of the mean difference (after debonding data – before bonding data) of the number parameter based on the random-effects model together with the 95 per cent confidence interval (CI). Figure 3. View largeDownload slide Forest plot of the mean difference (after debonding data – before bonding data) of the number parameter based on the random-effects model together with the 95 per cent confidence interval (CI). With regard to the changes in the length characteristic, debonding effect was also evident. The length of EMCs was on average 3.09 mm greater than before bracket removal (Figure 4; Table 6). Figure 4. View largeDownload slide Forest plot of the mean difference (after debonding data – before bonding data) of the length parameter based on the random-effects model together with the 95 per cent confidence interval (CI). Figure 4. View largeDownload slide Forest plot of the mean difference (after debonding data – before bonding data) of the length parameter based on the random-effects model together with the 95 per cent confidence interval (CI). Table 6. Details of the performed meta-analyses with tests on heterogeneity. No.  Variable  Studies  Effect size  Heterogeneity  MD  95% CIs  P  Tau2  I2 (%)  95% CIs  P  1.  Number  3  3.50  2.13, 4.87  <0.00001  1.37  94  87.2, 97.6  <0.00001  2.  Length  7  3.09  0.75, 5.43  0.010  9.52  97  96.1, 98.2  <0.00001  3.  Width  3  0.39  −0.01, 0.79  0.06  0.00  0  0.0, 89.6  0.54  No.  Variable  Studies  Effect size  Heterogeneity  MD  95% CIs  P  Tau2  I2 (%)  95% CIs  P  1.  Number  3  3.50  2.13, 4.87  <0.00001  1.37  94  87.2, 97.6  <0.00001  2.  Length  7  3.09  0.75, 5.43  0.010  9.52  97  96.1, 98.2  <0.00001  3.  Width  3  0.39  −0.01, 0.79  0.06  0.00  0  0.0, 89.6  0.54  CIs, confidence intervals; MD, mean difference. View Large Table 6. Details of the performed meta-analyses with tests on heterogeneity. No.  Variable  Studies  Effect size  Heterogeneity  MD  95% CIs  P  Tau2  I2 (%)  95% CIs  P  1.  Number  3  3.50  2.13, 4.87  <0.00001  1.37  94  87.2, 97.6  <0.00001  2.  Length  7  3.09  0.75, 5.43  0.010  9.52  97  96.1, 98.2  <0.00001  3.  Width  3  0.39  −0.01, 0.79  0.06  0.00  0  0.0, 89.6  0.54  No.  Variable  Studies  Effect size  Heterogeneity  MD  95% CIs  P  Tau2  I2 (%)  95% CIs  P  1.  Number  3  3.50  2.13, 4.87  <0.00001  1.37  94  87.2, 97.6  <0.00001  2.  Length  7  3.09  0.75, 5.43  0.010  9.52  97  96.1, 98.2  <0.00001  3.  Width  3  0.39  −0.01, 0.79  0.06  0.00  0  0.0, 89.6  0.54  CIs, confidence intervals; MD, mean difference. View Large Finally, for the width parameter the increase was observed following debonding, however the change was statistically insignificant (MD = 0.39 µm, 95% CI, −0.01 to 0.79, P = 0.06, Figure 5; Table 6). Figure 5. View largeDownload slide Forest plot of the mean difference (after debonding data – before bonding data) of the width parameter based on the random-effects model together with the 95 per cent confidence interval (CI). Figure 5. View largeDownload slide Forest plot of the mean difference (after debonding data – before bonding data) of the width parameter based on the random-effects model together with the 95 per cent confidence interval (CI). Risk of bias across studies Risk of bias across studies could not be performed due to limited number of trials. Additional analyses Sensitivity analysis showed that the included investigations dealing with the length and width parameters had a balanced impact on the calculated MD. With regard to the number of EMCs, further analysis was undertaken to gauge the exclusion of the study by Heravi et al. (16). The results did not change significantly (MD = 2.85, 95% CI, 2.41–3.29, P < 0.00001), however no statistical heterogeneity was found (Tau2 = 0, I2 = 0%, P = 0.83). Further sensitivity analysis revealed that if the study by Baherimoghadam et al. (18) was included in the meta-analysis, there would be only slight changes in the number and length values of EMCs (on average, the number of EMCs would increase by 2.98 and the length by 3.21 mm) with slight changes in the heterogeneity level following debonding compared to the original analysis (on average, the number increased by 3.50 and the length by 3.09 mm, Supplementary materials 1 and 2). Finally, sensitivity analysis showed that if studies with high risk of bias (5, 6, 14, 16) were excluded from the meta-analysis, the increase in length of EMCs would be, on average, 1.01 mm, i.e.~ 3 times lower compared to the original analysis (Supplementary material 3). Due to the limited number of studies no further sensitivity analysis (with exclusion of trials at high risk of bias) could be performed for the evaluation of the changes in number and width parameters following debonding. Discussion Summary of evidence This review included data from seven in vitro studies which assessed changes of EMCs characteristics (both qualitative and quantitative) following bracket removal from human teeth. Four investigations dealt with the number of EMCs (5, 13, 14, 16), seven studies measured length (5, 6, 13, 14, 16, 17, 21) and three trials examined width parameter (6, 17, 21). One study did not provide absolute values for number of EMCs, thus these results were not included in meta-analysis (5). As far as the number characteristic was concerned, results of the random-effects meta-analysis showed that following debonding there were significant changes of this parameter (on average, number of EMCs increased by 3.50 after bracket removal compared with the values before bonding). Since upper (4.87) and lower (2.13) limits of the 95 per cent CI do not cross zero line (line at 0) in the forest plot, the result can be considered as clinically significant (Figure 3). During further analysis of the forest plot, considerable between-study statistical heterogeneity was found (Tau2 = 1.37, I2 = 94%, 95% CI, 87.2–97.6, P < 0.00001, Figure 3). However, all identified trials dealing with number of EMCs lie to the right of the non-effect line (line at 0) in the forest plot, meaning that they all favor increase group. In this case, existing heterogeneity might have influence on the accurate calculation of the effect, i.e. what is the amount of the increase, but would not influence our decision, i.e. whether debonding leads to an increase in number of EMCs (31)? If the study by Heravi et al. (16) was excluded from the analysis, on average, the number would increase by 2.85 following removal of brackets and there would be no statistical heterogeneity (Tau2 = 0, I2 = 0%, P = 0.83). According to the methodology of this investigation (16), number of EMCs was calculated after debonding followed by residual adhesive removal, while in the rest two studies enamel surface analysis was performed without adhesive remnants elimination (13, 14). Better visibility of the buccal tooth surface and EMCs could lead to different results among the studies. However, considerable statistical heterogeneity should be interpreted with caution, because it is related to lack of investigations and the artificially narrow confidence intervals (28). All three studies evaluated number parameter following metal brackets removal. As for the adults’ esthetic brackets are usually the first choice appliance, additional future investigations analyzing ceramic brackets effect on EMCs would be desirable to produce more robust conclusions. The debonding procedure effect was also evident for the length characteristic. Although the effect of bracket removal varied among the included studies, the average of the various effects was an increase in length of EMCs by 3.09 mm compared to the values before bonding. Although 95 per cent CI of the overall effect (95% CI, 0.75–5.43) does not include zero value, however broad limits of the 95 per cent CI lead to doubtful clinical significance of the result. With regard to the heterogeneity evaluation, considerable between-study inconsistency was found (Tau2 = 9.52, I2 = 97%, 95% CI, 96.1–98.2, P < 0.00001, Figure 4). It is important to admit that the identified inconsistency could affect our decision, i.e. whether debonding leads to an increase in length of EMCs, because two trials (6, 17) are located on the left side and five studies (5, 13, 14, 16, 21) on the right side of the forest plot (31). Three investigations (6, 17, 21) where upper and lower limits of the 95 per cent CI cross the non-effect line, used the same device and methodology for the measurement of the length parameter. The rest four trials (5, 13, 14, 16) located on the right side of the forest plot utilized different techniques for EMCs analysis and did not present detailed description how the length was measured. The aforementioned differences might explain between-study inconsistency. Four out of seven investigations that calculated length of EMCs were judged as being in high risk of bias (5, 6, 14, 16) with the most problematic parameter being selective outcome reporting (5, 6, 14, 16). If studies with high risk of bias (5, 6, 14, 16) were excluded from further analysis, on average, length of EMCs would increase by 1.01 mm (95% CI, −0.91 to 2.93, P = 0.30, Supplementary material 3).The overall effect is ~ 3 times smaller compared to the original analysis. Upper and lower limits of the 95 per cent CI cross zero line in the forest plot, indicating that result is not significant (both clinically and statistically). Finally, there were no significant changes, neither clinically or statistically, in the width parameter after debonding (Figure 5). The average of the various effects was an increase in width of 0.39 µm (95% CI, −0.01 to 0.79, P = 0.06). Thus, additional future studies evaluating width of EMCs are needed to produce more robust conclusions. Based on the results of the systematic review, we summarized data about the changes of EMCs characteristics during orthodontic debonding. Since at the moment no method is invented and applied for direct measurement of EMCs parameters intraorally, precise examination of enamel damage under laboratory conditions remains the most important source of information about the changes of EMCs characteristics during orthodontic treatment. The summarized data could be important for clinicians in patient education as it is important to know which patients will benefit from traditional fixed appliances as well as which individuals possessing EMCs before the bonding procedure may require different appliances (e.g. lingual brackets, aligners) or debonding methods. Furthermore, results of the review might lead to the idea that EMCs increase following bracket removal could be regarded as an unavoidable consequence of debonding rather than orthodontic treatment failure. Such message is of particular importance clinically—patients should be fully informed of this issue before initiating orthodontic treatment as they are notified for e.g. of possible root resorption. Limitations Although no serious methodological limitations were found in the included investigations, their quality was moderate. For example, selective outcome reporting was observed in seven out of fourteen studies, complete outcome data before and after debonding was not presented clearly in eight trials (Figure 2). Moreover, due to the limited number of studies evaluating EMCs characteristics, especially number and width, the effect of debonding was analyzed without considering bracket type or residual adhesive removal. Therefore, additional future high-quality investigations that examine EMCs following debonding are necessary to draw more robust conclusions. Conclusions There is weak evidence indicating length and width of EMCs increase following bracket removal and the scientific evidence concerning quantitative evaluation of the number parameter before and after debonding is insufficient. However, there is a strong evidence that after debonding the number of EMCs is likely to increase. Supplementary Material Supplementary material is available at European Journal of Orthodontics online. Conflict of Interest None to declare. Acknowledgements European Commissions’s Seventh Framework Programme Laserlab-Europe IV JRA support BIOAPP (EC-GA 654148) is acknowledged. Authors are thankful to Dr. Vytautas Kazakevicius (Institute of Applied Mathematics at Vilnius University, Vilnius) for helping with the statistical analysis. References 1. Ryf, S., Flury, S., Palaniappan, S., Lussi, A., van Meerbeek, B. and Zimmerli, B. ( 2012) Enamel loss and adhesive remnants following bracket removal and various clean-up procedures in vitro. 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The European Journal of OrthodonticsOxford University Press

Published: Feb 21, 2018

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