TY - JOUR
AU - Bearn, David, R
AB - Summary Objective To compare orthodontically induced inflammatory root resorption (OIIRR) and patient perception of pain during orthodontic treatment between 0.018-inch and 0.022-inch slot bracket systems. Subjects and methods Eligible participants aged 12 years or above were allocated to treatment with the 0.018-inch or 0.022-inch slot MBT appliance (3M Unitek, Monrovia, California, USA) using block randomization in groups of 10. OIIRR was assessed radiographically using standardized periapical radiographs before and after 9 months from the start of treatment. Patient perception of pain was assessed using a validated patient questionnaire at 6 months from the start of treatment. Parametric tests (t-test) and non-parametric tests (chi-square with Fisher’s exact tests and Kruskal–Wallis test) assessed differences between the groups (P < 0.05). The correlation between severity of OIIRR and abnormal root morphology, history of dental trauma, and pain during treatment was assessed. Results Of the 187 participants randomized (1:1 ratio), 34 withdrew or were excluded (protocol deviations or poor cooperation). There were 77 patients in the 0.018-inch slot group and 76 patients in the 0.022-inch slot group (overall mean age: 19.1 years). Baseline characteristics were similar between groups (P > 0.05). There was no significant difference in the severity of the OIIRR nor patient perception of pain between the two study groups (P = 0.115 and P = 0.08 respectively). The correlation between the severity of OIIRR and abnormal root morphology or history of dental trauma was not statistically significant (P = 0.086 and P = 0.313). Moreover, there was no significant correlation between the severity of OIIRR and pain during treatment (R = 0.045, P = 0.617). Limitations It was impossible to blind clinicians or patients to allocation, and oral hygiene and periodontal outcomes were not assessed. Conclusions The effect of bracket slot size on the severity of OIIRR and patient perception of pain are not significant. Trial registration The trial was registered with ClinicalTrials.gov on 5 March 2014, registration number: NCT02080338. Introduction There are several fixed appliance systems used in contemporary orthodontics, which include multiple pre-adjusted edgewise fixed appliance systems. The orthodontic clinicians are divided around the world regarding preferences for the 0.018-inch or 0.022-inch slot size pre-adjusted edgewise bracket systems (1). Various theories of biomechanics are applied during different stages of the orthodontic treatment depending on the treatment objectives and operator preference. The proposed difference in the biomechanical interaction in both the 0.018-inch and 0.022-inch bracket slot systems and their archwires may influence the effectiveness of the different stages of orthodontic treatment (2). The alignment of malpositioned teeth begins in the initial stages of orthodontic treatment and is accomplished with flexible round archwires generating a combination of labiolingual and mesiodistal tipping (3). Rectangular archwires are almost always used at a later stage during alignment, to initiate torque control with rectangular stainless-steel archwires used as working archwires during the space-closure stage and correction of inter-arch relationships. The influence of treatment modalities on the effectiveness of orthodontic treatment had been investigated in the literature (4, 5); however, the influence of variation in the bracket slot system on the orthodontically induced inflammatory root resorption (OIIRR) and patient perception of pain during treatment remains to be investigated. During orthodontic tooth movement, unwanted biological side-effects can occur including OIIRR. It has been reported that OIIRR can be detected microscopically after 15 days (6) and using conventional radiographs after 7 weeks of orthodontic treatment (7). Several studies have detected OIIRR of variable severity after 6 months of orthodontic treatment (8, 9). Few studies have been conducted to investigate the influence of orthodontic bracket design, prescription, and bracket slot size on the severity of OIIRR. Most clinical trials have reported that the influence of orthodontic bracket design on the severity of OIIRR is insignificant (10, 11). However, a recent systematic review reported that OIIRR affecting maxillary central incisors can be influenced by the design of orthodontic brackets with reduced OIIRR being reported with a self-ligating bracket system (12). Reukers et al. (11) conducted a randomized clinical trial that investigated the difference in severity of OIIRR between the standard edgewise bracket system (with 0.018-inch slot) and pre-adjusted edgewise Roth prescription brackets (with 0.022-inch slot). The authors reported no statistically significant difference between the two bracket slot systems. However, the difference in bracket prescription between the two study groups was a potential confounding factor influencing the results. No orthodontic force can imitate the natural harmless physiologic forces (13). The orthodontic forces required for tooth movement are often associated with discomfort or pain (14). This is considered to be one of the biological side-effects that can have a significant influence on patient perception of orthodontic treatment particularly in early stages during alignment (14). Orthodontic pain can range from mild to severe discomfort (15). There is no evidence that archwire or bracket type choice can have an influence on pain perception during the orthodontic treatment (16). Currently, there is insufficient evidence relating the influence of different bracket slot systems to the effectiveness of orthodontic treatment. The randomized clinical trial is the study design of choice to compare the two common bracket slot size systems (0.018 inch and 0.022 inch) in terms of severity of OIIRR and patient perception of pain during treatment. Specific objectives or hypotheses This study is the third report of a randomized clinical trial that prospectively compared the effectiveness of orthodontic treatment with the two bracket slot sizes. Here, we present the secondary outcomes of the trial in terms of the biological side-effects in the form of OIIRR as well as patient perception of pain during treatment. Moreover, this report investigates several factors that potentially influence the severity of OIIRR, including a history of dental trauma and abnormal root morphology. The null hypothesis was as follows: there is no significant difference between the 0.018-inch or 0.022-inch slot bracket systems in terms of (1) severity of OIIRR and (2) patient perception of pain during treatment. Parts 1 and 2 report the results for the duration of treatment and quality of treatment, respectively (17, 18). Methods Trial design and any changes after trial commencement This was a two-arm, parallel-active-group randomized clinical trial with a 1:1 allocation ratio. There were no changes to the method after trial commencement. Participants, eligibility criteria, and setting In the UK, state-funded orthodontic treatment is provided through the National Health Service (NHS) for patients scoring Index of Orthodontic Treatment Need Dental Health Component of 3 and Aesthetic Component of 6 and above (moderate to complex cases) by office-based specialist orthodontists working with a team of orthodontic therapists, and hospital/faculty orthodontists trained to consultant level who also provide competitive-entry graduate programs for specialist and consultant-level training. All patients referred for hospital orthodontic care from January 2010 to September 2014 with good oral hygiene and a caries-free dentition were invited to participate in the study. The study was conducted in three sites; however, one site was unable to recruit to the study and so was withdrawn, leaving two sites that contributed the participants for the study. The participants were selected according to the following criteria: aged 12 years and above with any type of malocclusion who were scheduled for dual-arch fixed appliance orthodontic treatment. The exclusion criteria for the study were patients who (1) had undergone previous orthodontic treatment/functional appliances, (2) had orofacial clefts, (3) had severe hypodontia, (4) had special needs, and (5) required orthodontic–orthognathic surgery treatment. They did not take part and were not included in any analysis. Patients who met the inclusion criteria for the study received the patient information sheet and where relevant, the parent information sheet was also issued. The consent process was completed after obtaining patient/parent assent to participate in the study. The work was carried out in accordance with the Code of Medical Ethics of the World Medical Association (Declaration of Helsinki). Ethical approval was obtained from the NHS Tayside Committee on Medical Research Ethics (East of Scotland Ethics Service) in October 2009 (REC Reference: 09/S1401/56) and Research and Development (R&D) approval was obtained from the NHS Tayside R&D in November 2009. Interventions The treatment involved initially polishing the teeth with pumice and water, and using a self-etching primer (TransbondTM Plus Self Etching Primer, 3M Unitek, Monrovia, USA) to prepare the teeth for bracket placement. Adhesive pre-coated (APC) brackets/buccal tubes (APC™ II Victory Series™ Twin MBT™, 3M Unitek, Monrovia, USA) were bonded according to the allocation group, i.e. either 0.018-inch or 0.022-inch slot MBT prescription. Bands were used on molars where a transpalatal arch or quadhelix was required. A predetermined archwire sequence for each bracket slot system was followed (http://multimedia.3m.com/mws/media/736576O/wire-selection-for-optimal-biomechanic-efficiency-dr-d-segner.pdf). The archwire sequence for the 0.018-inch bracket slot system was as follows: 0.016-inch super elastic nickel–titanium (NiTi), 0.016 × 0.022-inch super elastic NiTi , and 0.016 × 0.022-inch stainless-steel archwires. For the 0.022-inch bracket slot system, the sequence was as follows: 0.016-inch super elastic NiTi, 0.019 × 0.025-inch super elastic NiTi, and 0.019 × 0.025-inch stainless-steel archwires. Appliances were routinely adjusted at an interval of 6–8 weeks. All appliances were ligated using conventional elastomeric ligation unless stainless-steel ligatures were required for severely rotated or ectopic teeth. All the participants received a standard treatment regimen according to the treatment protocol throughout the trial. Extraction spaces were closed using sliding mechanics with closed coil springs or elastomeric chains. Minor deviations from the standard protocol were accepted for certain clinical circumstances (e.g. use of ‘piggy back’ wires), but no special techniques or additional appointments were required for the study. Appliances were debonded and retainers were provided when a Class I incisor and canine relationship, a well-interdigitating buccal segment relationship, and all other treatment goals had been established. Prematurely terminated cases were due to poor patient compliance. Digital orthopantomographs were taken for all study participants before the start of treatment as part of the routine orthodontic assessment. Periapical radiographs with a long-cone paralleling technique for the maxillary central incisors were taken at the start of treatment and after 9 months from the start of treatment. In addition, digital lateral cephalometric radiographs were taken at the start and near end of treatment [UK orthodontic radiography guidelines by Isaacson et al. (19), updated by Isaacson et al.(20)]. Standardization of periapical radiographs All periapical radiographic request forms for the study were sent to the Dental and Maxillofacial Radiology Department and were colour-coded for trial identification to ensure standardization of the long-cone periapical radiograph technique. Radiographic films were placed using a film holder with a 40-cm film–source distance. The radiographs were generated at 60 kV and 7 mA DC with an exposure of 0.20 seconds. The periapical radiographs taken in this study were of two types depending on availability in the study centres: Digitized conventional film: conventional film radiographs [F speed film (www.carestream.com)] were digitized using a flatbed scanner [Epson perfection v750PRO (www.epson.com)] as 16-bit greyscale images at 300 dpi. Digital radiographs: taken using the phosphor plate (PPS) radiograph [Dürr Dental (www.duerr.co.uk)]. The radiographic images were coded (for blinding) and saved in JPG form and imported for measurements into Image J Link 1.4 software (http://rebweb.nih.gov/ij/index.html). An auxiliary validity in vitro experimental study was undertaken by the current research team to confirm the validity and agreement of measurements from digitized periapical radiographs produced by scanning conventional films in measuring root shortening when compared to the PPS digital imaging (21). Outcomes and any changes after trial commencement This article presents the secondary outcome measures of the randomized clinical trial that compared the severity of OIIRR and patient pain/discomfort during orthodontic treatment with 0.018-inch or 0.022-inch bracket slot systems. All the records were anonymized and the measurements were undertaken by the investigators (GM and AE) who were blinded to the study group allocation during assessment, and therefore identification of the group allocation was not possible. There were no outcome changes after trial commencement except for the dropout of one of the centres; however, as this was at the beginning of recruitment, it did not impact on the study results. The other two centres were able to recruit a sufficient number of patients. Orthodontically induced inflammatory root resorption OIIRR was evaluated in this study by assessing the severity of apical root resorption affecting the maxillary central incisors using standardized long-cone periapical radiographs. Pre-treatment radiographs were taken for all trial participants before the start of treatment (PA0) and 9 months after the start of treatment (PA1). Investigators were blinded for the study groups during radiographic analysis for assessing apical OIIRR as all the radiographs were coded in advance of being assessed. All the radiographs were rescored by the same investigators after an interval of 3 weeks to evaluate intra- and inter-investigator reliability. Method of assessing apical OIIRR from periapical radiograph The severity of OIIRR was assessed using the following scoring index that was adapted from Malmgren et al.(22): Grade 0: absence of apical root resorption Grade 1: irregular apical root contour Grade 2: minor apical root resorption, small area of root loss amounting to less than 2 mm Grade 3: severe apical root resorption from 2 mm to one-third of the original root length Grade 4: extreme apical root resorption exceeding one-third of the original root length The OIIRR scoring for the right and left maxillary central incisors for each participant was combined by taking the highest score (Figure 1) to represent a single dependent variable ‘upper central incisors OIIRR score’. Figure 1. View largeDownload slide (a) Periapical radiographs taken at the start of treatment showing an absence of orthodontically induced inflammatory root resorption (OIRR; grade 0). The root morphology was normal for both maxillary central incisors at the start of treatment (score 0). (b) Periapical radiographs taken at 9 months of treatment showing extreme OIIRR (grade 4) affecting the maxillary right central incisor and severe OIIRR (grade 3) affecting the maxillary left central incisor. Figure 1. View largeDownload slide (a) Periapical radiographs taken at the start of treatment showing an absence of orthodontically induced inflammatory root resorption (OIRR; grade 0). The root morphology was normal for both maxillary central incisors at the start of treatment (score 0). (b) Periapical radiographs taken at 9 months of treatment showing extreme OIIRR (grade 4) affecting the maxillary right central incisor and severe OIIRR (grade 3) affecting the maxillary left central incisor. Method of assessing root morphology Root morphology (Figure 1) was assessed for abnormality in the pre-treatment periapical radiograph using the following index that was adopted from Levander et al.(9): Score 0: normal root morphology Score 1: short root Score 2: blunt root Score 3: root with apical bend Score 4: root with apical pipette shape History of trauma History of dental trauma affecting the maxillary incisors was determined as a part of the initial orthodontic diagnostic assessment in the form of a yes or no question. Pain/discomfort A validated patient perception questionnaire was completed by the study participants at 6 months from the start of treatment (23). One of the domains of this questionnaire focused on assessing patient discomfort and soreness of both the teeth and the mouth during fixed appliance treatment. Sample size calculation Patients were recruited in this clinical trial according to the sample size calculation for the primary outcome, which is the full duration of orthodontic treatment. A total of 197 participants were recruited in the current study based on detecting a difference of 3 months with a standard deviation (SD) of 5.38, which was derived from the meta-analysis by Tsichlaki et al. (24). Moreover, a sample size calculation was also carried out for the severity of OIIRR as a representative of the secondary outcomes. A sample size of 16 participants in each group would have more than 80% power to detect a difference of 0.5 mm (equivalent to score 1) with a 0.05 significant difference level. Interim analyses and stopping guidelines This was determined if severe OIIRR was detected 9 months from the start of treatment using periapical radiographs in the majority of patients in one group. This would mandate that the trial monitoring committee should be convened to consider whether the study would be terminated. This evaluation was undertaken by an independent clinician to preserve masking regarding the study groups. Randomization Block randomization was used to form the allocation list for the two comparison groups. A computer random number generator was implemented to select random permuted blocks with a block size of 10 and an equal allocation ratio (http://www.graphpad.com/quickcalcs/randomn2.cfm). Then, the final allocation table for the participants in the study (which contained the study number and allocation group) was kept in a sealed envelope away from the clinical environment. Allocation concealment was achieved with sequentially numbered, identical, opaque, and sealed envelopes, which were prepared before the trial and contained the treatment allocation card. These were kept in a box and as the clinician obtained the informed consent, an independent dental nurse was responsible for identifying the next allocation envelope in the sequence to implement the randomization process. Blinding Due to the nature of this orthodontic trial, blinding to treatment allocation was only possible for the investigator and data analyst but was not possible for the clinicians and patients. The data were anonymized using 1 and 2 codes for the appliance types during the analysis. Thus, the data analyst could not identify allocation group during data analysis. As soon as the allocation envelope was opened in preparation for appliance placement, both clinician and participant knew the type of appliance used. This allowed the clinicians to follow the recommended standard sequence of archwires for each appliance. Although patients were aware of the allocation group, they did not have previous experience with orthodontic treatment and could not recognize the difference between appliances. Statistical analysis The data were analysed using the Statistical Package for Social Sciences for Windows, version 22.0 (SPSS Inc., Chicago, Illinois, USA). The following statistical analyses were used: Descriptive statistics: These included number, mean, SD, frequency, and percentages. Reliability statistics: The kappa test was used to test inter-examiner and intra-examiner reliability of periapical radiographs OIIRR scoring. Inferential statistics: A ‘per-protocol’ analysis was used. The two appliance groups were compared using t-test test for continuous data. Chi-square, Friedman test, Kruskal–Wallis test, and Wilcoxon signed-rank test were used for categorical data. The significance level was set as P less than 0.05. Spearman’s correlation coefficient test was used to assess the correlation between severity of OIIRR and several variables. Results Participant flow In the study, 197 patients were enrolled. Ten patients did not attend for appliance placement or declined to participate. Therefore, 187 patients were randomized to either the 0.018-inch or 0.022-inch group in a 1:1 ratio. The 34 (Figure 2) who were lost to follow-up or who either experienced a protocol deviation or where there was very poor compliance were excluded from the study. Therefore, 153 patients were included in the analysis (overall mean age: 19.1 ± 8.5 years). Patient recruitment started in January 2010 and ended in September 2014 and the trial was completed as planned. Figure 2. View largeDownload slide CONSORT flow chart describing the flow of participants through each stage of the trial. Figure 2. View largeDownload slide CONSORT flow chart describing the flow of participants through each stage of the trial. Baseline data Baseline characteristics including age at bonding, gender, type of malocclusion, pre-treatment peer assessment rating (PAR) score, and presence of extracted/missing and impacted teeth were found to be similar in both treatment arms (P greater than 0.05; Table 1). In addition, the baseline characteristics for the study dropout participants show almost similar distribution of age, gender, and pre-treatment PAR when compared to the analysed study sample in Table 1. Table 1. Baseline characteristics of participants in each study group Baseline characteristics 0.018 inch (N = 77) 0.022 inch (N = 76) Comparison between groups Continuous data Mean SD Mean SD t P Age 19.41 8.58 18.67 8.48 0.538 0.591 Pre-treatment PARa 31.22 10.77 31.56 13.73 −0.163 0.871 Categorical data Count % Count % Pearson chi-square P (Fisher’s exact test) Gender Female 56 73 49 64 1.210 0.299 Male 21 27 27 36 Type of malocclusion Class I 28 36 31 41 3.852 0.281 Class II Div. 1 19 25 23 30 Class II Div. 2 21 27 11 14 Class III 9 12 11 14 Extracted teeth Yes 59 77 53 70 0.925 0.366 No 18 23 23 30 Impacted teeth Yes 4 5 7 9 0.924 0.368 No 73 95 69 91 Baseline characteristics 0.018 inch (N = 77) 0.022 inch (N = 76) Comparison between groups Continuous data Mean SD Mean SD t P Age 19.41 8.58 18.67 8.48 0.538 0.591 Pre-treatment PARa 31.22 10.77 31.56 13.73 −0.163 0.871 Categorical data Count % Count % Pearson chi-square P (Fisher’s exact test) Gender Female 56 73 49 64 1.210 0.299 Male 21 27 27 36 Type of malocclusion Class I 28 36 31 41 3.852 0.281 Class II Div. 1 19 25 23 30 Class II Div. 2 21 27 11 14 Class III 9 12 11 14 Extracted teeth Yes 59 77 53 70 0.925 0.366 No 18 23 23 30 Impacted teeth Yes 4 5 7 9 0.924 0.368 No 73 95 69 91 aThe number of analysed cases for peer assessment rating score was 143 (0.018 inch = 73 and 0.022 inch = 70). View Large Table 1. Baseline characteristics of participants in each study group Baseline characteristics 0.018 inch (N = 77) 0.022 inch (N = 76) Comparison between groups Continuous data Mean SD Mean SD t P Age 19.41 8.58 18.67 8.48 0.538 0.591 Pre-treatment PARa 31.22 10.77 31.56 13.73 −0.163 0.871 Categorical data Count % Count % Pearson chi-square P (Fisher’s exact test) Gender Female 56 73 49 64 1.210 0.299 Male 21 27 27 36 Type of malocclusion Class I 28 36 31 41 3.852 0.281 Class II Div. 1 19 25 23 30 Class II Div. 2 21 27 11 14 Class III 9 12 11 14 Extracted teeth Yes 59 77 53 70 0.925 0.366 No 18 23 23 30 Impacted teeth Yes 4 5 7 9 0.924 0.368 No 73 95 69 91 Baseline characteristics 0.018 inch (N = 77) 0.022 inch (N = 76) Comparison between groups Continuous data Mean SD Mean SD t P Age 19.41 8.58 18.67 8.48 0.538 0.591 Pre-treatment PARa 31.22 10.77 31.56 13.73 −0.163 0.871 Categorical data Count % Count % Pearson chi-square P (Fisher’s exact test) Gender Female 56 73 49 64 1.210 0.299 Male 21 27 27 36 Type of malocclusion Class I 28 36 31 41 3.852 0.281 Class II Div. 1 19 25 23 30 Class II Div. 2 21 27 11 14 Class III 9 12 11 14 Extracted teeth Yes 59 77 53 70 0.925 0.366 No 18 23 23 30 Impacted teeth Yes 4 5 7 9 0.924 0.368 No 73 95 69 91 aThe number of analysed cases for peer assessment rating score was 143 (0.018 inch = 73 and 0.022 inch = 70). View Large Numbers analysed for each outcome, estimation and precision, subgroup analyses During the recruitment stage, 216 patients were invited to participate in the study; however, 19 patients declined and 197 participants were enrolled in the study with another 10 patient excluded before the randomization process (Figure 2). The total number of analysed participants in the current trial for the OIIRR outcome was 149 (74 for the 0.018-inch group and 75 for the 0.022-inch group) whereas for the patient perception of pain during treatment was 153 (77 for the 0.018-inch group and 76 for the 0.022-inch group). ‘Per-protocol’ analysis was carried out utilizing the data imputation wizard in SPSS for the OIIRR and patient perception to pain between the study groups. It was decided to use a ‘per-protocol’ analysis as the excluded patients were either not eligible to fulfil the protocol, failed to comply with treatment, or moved to another hospital or practice. However, to ensure that the dropouts from the study did not significantly influence the study results, an intention-to-treat analysis was also carried out, which showed agreement with the ‘pre-protocol analysis’. Reliability measurements Inter-examiner agreement for the OIIRR radiographic scoring was determined using the kappa statistic. This showed substantial agreement (0.749) between the two investigators. The same test was also used for intra-examiner reliability, which indicated high agreement (0.938) between the two episodes (21). Outcome measurements Orthodontically induced inflammatory root resorption Data for OIIRR at start of treatment PA0 and 9 months in treatment PA1 for both study groups and the total study sample are shown in Figure 3 and Table 2. The Friedman test for repeated ordinal variables was used to compare OIIRR score between T0 and T1 for the total sample and the two study groups. There was a statistically significant increase in the severity of OIIRR in T1 compared with T0 in the total sample and in the two study groups (P = 0.000). A Kruskal–Wallis test was used to compare the severity of OIIRR between 0.018 and 0.022 study groups at T0 and T1 (Table 3). No statistically significant difference was found between the two groups at neither T0 nor T1 (P = 0.847 and P = 0.115 respectively). Table 2. Distribution of pre- and post-treatment orthodontically induced inflammatory root resorption (OIIRR) and comparison between 0.018 and 0.022 study groups Pre-treatment root resorption scores Number Missing Score 0 Score 1 Score 2 Score 3 Score 4 0.018 group 74 0 58 (78.4%) 13 (17.6%) 2 (2.7%) 1 (1.4%) 0 (0%) 0.022 group 75 0 60 (80%) 11 (14.5%) 3 (4%) 1 (1.3%) 0 (0%) Total 149 0 118 (79.2%) 24 (16.1%) 5 (3.4%) 2 (1.3%) 0 (0%) Statistical test: Kruskal–Wallis test Mean rank Chi-square Df Significance 0.018 group = 75.49 0.022 group = 74.52 0.037 1 P = 0.847 Post-treatment root resorption scores Number Missing Score 0 Score 1 Score 2 Score 3 Score 4 0.018 group 74 0 14 (18.9%) 33 (44.6%) 20 (27%) 5 (6.8%) 2 (2.7%) 0.022 group 75 0 22 (29.7%) 33 (44.6%) 11 (14.9%) 6 (8.1%) 2 (2.7%) Total 149 0 36 (24.2%) 66 (44.3%) 31 (20.8%) 11 (7.4%) 4 (2.7%) Statistical test: Kruskal–Wallis test Mean rank Chi-square Df Significance 0.018 group = 79.74 2.489 1 P = 0.115 0.022 group = 69.26 Pre-treatment root resorption scores Number Missing Score 0 Score 1 Score 2 Score 3 Score 4 0.018 group 74 0 58 (78.4%) 13 (17.6%) 2 (2.7%) 1 (1.4%) 0 (0%) 0.022 group 75 0 60 (80%) 11 (14.5%) 3 (4%) 1 (1.3%) 0 (0%) Total 149 0 118 (79.2%) 24 (16.1%) 5 (3.4%) 2 (1.3%) 0 (0%) Statistical test: Kruskal–Wallis test Mean rank Chi-square Df Significance 0.018 group = 75.49 0.022 group = 74.52 0.037 1 P = 0.847 Post-treatment root resorption scores Number Missing Score 0 Score 1 Score 2 Score 3 Score 4 0.018 group 74 0 14 (18.9%) 33 (44.6%) 20 (27%) 5 (6.8%) 2 (2.7%) 0.022 group 75 0 22 (29.7%) 33 (44.6%) 11 (14.9%) 6 (8.1%) 2 (2.7%) Total 149 0 36 (24.2%) 66 (44.3%) 31 (20.8%) 11 (7.4%) 4 (2.7%) Statistical test: Kruskal–Wallis test Mean rank Chi-square Df Significance 0.018 group = 79.74 2.489 1 P = 0.115 0.022 group = 69.26 View Large Table 2. Distribution of pre- and post-treatment orthodontically induced inflammatory root resorption (OIIRR) and comparison between 0.018 and 0.022 study groups Pre-treatment root resorption scores Number Missing Score 0 Score 1 Score 2 Score 3 Score 4 0.018 group 74 0 58 (78.4%) 13 (17.6%) 2 (2.7%) 1 (1.4%) 0 (0%) 0.022 group 75 0 60 (80%) 11 (14.5%) 3 (4%) 1 (1.3%) 0 (0%) Total 149 0 118 (79.2%) 24 (16.1%) 5 (3.4%) 2 (1.3%) 0 (0%) Statistical test: Kruskal–Wallis test Mean rank Chi-square Df Significance 0.018 group = 75.49 0.022 group = 74.52 0.037 1 P = 0.847 Post-treatment root resorption scores Number Missing Score 0 Score 1 Score 2 Score 3 Score 4 0.018 group 74 0 14 (18.9%) 33 (44.6%) 20 (27%) 5 (6.8%) 2 (2.7%) 0.022 group 75 0 22 (29.7%) 33 (44.6%) 11 (14.9%) 6 (8.1%) 2 (2.7%) Total 149 0 36 (24.2%) 66 (44.3%) 31 (20.8%) 11 (7.4%) 4 (2.7%) Statistical test: Kruskal–Wallis test Mean rank Chi-square Df Significance 0.018 group = 79.74 2.489 1 P = 0.115 0.022 group = 69.26 Pre-treatment root resorption scores Number Missing Score 0 Score 1 Score 2 Score 3 Score 4 0.018 group 74 0 58 (78.4%) 13 (17.6%) 2 (2.7%) 1 (1.4%) 0 (0%) 0.022 group 75 0 60 (80%) 11 (14.5%) 3 (4%) 1 (1.3%) 0 (0%) Total 149 0 118 (79.2%) 24 (16.1%) 5 (3.4%) 2 (1.3%) 0 (0%) Statistical test: Kruskal–Wallis test Mean rank Chi-square Df Significance 0.018 group = 75.49 0.022 group = 74.52 0.037 1 P = 0.847 Post-treatment root resorption scores Number Missing Score 0 Score 1 Score 2 Score 3 Score 4 0.018 group 74 0 14 (18.9%) 33 (44.6%) 20 (27%) 5 (6.8%) 2 (2.7%) 0.022 group 75 0 22 (29.7%) 33 (44.6%) 11 (14.9%) 6 (8.1%) 2 (2.7%) Total 149 0 36 (24.2%) 66 (44.3%) 31 (20.8%) 11 (7.4%) 4 (2.7%) Statistical test: Kruskal–Wallis test Mean rank Chi-square Df Significance 0.018 group = 79.74 2.489 1 P = 0.115 0.022 group = 69.26 View Large Table 3. Descriptive data for root morphology and correlation with severity of orthodontically induced inflammatory root resorption (OIIRR) Root morphology Number Percentage Normal morphology 228 76.5 Abnormal root morphology (total) 70 23.5 Short root 24 8.1 Blunt root 32 10.7 Apical bend 6 2 Pipette shape 8 2.7 Total 298 100 OIIRR Root morphology/OIIRR Score 0 Score 1 Score 2 Score 3 Score 4 Normal morphology 93 (41.0%) 92 (40.6%) 35 (15.6%) 2 (1.1%) 3 (1.5%) Abnormal root morphology (total) 22 (31.4%) 31 (44.3%) 12 (17.1%) 4 (5.7%) 1 (1.5%) Spearman’s correlation coefficient test 0.10 Spearman’s significant at P < 0.05 test P = 0.086 Root morphology Number Percentage Normal morphology 228 76.5 Abnormal root morphology (total) 70 23.5 Short root 24 8.1 Blunt root 32 10.7 Apical bend 6 2 Pipette shape 8 2.7 Total 298 100 OIIRR Root morphology/OIIRR Score 0 Score 1 Score 2 Score 3 Score 4 Normal morphology 93 (41.0%) 92 (40.6%) 35 (15.6%) 2 (1.1%) 3 (1.5%) Abnormal root morphology (total) 22 (31.4%) 31 (44.3%) 12 (17.1%) 4 (5.7%) 1 (1.5%) Spearman’s correlation coefficient test 0.10 Spearman’s significant at P < 0.05 test P = 0.086 View Large Table 3. Descriptive data for root morphology and correlation with severity of orthodontically induced inflammatory root resorption (OIIRR) Root morphology Number Percentage Normal morphology 228 76.5 Abnormal root morphology (total) 70 23.5 Short root 24 8.1 Blunt root 32 10.7 Apical bend 6 2 Pipette shape 8 2.7 Total 298 100 OIIRR Root morphology/OIIRR Score 0 Score 1 Score 2 Score 3 Score 4 Normal morphology 93 (41.0%) 92 (40.6%) 35 (15.6%) 2 (1.1%) 3 (1.5%) Abnormal root morphology (total) 22 (31.4%) 31 (44.3%) 12 (17.1%) 4 (5.7%) 1 (1.5%) Spearman’s correlation coefficient test 0.10 Spearman’s significant at P < 0.05 test P = 0.086 Root morphology Number Percentage Normal morphology 228 76.5 Abnormal root morphology (total) 70 23.5 Short root 24 8.1 Blunt root 32 10.7 Apical bend 6 2 Pipette shape 8 2.7 Total 298 100 OIIRR Root morphology/OIIRR Score 0 Score 1 Score 2 Score 3 Score 4 Normal morphology 93 (41.0%) 92 (40.6%) 35 (15.6%) 2 (1.1%) 3 (1.5%) Abnormal root morphology (total) 22 (31.4%) 31 (44.3%) 12 (17.1%) 4 (5.7%) 1 (1.5%) Spearman’s correlation coefficient test 0.10 Spearman’s significant at P < 0.05 test P = 0.086 View Large Figure 3. View largeDownload slide Bar chart showing the percentage distribution of orthodontically induced inflammatory root resorption (OIIRR) severity score in the 0.018 and 0.022 study groups. Figure 3. View largeDownload slide Bar chart showing the percentage distribution of orthodontically induced inflammatory root resorption (OIIRR) severity score in the 0.018 and 0.022 study groups. No statistically significant correlation was found between either OIIRR and a history of trauma, or abnormal root morphology of the maxillary central incisors [R = 0.042, P = 0.313 and R = 0.10, P = 0.086 respectively (Table 4)]. No correlation was found between the duration of rectangular NiTi archwires use during the alignment stage and the severity of OIIRR (R = −0.43, P = 0.61). Table 4. Descriptive data for pain experience during treatment and correlation with orthodontically induced inflammatory root resorption (OIIRR) severity OIIRR/pain and discomfort Pain and discomfort correlation with OIIRR No pain Mild pain Severe pain Score 0 5 35 5 Score 1 8 42 4 Score 2 2 23 1 Score 3 0 5 0 Spearman’s test correlation coefficient R = 0.045 Spearman’s test significant at P < 0.05 P = 0.617 OIIRR/pain and discomfort Pain and discomfort correlation with OIIRR No pain Mild pain Severe pain Score 0 5 35 5 Score 1 8 42 4 Score 2 2 23 1 Score 3 0 5 0 Spearman’s test correlation coefficient R = 0.045 Spearman’s test significant at P < 0.05 P = 0.617 View Large Table 4. Descriptive data for pain experience during treatment and correlation with orthodontically induced inflammatory root resorption (OIIRR) severity OIIRR/pain and discomfort Pain and discomfort correlation with OIIRR No pain Mild pain Severe pain Score 0 5 35 5 Score 1 8 42 4 Score 2 2 23 1 Score 3 0 5 0 Spearman’s test correlation coefficient R = 0.045 Spearman’s test significant at P < 0.05 P = 0.617 OIIRR/pain and discomfort Pain and discomfort correlation with OIIRR No pain Mild pain Severe pain Score 0 5 35 5 Score 1 8 42 4 Score 2 2 23 1 Score 3 0 5 0 Spearman’s test correlation coefficient R = 0.045 Spearman’s test significant at P < 0.05 P = 0.617 View Large Patient perception of pain Data from the patient questionnaire completed by participants at 6 months from the start of treatment showed that 10.6% of the participants reported ‘a lot of sore teeth’ and 11.2% reported ‘no sore teeth’ whereas the majority of the sample 78.2% reported ‘little sore teeth’. There was no statistically significant difference in the patient perception of pain between the two study groups (P = 0.08). The correlation between the severity of pain and discomfort during fixed orthodontic treatment and severity of OIIRR was assessed for the total study sample using Spearman’s test (Table 4 and Figure 4). No statistically significant correlation was found between severity of OIIRR and severity of pain and discomfort during treatment (R = 0.045, P = 0.617). Figure 4. View largeDownload slide Bar chart showing the percentage distribution of patient perception of pain/discomfort according to severity of orthodontically induced inflammatory root resorption (OIIRR) score for the whole study sample. Figure 4. View largeDownload slide Bar chart showing the percentage distribution of patient perception of pain/discomfort according to severity of orthodontically induced inflammatory root resorption (OIIRR) score for the whole study sample. Harms No adverse reactions were reported during treatment. Discussion This report presents the secondary outcomes of the trial comparing the 0.018-inch and 0.022-inch bracket slot systems in the form of OIIRR and patient perception of pain during treatment. No statistically significant difference was found between the two study groups for either of the variables that were investigated. Comparison of the descriptive baseline variables indicated that there were no statistically significant differences between the two study groups. This ensured that the randomization process for the recruited sample was effective in producing study groups with almost similar pre-treatment characteristics. This reduced the influence of confounding factors when comparing between the two study groups and indicated that the results are valid and unlikely to be caused by any factor other than the intervention being investigated. The severity of malocclusion for the sample recruited was evaluated in this study using several methods that included PAR score, severity of crowding, and amount of irregularity in the upper and lower arches. The mean PAR score for both study groups was (31.2 and 31.6), which was higher than that reported by several previous studies with PAR scores between 24 and 29 (25, 26). This may be explained by the referral policy within NHS for mainly complex cases to be accepted for treatment in consultant-led clinics. The total number of participants analysed in the current trial for OIIRR outcome were 149 participants (20% dropout), whereas data were available for 153 for the perception of pain during treatment (18% dropout). It was decided to use a ‘per-protocol’ analysis as the excluded patients were either not eligible to fulfil the protocol, failed to comply with treatment, or moved to another hospital or practice. In addition, most of the dropouts had neither completed treatment nor reached a stage where outcomes could be predicted from the available baseline data, so imputing their data could result in bias. Finally, the analysed sample size for the secondary outcomes investigated in the current article was found to be more than adequately powered (90%). Moreover, baseline characteristics of the dropout participants and the sample analysed were found to be almost similar. The hypothesis investigated was that there is no significant difference between the 0.018-inch or 0.022-inch slot bracket systems in terms of (1) severity of OIIRR and (2) patient perception of pain during treatment. Severity of OIIRR In the current study, the biological side-effects of fixed appliance orthodontic treatment were evaluated by assessing the severity of OIIRR affecting the maxillary central incisors after 9 months from inserting the initial continuous archwire. The results of the current study did not reveal a statistically significant difference between the 0.018-inch and 0.022-inch slot brackets for OIIRR. Evaluation of OIIRR in the current sample was undertaken by assessing the severity of OIIRR affecting the maxillary central incisors as they have the highest prevalence of OIIRR (13, 27, 28). This is in agreement with several studies who evaluated OIIRR during orthodontic treatment (29, 30). Periapical radiographs were used in the current study to assess OIIRR as these are the routine gold-standard conventional radiograph for detecting OIIRR (31). Although periapical radiographs have been criticized for limited diagnostic information when compared to cone-beam CT imaging (CBCT), the relative increased radiation dose from CBCT could not be justified to detect any minimal differences in OIIRR, affecting the labial or palatal surfaces of the maxillary incisors, particularly where these differences are not clinically significant (32). Several techniques have been described in the literature for radiographically quantifying OIIRR including linear measurements, scoring indices, and digital image reconstruction (22, 33, 34). It has been reported that even with adequate standardization of the radiographic technique for consecutive periapical radiographs, potential errors in linear measurements of OIIRR can still occur due to several factors including change in the angulation of teeth during orthodontic tooth movement (35). In agreement with several studies (28, 36) the OIIRR scoring index suggested by Malmgren et al. (22) was used. The use of this index avoided error from linear measurements. Although the scoring index may be slightly subjective depending on morphological root changes in combination with measurement guidance, the high intra- and inter-examiner agreement of the OIIRR scores suggests high reliability of the results (0.938 and 0.749 respectively). Assessment of OIIRR at 9 months as a representative period is in line with the British Orthodontic Society radiography guidelines (20) where severe OIIRR can be detected early in treatment by radiographically assessing the maxillary incisors 6–9 months from start of treatment. This is also in accordance with several investigations that have reported OIIRR is detectable at least 6 months from start of treatment (8, 37, 38, 39). There was a statistically significant increase in the severity of root resorption at 9 months of treatment for the total sample and in the 2 study groups. Almost three-quarters (75.8%) of the sample in the current study showed some degree of OIIRR after 9 months from the start of orthodontic tooth movement. This relatively high percentage is in agreement with CBCT and histological studies, reporting that almost all teeth experience a degree of OIIRR, although for most patients, OIIRR is considered clinically insignificant (27). There was no statistically significant difference in the severity of OIIRR between the 0.018 and 0.022 groups for the radiographs taken pre-treatment (P = 0.847) and at 9 months from the start of treatment (P = 0.115). The difference in bracket slot size between the study groups allowed the use of larger dimension rectangular aligning archwires in combination with the 0.022-inch bracket slot system when compared with the 0.018 bracket slot system. This increase in archwire dimension and decrease in ‘play’ between the 0.018-inch bracket slot and the initial archwire (0.016 NiTi) can in turn increase orthodontic forces applied to teeth and lead to increased forces on the dentoalveolar process, respectively. According to the results from the current study, this difference in the interaction between the different bracket slot systems and archwires had no significant influence on the severity of OIIRR. Our results agree with those from a randomized clinical trial investigating the difference in severity of OIIRR between standard edgewise bracket system (0.018-inch slot) and pre-adjusted edgewise Roth prescription brackets (0.022-inch slot) (11). The authors found no statistically significant difference between the two groups; however, the bracket prescription could have been a potential confounding factor influencing the results. Moreover, Artun et al. (37) and Smale et al. (8) using the same sample reported no statistically significant difference between the patients treated with 0.018-inch or 0.022-inch slots after 6 and 12 months from starting treatment; however, the statistical tests were not reported in the published articles. Also, selection bias could have influenced the results due to a lack of random allocation on the level of the bracket slot size in these two studies. It has been well documented that the aetiology of OIIRR is multifactorial including individual and treatment factors (13). The findings from the current study determined that the effect of bracket slot size on the severity of OIIRR is insignificant. This agrees with Weltman et al. (27) who reported in a systematic review that OIIRR is unaffected by archwire sequencing, bracket prescription, or design. Correlation between OIIRR and dental trauma In the current trial 16.4% of the participants reported history of trauma to the upper anterior teeth. This percentage is similar to that reported by Brin et al. (40) No statistically significant correlation was found (P = 0.667) between severity of OIIRR at 9 months of treatment and history of trauma to the anterior teeth. This is in agreement with Artun et al. (37) and Smale et al. (8) who found no significant association between history of trauma and the severity of OIIRR at 6 and 12 months from the start of treatment. The current results are also in agreement with Weltman et al. (27) who reported that incisors with a history of trauma but no signs of root resorption at the beginning of treatment had the same prevalence of OIIRR as those without trauma. Correlation between OIIRR and abnormal root morphology In the current study, 23.5% of the maxillary central incisors had some form of abnormality in root morphology. This percentage is higher than that reported by Sameshima and Sinclair (41) at 2.7% and lower than that reported by Brin et al. (42) and Marques et al. (43) (35.5% and 31.5% respectively). This variation in the prevalence of abnormal root morphology among studies can be explained by the different criteria used in the subjective scoring indices for root morphology in each study. No statistically significant (P = 0.115) correlation was found in the current study between the teeth with abnormal root morphology and the severity of OIIRR at 9 months. The results from the current study did not agree with findings of the systematic review by Weltman et al. (27) who reported that there is evidence that abnormal roots may be at slightly higher risk of moderate-to-severe risk for OIIRR when compared to normal roots. However, Weltman et al. (27) based their finding on the results from a single randomized clinical trial (42), which surprisingly did not publish statistical tests to demonstrate significant influence of root morphology on the severity of OIIRR. Correlation between OIIRR and duration of rectangular NiTi archwires In the current study, the periapical radiographs were taken after 9 months from the start of orthodontic treatment, which corresponded with the end of the alignment stage. The use of rectangular NiTi archwires during the alignment stage introduces third-order movement (root torque). Previous studies have implicated rectangular archwires and torque expression for increased severity OIIRR (39). However, in the current study, the rectangular NiTi archwires were used for more than half the duration (52–57%) of the alignment stage, and no statistically significant correlation was found between the severity of OIIRR and the duration of rectangular NiTi archwire use. It is important to note that this is not a representation of the full duration of treatment, which requires stainless-steel rectangular archwires. This is in agreement with Mandall et al. (29) who reported no statistically significant difference in the severity of OIIRR when comparing different archwire sequences where one group had used rectangular archwires from day one for the alignment stage. Patient perception of pain during orthodontic treatment In the current study, most of the study participants experienced soreness related to teeth, mouth, and rubbing. However, the majority of those participants rated this teeth soreness as ‘a little’. It was noted that 10.6% of the participants reported ‘a lot of sore teeth’ and 11.2% reported ‘no sore teeth’ whereas the majority 78.2% of the sample reported little sore teeth at 6 months. This finding is in agreement with most studies that have investigated patient perception of wearing different types of orthodontic appliances (29, 44). Most of the studies in the literature, which have assessed pain/discomfort during orthodontic treatment, evaluated the first hours, days, or weeks of treatment (4, 44). Although pain/discomfort after the first visit can be relatively severe compared to that experienced during the rest of the treatment, the aim of the study was to have an overall picture of the effect of the different brackets slot/archwire systems on pain/discomfort experience during the treatment. The initial 6-month period of treatment is appropriate for the realistic assessment of pain/discomfort for the following reasons: any initial pain/discomfort arising immediately following fitting of appliances will not confound the assessment, and by this stage in treatment, participants had accommodated to the fixed appliances. No statistically significant difference was found between the two study groups, which is in agreement with Jian et al. (16) who found neither archwire nor bracket type have any influence on patient pain perception during orthodontic treatment (16). According to histological studies, OIIRR occurs during the elimination of the hyaline zone, which occurs due to reduced blood flow and ischemia after applying orthodontic forces (13, 45). Interestingly, pain during orthodontic tooth movement is thought to occur due to localized ischemia resulting from the orthodontic forces applied during tooth movement (14). It was therefore appropriate to investigate any correlation between orthodontic pain and OIIRR as both are related to localized ischemia. However, there was no statistically significant correlation between the severity of OIIRR and the severity of pain and discomfort during treatment (R = 0.045, P = 0.617). This indicates that pain and discomfort during orthodontic treatment are not a symptom of ongoing severe OIIRR. There are no studies in the literature that have investigated this topic and further studies are required. Limitations The data for OIIRR available from the current study are only for the initial stage of treatment (9 months). However, there is enough evidence in the literature to support the significant correlation between the severity of OIIRR at 6–12 months from start of treatment and the severity of OIIRR at the end of treatment. In addition, there are some limitations in using two-dimensional radiographs in assessing OIIRR. However, three-dimensional CBCT technology was not used in this study due to the relatively high radiation exposure for participants. Generalizability The external validity of the study was high as all eligible participants were recruited from a complete cohort presenting for state-funded orthodontic treatment in hospitals in the same health board area. However, the current study was undertaken in a teaching hospital environment, which might be different from orthodontic practice in primary care as the cohort included patients with all malocclusion types and both extraction and non-extraction cases. Opportunities for future clinical research Given that there was no statistically, nor clinically significant difference in the current study outcomes between the two study groups, this means the choice of bracket slot size remains the clinician’s preference. It would therefore be appropriate to investigate clinician perception and experience of both bracket slot systems for dual-arch orthodontic treatment. Conclusions The findings from the current study suggest that the effect of bracket slot size on the severity of OIIRR and patient perception of pain during treatment are not significant. Funding This trial was supported by the UK National Health Service (NHS) for NHS support costs. The University of Dundee provided academic sponsorship and 3M Unitek provided brackets and wires. Acknowledgements The authors would like to thank all patients who contributed to this study and Dundee Dental Hospital staff. Conflict of interest None declared. 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For permissions, please email: journals.permissions@oup.com This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)
TI - A randomized clinical trial of the effectiveness of 0.018-inch and 0.022-inch slot orthodontic bracket systems: part 3—biological side-effects of treatment
JF - The European Journal of Orthodontics
DO - 10.1093/ejo/cjy039
DA - 2019-03-29
UR - https://www.deepdyve.com/lp/oxford-university-press/a-randomized-clinical-trial-of-the-effectiveness-of-0-018-inch-and-0-XJ1SyAZhoJ
SP - 154
VL - 41
IS - 2
DP - DeepDyve
ER -