The effect of various adhesives, enamel etching, and base treatment on the failure frequency of customized lingual brackets: a randomized clinical trial

The effect of various adhesives, enamel etching, and base treatment on the failure frequency of... Summary Objectives The aim of this paper was to compare failure differences in precious metal customized lingual brackets bonded with three adhesive systems. Also, differences in failure of non-precious metal brackets with and without a silicatized base layer bonded with the same adhesive, as well as the influence of enamel etching prior to using a self-etching dual cure resin were explored. Materials/methods Five different groups were defined in a semi-randomized approach. Group 1 (IME): Maxcem Elite with 378 Incognito brackets and etched teeth, Group 2 (IMNE): Maxcem Elite with 193 Incognito brackets on non-etched teeth, Group 3 (INE): Nexus+Excite with 385 Incognito brackets, Group 4 (IRE): Relyx with 162 Incognito brackets, Group 5 (HRME) and Group 6 (HNRME): Maxcem Elite with 182 Harmony brackets with silicatized and non-slicatized bases respectively. Bracket failures were recorded over a 12-month period. Results The number of failures during the observation period was small in the various adhesives types of groups, as well as in HRME and HNRME groups, and the comparisons among those groups were non-significant (P > 0.05). A statistically significant difference (P < 0.05) was found between the IME and IMNE groups. Conclusions 1. During the first year of treatment customized lingual brackets failure frequencies (rates) are not different for the three adhesive materials tested. 2. Eliminating the etching stage when using self-etch/self-adhesive adhesives, may lead to a dramatic increase in the failure rates. 3. Silicoating of stainless steel customized lingual brackets does not seem to influence the failure of the bonds. Introduction Since its early conception in the late ’70s lingual orthodontics have suffered significant changes but progressively have acquired approval by the orthodontic community. Although the acceptability of orthodontic care with lingual appliances has increased for those patients who have strong concerns over the aesthetic appearance of appliances (1) with a consequent willingness to pay more money for them (2), it is not as high as expected among orthodontists (3), due to their perceived disadvantages (4,5). Multiple factors like the bonding agent employed, bonding technique used, etching time, concentration of the etch, characteristics of the bracket base, patients’ involvement, or the assistant’s role in the bonding procedure have been set responsible for success rate (6,7). A major apprehension for orthodontists has been the alleged difficulty to effectively bond lingual brackets with high precision as the access and visibility to the lingual surfaces of the teeth are compromised (8), and moisture isolation can be more challenging. In order to improve the adherence of lingual brackets different bonding protocols have been developed as well as the use of various adhesives has been proposed. Indirect bonding has been widely adopted as the preferred method since it decreases rotational and torque errors (9), accuracy in tooth positioning (10), and reduction in clinical time for fitting the appliances (11,12). In an effort to improve predictability of the procedure, and depending on the appliance design, various adhesive materials have been combined with indirect bonding for lingual brackets, with the most commonly used being either filled or un-filled, methyl methacrylate or bis-GMA resins (8). Silicoating of bracket bases has proved to strengthen the bond between the adhesive and the metal bracket (13). Thus, the silicatizing of the dental aspect of the brackets has been employed by manufacturers as an extra mean of enhancing the strength of bonding (14,15). An extra thin layer of single enamel-dentin bonding hydrophilic agent, may be additionally applied on the tooth to decrease the gaps that can develop due to the minor movements of the teeth that could occur from the day that the first impression is taken to the day of bonding (16). Also, enamel sandblasting has been shown to influence the bond strength of indirectly bonded lingual appliances (17). A recent meta-regressions analysis indicated that the adhesive resin application can be set aside during metal bracket bonding to enamel regardless of the type of orthodontic adhesive used (18). When self-adhesive systems were tested, they performed differently depending on the precedence of enamel etching (19,20). Reduction of bracket failures is an issue of great concern in routine orthodontic practicing as it may save considerable treatment time (less number of appointments, undisturbed treatment progress), and the evidence regarding the influence of the adhesives used with lingual brackets in clinical settings is not compelling (21). Therefore, the aim of this investigation was to compare the differences in bracket failure among three adhesive systems used regularly for bonding precious metal customized lingual brackets treated with SiO2 (Rocatec)™ (3M ESPE Dental Products, St. Paul, MN). In addition, differences in failure of non-precious metal brackets with and without a silicatized base layer bonded with the same adhesive, as well as the influence of enamel etching to the performance of a self-etching dual cure resin were explored. The null hypothesis was there would be no difference in the number of failing brackets among the different groups. Materials and methods All the participants (n = 208) were treated in a single private setting by the same clinician. Two different individualized lingual bracket types (Incognito Appliance; 3M-Unitek, Monrovia, CA, USA; formerly, TOP Service for Lingualtechnik, Bad Essen, Germany, and Harmony; Paris, France; distributed by American Orthodontics, Sheboygan, WI, USA) were bonded using three different adhesives: Maxcem Elite (Kerr, Orange, California) Nexus (Kerr, Orange, California) RelyX (3 M ESPE, AG Dental Products, Seefeld, Germany) The patients were randomly assigned by an assistant—The randomization scheme was generated by using the Web site randomization.com (http://www.randomization.com)—to form the following six groups, in a split-mouth design: Group 1 (IME): Maxcem Elite® was used to bond 378 Incognito brackets, on etched teeth. (34 female, 15 male patients, mean age: 31.6 years (range 15–59 years)). Group 2 (IMNE): Maxcem Elite® was used to bond 193 Incognito brackets, ‘on non-etched teeth’. (19 female, 7 male patients, mean age: 31.6 years (range 15–52 years)). Group 3 (INE): Nexus® adhesive in combination with Excite® which is a hydrophylic enamel/dentin agent was used to bond 385 Incognito brackets, on etched teeth. (37 female, 12 male patients, mean age: 34.9 years (range: 15–59 years)). Group 4 (IRE): Relyx® was applied to 162 Incognito brackets, on etched teeth. (16 female, 10 male patients, mean age: 32 years (range: 12–56 years)). Group 5 (HRME): Maxcem Elite® was applied to 182 Harmony brackets with silicatized bases, on etched teeth. (16 female, 10 male patients, mean age: 32 years (range: 12–56 years)). Group 6 (HNRME): Maxcem Elite® was used to bond 182 Harmony non-silicatized brackets, on etched teeth. (20 female, 12 male patients, mean age: 26,5 years (range: 15–69 years)). In total, 1482 brackets were bonded. No patients dropped out after the randomization or during the study (Figure 1). Figure 1. View largeDownload slide Flowchart describing the protocol and the patients included in the study. No patients dropped out; (n = number of patients, N = number of brackets, F = Female, M = Male). Figure 1. View largeDownload slide Flowchart describing the protocol and the patients included in the study. No patients dropped out; (n = number of patients, N = number of brackets, F = Female, M = Male). A standard bonding protocol was followed for all the patients. The lingual surfaces of the teeth were first cleaned with a rubber cup and slurry with pumice and water, rinsed with water and dried with compressed air. Then, they were sandblasted with 50μm aluminium oxide powder (Al2O3), and rinsed with water. A Nola retractor was used for cheek retraction and isolation, and etching was performed with a 37 per cent phosphoric acid gel for 1 minute. Etchant was not applied to those teeth that belonged in the non-etching group (Group 2). The teeth were rinsed and dried carefully again, and the etched surface was coated with Excite® (Ivoclar Vivadent, Ellwangen, Germany) in the Nexus group. The corresponding bonding material was finally applied in a thin layer on the brackets bases of all groups. The brackets were embedded in clear vacuum mold trays, the trays were next inserted in the mouth, and the adhesives were polymerized by light curing for 20 seconds per tooth. The trays were then removed and the brackets were inspected for proper seating. Bracket failures were recorded over a 12-month period. A failed bracket was not recorded twice if it failed again during the observation period. Statistical method Descriptive analysis was performed and presented as frequencies (percentages) representing the performance related to the different agents, the presence of enamel etching, and the bracket base treatment. The different adhesive groups were compared by means of the Fisher’s exact test since some of the cells in this 2 × 3 table contained less than five observations, and the chi-square test was used for the rest for the comparisons. The α-level of confidence was set to 0.05 and the Statistical Package for the Social Sciences (SPSS, Chicago, IL)) was used to perform the calculations. Results The number of failures during the observation period was small in the various adhesives groups. Only 9 brackets (2.4 per cent) failed in ‘group 1’ (Maxcem-adhesive), 17 (4.5 per cent) in ‘group 3’ (Nexus-adhesive), and 3 (1.9 per cent) in ‘group 4’ (RelyX-adhesive) (Table 1). Similar behaviour was noticed in the two groups differing in the silicatization of the bracket bases. Eight brackets (4.4 per cent) failed in the Rocatec, and ten (5.5 per cent) in the non-Rocatec group (Table 2). The differences among the failures in the different adhesives groups, as well as between the silicatized and non-silicatized groups were statistically non-significant (P > 0.05), and the null hypothesis was not rejected. In contrast to the previous, when the etched and non-etched groups (‘groups 1 and 2’) were compared the difference was statistically significant (P < 0.01), and the null hypothesis was rejected with the latter group (‘group 2’) presenting a considerable number of failing brackets (28) and raising the frequency of failures as high as 14.6 per cent compared to the much lower frequency (2.4 per cent) of the brackets bonded on etched enamel. (Table 3). Table 1. Number of brackets failed and those that stayed on teeth, as well as frequencies of failures and successes during the observation period, depending on the type of adhesive used. (P > 0.05). Successful bonding Type of adhesive Maxcem Elite (‘group1’) Nexus (‘group 3’) RelyX (‘group 4’) Total Yes 369 (97.6%) 368 (95.55%) 159 (98.1%) 896 No 9 (2.4%) 17 (4.5%) 3 (1.9%) 29 Total 378 385 162 925 Successful bonding Type of adhesive Maxcem Elite (‘group1’) Nexus (‘group 3’) RelyX (‘group 4’) Total Yes 369 (97.6%) 368 (95.55%) 159 (98.1%) 896 No 9 (2.4%) 17 (4.5%) 3 (1.9%) 29 Total 378 385 162 925 View Large Table 1. Number of brackets failed and those that stayed on teeth, as well as frequencies of failures and successes during the observation period, depending on the type of adhesive used. (P > 0.05). Successful bonding Type of adhesive Maxcem Elite (‘group1’) Nexus (‘group 3’) RelyX (‘group 4’) Total Yes 369 (97.6%) 368 (95.55%) 159 (98.1%) 896 No 9 (2.4%) 17 (4.5%) 3 (1.9%) 29 Total 378 385 162 925 Successful bonding Type of adhesive Maxcem Elite (‘group1’) Nexus (‘group 3’) RelyX (‘group 4’) Total Yes 369 (97.6%) 368 (95.55%) 159 (98.1%) 896 No 9 (2.4%) 17 (4.5%) 3 (1.9%) 29 Total 378 385 162 925 View Large Table 2. Number of brackets failed and those that stayed on teeth—all bonded with Maxcem Elite®—as well as frequencies of failures and successes during the observation period, depending on the prior etching of enamel (P < 0.05). Enamel etching Successful bonding Etched (‘group 1’) Non-etched (‘group 2’) Total Yes 369 (97.6%) 165 (85.4%) 534 No 9 (2.4%) 28 (14.6%) 37 Total 378 193 571 Enamel etching Successful bonding Etched (‘group 1’) Non-etched (‘group 2’) Total Yes 369 (97.6%) 165 (85.4%) 534 No 9 (2.4%) 28 (14.6%) 37 Total 378 193 571 View Large Table 2. Number of brackets failed and those that stayed on teeth—all bonded with Maxcem Elite®—as well as frequencies of failures and successes during the observation period, depending on the prior etching of enamel (P < 0.05). Enamel etching Successful bonding Etched (‘group 1’) Non-etched (‘group 2’) Total Yes 369 (97.6%) 165 (85.4%) 534 No 9 (2.4%) 28 (14.6%) 37 Total 378 193 571 Enamel etching Successful bonding Etched (‘group 1’) Non-etched (‘group 2’) Total Yes 369 (97.6%) 165 (85.4%) 534 No 9 (2.4%) 28 (14.6%) 37 Total 378 193 571 View Large Table 3. Distribution and frequencies of successful and failed Harmony® brackets—all bonded with Maxcem Elite® in the silicatized and non-silicatized groups (P > 0.05). Bracket base silicatization Successful bonding Rocatec (‘group 5’) No Rocatec (‘group 6’) Total Yes 174 (95.6%) 172 (94.5%) 346 No 8 (4.4%) 10 (5.5%) 18 Total 182 182 364 Bracket base silicatization Successful bonding Rocatec (‘group 5’) No Rocatec (‘group 6’) Total Yes 174 (95.6%) 172 (94.5%) 346 No 8 (4.4%) 10 (5.5%) 18 Total 182 182 364 View Large Table 3. Distribution and frequencies of successful and failed Harmony® brackets—all bonded with Maxcem Elite® in the silicatized and non-silicatized groups (P > 0.05). Bracket base silicatization Successful bonding Rocatec (‘group 5’) No Rocatec (‘group 6’) Total Yes 174 (95.6%) 172 (94.5%) 346 No 8 (4.4%) 10 (5.5%) 18 Total 182 182 364 Bracket base silicatization Successful bonding Rocatec (‘group 5’) No Rocatec (‘group 6’) Total Yes 174 (95.6%) 172 (94.5%) 346 No 8 (4.4%) 10 (5.5%) 18 Total 182 182 364 View Large Discussion Randomization aims at allocating interventions in such a way as to ensure that either the participants or the investigators will not know the kind of treatment that the patients may receive. Randomization in this study had the form of a split-mouth design which is considered an appropriate method for testing orthodontic materials because patients act as their own controls (22). The lack of use an adhesive as a control could be considered as a weakness of this study. However, due to the rather sparse use of lingual appliances there is not any adhesive universally accepted as ‘a gold standard’ to be used with them, and thus taken as a control. On the other hand, when considering the etching of the teeth, and the priming of the bracket base with silicon oxides the study could be considered a randomized controlled trial since the participants served as their own controls. Although the failure of a bracket was not recorded again if the same bracket failed a second time, the possibility that repeated bracket failures in the same individual could be a confounding factor among others (e.g. sex, anterior or posterior tooth, etc.) cannot be excluded. It has been shown that with customized lingual appliances bond failures occur most often during the first few months of treatment (23), thus, the first 1 year of treatment which was chosen as the observation period in this study reflects a realistic time as well as from a practical aspect. An additional weakness could be considered the lack of ‘a priori’ calculation of the number of brackets that should be included in the study in order to achieve appropriate α- and β-levels of confidence. It is probable that with the above low frequencies of failure among different adhesives an extremely big number of brackets should have been grouped for the aforementioned difference—if existed—to be detected. The failure rates reported in the literature pertaining to brackets bonded on the buccal side of the teeth vary from 2.9 per cent to 6.6 per cent (24–26), and they are in accordance with those measured in this project with the exception of the unusually high rate corresponding to the non-etched teeth. However, Ziebura et al. (21) comparing accidental debondings of buccal versus fully individualized lingual appliances, found a mean number of 2.63 bond failures per patient. The number of patients included in that study was 103, and this allows a lose calculation of the number of failures to two hundred and seventy (103 × 2.63 = 270.89 brackets failed). Considering that the total number of brackets bonded were 2543, this corresponds to a rather high failure frequency of 10.65 per cent. This could be partly attributed to the adhesive used in their study (Maximum Cure Sealant A and B; Reliance Orthodontic Products, Itasca, Ill) which was a dual part chemically curing filled adhesive, as opposed to the dual cure adhesives used in the present study. Another explanation could be that authors may recorded repeated failures on the same tooth of a single patient. In a retrospective survey by Roelofs et al. (6) aiming to identifying the role of an antisialagogue on the failure rate of buccally bonded attachments it was noted that the bonding process is very much operator depended and this may offer an additional explanation to the differences noted. The findings of the present clinical study, also contradict those of laboratory testing RelyX® and/or Maxcem as a clinically acceptable adhesive, where its mean shear bond strength (SBS) was measured to be lower than that of the control materials, and these adhesives seemed to be considered unsuitable for orthodontic bracket bonding (19,27–29). The difference could be due to the lack of etching prior to bonding in the teeth tested. Both agents have been promoted as a self-etching dual-cured resin, but in the present study all the teeth bonded with Relyx were etched before applying the cement, thus micromechanical retention was significantly enhanced. When Maxcem Elite® was tested on etched teeth it did not show any significant difference compared to Transbond XT® which was used as a control (20). Also, the combination of Nexus with Excite used to bond lingual brackets gave similar results as only 1 bracket failure per patient per year was recorded (23).This confirms the findings of this study, since only the teeth without etching presented a clinically and statistically significant difference in failures. The relative risk for a bracket to fail in the non-etched group was estimated to be 6.09 (95 per cent CI: 2.93–12.65) namely, the risk of failure (proportion of failure) for brackets on non-etched teeth is six times that of brackets on etched teeth. With the absolute risk difference deriving from the figures in Table 2, the calculated ‘numbers to treat’ are 8.9. Thus, 1 bracket failure may be prevented for every 8.9 brackets bonded on non-etched teeth, in case the manufacturer’s instructions are followed and the tested adhesive is employed as self-etch/self-adhesive bonding agent. This increase in bracket failure can provoke a severe escalation to the costs of treatment, disrupt the schedule of a practice, and prolong treatment duration. The evidence regarding the sandblasting of teeth surfaces prior to bonding lingual brackets are contradictory. There are reports supporting the view that the effect of this procedure does not increase the clinical performance of the attachments (17), although it increases the bond strength (17,30), and others promoting the use of the Al2O3 particles as a mean of conditioning the enamel before etching and consequently improving the bond (12,31). This process has become a routine in bonding lingual orthodontic appliances (8), and its use in this study did not seem to have any undesirable effect on the frequency of bracket failure. Stainless steel brackets which received tribochemical treatment (Rocatec application) showed (‘in vitro’) a slight improvement of the bond strength compared to non-treated brackets (13). In contrast to this, in a study by Algera et al. the investigated silicoating of the base did not have such a beneficial influence on bond strength that improved clinical results can be expected (32). This seems to confirm our results where the failure rate—within the observation period—of the Harmony® brackets which are made of stainless steel and bonded with Maxcem Elite® did not seem to be influenced by the presence of the SiOx layer. However, failures regarding Incognito® brackets which are cast in an alloy with a high gold content (15), without silane treatment were not tested in this study and thus, any conclusions as to the influence of this extra layer on adhesion cannot by drawn. Future research could be undertaken to clarify this issue further. In a recent meta-regression analysis, the authors suggested that the adhesive resin application can be set aside during metal bracket bonding to enamel regardless of the type of orthodontic adhesive used (18), but it is suggested that when bonding customized lingual appliances an extra layer of hydrophilic resin containing fluoride should be added to the teeth of children and adolescents, due to the preventive effect against decalcification (16). Since there was no difference among the failure frequencies of the adhesives with and without this intermediate layer tested in our study, the use of this supplementary layer of resin for the above reasons cannot be qualified with certainty. Effective bonding of customized lingual appliances can be characterized by accuracy in bracket placement and a very low frequency of bond failures. The bonding technique can be considered very sensitive since its success can be depended on multiple factors, e.g. the quality of the transfer tray, the preparation of the bracket pad, the control of moisture, and the curing method (8). The frequencies of bracket failures as measured in this project reflect the strengths/weaknesses of the process followed in a single practice by a single practitioner while even minor deviations from the attended protocol could had produced different outcomes. Properly randomized multi-centre clinical trials, probably regarding each of the different stages should be undertaken in order to draw more generalized conclusions. Conclusions Customized lingual brackets failure frequencies (rates) are not different for the three adhesive materials tested during the first year of treatment. Despite the instructions by different manufacturers, eliminating the enamel etching stage when using self-etch/self-adhesive adhesives, may lead to a dramatic increase in the failure rates of these brackets. Silicoating of stainless steel customized lingual brackets does not seem to influence the failure of bonds when Maxcem Elite® is used as the adhesive agent. Further research is needed to demonstrate the impact of each factor of the lingual bonding technique on the effectiveness of the adhesion. Conflict of interest The authors confirm and declare that the submitted research project is original, not under consideration for presentation elswhere, free of conflict of interest and conducted under the highest human welfare. References 1. McDonald , F. and Cobourne , M . ( 2007 ) Adult orthodontics: perils and pitfalls . Progress in Orthodontics , 8 , 308 – 313 . Google Scholar PubMed 2. Rosvall , M.D. , Fields , H.W. , Ziuchkovski , J. , Rosenstiel , S.F. and Johnston , W.M . 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Schnebel , B. , Mateer , S. , Maganzini , A.L. and Freeman , K . ( 2012 ) Clinical acceptability of two self-etch adhesive resins for the bonding of orthodontic brackets to enamel . Journal of Orthodontics , 39 , 256 – 261 . Google Scholar CrossRef Search ADS PubMed 28. Sethusa , M.P.S , Seedat , A.K. , du Preez , I.C. and Hlongwa , P . ( 2009 ) Shear bond strength comparison of RelyX Unicem with six other orthodontic resin adhesive systems . Journal of the South African Dental Association , 64 , 72 – 75 . Google Scholar PubMed 29. Vicente , A. , Bravo , L.A. , Romero , M. , Ortiz , A.J. and Canteras , M . ( 2005 ) A comparison of the shear bond strength of a resin cement and two orthodontic resin adhesive systems . Angle Orthodontist , 75 , 109 – 113 . Google Scholar PubMed 30. Robles-Ruiz , J.J. , Ciamponi , A.L. , Medeiros , I.S. and Kanashiro , L.K . ( 2014 ) Effect of lingual enamel sandblasting with aluminum oxide of different particle sizes in combination with phosphoric acid etching on indirect bonding of lingual brackets . Angle Orthodontist , 84 , 1068 – 1073 . Google Scholar CrossRef Search ADS PubMed 31. Canay , S. , Kocadereli , I. and Ak"ca , E . ( 2000 ) The effect of enamel air abrasion on the retention of bonded metallic orthodontic brackets . American Journal of Orthodontics & Dentofacial Orthopedics , 117 , 15 – 19 . Google Scholar CrossRef Search ADS 32. Algera , T.J. , Kleverlaan , C.J. , Prahl-Andersen , B. and Feilzer , A.J . ( 2008 ) The influence of different bracket base surfaces on tensile and shear bond strength . European Journal of Orthodontics , 30 , 490 – 494 . Google Scholar CrossRef Search ADS PubMed © The Author(s) 2017. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. 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/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The European Journal of Orthodontics Oxford University Press

The effect of various adhesives, enamel etching, and base treatment on the failure frequency of customized lingual brackets: a randomized clinical trial

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Abstract

Summary Objectives The aim of this paper was to compare failure differences in precious metal customized lingual brackets bonded with three adhesive systems. Also, differences in failure of non-precious metal brackets with and without a silicatized base layer bonded with the same adhesive, as well as the influence of enamel etching prior to using a self-etching dual cure resin were explored. Materials/methods Five different groups were defined in a semi-randomized approach. Group 1 (IME): Maxcem Elite with 378 Incognito brackets and etched teeth, Group 2 (IMNE): Maxcem Elite with 193 Incognito brackets on non-etched teeth, Group 3 (INE): Nexus+Excite with 385 Incognito brackets, Group 4 (IRE): Relyx with 162 Incognito brackets, Group 5 (HRME) and Group 6 (HNRME): Maxcem Elite with 182 Harmony brackets with silicatized and non-slicatized bases respectively. Bracket failures were recorded over a 12-month period. Results The number of failures during the observation period was small in the various adhesives types of groups, as well as in HRME and HNRME groups, and the comparisons among those groups were non-significant (P > 0.05). A statistically significant difference (P < 0.05) was found between the IME and IMNE groups. Conclusions 1. During the first year of treatment customized lingual brackets failure frequencies (rates) are not different for the three adhesive materials tested. 2. Eliminating the etching stage when using self-etch/self-adhesive adhesives, may lead to a dramatic increase in the failure rates. 3. Silicoating of stainless steel customized lingual brackets does not seem to influence the failure of the bonds. Introduction Since its early conception in the late ’70s lingual orthodontics have suffered significant changes but progressively have acquired approval by the orthodontic community. Although the acceptability of orthodontic care with lingual appliances has increased for those patients who have strong concerns over the aesthetic appearance of appliances (1) with a consequent willingness to pay more money for them (2), it is not as high as expected among orthodontists (3), due to their perceived disadvantages (4,5). Multiple factors like the bonding agent employed, bonding technique used, etching time, concentration of the etch, characteristics of the bracket base, patients’ involvement, or the assistant’s role in the bonding procedure have been set responsible for success rate (6,7). A major apprehension for orthodontists has been the alleged difficulty to effectively bond lingual brackets with high precision as the access and visibility to the lingual surfaces of the teeth are compromised (8), and moisture isolation can be more challenging. In order to improve the adherence of lingual brackets different bonding protocols have been developed as well as the use of various adhesives has been proposed. Indirect bonding has been widely adopted as the preferred method since it decreases rotational and torque errors (9), accuracy in tooth positioning (10), and reduction in clinical time for fitting the appliances (11,12). In an effort to improve predictability of the procedure, and depending on the appliance design, various adhesive materials have been combined with indirect bonding for lingual brackets, with the most commonly used being either filled or un-filled, methyl methacrylate or bis-GMA resins (8). Silicoating of bracket bases has proved to strengthen the bond between the adhesive and the metal bracket (13). Thus, the silicatizing of the dental aspect of the brackets has been employed by manufacturers as an extra mean of enhancing the strength of bonding (14,15). An extra thin layer of single enamel-dentin bonding hydrophilic agent, may be additionally applied on the tooth to decrease the gaps that can develop due to the minor movements of the teeth that could occur from the day that the first impression is taken to the day of bonding (16). Also, enamel sandblasting has been shown to influence the bond strength of indirectly bonded lingual appliances (17). A recent meta-regressions analysis indicated that the adhesive resin application can be set aside during metal bracket bonding to enamel regardless of the type of orthodontic adhesive used (18). When self-adhesive systems were tested, they performed differently depending on the precedence of enamel etching (19,20). Reduction of bracket failures is an issue of great concern in routine orthodontic practicing as it may save considerable treatment time (less number of appointments, undisturbed treatment progress), and the evidence regarding the influence of the adhesives used with lingual brackets in clinical settings is not compelling (21). Therefore, the aim of this investigation was to compare the differences in bracket failure among three adhesive systems used regularly for bonding precious metal customized lingual brackets treated with SiO2 (Rocatec)™ (3M ESPE Dental Products, St. Paul, MN). In addition, differences in failure of non-precious metal brackets with and without a silicatized base layer bonded with the same adhesive, as well as the influence of enamel etching to the performance of a self-etching dual cure resin were explored. The null hypothesis was there would be no difference in the number of failing brackets among the different groups. Materials and methods All the participants (n = 208) were treated in a single private setting by the same clinician. Two different individualized lingual bracket types (Incognito Appliance; 3M-Unitek, Monrovia, CA, USA; formerly, TOP Service for Lingualtechnik, Bad Essen, Germany, and Harmony; Paris, France; distributed by American Orthodontics, Sheboygan, WI, USA) were bonded using three different adhesives: Maxcem Elite (Kerr, Orange, California) Nexus (Kerr, Orange, California) RelyX (3 M ESPE, AG Dental Products, Seefeld, Germany) The patients were randomly assigned by an assistant—The randomization scheme was generated by using the Web site randomization.com (http://www.randomization.com)—to form the following six groups, in a split-mouth design: Group 1 (IME): Maxcem Elite® was used to bond 378 Incognito brackets, on etched teeth. (34 female, 15 male patients, mean age: 31.6 years (range 15–59 years)). Group 2 (IMNE): Maxcem Elite® was used to bond 193 Incognito brackets, ‘on non-etched teeth’. (19 female, 7 male patients, mean age: 31.6 years (range 15–52 years)). Group 3 (INE): Nexus® adhesive in combination with Excite® which is a hydrophylic enamel/dentin agent was used to bond 385 Incognito brackets, on etched teeth. (37 female, 12 male patients, mean age: 34.9 years (range: 15–59 years)). Group 4 (IRE): Relyx® was applied to 162 Incognito brackets, on etched teeth. (16 female, 10 male patients, mean age: 32 years (range: 12–56 years)). Group 5 (HRME): Maxcem Elite® was applied to 182 Harmony brackets with silicatized bases, on etched teeth. (16 female, 10 male patients, mean age: 32 years (range: 12–56 years)). Group 6 (HNRME): Maxcem Elite® was used to bond 182 Harmony non-silicatized brackets, on etched teeth. (20 female, 12 male patients, mean age: 26,5 years (range: 15–69 years)). In total, 1482 brackets were bonded. No patients dropped out after the randomization or during the study (Figure 1). Figure 1. View largeDownload slide Flowchart describing the protocol and the patients included in the study. No patients dropped out; (n = number of patients, N = number of brackets, F = Female, M = Male). Figure 1. View largeDownload slide Flowchart describing the protocol and the patients included in the study. No patients dropped out; (n = number of patients, N = number of brackets, F = Female, M = Male). A standard bonding protocol was followed for all the patients. The lingual surfaces of the teeth were first cleaned with a rubber cup and slurry with pumice and water, rinsed with water and dried with compressed air. Then, they were sandblasted with 50μm aluminium oxide powder (Al2O3), and rinsed with water. A Nola retractor was used for cheek retraction and isolation, and etching was performed with a 37 per cent phosphoric acid gel for 1 minute. Etchant was not applied to those teeth that belonged in the non-etching group (Group 2). The teeth were rinsed and dried carefully again, and the etched surface was coated with Excite® (Ivoclar Vivadent, Ellwangen, Germany) in the Nexus group. The corresponding bonding material was finally applied in a thin layer on the brackets bases of all groups. The brackets were embedded in clear vacuum mold trays, the trays were next inserted in the mouth, and the adhesives were polymerized by light curing for 20 seconds per tooth. The trays were then removed and the brackets were inspected for proper seating. Bracket failures were recorded over a 12-month period. A failed bracket was not recorded twice if it failed again during the observation period. Statistical method Descriptive analysis was performed and presented as frequencies (percentages) representing the performance related to the different agents, the presence of enamel etching, and the bracket base treatment. The different adhesive groups were compared by means of the Fisher’s exact test since some of the cells in this 2 × 3 table contained less than five observations, and the chi-square test was used for the rest for the comparisons. The α-level of confidence was set to 0.05 and the Statistical Package for the Social Sciences (SPSS, Chicago, IL)) was used to perform the calculations. Results The number of failures during the observation period was small in the various adhesives groups. Only 9 brackets (2.4 per cent) failed in ‘group 1’ (Maxcem-adhesive), 17 (4.5 per cent) in ‘group 3’ (Nexus-adhesive), and 3 (1.9 per cent) in ‘group 4’ (RelyX-adhesive) (Table 1). Similar behaviour was noticed in the two groups differing in the silicatization of the bracket bases. Eight brackets (4.4 per cent) failed in the Rocatec, and ten (5.5 per cent) in the non-Rocatec group (Table 2). The differences among the failures in the different adhesives groups, as well as between the silicatized and non-silicatized groups were statistically non-significant (P > 0.05), and the null hypothesis was not rejected. In contrast to the previous, when the etched and non-etched groups (‘groups 1 and 2’) were compared the difference was statistically significant (P < 0.01), and the null hypothesis was rejected with the latter group (‘group 2’) presenting a considerable number of failing brackets (28) and raising the frequency of failures as high as 14.6 per cent compared to the much lower frequency (2.4 per cent) of the brackets bonded on etched enamel. (Table 3). Table 1. Number of brackets failed and those that stayed on teeth, as well as frequencies of failures and successes during the observation period, depending on the type of adhesive used. (P > 0.05). Successful bonding Type of adhesive Maxcem Elite (‘group1’) Nexus (‘group 3’) RelyX (‘group 4’) Total Yes 369 (97.6%) 368 (95.55%) 159 (98.1%) 896 No 9 (2.4%) 17 (4.5%) 3 (1.9%) 29 Total 378 385 162 925 Successful bonding Type of adhesive Maxcem Elite (‘group1’) Nexus (‘group 3’) RelyX (‘group 4’) Total Yes 369 (97.6%) 368 (95.55%) 159 (98.1%) 896 No 9 (2.4%) 17 (4.5%) 3 (1.9%) 29 Total 378 385 162 925 View Large Table 1. Number of brackets failed and those that stayed on teeth, as well as frequencies of failures and successes during the observation period, depending on the type of adhesive used. (P > 0.05). Successful bonding Type of adhesive Maxcem Elite (‘group1’) Nexus (‘group 3’) RelyX (‘group 4’) Total Yes 369 (97.6%) 368 (95.55%) 159 (98.1%) 896 No 9 (2.4%) 17 (4.5%) 3 (1.9%) 29 Total 378 385 162 925 Successful bonding Type of adhesive Maxcem Elite (‘group1’) Nexus (‘group 3’) RelyX (‘group 4’) Total Yes 369 (97.6%) 368 (95.55%) 159 (98.1%) 896 No 9 (2.4%) 17 (4.5%) 3 (1.9%) 29 Total 378 385 162 925 View Large Table 2. Number of brackets failed and those that stayed on teeth—all bonded with Maxcem Elite®—as well as frequencies of failures and successes during the observation period, depending on the prior etching of enamel (P < 0.05). Enamel etching Successful bonding Etched (‘group 1’) Non-etched (‘group 2’) Total Yes 369 (97.6%) 165 (85.4%) 534 No 9 (2.4%) 28 (14.6%) 37 Total 378 193 571 Enamel etching Successful bonding Etched (‘group 1’) Non-etched (‘group 2’) Total Yes 369 (97.6%) 165 (85.4%) 534 No 9 (2.4%) 28 (14.6%) 37 Total 378 193 571 View Large Table 2. Number of brackets failed and those that stayed on teeth—all bonded with Maxcem Elite®—as well as frequencies of failures and successes during the observation period, depending on the prior etching of enamel (P < 0.05). Enamel etching Successful bonding Etched (‘group 1’) Non-etched (‘group 2’) Total Yes 369 (97.6%) 165 (85.4%) 534 No 9 (2.4%) 28 (14.6%) 37 Total 378 193 571 Enamel etching Successful bonding Etched (‘group 1’) Non-etched (‘group 2’) Total Yes 369 (97.6%) 165 (85.4%) 534 No 9 (2.4%) 28 (14.6%) 37 Total 378 193 571 View Large Table 3. Distribution and frequencies of successful and failed Harmony® brackets—all bonded with Maxcem Elite® in the silicatized and non-silicatized groups (P > 0.05). Bracket base silicatization Successful bonding Rocatec (‘group 5’) No Rocatec (‘group 6’) Total Yes 174 (95.6%) 172 (94.5%) 346 No 8 (4.4%) 10 (5.5%) 18 Total 182 182 364 Bracket base silicatization Successful bonding Rocatec (‘group 5’) No Rocatec (‘group 6’) Total Yes 174 (95.6%) 172 (94.5%) 346 No 8 (4.4%) 10 (5.5%) 18 Total 182 182 364 View Large Table 3. Distribution and frequencies of successful and failed Harmony® brackets—all bonded with Maxcem Elite® in the silicatized and non-silicatized groups (P > 0.05). Bracket base silicatization Successful bonding Rocatec (‘group 5’) No Rocatec (‘group 6’) Total Yes 174 (95.6%) 172 (94.5%) 346 No 8 (4.4%) 10 (5.5%) 18 Total 182 182 364 Bracket base silicatization Successful bonding Rocatec (‘group 5’) No Rocatec (‘group 6’) Total Yes 174 (95.6%) 172 (94.5%) 346 No 8 (4.4%) 10 (5.5%) 18 Total 182 182 364 View Large Discussion Randomization aims at allocating interventions in such a way as to ensure that either the participants or the investigators will not know the kind of treatment that the patients may receive. Randomization in this study had the form of a split-mouth design which is considered an appropriate method for testing orthodontic materials because patients act as their own controls (22). The lack of use an adhesive as a control could be considered as a weakness of this study. However, due to the rather sparse use of lingual appliances there is not any adhesive universally accepted as ‘a gold standard’ to be used with them, and thus taken as a control. On the other hand, when considering the etching of the teeth, and the priming of the bracket base with silicon oxides the study could be considered a randomized controlled trial since the participants served as their own controls. Although the failure of a bracket was not recorded again if the same bracket failed a second time, the possibility that repeated bracket failures in the same individual could be a confounding factor among others (e.g. sex, anterior or posterior tooth, etc.) cannot be excluded. It has been shown that with customized lingual appliances bond failures occur most often during the first few months of treatment (23), thus, the first 1 year of treatment which was chosen as the observation period in this study reflects a realistic time as well as from a practical aspect. An additional weakness could be considered the lack of ‘a priori’ calculation of the number of brackets that should be included in the study in order to achieve appropriate α- and β-levels of confidence. It is probable that with the above low frequencies of failure among different adhesives an extremely big number of brackets should have been grouped for the aforementioned difference—if existed—to be detected. The failure rates reported in the literature pertaining to brackets bonded on the buccal side of the teeth vary from 2.9 per cent to 6.6 per cent (24–26), and they are in accordance with those measured in this project with the exception of the unusually high rate corresponding to the non-etched teeth. However, Ziebura et al. (21) comparing accidental debondings of buccal versus fully individualized lingual appliances, found a mean number of 2.63 bond failures per patient. The number of patients included in that study was 103, and this allows a lose calculation of the number of failures to two hundred and seventy (103 × 2.63 = 270.89 brackets failed). Considering that the total number of brackets bonded were 2543, this corresponds to a rather high failure frequency of 10.65 per cent. This could be partly attributed to the adhesive used in their study (Maximum Cure Sealant A and B; Reliance Orthodontic Products, Itasca, Ill) which was a dual part chemically curing filled adhesive, as opposed to the dual cure adhesives used in the present study. Another explanation could be that authors may recorded repeated failures on the same tooth of a single patient. In a retrospective survey by Roelofs et al. (6) aiming to identifying the role of an antisialagogue on the failure rate of buccally bonded attachments it was noted that the bonding process is very much operator depended and this may offer an additional explanation to the differences noted. The findings of the present clinical study, also contradict those of laboratory testing RelyX® and/or Maxcem as a clinically acceptable adhesive, where its mean shear bond strength (SBS) was measured to be lower than that of the control materials, and these adhesives seemed to be considered unsuitable for orthodontic bracket bonding (19,27–29). The difference could be due to the lack of etching prior to bonding in the teeth tested. Both agents have been promoted as a self-etching dual-cured resin, but in the present study all the teeth bonded with Relyx were etched before applying the cement, thus micromechanical retention was significantly enhanced. When Maxcem Elite® was tested on etched teeth it did not show any significant difference compared to Transbond XT® which was used as a control (20). Also, the combination of Nexus with Excite used to bond lingual brackets gave similar results as only 1 bracket failure per patient per year was recorded (23).This confirms the findings of this study, since only the teeth without etching presented a clinically and statistically significant difference in failures. The relative risk for a bracket to fail in the non-etched group was estimated to be 6.09 (95 per cent CI: 2.93–12.65) namely, the risk of failure (proportion of failure) for brackets on non-etched teeth is six times that of brackets on etched teeth. With the absolute risk difference deriving from the figures in Table 2, the calculated ‘numbers to treat’ are 8.9. Thus, 1 bracket failure may be prevented for every 8.9 brackets bonded on non-etched teeth, in case the manufacturer’s instructions are followed and the tested adhesive is employed as self-etch/self-adhesive bonding agent. This increase in bracket failure can provoke a severe escalation to the costs of treatment, disrupt the schedule of a practice, and prolong treatment duration. The evidence regarding the sandblasting of teeth surfaces prior to bonding lingual brackets are contradictory. There are reports supporting the view that the effect of this procedure does not increase the clinical performance of the attachments (17), although it increases the bond strength (17,30), and others promoting the use of the Al2O3 particles as a mean of conditioning the enamel before etching and consequently improving the bond (12,31). This process has become a routine in bonding lingual orthodontic appliances (8), and its use in this study did not seem to have any undesirable effect on the frequency of bracket failure. Stainless steel brackets which received tribochemical treatment (Rocatec application) showed (‘in vitro’) a slight improvement of the bond strength compared to non-treated brackets (13). In contrast to this, in a study by Algera et al. the investigated silicoating of the base did not have such a beneficial influence on bond strength that improved clinical results can be expected (32). This seems to confirm our results where the failure rate—within the observation period—of the Harmony® brackets which are made of stainless steel and bonded with Maxcem Elite® did not seem to be influenced by the presence of the SiOx layer. However, failures regarding Incognito® brackets which are cast in an alloy with a high gold content (15), without silane treatment were not tested in this study and thus, any conclusions as to the influence of this extra layer on adhesion cannot by drawn. Future research could be undertaken to clarify this issue further. In a recent meta-regression analysis, the authors suggested that the adhesive resin application can be set aside during metal bracket bonding to enamel regardless of the type of orthodontic adhesive used (18), but it is suggested that when bonding customized lingual appliances an extra layer of hydrophilic resin containing fluoride should be added to the teeth of children and adolescents, due to the preventive effect against decalcification (16). Since there was no difference among the failure frequencies of the adhesives with and without this intermediate layer tested in our study, the use of this supplementary layer of resin for the above reasons cannot be qualified with certainty. Effective bonding of customized lingual appliances can be characterized by accuracy in bracket placement and a very low frequency of bond failures. The bonding technique can be considered very sensitive since its success can be depended on multiple factors, e.g. the quality of the transfer tray, the preparation of the bracket pad, the control of moisture, and the curing method (8). The frequencies of bracket failures as measured in this project reflect the strengths/weaknesses of the process followed in a single practice by a single practitioner while even minor deviations from the attended protocol could had produced different outcomes. Properly randomized multi-centre clinical trials, probably regarding each of the different stages should be undertaken in order to draw more generalized conclusions. Conclusions Customized lingual brackets failure frequencies (rates) are not different for the three adhesive materials tested during the first year of treatment. Despite the instructions by different manufacturers, eliminating the enamel etching stage when using self-etch/self-adhesive adhesives, may lead to a dramatic increase in the failure rates of these brackets. Silicoating of stainless steel customized lingual brackets does not seem to influence the failure of bonds when Maxcem Elite® is used as the adhesive agent. Further research is needed to demonstrate the impact of each factor of the lingual bonding technique on the effectiveness of the adhesion. Conflict of interest The authors confirm and declare that the submitted research project is original, not under consideration for presentation elswhere, free of conflict of interest and conducted under the highest human welfare. References 1. McDonald , F. and Cobourne , M . ( 2007 ) Adult orthodontics: perils and pitfalls . Progress in Orthodontics , 8 , 308 – 313 . Google Scholar PubMed 2. Rosvall , M.D. , Fields , H.W. , Ziuchkovski , J. , Rosenstiel , S.F. and Johnston , W.M . 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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/about_us/legal/notices)

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The European Journal of OrthodonticsOxford University Press

Published: Jul 10, 2017

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