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ORIGINAL ARTICLE Transverse stability of Class II malocclusion correction with the pendulum appliance Grego rio Pelayo Guerra, Luiz Eduardo Alessio Junior, Renato Rodrigues de Almeida, Jose rio Vieira Maranha ~o, and Guilherme Janson Olga Bena Bauru, Brazil Introduction: This study aimed to evaluate the stability of transverse changes after Class II malocclusion correction with the pendulum fixed distalizer, followed by preadjusted edgewise fixed orthodontic appliances. Methods: This longitudinal study was conducted in the maxillary dental casts of 20 Class II malocclusion subjects (mean age, 12.5 years; 14 females and 6 males). Eighty 3-dimensional maxillary dental casts were analyzed; 20 at the beginning of treatment, 20 after distalization, 20 after edgewise appliance debonding, and 20 at 5 years posttreatment. Maxillary transverse distances between canines, first premolars, second premolars, first molars, and second molars were analyzed using Geomagic Studio 5 (3D Systems, Rock Hill, SC). Results: There were no significant changes in intercanine distance during and after treatment. There were significant interfirst and intersecond premolar distance increases during treatment. There were significant interfirst and intersecond molar distance increases during the distalization phase. However, there were significant decreases in these distances at the end of treatment. There were no significant long-term posttreatment changes. Conclusions: The intercanine distance remains stable during and after treatment. The interfirst and intersecond premolar distances significantly increase during treatment and remain stable after treatment. The interfirst and intersecond molar distances increase during the distalization phase, decrease at the end of treatment, and remain stable after treatment. (Am J Orthod Dentofacial Orthop 2020;158:357-62) C lass II malocclusion should be considered not only a sagittal but also a vertical and transverse problem.1-3 There are several treatments and devices that have been widely used as alternatives for Class II malocclusion correction and nonextraction treatment.4-8 The pendulum fixed distalizer (PFD) is indicated for the nonextraction treatment of dental Class II malocclusions during the mixed or early permanent dentition.9,10 It provides dental effects in short treatment time, so that in 3-4 months, it is possible to obtain approximately 5 mm of molar distalization.6 In addition, it does not depend on patient compliance and is well accepted by them.9 Besides the positive changes produced by the PFD, there are also premolar and canine mesialization and Department of Orthodontics, Bauru Dental School, University of S~ao Paulo, Bauru, Brazil. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Address correspondence to: Guilherme Janson, Department of Orthodontics, Bauru Dental School, University of S~ao Paulo, Alameda Octavio Pinheiro Brisolla 9-75, Bauru, 17012-901, Brazil; e-mail, [email protected] Submitted, August 2018; revised and accepted, August 2019. 0889-5406/$36.00 Ó 2020 by the American Association of Orthodontists. All rights reserved. https://doi.org/10.1016/j.ajodo.2019.08.017 incisor protrusion as side effects.10,11 Consequently, 55%-70% of the space obtained is provided by molar distalization, whereas 30%-45% results from anchorage loss.11 Adequate transverse dimension is a fundamental component of an adequate and stable occlusion.12 The PFD has shown to be an effective appliance that promotes sagittal, transverse, and vertical maxillary arch changes.12-19 The PFD showed relative stability when evaluated by the peer assessment rating index.6,20,21 Transverse relapse is a usual occurrence, usually caused by archwire shapes used in conventional edgewise techniques, which decrease the intercanine width.22-24 Many distalization treatments show that relapses come from accentuated molar distal crown angulation, which is shown in lateral headfilms and panoramic radiographs.20,21 Previous articles investigated the relationship between transverse relapse and patient's age and gender, malocclusion, growth pattern, and dental intercuspation, during treatment with the pendulum appliance. However, the measuring methods were not standardized.25-27 Consequently, it is difficult to compare the results. The use of digital dental casts enables more 357 Downloaded for Anonymous User (n/a) at Francisco Marroquín University from ClinicalKey.com by Elsevier on November 01, 2021. For personal use only. No other uses without permission. Copyright ©2021. Elsevier Inc. All rights reserved. Alessio Junior et al 358 accurate and comparable measurements.28,29 These previous studies also did not consider the possible influence of fixed orthodontic therapy on the transverse dimension of the maxillary arch. Therefore, the purpose of this study was to evaluate the maxillary dental arch transverse changes and longterm stability of Class II malocclusion treatment with the pendulum, followed by fixed orthodontic appliances. MATERIAL AND METHODS This longitudinal study was approved by the Ethics in Research Committee at the Department of Orthodontics, Bauru Dental School, University of S~ao Paulo. A pilot study was conducted with 5 patients to allow sample size calculation. The mean intersecond molar transverse relapse obtained in the pilot study, which was 2.5 mm, was taken as a parameter. Therefore, to detect a minimum difference of 2.5 mm in intersecond molar transverse relapse, with an alpha of 0.05 and 80% of test power, 20 subjects were needed in each group. Written informed consent was obtained from all subjects. The inclusion criteria for the dental casts were (1) initial Class II molar relationship and Class I molar relationship with 2 mm overcorrection at the end of treatment with the PFD, followed by edgewise appliances; (2) no deciduous teeth present; (3) 5-year follow-up records after the end of treatment; and (4) plaster models in good condition, with no blisters, fractures, or wear, in the 4 evaluated stages. Therefore, all patients previously treated with the pendulum fixed appliance, followed-up on for more than 5 years, and with adequate orthodontic records were selected. As a result, the sample comprised 80 maxillary 3-dimensional dental casts of 20 patients (14 female and 6 male) with a mean age of 12.5 years (range, 11-14 years) selected from the files of the Department of Orthodontics, Bauru Dental School, University of S~ao Paulo. Initially, the patients were treated by the PFD, and its coils were activated by a 60 distal bend, providing a distal 253 g of force per side, for 5 months (Fig 1).9,10,30 Immediately after distalizer removal, a Nance button was used as anchorage to avoid mesial movement of the molars. In addition, a cervical extraoral appliance was inserted with no expansion in the inner bow to maintain the arch transverse and anteroposterior dimensions and to upright the first molars. It was used during the sleeping hours, with 400 g of force on each side for an average of 4 months, until the fixed appliances were installed and leveling and alignment reached a rectangular stainless September 2020 Vol 158 Issue 3 Fig 1. Pendulum distalizer appliance. steel archwire. No further distalization was produced by the extraoral appliances. After 5 months of distalization, treatment was continued by the bonding of 0.022 3 0.028-inch preadjusted edgewise fixed orthodontic appliances. Leveling and alignment were performed with the conventional wire sequence until a 0.019 3 0.025-inch rectangular stainless steel archwire was used for maxillary premolar and canine retraction. Subsequently, the Nance button was removed to allow anterior retraction, and the extraoral appliance was replaced by Class II elastics, recommended to be used for 20 hours/day. After closing the spaces, finishing procedures were undertaken. After the end of treatment, a Hawley retainer was used in the maxillary arch, and a fixed canine-tocanine retainer was bonded in the mandibular arch. The Hawley retainer was recommended to be used full-time for 6 months, followed by nights-only use for 6 months. The mandibular canine-to-canine bonded fixed retainer was recommended to be used for a mean period of 3 years. Four pairs of dental casts of each patient were digitized at the following stages: pretreatment (T1), after distalization with the PFD (T2), posttreatment (T3), and at 5-year follow-up (T4). Only the maxillary dental casts were used in this investigation. The dental casts were scanned with the Rexcan DS2 scanner (Solutionix, Seoul, South Korea). Landmarks were identified on the maxillary dental cast of each patient, which allowed the measurement of several transverse variables (Fig 2). These variables were measured with Geomagic Studio 5 (3D Systems, Rock Hill, SC) software. Twenty percent of the sample was randomly selected, and the landmarks were again identified and the American Journal of Orthodontics and Dentofacial Orthopedics Downloaded for Anonymous User (n/a) at Francisco Marroquín University from ClinicalKey.com by Elsevier on November 01, 2021. For personal use only. No other uses without permission. Copyright ©2021. Elsevier Inc. All rights reserved. Alessio Junior et al 359 Table I. Results of the random and systematic errors evaluation (n 5 20) 1a Measurement, Variables mm 3-3 34.89 (1.33) 4-4 41.84 (2.62) 5-5 46.12 (3.29) 6-6 51.07 (3.67) 7-7 56.86 (2.89) 2a Measurement, mm Dahlberg P 35.08 (1.59) 0.184 0.448 41.87 (2.81) 0.079 0.755 46.34 (3.34) 0.077 0.951 51.16 (3.83) 0.054 0.859 57.06 (2.95) 0.111 0.935 3-3, intercanine distance; 4-4, interfirst premolar distance; 5-5, intersecond premolar distance; 6-6, intermolar distance; 7-7, intersecond molar distance. Note. Values are mean (standard deviation). Fig 2. Scanned maxillary dental cast showing the measured transverse variables. A, intercanine distance—measured from right to left maxillary canine cusp tips; B, interfirst premolar distance—measured from right to left maxillary first premolar cusp tips; C, intersecond premolar distance—measured from right to left maxillary cusp tips; D, interfirst molar distance measured from right to left maxillary mesiobuccal cusp tips; E, intersecond molar distance measured from right to left maxillary mesiobuccal cusp tips. variables were remeasured by the same examiner 1 month after the first evaluation. The random errors were calculated according to the Dahlberg31 formula, S2 5 Sd2/2n, in which S2 is the error variance d is the difference between 2 determinations of the same variable, and the systematic errors were estimated with dependent t tests, at P \0.05.32 Statistical analysis Kolmogorov-Smirnov tests were used to evaluate normal distribution. All variables presented normal distributions. The changes between the 4 stages were evaluated with repeated measures ANOVA, followed by Tukey tests. All statistical procedures were performed with Statistica (version 7.0; Statsoft, Tulsa, Okla) at P \0.05. RESULTS The random errors ranged from 0.054 (intermolar distance) to 0.184 (intercanine distance) and were within acceptable limits33,34 (Table I). There were no significant systematic errors. The intercanine distance did not show significant treatment and posttreatment changes (Table II; Fig 3). The interfirst premolar distance increased significantly from T2 to T3 and did not show significant posttreatment changes. The intersecond premolar distance significantly increased from T1 to T3 and did not show significant posttreatment changes. The interfirst and intersecond molar distances significantly increased from T1 to T2, then significantly decreased from T2 to T3, and did not show significant posttreatment changes. DISCUSSION There was no significant treatment and posttreatment intercanine distance changes as has been previously shown (Table II; Fig 3).6,14,15,17,35 Maxillary intercanine width usually does not show significant treatment and posttreatment changes with the pendulum appliance.36-39 Therefore, maintenance of the initial intercanine distance may have contributed to its stability. There were no significant interfirst and intersecond premolar distance increases after the distalization period with the PFD (Table II; Fig 3). In contrast, other studies reported increases of the interfirst and intersecond premolar distances because of side effects related to PFD treatment, including buccal tipping of the maxillary premolars.4,6,14,15 The palatal button was effective in preventing these transverse increases, in this study, which probably did not happen in the other studies. However, there were significant increases in these distances, from the beginning to the end of treatment (Table II; Fig 3). Because the palatal button was removed after distalization, there was less transverse control of the premolars, which may have buccally moved during retraction, which corroborates other studies.14,22,38,40-44 After that, these distances remained stable in the longterm posttreatment stage. This increase in premolar transverse distance from the beginning to the end of treatment is clinically relevant because as the premolars are distalized to a broader section of the dental arch to correct the Class II American Journal of Orthodontics and Dentofacial Orthopedics September 2020 Vol 158 Issue 3 Downloaded for Anonymous User (n/a) at Francisco Marroquín University from ClinicalKey.com by Elsevier on November 01, 2021. For personal use only. No other uses without permission. Copyright ©2021. Elsevier Inc. All rights reserved. Alessio Junior et al 360 Table II. Treatment and posttreatment changes Region 3-3 4-4 5-5 6-6 7-7 T1, mm 34.10 (1.93) 40.41 (2.07)a 46.38 (2.41)a 50.74 (2.89)a 57.05 (2.64)a T2, mm 34.20 (1.95) 40.89 (2.13)a 46.79 (2.38)ab 54.88 (2.89)b 60.71 (3.49)b T3, mm 34.67 (1.83) 42.63 (1.72)b 47.56 (1.88)b 50.56 (2.11)a 58.83 (2.71)c T4, mm 34.23 (1.91) 42.62 (1.96)b 47.36 (2.17)b 51.06 (2.44)a 58.61 (3.02)c P 0.699 \0.001* \0.001* \0.001* \0.001* 3-3, intercanine distance; 4-4, interfirst premolar distance; 5-5, intersecond premolar distance; 6-6, intermolar distance; 7-7, intersecond molar distance. Note. Values are mean (standard deviation). Comparisons were made using repeated measures ANOVA, followed by Tukey tests. Different letters in a row represent statistically significant differences among time points. *Statistically significant at P \0.05. malocclusion, there has to be an increase in interpremolar distances.12,45 Because this increase was not produced by the PFD, it was most likely produced by the coordinated leveling archwires. The transverse interfirst and intersecond molar distances increased significantly after the distalization period with the PFD, as a side-effect of the distalization springs that have a buccal component of force (Table II; Fig 3). The same behavior was reported previously by Hilgers,6 and Gosh and Nanda,46 who also observed significant increases in interfirst and intersecond molar distances. After treatment, the transverse distance between the first molars significantly decreased to a value similar to the pretreatment stage (Table II; Fig 3). The intersecond molar distance also significantly decreased after treatment; nevertheless, it remained significantly greater than in the pretreatment stage. This decrease in transverse interfirst and intersecond molar distances was probably caused by the correction of the buccal movement by the fixed appliances. To correct Class II malocclusion by distalization, there is usually a significant increase in the interfirst molar distance, which did not occur from the beginning to the end of treatment in this sample. Because the transverse interarch relationship Fig 3. Overlapping of canines, premolars, and molars transversal changes in the phases. T1 (blue), T2 (red), T3 (green), and T4 (yellow). September 2020 Vol 158 Issue 3 was good at the end of treatment, there may be some narrowing of the mandibular arch during treatment. This possibility should be further investigated. As mentioned previously, there were statistically and clinically significant increases in interfirst and intersecond molar distances produced as side effects of the PFD. In Class II malocclusion correction, these increases are desirable because the teeth will move to a broader section of the dental arch. However, at the end of treatment, these distances significantly decreased. This finding did not produce any transverse problems because it is likely that some narrowing of the mandibular arch also occurred, as described. Greater attention has to be given to the transverse dimension to prevent this. The transverse interfirst and intersecond molar distances remained stable in the long-term posttreatment stage, as described in the literature.38,47,48 These transverse changes corroborate with other studies (Table II; Fig 3).14,24,38,40,42,44,45,49 Overall, treatment with the pendulum, followed by with fixed appliances, does not change the maxillary intercanine distance and causes significant and permanent increases in only the first and second premolar transverse distances. Interfirst and intersecond molar transverse distances increase immediately after the distalization phase but return to similar original dimensions at the end of treatment. After that, there is long-term stability of the transverse dimensions. Therefore, changes in transverse dimensions of the first molars are only clinically relevant during the distalization phase. The subsequent use of multibracket appliances will restore the initial transverse dimensions. This knowledge may help the clinician during treatment planning. However, because of the reduced number of observations and the lack of evaluation of the mandibular arch, these results must be regarded with caution. Besides, there is also the limitation of a retrospective sample and the potential bias of a convenience sample. Future American Journal of Orthodontics and Dentofacial Orthopedics Downloaded for Anonymous User (n/a) at Francisco Marroquín University from ClinicalKey.com by Elsevier on November 01, 2021. For personal use only. No other uses without permission. Copyright ©2021. Elsevier Inc. All rights reserved. Alessio Junior et al studies with a greater number of patients and with simultaneous analysis of the mandibular arch should provide more reliable data. CONCLUSIONS 1. 2. The transverse changes observed during Class II treatment with the pendulum appliance in conjunction with headgear and fixed appliances were temporary and not clinically significant. 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Janson G, Caffer DC, Henriques JF, de Freitas MR, Neves LS. Stability of class II, division 1 treatment with the headgear-activator combination followed by the edgewise appliance. Angle Orthod 2004;74:594-604. American Journal of Orthodontics and Dentofacial Orthopedics Downloaded for Anonymous User (n/a) at Francisco Marroquín University from ClinicalKey.com by Elsevier on November 01, 2021. For personal use only. No other uses without permission. Copyright ©2021. Elsevier Inc. All rights reserved.