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.
Highlights
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We studied the stability of transverse changes after Class II correction with the pendulum appliance.
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Transverse dimension is a fundamental component of an adequate and stable occlusion.
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Intercanine distance did not show significant treatment and posttreatment changes.
Class II malocclusion should be considered not only a sagittal but also a vertical and transverse problem. There are several treatments and devices that have been widely used as alternatives for Class II malocclusion correction and nonextraction treatment.
The pendulum fixed distalizer (PFD) is indicated for the nonextraction treatment of dental Class II malocclusions during the mixed or early permanent dentition. , 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. In addition, it does not depend on patient compliance and is well accepted by them.
Besides the positive changes produced by the PFD, there are also premolar and canine mesialization and incisor protrusion as side effects. , Consequently, 55%-70% of the space obtained is provided by molar distalization, whereas 30%-45% results from anchorage loss.
Adequate transverse dimension is a fundamental component of an adequate and stable occlusion. The PFD has shown to be an effective appliance that promotes sagittal, transverse, and vertical maxillary arch changes. The PFD showed relative stability when evaluated by the peer assessment rating index. , ,
Transverse relapse is a usual occurrence, usually caused by archwire shapes used in conventional edgewise techniques, which decrease the intercanine width. Many distalization treatments show that relapses come from accentuated molar distal crown angulation, which is shown in lateral headfilms and panoramic radiographs. ,
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. Consequently, it is difficult to compare the results. The use of digital dental casts enables more accurate and comparable measurements. , 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 long-term 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 São 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 São 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 ). , , 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 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 × 0.028-inch preadjusted edgewise fixed orthodontic appliances. Leveling and alignment were performed with the conventional wire sequence until a 0.019 × 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-to-canine 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 variables were remeasured by the same examiner 1 month after the first evaluation. The random errors were calculated according to the Dahlberg formula, S 2 = Σd 2 /2n, in which S 2 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.
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 limits , ( Table I ). There were no significant systematic errors.
| Variables | 1 a Measurement, mm | 2 a Measurement, mm | Dahlberg | P |
|---|---|---|---|---|
| 3-3 | 34.89 (1.33) | 35.08 (1.59) | 0.184 | 0.448 |
| 4-4 | 41.84 (2.62) | 41.87 (2.81) | 0.079 | 0.755 |
| 5-5 | 46.12 (3.29) | 46.34 (3.34) | 0.077 | 0.951 |
| 6-6 | 51.07 (3.67) | 51.16 (3.83) | 0.054 | 0.859 |
| 7-7 | 56.86 (2.89) | 57.06 (2.95) | 0.111 | 0.935 |
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