Introduction
The aim of this study was to evaluate the relapse of occlusal characteristics and maxillary and mandibular anterior crowding 3 and 33 years postretention.
Methods
The sample comprised 28 patients, 15 Class I and 13 Class II, treated with 4 premolar extractions, with a mean initial age of 12.72 years (SD, 0.99), a mean final age of 14.74 years (SD, 1.26), and a mean treatment time of 2.02 years (SD, 0.66). The mean short-term postretention age was 20.15 years (SD, 1.34), and the mean long-term postretention age was 49.40 years (SD, 4.54). The mean time of short-term postretention evaluation was 3.70 years (SD, 0.87) and the mean long-term postretention evaluation was 32.95 years (SD, 4.31). The maxillary and mandibular irregularity indexes were assessed on the initial, final, short-term, and long-term postretention stage dental casts. Peer Assessment Rating and the Little indexes were compared among the 4 stages by repeated measures analysis of variance and Tukey tests.
Results
Peer Assessment Rating index and maxillary anterior crowding were significantly improved with treatment, had significant relapses in the short term, and a slight and not statistically significant increase from short-term to long-term postretention evaluation. The mandibular irregularity index significantly decreased with treatment, and then significantly and progressively increased in the postretention stages.
Conclusions
The occlusal characteristics and maxillary anterior crowding had significant relapses in the short term and remained stable from the short-term to the long-term postretention stages. Mandibular anterior crowding significantly decreased with treatment, showed a significant relapse in the short term, and continued to significantly increase in the long-term postretention stage.
Highlights
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This was a 35-year posttreatment, 33-year postretention study of occlusal characteristics and alignment stability.
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It was a really long-term study of stability and relapse of maxillary and mandibular anterior crowding.
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Occlusal characteristics and maxillary anterior crowding had significant relapses in the short term and were stable from short- to long-term posttreatment evaluation.
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Mandibular anterior crowding had significant relapse in the short term and continued to relapse significantly in the long term.
Orthodontic treatment has several objectives, and stability of the corrections achieved is one of the most important. There is consensus in the orthodontic literature that some occlusal changes will inevitably occur after treatment. It would be a great benefit to orthodontists to have a detailed prediction of these occlusal changes so that they can be prevented. For this reason, the effects of various diagnostic and treatment factors on occlusal stability in the short and long terms have been extensively investigated.
Only 3 studies have evaluated relapse of anterior crowding in the long term. Little et al found that crowding continues to increase from 10 to 20 years postretention, and only 10% of the patients had a clinically acceptable mandibular anterior alignment in the last evaluation. Vaden et al assessed the changes in irregularity of the maxillary and mandibular incisors and dental arch dimensions 6 to 15 years after removal of the retainers. Fifty-eight percent of the mandibular incisor crowding correction was maintained; 15 years after treatment, the mandibular incisor irregularity index averaged 2.6 mm, within the range of “minimal irregularity,” and there was a reduction of only 0.3 mm in the irregularity of the maxillary incisors, which corresponded to 96% stability. Dyer et al conducted a 25-year, long-term study and found that irregularity of the mandibular incisors was less than 3.5 mm in 77% of the patients. Correction of maxillary crowding was relatively stable in the long term.
As mentioned above, long-term stability of orthodontic corrections has been widely studied. However, most studies evaluated stability only a few years after treatment and mainly focused on mandibular anterior crowding relapse. There is a lack of long-term studies, comparing the long-term with the short-term postretention changes, regarding maxillary and mandibular anterior crowding stability. Therefore, we aimed to evaluate the relapse of maxillary and mandibular anterior crowding at 3 and 33 years postretention.
Material and methods
This study was approved by the ethics committee in human research of the Bauru Dental School, University of Sao Paulo in Bauru, SP, Brazil.
The sample size calculation was based on an alpha significance level of 5% and a beta of 20% to achieve 80% test power to detect a mean difference of 0.96 mm, with a standard deviation of 1.26 for the mandibular irregularity index ( Fig 1 ). Thus, the sample size calculation showed the need for 28 subjects.
The sample comprised retrospective records of subjects treated by graduate students at Bauru Dental School, University of Sao Paulo, Bauru, SP, Brazil chosen according to the following criteria: (1) Class I or Class II malocclusion at the beginning of orthodontic treatment; (2) treatment protocol with extraction of 4 first premolars; (3) complete orthodontic treatment with full maxillary and mandibular fixed edgewise appliances (0.022 × 0.028-in slot); (4) all permanent teeth erupted up to the first molars at pretreatment; (5) no tooth agenesis or anomalies; (6) maxillary removable appliance (Hawley plate) worn for 1 year, and mandibular fixed canine-to-canine retainers worn for at least 1 year, and a maximum of 3 years posttreatment, without retention at the time of the follow-up records; (7) pretreatment (T1), posttreatment (T2), and 3-year postretention (T3) dental casts available for the study, and when the subjects were called for a new follow-up that should be at least 20 years after the orthodontic treatment (T4).
The sample comprised 28 subjects of both sexes (9 male, 19 female), with a mean pretreatment age of 12.72 years (SD, 0.99; minimum, 10.58; maximum, 14.85). The mean final age was 14.74 years (SD, 1.26; minimum, 12.58; maximum, 18.09), and the mean treatment time was 2.02 years (SD, 0.66; minimum, 0.99; maximum, 3.33). The mean age at the short-term evaluation was 20.15 years (SD, 1.34; minimum, 17.75; maximum, 24.08), and the mean age at the long-term evaluation was 49.40 years (SD, 4.54; minimum, 35.76; maximum, 55.12). The mean time of short-term postretention evaluation was 3.70 years (SD, 0.87; minimum, 3.02; maximum, 5.35), and the mean time of long-term postretention follow-up was 32.95 years (SD, 4.31; minimum, 21.10; maximum, 38.01).
As retention, at the end of active orthodontic treatment, all patients used a removable Hawley plate in the maxillary arch and a canine-to-canine fixed bonded retainer in the mandibular arch. The mandibular canine-to-canine retainer was used, on average, for 1.70 years (SD, 0.60; minimum, 0.79; maximum, 3.33).
Fifteen subjects had Class I and 13 had Class II malocclusions (severity, 8 half-cusp Class II and 5 full-cusp Class II ); all were treated with extraction of the 4 first premolars. Because of this, the sample was divided into 2 groups to evaluate any difference in stability between these types of malocclusion in a pilot study.
Group 1, with Class I malocclusion patients, consisted of 15 subjects (5 male, 10 female) with a mean initial age of 12.63 years (SD, 0.94), a final age of 14.41 years (SD, 0.90), a short-term follow-up age of 19.91 years (SD, 1.02), and a long-term postretention evaluation age of 50.17 years (SD, 3.20). The mean treatment time was 1.78 years (SD, 0.42). The mean time of short-term evaluation was 3.87 years (SD, 0.74), and the mean time of long-term postretention was 34.12 years (SD, 3.20) ( Table 1 ).
| Variable (y) | Mean | SD | Minimum | Maximum |
|---|---|---|---|---|
| Initial age (T1) | 12.72 | 0.99 | 10.58 | 14.85 |
| Final age (T2) | 14.74 | 1.26 | 12.58 | 18.09 |
| Age at short-term postretention evaluation (T3) | 20.15 | 1.34 | 17.75 | 24.08 |
| Age at long-term postretention evaluation (T4) | 49.40 | 4.54 | 35.76 | 55.12 |
| Treatment time (T2-T1) | 2.02 | 0.66 | 0.99 | 3.33 |
| Retention time | 1.70 | 0.60 | 0.79 | 3.33 |
| Time of short-term postretention evaluation (T3-T2) | 3.70 | 0.87 | 3.02 | 5.35 |
| Time of long-term postretention evaluation (T4-T2) | 32.95 | 4.31 | 21.10 | 38.01 |
Group 2, with Class II malocclusion patients, comprised 13 subjects (4 male, 9 female) with a mean initial age of 12.82 years (SD, 1.09), a final age of 15.12 years (SD, 1.53), a short-term evaluation age of 20.41 years (SD, 1.64), and a long-term postretention age of 48.51 years (SD, 5.74). The mean treatment time was 2.29 years (SD, 0.79). The mean time of short-term evaluation was 3.50 years (SD, 0.99), and the mean time of long-term postretention follow-up was 31.60 years (SD, 5.10) ( Table 1 ).
Figures 2 to 5 show the models of the 4 stages (T1, T2, T3, and T4) of the patient with the worst long-term postretention relapse, and Figures 6 to 9 show the models of the 4 stages (T1, T2, T3, and T4) of the patient with the best long-term postretention outcome.
Dental casts from T1, T2, T3, and T4 were used.
The Peer Assessment Rating (PAR) index, as described by Richmond et al and scored with the American weightings, was used.
The irregularity index of Little for the maxillary and mandibular arches was measured on the dental casts, with a 0.01-mm precision digital caliper (Mitutoyo America, Aurora, Ill) by a calibrated examiner (K.M.S.F.) ( Fig 1 ).
The differences between the final and initial values of the PAR and Little indexes (T2–T1) were calculated to express the amount of correction with treatment. The differences from the short-term and long-term postretention stages with the final stage of the PAR and Little indexes (T3–T2 and T4–T2) were calculated to express the changes after retention in the 2 follow-up evaluations. The differences between the long-term and short-term postretention stages (T4–T3) were also calculated.
For the error study, a month after the first measurement, the dental casts of 10 subjects (40 pairs of dental casts) were randomly selected and remeasured by the same examiner. The random errors were calculated according to Dahlberg’s formula (Se 2 = Σd 2 /2n), and the systematic errors were evaluated with dependent t tests, at P <0.05.
Statistical analysis
Descriptive statistics were performed (means, standard deviations, maximums, and minimums) for the initial, final, short-term, and long-term postretention stages; treatment times; retention times; and time of short-term and long-term postretention evaluations; and for the PAR and maxillary and mandibular Little irregularity indexes at T1, T2, T3, and T4 and also in the evaluated periods (T2-T1, T3-T2, T4-T3, T4-T2).
The normal distribution of the data was checked and confirmed using Kolmogorov-Smirnov tests for the whole sample and for the groups.
To evaluate changes in the PAR and maxillary and mandibular Little irregularity indexes among the 4 evaluated stages (T1, T2, T3, and T4), repeated measures analysis of variance (ANOVA) and Tukey tests were used.
Intergroup comparability of sex distribution and ages and times of evaluation was verified with chi-square and t tests, respectively.
Intergroup comparisons of PAR and maxillary and mandibular Little irregularity indexes in the stages and periods evaluated were performed by t tests.
All tests were performed with software (Statistica for Windows, version 7.0; StatSoft, Tulsa, Okla), at P <0.05.
Results
There was no systematic error, and the random errors varied from 0.12 mm for the final mandibular Little irregularity index to 0.50 for the short-term PAR index.
Short-term relapses were 5.36 for the PAR index, and 2.18 and 1.58 mm for maxillary and mandibular anterior crowding, respectively ( Table II ). Long-term relapses were 7.89 for the PAR index, and 2.59 and 3.86 mm for the maxillary and mandibular Little irregularity indexes, respectively ( Table II ).
| Variable | Mean | SD | Minimum | Maximum |
|---|---|---|---|---|
| Initial PAR (T1) | 25.14 | 6.84 | 9.00 | 38.00 |
| Final PAR (T2) | 2.71 | 2.27 | 0.00 | 8.00 |
| Short-term postretention PAR (T3) | 8.07 | 3.38 | 4.00 | 16.00 |
| Long-term postretention PAR (T4) | 10.60 | 6.01 | 4.00 | 26.00 |
| PAR treatment change (T2-1) | −22.43 | 7.30 | −34.00 | −8.00 |
| PAR short-term postretention change (T3-T2) | 5.36 | 4.49 | 0.00 | 16.00 |
| PAR long-term postretention change (T4-T2) | 7.89 | 7.21 | 0.00 | 24.00 |
| PAR short- to long-term postretention change (T4-T3) | 2.53 | 4.32 | 0.00 | 14.00 |
| Initial maxillary Little irregularity index (T1) | 10.14 | 3.27 | 5.12 | 16.46 |
| Final maxillary Little irregularity index (T2) | 1.07 | 0.39 | 0.00 | 1.59 |
| Short-term postretention maxillary Little irregularity index (T3) | 3.25 | 1.21 | 1.58 | 5.34 |
| Long-term postretention maxillary Little irregularity index (T4) | 3.66 | 1.18 | 1.91 | 5.87 |
| Maxillary Little irregularity index treatment change (T2-1) | −9.07 | 3.27 | −15.34 | −4.24 |
| Maxillary Little irregularity index short-term postretention change (T3-T2) | 2.18 | 1.15 | 0.13 | 4.48 |
| Maxillary Little irregularity index long-term postretention change (T4-T2) | 2.59 | 1.07 | 0.46 | 4.80 |
| Maxillary Little irregularity index short- to long-term postretention change (T4-T3) | 0.41 | 0.43 | 0.02 | 1.63 |
| Initial mandibular Little irregularity index (T1) | 8.66 | 3.88 | 2.35 | 15.31 |
| Final mandibular Little irregularity index (T2) | 1.20 | 1.00 | 0.00 | 3.52 |
| Short-term postretention mandibular Little irregularity index (T3) | 2.78 | 1.44 | 0.00 | 5.12 |
| Long-term postretention mandibular Little irregularity index (T4) | 5.06 | 2.39 | 0.00 | 9.61 |
| Mandibular Little irregularity index treatment change (T2-T1) | −7.46 | 3.59 | −14.06 | −1.03 |
| Mandibular Little irregularity index short-term postretention change (T3-T2) | 1.58 | 1.38 | 0.00 | 3.91 |
| Mandibular Little irregularity index long-term postretention change (T4-T2) | 3.86 | 2.61 | 0.00 | 8.62 |
| Mandibular Little irregularity index short- to long-term postretention change (T4-T3) | 2.28 | 1.62 | 0.00 | 5.24 |
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