Introduction
The purpose of this study was to compare the occlusal stability of Class II malocclusion treatment with and without extraction of 2 maxillary premolars.
Methods
A sample of 59 records from patients with complete Class II malocclusion was used. This sample was divided into 2 groups with the following characteristics: group 1, comprising 29 patients treated without extractions, and group 2, comprising 30 patients treated with extraction of 2 maxillary premolars. Dental cast measurements were obtained before and after treatment and at a minimum of 2.4 years after treatment. The pretreatment, posttreatment, and postretention occlusal statuses were evaluated with the peer assesment rating index. The occlusal indexes at the postretention stage and the posttreatment changes and percentages of posttreatment changes were compared with t tests.
Results
The nonextraction and the 2 maxillary premolar extraction treatment protocols of complete Class II malocclusions had no statistically significant differences in occlusal stability.
Conclusions
Finishing Class II malocclusion treatment with the molars in a Class II relationship has similar occlusal stability as finishing with the molars in a Class I relationship.
Initially, it was thought that the molars should always finish in a Class I relationship. It was also suspected that finishing with the molars in a Class II relationship could cause temporomandibular joint problems and that stability could be compromised. Later, many orthodontists realized, and researchers proved, that, in some Class II malocclusions, the molars could be finished in a Class II relationship without unfavorable collateral effects. Enough clinical and scientific evidence has been provided to support finishing treatment of certain Class II malocclusions with the molars in a Class II relationship. Indirect evidence also suggests that stability is not compromised when finishing with the molars in a Class II relationship.
It has been shown that the 2 maxillary premolar extraction protocol has greater efficiency than the nonextraction treatment of Class II malocclusions. In addition to efficiency, long-term stability is a primary goal in orthodontics; this is difficult to obtain. Studies have shown that, even though improvement can be obtained through orthodontic treatment, there is a tendency of relapse to the original malocclusion many years after appliance removal. Consequently, every effort should be directed to minimize the risks that can compromise the results of orthodontic treatment.
Studies comparing the stability of Class II malocclusion treatment with 4 premolar extractions and nonextraction found no significant differences between these protocols. However, similar studies comparing the long-term stability of the 2 maxillary premolar extraction protocol with the nonextraction approach have not been performed. Therefore, to further clarify these issues, we compared the long-term stability of Class II malocclusions treated with and without extraction of 2 maxillary premolars.
Material and methods
The sample was retrospectively selected from the files of the orthodontic department at Bauru Dental School, University of São Paulo, in Brazil; the files include over 4000 documented patients. The records and the initial (T1), final (T2) and long-term posttreatment (T3) (at least 2.3 years) dental study models of all patients who initially had complete bilateral Class II malocclusion (molar relationship) and were treated without extractions or with 2 maxillary premolar extractions and standard fixed edgewise appliances were selected and divided into 2 groups. Sample selection was based exclusively on the initial anteroposterior dental relationship, regardless of any other dentoalveolar or skeletal characteristic. Additionally, patients had all permanent teeth up to the first molars and no dental anomalies of number, size, and form. Group 1 consisted of 29 patients (14 boys, 15 girls) treated without extractions at an initial mean age (age 1) of 12.65 ± 1.38 years (range, 9.52-15.90 years); 22 had Class II Division 1 malocclusion, and 5 had Class II Division 2 malocclusion. The posttreatment age (age 2) of the patients was 15.17 ± 1.58 years (range, 12.94-18.72 years), and the postretention age (age 3) was 22.44 ± 3.50 years (range, 16.29-31.76 years). The average treatment time was 2.51 ± 0.98 years (range, 0.88-4.70 years), and the average postretention time was 7.26 ± 3.43 years (range, 2.40-16.15 years). Group 2 consisted of 30 patients (17 boys, 13 girls) treated with 2 maxillary premolar extractions; at age 1, they were 13.32 ± 1.52 years (range, 11.21-17.09 years); 22 had Class II Division 1 malocclusion, and 8 had Class II Division 2 malocclusion. At age 2, they were 15.57 ± 1.71 years (range, 12.55-19.48 years). and, at age 3, they were 25.18 ± 3.97 years (range, 19.02-34.04 years). The average treatment time was 2.24 ± 0.75 years (range, 0.93-4.19 years), and the average postretention time was 9.60 ± 3.55 years (range, 3.23-15.99 years).
Orthodontic mechanics included fixed edgewise appliances, with 0.022 X 0.028-in conventional brackets and a usual wire sequence characterized by an initial 0.015-in Twist-Flex or 0.016-in Nitinol, followed by 0.016-, 0.018-, 0.020-, and 0.021 × 0.025- or 0.018 × 0.025-in stainless steel wires (all from 3M Unitek, Monrovia, Calif). Deepbites were corrected with accentuated and reversed curve of Spee. In group 2, the anterior teeth were retracted en masse with a rectangular wire and elastic chains for overjet and Class II canine correction. Extraoral headgear was used to correct the Class II anteroposterior relationship in group 1; in group 2, an extraoral appliance was indicated to reinforce anchorage and maintain the Class II molar relationship. Twelve patients in group 1 used functional appliances either alone or with extraoral headgear. When necessary, Class II elastics were used in group 1 to help obtain a Class I molar relationship; in group 2, this procedure was used to help maintain a Class II molar relationship. A Hawley plate was used for retention during a mean period of 1 year, and a mandibular canine-to-canine fixed retainer was recommended to be used for a mean period of 3 years. However, at the postretention stage, 15 patients in group 1 and 13 in group 2 still had their mandibular fixed retainers.
The peer assessment rating (PAR) index was calculated on the pretreatment, posttreatment, and postretention study models of each patient, according to the American weightings suggested by De Guzman et al by 1 examiner (L.T.C.). Initial, final, and postretention occlusal characteristics were ranked by scores for molar and premolar anteroposterior (AP) relationship, overjet (OJ), overbite (OB), midline, crossbite, and crowding to quantify the initial malocclusion severity (PAR 1), the treatment occlusal results (PAR 2), the percentage of PAR treatment changes, and the percentage of PAR posttreatment changes, which are better estimates of the occlusal changes.
Twenty-five maxillary and mandibular final dental models were randomly selected and remeasured by the same examiner. Student paired t tests were used to evaluate the systematic error at P <0.05. Casual errors were calculated according to Dahlberg’s formula, Se2=∑d2/2n
Se 2 = ∑ d 2 / 2 n
, where d is the difference between duplicate measurements and n is the number of double measurements.
Statistical analysis
Compatibility of the groups concerning the distributions of Class II malocclusion types and sex was evaluated with chi-square tests. The t test was used to evaluate compatibility at PAR 1 and PAR 2, and at age 1, age 2, and age 3. It was also used to compare the groups at PAR 3 for the amounts and percentages of posttreatment changes.
The occlusal results obtained for each component of the PAR index at T2 and T3, and the posttreatment changes were individually compared between the groups with the Mann-Whitney U test. A nonparametric test was used because the values of each PAR component did not have normal distribution, according to the Kolmogorov-Smirnov test.
Because the 2 groups had patients with and without mandibular fixed canine-to-canine retention, t tests were used to compare the stability of the patients in each group to determine whether the fixed retention influenced the stability.
To investigate whether the posttreatment changes were associated with the treatment changes, the Pearson correlation test was used. The Spearman correlation test was used to evaluate whether the posttreatment changes of OJ and OB were associated with the treatment changes.
With the objective of assessing the influence of treatment time in Class II treatment stability, the sample was divided into 2 groups, independent of the treatment protocol, and compared with t tests. One group had treatment times less than 2 years, and the other, more than 3 years. The results were considered statistically significant at P <0.05.
Results
There was no statistically significant systematic error, and the random error was 0.98 for the PAR index.
The groups were compatible regarding malocclusion type and sex distribution, PAR 1, PAR 2, treatment time, age 1, and age 2. However, group 2 had greater values for posttreatment time and age 3 ( Tables I and II ) .
| Class II Division 1 (n) |
Class II Division 2 (n) |
Total (n) | |
|---|---|---|---|
| Group 1 | 24 | 5 | 29 |
| Group 2 | 22 | 8 | 30 |
| Total | 46 | 13 | 59 |
| Male (n) | Female (n) | Total (n) | |
|---|---|---|---|
| Group 1 | 14 | 15 | 29 |
| Group 2 | 17 | 13 | 30 |
| Total | 31 | 28 | 59 |
| Group 1 (nonextraction), n = 29 | Group 2 (2 maxillary premolar extractions), n = 30 | ||||
|---|---|---|---|---|---|
| Variable | Mean | SD | Mean | SD | P |
| PAR 1 | 23.5 | 6.89 | 23.70 | 6.78 | 0.918 |
| PAR 2 | 3.55 | 3.50 | 2.03 | 2.59 | 0.062 |
| Treatment time (y) | 2.51 | 0.98 | 2.24 | 0.75 | 0.237 |
| Posttreatment time (y) | 7.26 | 3.43 | 9.60 | 3.55 | 0.012 ∗ |
| Age 1 (y) | 12.65 | 1.38 | 13.32 | 1.52 | 0.081 |
| Age 2 (y) | 15.17 | 1.58 | 15.57 | 1.71 | 0.357 |
| Age 3 (y) | 22.44 | 3.50 | 25.18 | 3.97 | 0.006 ∗ |
| PAR 3 | 4.41 | 3.71 | 5.13 | 5.53 | 0.561 |
| PAR posttreatment changes | 0.86 | 3.49 | 3.10 | 5.24 | 0.059 |
| PAR posttreatment changes (%) | 3.60 | 15.80 | 15.13 | 32.33 | 0.088 |
There were no intergroup differences regarding PAR 3, the posttreatment occlusal changes, and the percentage of posttreatment occlusal changes ( Table II ). Because group 2 had greater posttreatment time and postretention age, these variables were again compared after matching the groups for posttreatment time and postretention age. The differences were also nonsignificant ( Table III ).
| Subgroup 1 (nonextraction), n = 28 | Subgroup 2 (2 maxillary premolar extractions), n = 26 | ||||
|---|---|---|---|---|---|
| Variable | Mean | SD | Mean | SD | P |
| Treatment time (y) | 2.51 | 1.00 | 2.26 | 0.63 | 0.269 |
| Posttreatment time (y) | 7.31 | 3.48 | 8.89 | 3.16 | 0.087 |
| Age 1 (y) | 12.64 | 1.40 | 13.05 | 1.35 | 0.276 |
| Age 2 (y) | 15.16 | 1.61 | 15.31 | 1.48 | 0.713 |
| Age 3 (y) | 22.47 | 3.56 | 24.21 | 3.27 | 0.068 |
| PAR 3 | 4.46 | 3.77 | 5.07 | 5.89 | 0.648 |
| PAR posttreatment changes | 1.14 | 3.20 | 3.19 | 5.60 | 0.102 |
| PAR posttreatment changes (%) | 4.35 | 15.55 | 16.06 | 34.60 | 0.110 |
There were no intergroup differences regarding the several individual PAR components at the posttreatment and postretention stages and their changes between these stages ( Table IV ).
| Group 1 (non-extraction), n = 29 | Group 2 (2 maxillary premolar extractions), n = 30 | ||
|---|---|---|---|
| Variable | Mean rank | P | |
| Posterior segments AP discrepancy at T2 | 31.50 | 28.55 | 0.509 |
| Posterior segments AP discrepancy at T3 | 33.72 | 26.40 | 0.101 |
| Posttreatment change in posterior segments AP discrepancy (T3-T2) | 32.60 | 27.48 | 0.252 |
| OJ at T2 | 30.53 | 29.48 | 0.814 |
| OJ at T3 | 28.50 | 31.45 | 0.509 |
| Posttreatment change in OJ (T3-T2) | 28.10 | 31.83 | 0.404 |
| OB at T2 | 31.09 | 28.95 | 0.632 |
| OB at T3 | 30.28 | 29.73 | 0.903 |
| Posttreatment change in OB (T3-T2) | 29.90 | 30.10 | 0.963 |
| Crowding at T2 | 29.50 | 30.48 | 0.825 |
| Crowding at T3 | 28.47 | 31.48 | 0.499 |
| Posttreatment change in crowding (T3-T2) | 28.93 | 31.03 | 0.638 |
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