In this study, we aimed to compare the relapse of maxillary and mandibular anterior crowding, overjet, and overbite 5 years after treatment in subjects with Class I and Class II malocclusions treated with and without extractions, and also to evaluate the correlations among these factors.
The sample comprised 84 subjects with Class I and Class II malocclusions, treated with and without extractions. Group 1 comprised 44 subjects with an initial mean age of 12.96 years treated without extractions. Group 2 included 40 subjects with an initial mean age of 13.01 years treated with 4 premolar extractions. Data were obtained from dental casts at the pretreatment, posttreatment, and long-term posttreatment stages. Intergroup comparisons were performed with t tests. To verify the correlations among the relapse of overjet, overbite, and anterior crowding, the Pearson correlation test was used.
Maxillary incisor irregularity and its relapse in the nonextraction group were significantly greater at the long-term posttreatment stage and the long-term posttreatment period, respectively. Long-term postreatment overjet changes were similar in the groups. Overbite and its relapse were significantly greater in the extraction group in the long-term posttreatment stage and period, respectively. There was a positive correlation of the relapse of mandibular incisor crowding with the relapse of overjet and overbite, and also a correlation of overjet and overbite relapses.
There was greater maxillary crowding relapse in the nonextraction group and greater overbite relapse in the extraction group. There were significant and positive correlations of overjet and overbite relapses with mandibular anterior crowding relapse and consequently between overjet and overbite relapses.
Orthodontic treatment has several goals, and one of the most important is the stability of the achieved corrections. It is a consensus in the literature that some occlusal changes will inevitably occur after orthodontic treatment. It would be greatly interesting if orthodontists could precisely predict the occlusal changes that occur after treatment. For this reason, the effects of different diagnosis and treatment factors in long-term treatment stability have been extensively studied. It is well accepted that the stability of tooth alignment is highly variable and unpredictable. Many authors have considered stability of the mandibular incisors after orthodontic treatment as an unreachable ideal and suggested long-term retention as the most plausible solution.
Recent research has also shown that overjet is often corrected during treatment; however, a significant posttreatment relapse of this characteristic is often observed. Relapse is related to the amount of overjet at the beginning of treatment, the initial inclination of the maxillary incisors, the labial inclination of the maxillary incisors in the postretention period, the lingual inclination of the mandibular incisors in the postretention period, and the increase of the interincisal angle at the end of treatment.
Several factors are related to overbite relapse, including overjet, movement of the incisors and molars, interincisal angle, anterior face height, pattern of craniofacial growth, initial incisor crowding (the Little irregularity index), and even the amount of overbite correction during orthodontic treatment. Because relapse seems to be a constant, some authors recommend overcorrection. Many studies have been conducted on the subject but focused on only 1 factor or variable.
Because stability is a fundamental key to the successful outcome of orthodontic treatment, in this study we aimed to compare the relapse of maxillary and mandibular anterior crowding, overjet, and overbite 5 years after treatment in subjects with Class I and Class II malocclusions treated with and without extractions, and also to evaluate the correlations among these factors.
Material and methods
The sample comprised the retrospective dental casts of 84 patients obtained from the files of the Orthodontic Department at Bauru Dental School, University of São Paulo, Brazil. The patients were treated with fixed appliances and selected according to the following criteria: (1) Class I or Class II malocclusion at the beginning of orthodontic treatment; (2) treatment protocol with or without extractions; (3) at least 4 mm of overjet and 3 mm of overbite, and maxillary and mandibular crowding from slight to severe; (4) all permanent teeth erupted up to the first molars before treatment; (5) no tooth agenesis or anomalies; (6) maxillary removable Hawley plate worn for 1 year, mandibular fixed canine-to-canine retainers worn for at least 1 year, a maximum of 2 years posttreatment, and no retention at the follow-up records; (7) pretreatment (T1), posttreatment (T2), and long-term posttreatment (T3) dental casts available for the study; and (8) treated with edgewise mechanics and achieved acceptable posttreatment results.
The sample was divided into 2 groups.
Group 1, treated without extractions, comprised 44 patients of both sexes (17 boys, 27 girls). Twenty-one patients had a Class I malocclusion, and 23 had a Class II malocclusion (4 half cusp, Class II; 6 three quarter cusp, Class II; 13 full cusp, Class II). At the end of treatment, all patients had Class I molar relationships. The mean ages were 12.96 years (SD, 1.10) at T1, 15.12 years (SD, 1.23) at T2, and 20.37 years (SD, 1.20) at T3. The mean treatment time was 2.16 years (SD, 0.75), the mean long-term posttreatment time was 5.25 years (SD, 0.79), and the mean retention time was 1.44 years (SD, 0.48).
The orthodontic mechanics included fixed edgewise appliances, with 0.022 × 0.028-in conventional brackets and the usual wire sequence characterized by an initial 0.014-in nickel-titanium alloy, followed by 0.016-in, 0.018-in, 0.020-in, and 0.018 × 0.025-in or 0.019 × 0.025-n stainless steel archwires. Deepbites were corrected with accentuated and reversed curve of Spee. Maxillary and mandibular crowding was corrected with expansion of the leveling archwires. Class II malocclusions were corrected with either extraoral headgear or functional appliances. Class II elastics were also used to aid in correcting the anteroposterior relationships.
Group 2, treated with extraction of 4 first premolars, comprised 40 patients of both sexes (15 boys, 25 girls). Twenty-five patients had a Class I malocclusion, and 15 had a Class II malocclusion (6 half cusp, Class II; 1 three quarter cusp, Class II; 8 full cusp, Class II). At the end of treatment, all patients had a Class I molar relationship. The mean ages were 13.01 years (SD, 0.99) at T1, 15.16 years (SD, 1.07) at T2, and 20.61 years (SD, 1.37) at T3. The mean treatment time was 2.15 years (SD, 0.53), the long-term posttreatment time was 5.45 years (SD, 1.00), and the mean retention time was 1.63 years (SD, 0.69).
Orthodontic mechanics in this group also consisted of fixed edgewise appliances, with 0.022 × 0.028-in conventional brackets. After the extractions, the initial canine retraction was performed on a round continuous 0.014-in nickel-titanium alloy archwire until space was obtained to align the anterior teeth, correcting their crowding. Subsequently, the usual wire sequence, characterized by an initial 0.014-in nickel-titanium alloy, followed by 0.016-in, 0.018-in, 0.020-in, and 0.018 × 0.025-in or 0.019 × 0.025-in stainless steel archwires, was used. Deepbites were corrected with accentuated and reversed curve of Spee. After leveling and alignment, the anterior teeth were retracted en masse with rectangular archwires and elastic chains. Extraoral headgear was used to correct the Class II relationship in Class II patients, whereas in Class I patients it was used to reinforce anchorage and maintain the Class I molar relationship, if needed. When necessary, Class II elastics were used to help obtain a Class I molar relationship in the Class II patients.
With the described numbers of patients in each group, the statistical power of the test was of 80%, at a significance level of 5%, to detect a mean change of 0.61 mm (SD, 0.96) with the Little irregularity index between T2 and T3.
As retention, both groups used a maxillary Hawley plate worn full time during the initial 6 months and then worn at night for the next 6 months, on average. Fixed canine-to-canine mandibular retainers were used for mean periods of 1.44 years in group 1 and 1.63 years in group 2 ( Table I ).
|Variable||Group 1 (nonextraction)
n = 44
|Group 2 (extraction)
n = 40
|Age at stage of treatment|
|T1 age (y)||12.96||1.10||13.01||0.99||0.826|
|T2 age (y)||15.12||1.23||15.16||1.07||0.859|
|T3 age (y)||20.37||1.20||20.61||1.37||0.400|
|Duration of each evaluation period|
|Treatment time (y)||2.16||0.75||2.15||0.53||0.971|
|Long-term posttreatment time (y)||5.25||0.79||5.45||1.00||0.330|
|Retention time (y)||1.44||0.48||1.63||0.69||0.138|
|Little irregularity index, overjet, and overbite at T1|
|Maxillary Little index, T1 (mm)||8.92||4.35||10.62||3.98||0.067|
|Mandibular Little index, T1 (mm)||5.93||2.92||8.06||3.55||0.003 ∗|
|Overjet, T1 (mm)||6.78||2.69||6.83||2.47||0.926|
|Overbite, T1 (mm)||4.40||1.40||4.51||1.26||0.708|
The maxillary and mandibular dental casts were measured by 1 investigator (R.C.G.O.) to the nearest 0.01 mm with a digital caliper (500-143B; Mitutoyo America, Aurora, Ill). The following linear measurements were obtained for each pair of dental casts.
Overjet: the distance from the incisal edges of the most labial maxillary incisor to the most labial mandibular central incisor, parallel to the occlusal plane, recorded in millimeters.
Overbite: the amount of vertical incisal overlap of the maxillary and mandibular central incisors, recorded in millimeters.
Incisor irregularity: the sum, in millimeters, of the 5 distances between the anatomic contacts from the mesial aspect of the left canine through the mesial aspect of the right canine according to the method described by Little.
Thirty dental casts were randomly selected and remeasured by the same examiner (R.C.G.O.) after 30 days. Random and systematic errors were calculated comparing the first and second measurements with, respectively, Dahlberg’s formula and dependent t tests at a significance level of 5%.
Because all variables showed normal distributions according to Kolmogorov-Smirnov tests, intergroup comparisons were performed with t tests.
Intergroup comparability evaluation regarding ages at T1, T2, and T3; times at T1, T2, and T3; and T1 maxillary and mandibular incisor irregularity index values, overjet, and overbite were evaluated with t tests. Sex distribution, malocclusion types, and malocclusion severity at T1 between the 2 groups were assessed with chi-square tests.
Treatment changes were calculated by subtracting the T1 values from the T2 values. The amount of relapse was calculated by subtracting the T2 values from the T3 values. Intergroup comparisons at the T2 and T3 stages and during the treatment and long-term posttreatment periods were performed with t tests.
To evaluate whether, generally, there was any correlation between maxillary and mandibular crowding relapses, overjet and overbite relapses, and anterior crowding relapse, and between overjet and overbite relapses, Pearson correlation tests were used. Results were considered significant at P <0.05. All statistical analyses were performed with software (Statistica for Windows, version 6.0; StatSoft, Tulsa, Okla).
No evaluated variable showed a statistically significant systematic error, and the random errors varied from 0.38 (overbite) to 0.55 mm (the Little mandibular index).
The groups were comparable regarding ages at T1, T2, and T3; treatment time, long-term posttreatment time, and retention time; initial maxillary incisor irregularity, overjet, and overbite; sex distribution; type of malocclusion; and severity of Class II molar relationship ( Tables I-IV ). The initial Little mandibular irregularity index was greater in the extraction group ( Table I ).
|Class I||Class II|
|Half cusp, Class II||Three quarter cusp, Class II||Full cusp, Class II|
Maxillary incisor irregularity was similar in the posttreatment stage in the groups, but at T3 it was significantly greater in the nonextraction group. Treatment produced similar decreases in both groups, and the nonextraction group had a significantly greater relapse than did the extraction group ( Table V ).
|Variable||Group 1 (nonextraction)
n = 44
|Group 2 (extraction)
n = 40
|Maxillary Little index, T2 (mm)||1.60||1.24||1.54||1.14||0.798|
|Maxillary Little index, T3 (mm)||3.25||1.96||2.43||1.42||0.033 ∗|
|Maxillary Little index, T2-T1 (mm)||−7.31||4.40||−9.07||3.83||0.055|
|Maxillary Little index, T3-T2 (mm)||1.64||1.37||0.89||1.48||0.018 ∗|
|Mandibular Little index, T2 (mm)||1.17||1.05||1.24||0.80||0.727|
|Mandibular Little index, T3 (mm)||2.54||1.49||2.88||1.53||0.295|
|Mandibular Little index, T2-T1 (mm)||−4.76||3.05||−6.81||3.50||0.005 ∗|
|Mandibular Little index, T3-T2 (mm)||1.36||1.33||1.64||1.75||0.416|
|Overjet, T2 (mm)||3.15||0.89||2.90||0.93||0.210|
|Overjet, T3 (mm)||3.57||1.43||3.42||1.26||0.612|
|Overjet, T2-T1 (mm)||−3.63||2.55||−3.93||2.47||0.581|
|Overjet, T3-T2 (mm)||0.42||1.06||0.52||1.11||0.671|
|Overbite, T2 (mm)||2.87||0.79||2.88||0.91||0.927|
|Overbite, T3 (mm)||2.73||1.19||3.32||1.20||0.027 ∗|
|Overbite, T2-T1 (mm)||−1.53||1.21||−1.62||1.41||0.747|
|Overbite, T3-T2 (mm)||−0.14||0.91||0.43||1.22||0.016 ∗|