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Overjet, overbite, and anterior crowding relapses in extraction and nonextraction patients, and their correlations
ORIGINAL ARTICLE
Overjet, overbite, and anterior crowding relapses in extraction and nonextraction patients, and their correlations varo Francisconi,a Guilherme Janson,b Karina Maria Salvatore Freitas,c Manoela Fa sar Gobbi de Oliveira,a Marcos Roberto de Freitas,b Renata Cristina Gobbi de Oliveira,a Ricardo Ce Fernando Castanha Henriquesb and Jose Bauru, S~ao Paulo, and Maringa, Parana, Brazil
Introduction: 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. Methods: 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. Results: 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. Conclusions: 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. (Am J Orthod Dentofacial Orthop 2014;146:67-72)
O
rthodontic 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.1,2 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 a Graduate student, Department of Orthodontics, Bauru Dental School, University of S~ao Paulo, Bauru, S~ao Paulo, Brazil. b Professor, Department of Orthodontics, Bauru Dental School, University of S~ao Paulo, Bauru, S~ao Paulo, Brazil. c Associate professor, Department of Orthodontics, Inga Dental School, Maringa, Parana, Brazil. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Address correspondence to: Manoela Favaro Francisconi, Department of Orthodontics, Bauru Dental School, University of S~ao Paulo, Alameda Octavio Pinheiro Brisolla 9-75, Bauru, S~ao Paulo 17012-901, Brazil; e-mail, [email protected]. Submitted, October 2013; revised and accepted, April 2014. 0889-5406/$36.00 Copyright Ó 2014 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2014.04.012
long-term treatment stability have been extensively studied.1,3-5 It is well accepted that the stability of tooth alignment is highly variable and unpredictable.1 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.1,2,6 Recent research has also shown that overjet is often corrected during treatment; however, a significant posttreatment relapse of this characteristic is often observed.7,8 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.8,9 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 67
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irregularity index), and even the amount of overbite correction during orthodontic treatment.10 Because relapse seems to be a constant, some authors recommend overcorrection.11 Many studies have been conducted on the subject but focused on only 1 factor or variable.12-16 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 S~ao 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 3 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 3 0.025-in or 0.019 3 0.025-n stainless steel archwires. Deepbites were corrected with accentuated and reversed curve of
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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 3 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 3 0.025-in or 0.019 3 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 T3.17 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). 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.
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Table I. Intergroup comparisons of ages at T1, T2,
and T3 stages; of duration of treatment, long-term posttreatment, and retention; and of the Little irregularity index, overjet, and overbite at T1 (t tests) Group 1 Group 2 (nonextraction) (extraction) n 5 44 n 5 40 Variable Mean SD Mean Age at stage of treatment T1 age (y) 12.96 1.10 13.01 T2 age (y) 15.12 1.23 15.16 T3 age (y) 20.37 1.20 20.61 Duration of each evaluation period Treatment time (y) 2.16 0.75 2.15 Long-term posttreatment 5.25 0.79 5.45 time (y) Retention time (y) 1.44 0.48 1.63 Little irregularity index, overjet, and overbite at T1 Maxillary Little index, 8.92 4.35 10.62 T1 (mm) Mandibular Little index, 5.93 2.92 8.06 T1 (mm) Overjet, T1 (mm) 6.78 2.69 6.83 Overbite, T1 (mm) 4.40 1.40 4.51
SD
P
0.99 0.826 1.07 0.859 1.37 0.400 0.53 0.971 1.00 0.330 0.69 0.138 3.98 0.067 3.55 0.003* 2.47 0.926 1.26 0.708
*Statistically significant at P \0.05.
1.
2.
3.
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).
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.18
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 formula19 and dependent t tests at a significance level of 5%. Statistical analysis
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
RESULTS
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). 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). Treatment changes of mandibular incisor irregularity were significantly greater in the extraction group (Table V). Overjet was similar at T2 and T3 and showed similar changes with treatment and in the long-term posttreatment period in the 2 groups (Table V). Overbite was similar in the posttreatment stage in the groups, but at T3 it was significantly smaller in the nonextraction group. Treatment produced a similar decrease in both groups, and the nonextraction group had a significantly smaller relapse than did the extraction group (Table V). There was a positive correlation of the relapse of mandibular incisor crowding with relapses of overjet and overbite, and also a correlation of overjet and overbite relapses (Table VI).
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Table II. Comparison of sex distributions between the
Table V. Intergroup comparisons at the posttreat-
groups (chi-square test)
ment (T2) and long-term posttreatment (T3) stages and during the treatment (T2-T1) and long-term posttreatment (T3-T2) periods (t tests)
Sex Group 1 (nonextraction) 2 (extraction) Total
Girls 27 25 52
Boys 17 15 32
Total 44 40 84
Chi-square 5 0.07; df 5 1; P 5 0.782.
Table III. Comparison of malocclusion types between
the groups (chi-square test) Class Group 1 (nonextraction) 2 (extraction) Total
Class I 21 25 46
Class II 23 15 38
Total 44 40 84
Chi-square 5 1.84; df 5 1; P 5 0.174.
Table IV. Comparison of Class II molar relationship severity between the groups (chi-square test) Molar Relationship Group 1 (nonextraction) 2 (extraction) Total
Half cusp, Class II 4 6 10
Three quarter Full cusp, cusp, Class II Class II 6 13 1 8 7 21
Total 23 15 38
Variable Maxillary Little index, T2 (mm) Maxillary Little index, T3 (mm) Maxillary Little index, T2-T1 (mm) Maxillary Little index, T3-T2 (mm) Mandibular Little index, T2 (mm) Mandibular Little index, T3 (mm) Mandibular Little index, T2-T1 (mm) Mandibular Little index, T3-T2 (mm) Overjet, T2 (mm) Overjet, T3 (mm) Overjet, T2-T1 (mm) Overjet, T3-T2 (mm) Overbite, T2 (mm) Overbite, T3 (mm) Overbite, T2-T1 (mm) Overbite, T3-T2 (mm)
Group 1 (nonextraction) n 5 44
Group 2 (extraction) n 5 40
Mean 1.60
SD 1.24
Mean SD P 1.54 1.14 0.798
3.25
1.96
2.43 1.42 0.033*
7.31
4.40
9.07 3.83 0.055
1.64
1.37
0.89 1.48 0.018*
1.17
1.05
1.24 0.80 0.727
2.54
1.49
2.88 1.53 0.295
4.76
3.05
6.81 3.50 0.005*
1.36
1.33
1.64 1.75 0.416
3.15 3.57 3.63 0.42 2.87 2.73 1.53 0.14
0.89 1.43 2.55 1.06 0.79 1.19 1.21 0.91
2.90 3.42 3.93 0.52 2.88 3.32 1.62 0.43
0.93 1.26 2.47 1.11 0.91 1.20 1.41 1.22
0.210 0.612 0.581 0.671 0.927 0.027* 0.747 0.016*
*Statistically significant at P \0.05.
Chi-square 5 3.63; df 5 2; P 5 0.162.
DISCUSSION
The groups were matching regarding several aspects, with the exception of the initial Little mandibular irregularity index, which was significantly greater in the extraction group (Tables I-IV). This was expected, since crowding is a major reason for extraction treatment.20-23 All subjects used a similar retention protocol, so this would not have interfered with the evaluation.5,24,25 The Class I and Class II patients were pooled because they often displayed similar percentages of anterior crowding relapse after treatment (Table III).14,25,26 Controversy exists as to which treatment decision (extraction or nonextraction) will lead to stability. It is therefore important to investigate long-term changes in the dentitions of patients treated with both treatment protocols.27 Maxillary incisor irregularity in the nonextraction group was significantly greater in the long-term posttreatment stage because its relapse was greater than in the extraction group during the long-term
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posttreatment period (Table V). This probably occurred because in the extraction group, maxillary alignment was obtained with some canine distalization into the extraction spaces to correct crowding, whereas in the nonextraction group, crowding was corrected with the transverse increase of the maxillary arch and some protrusion of the incisors, which are more prone to relapse.17 Because the initial amount of maxillary crowding in the nonextraction group was numerically smaller than in the extraction group, it seems that actually there is a greater crowding relapse tendency in the maxillary arch when these patients were treated without extractions. This amount of relapse was considered to be small to moderate.18 Nevertheless, in this study it was greater than in a previous report, probably because our patients had a relatively shorter maxillary retention with the Hawley plate, used for 8.4 years.6 This suggests that similar to the mandibular arch, a prolonged retention time might be important for long-term stability.5,6 Because crowding at T1 was significantly greater in the extraction group, and the groups ended with similar
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between maxillary and mandibular crowding relapses, overjet and overbite relapses, and anterior crowding relapse, and between overjet and overbite relapses (Pearson correlation tests) Table
VI. Correlations
Correlation Maxillary Little index, T3-T2 3 mandibular Little index, T3-T2 Overjet, T3-T2 3 maxillary Little index, T3-T2 Overjet, T3-T2 3 mandibular Little index, T3-T2 Overbite, T3-T2 3 maxillary Little index, T3-T2 Overbite, T3-T2 3 mandibular Little index, T3-T2 Overjet, T3-T2 3 overbite, T3-T2
r P 0.166 0.130 0.192 0.216 0.128 0.236 0.578
0.078 0.047* 0.243 0.030* 0.000*
*Statistically significant at P \0.05.
mandibular irregularity index values, there were significantly greater treatment changes in the extraction group (Tables I and V). Mandibular incisor irregularity at T3 in both groups was smaller than shown by other studies probably because the long-term posttreatment observation period was longer in those studies.25,28 There is a tendency of mandibular anterior crowding to increase with time.29,30 A slight and similar mandibular crowding relapse occurred in both groups, within clinically acceptable standards (Table V).18 Rossouw et al31,32 and Artun et al28 also reported no significant differences in mandibular crowding relapse between groups treated with and without extractions. However, there is some controversy in this respect. Uhde et al33 and Paquette et al34 found greater amounts of relapse in nonextraction patients, but Kahl-Nieke et al35 found the opposite. The greater initial mandibular anterior crowding in our extraction group might have been responsible for the absence of a significant difference in crowding relapse.17 The behavior of overjet during treatment and in the long-term posttreatment period was similar in the groups (Table V). There was a slight nonsignificant relapse in both groups at T3. Hellekant et al,36 evaluating Class II malocclusion patients treated with or without extractions, observed significant overjet relapses in both groups. Perhaps this occurred because they evaluated only Class II subjects, who had accentuated initial overjets. Overbite was significantly greater in the extraction group in the long-term posttreatment stage because there were significantly greater overbite relapses in this group in that period (Table V). This was probably because extractions usually tend to increase overbite.20,37 While the appliances are still in place they can control the overbite, but when the appliances are removed there is a greater tendency of the overbite to increase.37
There were significant and positive correlations of overjet and overbite relapses with mandibular anterior crowding relapse and consequently between overjet and overbite relapses (Table VI). According to Little,18 long-term posttreatment crowding of the mandibular incisors is the first evidence of progressive instability of orthodontic treatment. Once mandibular crowding relapse occurs, the mandibular incisors are lingually tipped, and there are consequent increases in overjet and overbite. The maxillary incisors are not directly involved in the changes caused by this relapse. Regardless of the relapse etiology, irregularity of the mandibular incisors seems to be the precursor of maxillary crowding, overbite, and deterioration of treatment.18 However, these results should be interpreted with caution, since the correlation coefficients are low and relapse is multifactorial. Correlations of the investigated factors were performed in the whole sample because the objective was to evaluate whether these factors are generally correlated. It was not our intention to determine the correlations among these factors in the groups individually. This can be investigated in future studies. Long-term stability is a challenge for orthodontists because it is almost impossible to guarantee absolute posttreatment stability. This implies that orthodontists and patients associate treatment success with longterm stability.29 In this study, there was greater maxillary crowding relapse in the nonextraction group and greater overbite relapse in the extraction group. However, these long-term posttreatment changes remained within clinically acceptable limits for stability. These changes could be described as “physiologic adaptations,”38,39 or as part of normal developmental changes.38,40,41 Because orthodontists have little control over these biologic processes,27 they should clearly explain to their patients and parents these phenomena and also consider them during treatment planning, regardless of whether the patient will be treated with or without extractions.42 CONCLUSIONS
1.
2.
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.
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American Journal of Orthodontics and Dentofacial Orthopedics
Overjet, overbite, and anterior crowding relapses in extraction and nonextraction patients, and their correlations varo Francisconi,a Guilherme Janson,b Karina Maria Salvatore Freitas,c Manoela Fa sar Gobbi de Oliveira,a Marcos Roberto de Freitas,b Renata Cristina Gobbi de Oliveira,a Ricardo Ce Fernando Castanha Henriquesb and Jose Bauru, S~ao Paulo, and Maringa, Parana, Brazil
Introduction: 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. Methods: 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. Results: 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. Conclusions: 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. (Am J Orthod Dentofacial Orthop 2014;146:67-72)
O
rthodontic 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.1,2 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 a Graduate student, Department of Orthodontics, Bauru Dental School, University of S~ao Paulo, Bauru, S~ao Paulo, Brazil. b Professor, Department of Orthodontics, Bauru Dental School, University of S~ao Paulo, Bauru, S~ao Paulo, Brazil. c Associate professor, Department of Orthodontics, Inga Dental School, Maringa, Parana, Brazil. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Address correspondence to: Manoela Favaro Francisconi, Department of Orthodontics, Bauru Dental School, University of S~ao Paulo, Alameda Octavio Pinheiro Brisolla 9-75, Bauru, S~ao Paulo 17012-901, Brazil; e-mail, [email protected]. Submitted, October 2013; revised and accepted, April 2014. 0889-5406/$36.00 Copyright Ó 2014 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2014.04.012
long-term treatment stability have been extensively studied.1,3-5 It is well accepted that the stability of tooth alignment is highly variable and unpredictable.1 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.1,2,6 Recent research has also shown that overjet is often corrected during treatment; however, a significant posttreatment relapse of this characteristic is often observed.7,8 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.8,9 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 67
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irregularity index), and even the amount of overbite correction during orthodontic treatment.10 Because relapse seems to be a constant, some authors recommend overcorrection.11 Many studies have been conducted on the subject but focused on only 1 factor or variable.12-16 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 S~ao 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 3 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 3 0.025-in or 0.019 3 0.025-n stainless steel archwires. Deepbites were corrected with accentuated and reversed curve of
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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 3 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 3 0.025-in or 0.019 3 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 T3.17 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). 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.
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Table I. Intergroup comparisons of ages at T1, T2,
and T3 stages; of duration of treatment, long-term posttreatment, and retention; and of the Little irregularity index, overjet, and overbite at T1 (t tests) Group 1 Group 2 (nonextraction) (extraction) n 5 44 n 5 40 Variable Mean SD Mean Age at stage of treatment T1 age (y) 12.96 1.10 13.01 T2 age (y) 15.12 1.23 15.16 T3 age (y) 20.37 1.20 20.61 Duration of each evaluation period Treatment time (y) 2.16 0.75 2.15 Long-term posttreatment 5.25 0.79 5.45 time (y) Retention time (y) 1.44 0.48 1.63 Little irregularity index, overjet, and overbite at T1 Maxillary Little index, 8.92 4.35 10.62 T1 (mm) Mandibular Little index, 5.93 2.92 8.06 T1 (mm) Overjet, T1 (mm) 6.78 2.69 6.83 Overbite, T1 (mm) 4.40 1.40 4.51
SD
P
0.99 0.826 1.07 0.859 1.37 0.400 0.53 0.971 1.00 0.330 0.69 0.138 3.98 0.067 3.55 0.003* 2.47 0.926 1.26 0.708
*Statistically significant at P \0.05.
1.
2.
3.
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).
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.18
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 formula19 and dependent t tests at a significance level of 5%. Statistical analysis
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
RESULTS
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). 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). Treatment changes of mandibular incisor irregularity were significantly greater in the extraction group (Table V). Overjet was similar at T2 and T3 and showed similar changes with treatment and in the long-term posttreatment period in the 2 groups (Table V). Overbite was similar in the posttreatment stage in the groups, but at T3 it was significantly smaller in the nonextraction group. Treatment produced a similar decrease in both groups, and the nonextraction group had a significantly smaller relapse than did the extraction group (Table V). There was a positive correlation of the relapse of mandibular incisor crowding with relapses of overjet and overbite, and also a correlation of overjet and overbite relapses (Table VI).
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Table II. Comparison of sex distributions between the
Table V. Intergroup comparisons at the posttreat-
groups (chi-square test)
ment (T2) and long-term posttreatment (T3) stages and during the treatment (T2-T1) and long-term posttreatment (T3-T2) periods (t tests)
Sex Group 1 (nonextraction) 2 (extraction) Total
Girls 27 25 52
Boys 17 15 32
Total 44 40 84
Chi-square 5 0.07; df 5 1; P 5 0.782.
Table III. Comparison of malocclusion types between
the groups (chi-square test) Class Group 1 (nonextraction) 2 (extraction) Total
Class I 21 25 46
Class II 23 15 38
Total 44 40 84
Chi-square 5 1.84; df 5 1; P 5 0.174.
Table IV. Comparison of Class II molar relationship severity between the groups (chi-square test) Molar Relationship Group 1 (nonextraction) 2 (extraction) Total
Half cusp, Class II 4 6 10
Three quarter Full cusp, cusp, Class II Class II 6 13 1 8 7 21
Total 23 15 38
Variable Maxillary Little index, T2 (mm) Maxillary Little index, T3 (mm) Maxillary Little index, T2-T1 (mm) Maxillary Little index, T3-T2 (mm) Mandibular Little index, T2 (mm) Mandibular Little index, T3 (mm) Mandibular Little index, T2-T1 (mm) Mandibular Little index, T3-T2 (mm) Overjet, T2 (mm) Overjet, T3 (mm) Overjet, T2-T1 (mm) Overjet, T3-T2 (mm) Overbite, T2 (mm) Overbite, T3 (mm) Overbite, T2-T1 (mm) Overbite, T3-T2 (mm)
Group 1 (nonextraction) n 5 44
Group 2 (extraction) n 5 40
Mean 1.60
SD 1.24
Mean SD P 1.54 1.14 0.798
3.25
1.96
2.43 1.42 0.033*
7.31
4.40
9.07 3.83 0.055
1.64
1.37
0.89 1.48 0.018*
1.17
1.05
1.24 0.80 0.727
2.54
1.49
2.88 1.53 0.295
4.76
3.05
6.81 3.50 0.005*
1.36
1.33
1.64 1.75 0.416
3.15 3.57 3.63 0.42 2.87 2.73 1.53 0.14
0.89 1.43 2.55 1.06 0.79 1.19 1.21 0.91
2.90 3.42 3.93 0.52 2.88 3.32 1.62 0.43
0.93 1.26 2.47 1.11 0.91 1.20 1.41 1.22
0.210 0.612 0.581 0.671 0.927 0.027* 0.747 0.016*
*Statistically significant at P \0.05.
Chi-square 5 3.63; df 5 2; P 5 0.162.
DISCUSSION
The groups were matching regarding several aspects, with the exception of the initial Little mandibular irregularity index, which was significantly greater in the extraction group (Tables I-IV). This was expected, since crowding is a major reason for extraction treatment.20-23 All subjects used a similar retention protocol, so this would not have interfered with the evaluation.5,24,25 The Class I and Class II patients were pooled because they often displayed similar percentages of anterior crowding relapse after treatment (Table III).14,25,26 Controversy exists as to which treatment decision (extraction or nonextraction) will lead to stability. It is therefore important to investigate long-term changes in the dentitions of patients treated with both treatment protocols.27 Maxillary incisor irregularity in the nonextraction group was significantly greater in the long-term posttreatment stage because its relapse was greater than in the extraction group during the long-term
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posttreatment period (Table V). This probably occurred because in the extraction group, maxillary alignment was obtained with some canine distalization into the extraction spaces to correct crowding, whereas in the nonextraction group, crowding was corrected with the transverse increase of the maxillary arch and some protrusion of the incisors, which are more prone to relapse.17 Because the initial amount of maxillary crowding in the nonextraction group was numerically smaller than in the extraction group, it seems that actually there is a greater crowding relapse tendency in the maxillary arch when these patients were treated without extractions. This amount of relapse was considered to be small to moderate.18 Nevertheless, in this study it was greater than in a previous report, probably because our patients had a relatively shorter maxillary retention with the Hawley plate, used for 8.4 years.6 This suggests that similar to the mandibular arch, a prolonged retention time might be important for long-term stability.5,6 Because crowding at T1 was significantly greater in the extraction group, and the groups ended with similar
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between maxillary and mandibular crowding relapses, overjet and overbite relapses, and anterior crowding relapse, and between overjet and overbite relapses (Pearson correlation tests) Table
VI. Correlations
Correlation Maxillary Little index, T3-T2 3 mandibular Little index, T3-T2 Overjet, T3-T2 3 maxillary Little index, T3-T2 Overjet, T3-T2 3 mandibular Little index, T3-T2 Overbite, T3-T2 3 maxillary Little index, T3-T2 Overbite, T3-T2 3 mandibular Little index, T3-T2 Overjet, T3-T2 3 overbite, T3-T2
r P 0.166 0.130 0.192 0.216 0.128 0.236 0.578
0.078 0.047* 0.243 0.030* 0.000*
*Statistically significant at P \0.05.
mandibular irregularity index values, there were significantly greater treatment changes in the extraction group (Tables I and V). Mandibular incisor irregularity at T3 in both groups was smaller than shown by other studies probably because the long-term posttreatment observation period was longer in those studies.25,28 There is a tendency of mandibular anterior crowding to increase with time.29,30 A slight and similar mandibular crowding relapse occurred in both groups, within clinically acceptable standards (Table V).18 Rossouw et al31,32 and Artun et al28 also reported no significant differences in mandibular crowding relapse between groups treated with and without extractions. However, there is some controversy in this respect. Uhde et al33 and Paquette et al34 found greater amounts of relapse in nonextraction patients, but Kahl-Nieke et al35 found the opposite. The greater initial mandibular anterior crowding in our extraction group might have been responsible for the absence of a significant difference in crowding relapse.17 The behavior of overjet during treatment and in the long-term posttreatment period was similar in the groups (Table V). There was a slight nonsignificant relapse in both groups at T3. Hellekant et al,36 evaluating Class II malocclusion patients treated with or without extractions, observed significant overjet relapses in both groups. Perhaps this occurred because they evaluated only Class II subjects, who had accentuated initial overjets. Overbite was significantly greater in the extraction group in the long-term posttreatment stage because there were significantly greater overbite relapses in this group in that period (Table V). This was probably because extractions usually tend to increase overbite.20,37 While the appliances are still in place they can control the overbite, but when the appliances are removed there is a greater tendency of the overbite to increase.37
There were significant and positive correlations of overjet and overbite relapses with mandibular anterior crowding relapse and consequently between overjet and overbite relapses (Table VI). According to Little,18 long-term posttreatment crowding of the mandibular incisors is the first evidence of progressive instability of orthodontic treatment. Once mandibular crowding relapse occurs, the mandibular incisors are lingually tipped, and there are consequent increases in overjet and overbite. The maxillary incisors are not directly involved in the changes caused by this relapse. Regardless of the relapse etiology, irregularity of the mandibular incisors seems to be the precursor of maxillary crowding, overbite, and deterioration of treatment.18 However, these results should be interpreted with caution, since the correlation coefficients are low and relapse is multifactorial. Correlations of the investigated factors were performed in the whole sample because the objective was to evaluate whether these factors are generally correlated. It was not our intention to determine the correlations among these factors in the groups individually. This can be investigated in future studies. Long-term stability is a challenge for orthodontists because it is almost impossible to guarantee absolute posttreatment stability. This implies that orthodontists and patients associate treatment success with longterm stability.29 In this study, there was greater maxillary crowding relapse in the nonextraction group and greater overbite relapse in the extraction group. However, these long-term posttreatment changes remained within clinically acceptable limits for stability. These changes could be described as “physiologic adaptations,”38,39 or as part of normal developmental changes.38,40,41 Because orthodontists have little control over these biologic processes,27 they should clearly explain to their patients and parents these phenomena and also consider them during treatment planning, regardless of whether the patient will be treated with or without extractions.42 CONCLUSIONS
1.
2.
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.
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