Occlusal changes in orthodontically treated subjects 40 years after treatment and comparison with untreated control subjects

Introduction

The objective of this study was to compare the aging changes of the dental arches in orthodontically treated and untreated subjects after a 4-decade follow-up period.

Methods

This retrospective study analyzed 2 groups. The treated group comprised 29 patients (11 male, 18 female) presenting with Class I or Class II malocclusions orthodontically treated with extractions of 4 first premolars. Dental models taken at pretreatment (12.84 years), posttreatment (14.95 years), and long-term posttreatment (51.37 years) were evaluated. The untreated (control) group consisted of 22 untreated patients with dental models taken at 13.32, 17.82, and 60.95 years of age. The dental models were digitized, and the following variables were evaluated: Little irregularity index, intercanine, interpremolar and intermolar widths, arch length, arch perimeter, overjet, and overbite. Interphase comparison of the treated group was performed with repeated measures analysis of variance and Tukey tests. Intergroup comparisons were performed using t tests ( P <0.05).

Results

Crowding was corrected with treatment but relapsed significantly in the long term. Intercanine width increased with treatment and decreased in the long term. Interpremolar and intermolar widths, arch perimeter, and length decreased with treatment and continued to decrease long-term posttreatment. Overjet and overbite were corrected with treatment and remained stable in the long term. From posttreatment to long-term posttreatment, a greater crowding increase was observed in the treated group than in the untreated group. The treated group demonstrated a greater decrease in mandibular intercanine and maxillary and mandibular interpremolar widths than the untreated sample. Overbite increased in the treated group and decreased in the untreated group. The multiple regression analysis showed that previous 4-premolar extractions orthodontic treatment is significantly associated with anterior crowding in the long term.

Conclusions

In the long-term, the treated patients showed relapse of crowding and a decrease in arch form. Long-term changes of treated patients were different from untreated subjects. Relapse might have contributed to greater changes in incisor crowding and arch widths observed in the treated patients.

Highlights

  • Occlusal changes in treated and untreated groups were compared over 40 years.

  • Maxillary and mandibular anterior crowding increased more in the treated group.

  • Maturational changes in the treated group differed from those in the untreated group.

  • Relapse contributes to greater changes in crowding and arch width in treated subjects.

There is consensus in the literature that some occlusal changes will inevitably occur after the end of orthodontic treatment, known as relapse. Prediction of these posttreatment changes and underlying causes are of great value to orthodontists, and the incessant search for these answers is seen in the orthodontic literature. The continuous occlusal posttreatment changes sometimes cannot be distinguished from the normal process of aging of the occlusion that occurs regardless of whether the individual has been orthodontically treated or not.

The physiological and maturational changes of the dentition, from childhood to adolescence and from young adulthood to late adulthood, constitute a gradual process. Longitudinal studies in untreated subjects , , showed that the arch dimensions change over the years. It is also known that the aging process slightly deteriorates some occlusal features of patients with normal occlusion.

From 21 to 28 years of age, patients with a Class I malocclusion with good occlusion showed significant changes in overbite, incisors irregularity, and arch perimeter. From late adolescence until about half a century of life, dental arch dimensions tend to decrease, and incisors irregularity tends to increase in untreated occlusion patients. , , , Changes of the dental arches are continuous as well as physiological mesial migration of the permanent dentition that results in anterior crowding, especially in the mandible. Overbite and overjet are generally stable during adulthood. , ,

Evaluation of qualitative occlusal changes in patients with normal occlusion over 47 years showed deterioration of the anteroposterior occlusal relationship. However, the marginal ridges, buccolingual inclination, and interproximal contacts improved. The occurrence of dental crowding was the most frequently detected change throughout life in untreated patients and caused dissatisfaction with this occlusal feature in 35% of the sample.

Comparisons between untreated normal occlusions and treated patients to clarify the differences of the aging process and the relapse or posttreatment changes are extremely important. Some changes in transverse arch dimensions appear to be similar in patients treated without extractions and in untreated subjects aged up to 18 years. The short-term posttreatment occlusal relapse and maxillary irregularity are greater than the physiological changes caused by the natural development of untreated patients from 12 to 20 years of age. Mandibular incisor irregularity increases similarly in both treated and untreated groups from 12 to 20-28 years of age. ,

To our knowledge, there is no long-term comparison between treated subjects and untreated occlusions followed into late adulthood. Therefore, the objective of this study was to compare the aging changes of the dental arches in orthodontically treated and untreated subjects after a 4-decade follow-up.

Material and methods

This study was approved by the Ethics Committee in Human Research of the Bauru Dental School, University of São Paulo. Sample size calculation was based on an α significance level of 5% and a β of 20% to detect a minimum difference of 0.8 mm, with a standard deviation (SD) of 0.74 for the maxillary irregularity index. The sample size calculation showed the need for 22 patients in each group.

Two study samples were analyzed. The orthodontically treated group comprised retrospective records of subjects treated by graduate students at Bauru Dental School, University of São Paulo, chosen according to the following criteria: Class I or Class II Division 1 malocclusion at the beginning of orthodontic treatment; patients with skeletal Class II malocclusion were not included in the sample; treatment protocol with extractions of 4 first premolars; complete orthodontic treatment with full maxillary and mandibular fixed edgewise appliances (0.022 × 0.028-in slot); all permanent teeth erupted up to the first molars, at the pretreatment stage; absence of tooth agenesis and anomalies; and no retention at the time of the follow-up records. Pretreatment (T1), posttreatment (T2), and long-term follow-up of at least 25 years after the end of orthodontic treatment (T3) dental models should be available at the time of the study. The sample comprised 29 subjects of both sexes (11 male; 18 female), with a mean pretreatment age of 12.84 years (SD, 0.98; range, 11.50-15.30). The mean final age was 14.95 years (SD, 1.24; range, 12.77-18.09), and the mean treatment time was 2.10 years (SD, 0.65; range, 0.99-3.33). The mean age at the long-term evaluation was 51.37 years (SD, 4.22; range, 42.10-59.09). The mean time of long-term posttreatment follow-up was 36.42 years (SD, 3.94; range, 27.47-43.05). Sixteen subjects presented with Class I malocclusions, and 13 had Class II malocclusions (severity: 8 half-cusp Class II and 5 full-cusp Class II), all treated with extraction of the 4 first premolars. As retention, at the end of active orthodontic treatment, all patients used a removable Hawley plate in the maxillary arch, and 0.028-in stainless steel round wire fixed retainer was bonded canine-to-canine in the mandibular arch. The maxillary removable and the mandibular canine-to-canine fixed retainer were used on average 1.77 years (SD, 0.67; range, 0.79-3.33). All maxillary removable and mandibular fixed retainers were removed no later than 3.3 years after the end of active orthodontic treatment. At T3, all subjects of the treated group were free of retainers for more than 30 years.

Orthodontic mechanics for patients with Class I and II malocclusions in the treated group was similar and included fixed edgewise appliance 0.022 × 0.028-in slot; extraoral headgear was used as anchorage to maintain Class I relationship or to correct the Class II molar relationship; the anterior teeth were retracted to the extraction spaces with a rectangular archwire and elastic chains, by sliding mechanics; Class II elastics were used when necessary. All patients finished in Class I molar and canine relationships, with adequate overjet, overbite, and teeth alignment. The mean Peer Assessment Rating index at the end of treatment was 2.68 (SD, 1.52), indicating a good orthodontic finishing. ,

The untreated group (with untreated occlusion) comprised 22 subjects (12 males, 10 females) assessed at 3 time points (T1, T2, and T3), with a mean age of the subjects of 13.32 (SD, 1.00; range, 11.91-15.16), 17.82 (SD, 1.35; range, 16.08-22.08), and 60.95 years (SD, 1.47; range, 58.41-63.41), respectively. The mean period between the first and second evaluation (T2 −T1) was 4.50 years (SD, 0.89; range, 4.08-8.25), and the mean follow-up time was 43.12 years (SD, 1.51; range, 39.58-45.33). The initial untreated sample group was obtained from 1967 to 1974 and comprised 82 White subjects (39 men, 43 women). Dental models were obtained at 13 (T1) and 17 years of age (T2). At T1, all subjects had a clinically acceptable occlusion , in the complete permanent dentition, dental and skeletal Class I relationships (molar and canine Class I relationship) in the permanent dentition, no crossbite, positive overjet and overbite (ranging from 2 to 4 mm), and a maximum 2 mm of incisors’ crowding with no previous orthodontic treatment. From April 2015 to May 2016, the sample was recalled, and dental models were obtained (T3). Thirty-eight subjects were contacted, and 27 were enrolled. Five of them were excluded because of the following exclusion criteria: orthodontic treatment performed until the follow-up evaluation, complete tooth loss, and no dental models at any of the 3 time points.

In the treated group, the only extracted teeth were the 4 first premolars for orthodontic reasons. Patients with other missing teeth were excluded from the sample. However, for the untreated group, most patients missed teeth from T2 to T3 and were not excluded from the sample. Out of 22 patients of the UT group, 15 showed at least 1 permanent tooth loss, but several missing teeth were already rehabilitated with implants/prostheses. Table I describes each missing/rehabilitated tooth of the patients from the untreated group at T3. All subjects at T3 presented good oral health, no periodontal disease, and good overall health condition, without any systemic disease.

Table I
List of patients from the untreated group showing the missing/rehabilitated teeth at the T3
Subject Sex Age at T3 (y) Tooth missing Rehabilitated with implant Rehabilitated with crown/prosthesis
1 F 60.08 27, 37
2 F 63.08 17, 47
3 F 60.91 26, 47 16, 24
4 M 61.25 16, 17, 36 22
5 M 58.41
6 M 61.66 36
7 F 59.16
8 F 61.50 36 12, 22, 25, 26, 47
9 F 58.66 24, 27, 47 15, 16, 25, 26, 35, 36, 37, 45, 46
10 F 60.08 27, 37, 47 45, 46 14, 16, 25, 35
11 M 62.08 26, 34, 37, 46, 47 14, 25, 36
12 F 60.33 25, 47 46 14, 15, 24, 26, 36, 37, 43, 44, 45
13 M 61.41 16, 36, 45 34, 35, 37 46, 47
14 M 61.25 16, 17, 25, 26, 36, 47
15 F 62.25 25, 37, 47 26, 35, 36, 44, 46 27
16 M 61.75 16, 26
17 M 63.41
18 M 59.41 16, 17, 24, 26, 27, 36, 37, 46, 47 14, 15, 22, 25, 35, 45
19 F 60.08 45, 46, 47 17, 24, 25, 26, 27, 35, 36, 37
20 M 59.00 15, 26 36, 37 46
21 M 62.00 26, 27, 46
22 M 63.25 27 16, 36, 46 45, 47

F, Female; M, male.

Dental models from 3 stages of each individual were used: T1, T2, and T3 for the treated subjects and in similar stages for the untreated sample. All dental models were digitized using an R700 3-dimensional (3D) scanner (3Shape, Copenhagen, Denmark). Dental model measurements were performed using the OrthoAnalyzer 3-dimensional software (3Shape) by a single examiner (K.M.S.F.).

The Peer Assessment Rating index, as described by Richmond et al and scored with the American weightings was assessed in the posttreatment dental casts of the treated group to indicate the quality of the orthodontic finishing.

The Little irregularity index for maxillary and mandibular arches , was measured to evaluate anterior crowding. Arch dimensions measurements included intercanine, interpremolar and intermolar widths, arch perimeter, and arch length. Overjet and overbite were also measured in the dental models. Missing teeth and prostheses were not considered for measurements.

The differences between the final and initial stages (T2 −T1) were calculated to express the amount of correction with treatment and amount of changes from T1 to T2 in the untreated group. The differences from the long-term posttreatment stage with the posttreatment stage (T3 − T2) were calculated to express the amount of changes after treatment in the long-term follow-up evaluation for the treated group and from T2 to T3 to express the long-term follow-up changes in the untreated group.

After a month from the first measurement, the dental models of 15 subjects (45 pairs of dental casts) were randomly selected and remeasured by the same examiner (K.M.S.F.). The intraexaminer reliability was assessed using intraclass correlation coefficients and the Bland-Altman method. Normal distribution of data was evaluated by the Shapiro-Wilk test. In contrast, intergroup comparability of sex distribution and the age and period of the evaluation was performed using chi-square and t tests, respectively. Interphase comparisons of the treated group were performed with repeated measures analysis of variance and Tukey tests. Intergroup comparisons at T1 and interphase changes were evaluated using t tests.

A multiple regression analysis was performed to verify the predictive factors for the long-term changes of maxillary and mandibular anterior crowding separately. Only variables with significant differences between the groups at T3 − T2 were considered for the analysis. This way, the long-term changes of Little irregularity index (Little T3-2) was considered as the dependent variable for the following independent variables: long-term overbite change (overbite T3-2), long-term intercanine width change (3-3 T3-2), long-term interpremolar width change (5-5 T3-2), and treated/untreated group (T/UT).

All tests were performed with Statistica software (version 7.0; Stat Soft, Tulsa, Okla), at P <0.05.

Results

Intraclass correlation coefficients of the variables varied from 0.92 to 0.99, indicating excellent intrarater agreement. The variable with the widest limit of agreement was the maxillary arch perimeter (−1.12 and 1.19).

The groups were comparable regarding sex distribution ( Table II ) and initial age ( Table II ). The untreated group was older in the T2 and T3 time points and had a greater follow-up period than the treated group ( Table II ).

Table II
Results of the intergroup comparability of sex distribution (chi-square test) ages and observation times (independent t tests)
Variables Treated group, N = 29 Untreated group, N = 22 P value
Sex 0.237
Males 11 12
Females 18 10

Variables, y Treated group, N = 29 Untreated group, N = 22 P value
Mean SD (range) Mean SD (range)
Age T1 12.84 0.98 (11.50-15.30) 13.32 1.00 (11.91-15.16) 0.094
Age T2 14.95 1.24 (12.77-18.09) 17.82 1.35 (16.08-22.08) 0.000 ,
Age T3 51.37 4.22 (42.10-59.09) 60.95 1.47 (58.41-63.41) 0.000 ,
Treatment/evaluation time T2 −T1 2.10 0.65 (0.99-3.33) 4.50 0.89 (4.08-8.25) 0.000 ,
Long-term posttreatment/follow-up time T3 − T2 36.42 3.94 (27.47-43.05) 43.12 1.51 (39.58-45.33) 0.000 ,

Statistically significant at P <0.05.

Chi-square test.

Independent t test.

Because groups were not comparable regarding follow-up time from T2 to T3, the untreated group changes (T3 − T2) were therefore annualized to the corresponding treated group follow-up time. Therefore, all subjects in the untreated group had their follow-up changes, for each variable, divided by their follow-up time (of each patient individually), and then multiplied by the mean long-term posttreatment time (T3 − T2) of the treated group.

In the treated group, crowding was corrected with treatment and showed statistically significant relapse in the long term. Intercanine width increased with treatment and decreased in the long term. Interpremolar and intermolar widths, arch perimeter, and length decreased with treatment and continued to decrease long-term posttreatment. Overjet and overbite were corrected with treatment and remained stable in the long term ( Table III ).

Table III
Results of the interphase comparison of the treated group (repeated measures analysis of variance and Tukey tests)
Variables, mm T1 T2 T3 P value
Mean (SD) Mean (SD) Mean (SD)
Maxillary dental casts measurements
Mx Little 10.02 (3.80) A 0.93 (0.50) B 4.04 (1.47) C 0.000
Mx 3-3 width 33.33 (3.13) A 34.54 (2.02) B 33.29 (2.27) A 0.000
Mx 5-5 width 43.81 (3.09) A 42.91 (2.05) AB 41.30 (2.60) B 0.000
Mx 6-6 width 48.58 (3.47) A 47.62 (2.43) AB 46.65 (2.92) B 0.000
Mx arch perimeter 78.02 (6.15) A 64.59 (3.62) B 62.29 (3.10) C 0.000
Mx arch length 30.03 (3.84) A 23.01 (2.82) B 21.89 (2.48) B 0.000
Mandibular dental casts measurements
Md Little 8.92 (3.74) A 1.11 (1.01) B 5.39 (2.49) C 0.000
Md 3-3 width 25.59 (1.75) A 27.00 (1.68) B 25.25 (1.79) A 0.000
Md 5-5 width 37.83 (3.19) A 36.01 (1.65) B 34.07 (2.27) C 0.000
Md 6-6 width 43.27 (2.97) A 41.12 (2.32) B 40.14 (2.74) C 0.000
Md arch perimeter 65.34 (3.18) A 53.79 (2.39) B 51.13 (3.34) C 0.000
Md arch length 22.74 (1.75) A 17.77 (1.30) B 16.91 (1.77) C 0.000
Anterior relationships
Overjet 7.24 (3.04) A 2.70 (0.59) B 3.85 (1.84) B 0.000
Overbite 3.38 (1.65) A 2.55 (0.51) B 2.86 (1.07) B 0.041

Note. Different letters in the same row indicate the presence of a statistically significant between the groups indicated by the Tukey test.
Mx, Maxillary; Md, mandibular.

Statistically significant at P <0.05.

The comparison of the starting forms demonstrated that the treated group presented greater crowding and overjet than the untreated group ( Table IV ). Maxillary and mandibular interpremolar widths and maxillary intermolar width were greater in the untreated group than in the treated group ( Table IV ). Maxillary arch perimeter and length were greater in the treated than in the untreated group ( Table IV ).

Table IV
Intergroup comparison of the starting forms (independent t tests)
Variables, mm Treated group, N = 29 Untreated group, N = 22 P value
Mean SD Mean SD
T1
Maxillary dental casts measurements
Mx Little 10.02 3.80 0.37 0.74 0.000
Mx 3-3 width 33.33 3.13 33.24 2.08 0.905
Mx 5-5 width 43.81 3.09 46.91 2.22 0.000
Mx 6-6 width 48.58 3.47 52.01 2.97 0.000
Mx arch perimeter 78.02 6.15 73.56 3.41 0.004
Mx arch length 30.03 3.84 27.01 1.71 0.003
Mandibular dental casts measurements
Md Little 8.92 3.74 2.26 1.96 0.000
Md 3-3 width 25.59 1.75 25.50 1.48 0.842
Md 5-5 width 37.83 3.19 39.95 2.08 0.009
Md 6-6 width 43.27 2.97 45.13 3.50 0.053
Md arch perimeter 65.34 3.18 64.42 3.15 0.316
Md arch length 22.74 1.75 22.96 1.78 0.672
Anterior relationship
Overjet 7.24 3.04 2.87 0.66 0.000
Overbite 3.38 1.65 3.13 0.98 0.551
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Oct 30, 2021 | Posted by in Orthodontics | Comments Off on Occlusal changes in orthodontically treated subjects 40 years after treatment and comparison with untreated control subjects
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