Factors associated with the stability of compensatory orthodontic treatment of Class III malocclusion in the permanent dentition

Introduction

This study aimed to assess the stability of compensatory treatment of Class III malocclusion in permanent dentition.

Methods

Thirty-six patients (21 women and 15 men; mean age, 20 years) with Class III malocclusion were subjected to the compensatory treatment of permanent dentition and followed up for at least 3 years after orthodontic treatment (T3). Multivariate Poisson regression was performed to assess the influence of clinical, cephalometric, and dental cast variables at the beginning (T1) and the end of treatment on the stability of Class III malocclusion.

Results

Overjet changed from −0.25 mm (−3 to 0.5 mm) at T1 to 1.4 mm (1-2.5 mm) at the end of treatment and 0.8 mm (0-1.5 mm) at T3. Clinical relapse (overjet <1 mm and/or canine Class III relations) was observed in 11 patients (30.6%). Patients treated with extraction of mandibular premolars (risk ratio [RR] = 2.13 × 10 −07 , P <0.001), with better orthodontic end outcomes (RR = 1.16, P = 0.009) and which had lower maxillary incisor inclination at T1 (RR = 1.08, P = 0.035) showed a lower risk of relapse. Demographic (sex, age), clinical (length of treatment and posttreatment, number of treatment phases, time of Class III elastics), cephalometric (SNA, SNB, ANB, Wits appraisal, SNGoGn, IMPA), and dental cast (peer assessment rating index and arch dimensions) variables were not significantly associated with clinical relapse at T3.

Conclusions

The stability of compensatory treatment of Class III malocclusion in permanent dentition is multifactorial, with few predictive variables. Patients treated with extraction and better orthodontic finishing had a lower risk of relapse, whereas larger maxillary incisor inclination at baseline increased the risk of relapse.

Highlights

  • Data regarding the stability of compensatory treatment of Class III malocclusion is scarce.

  • The stability of this treatment is multifactorial, with few predictive variables.

  • Greater maxillary incisor inclination before treatment increases the risk of relapse.

  • Patients treated with mandibular premolar extraction had good stability.

  • Patients with better orthodontic treatment finishing had a lower risk of relapse.

Despite the low prevalence (<5%) of Class III malocclusion in the Western population, it has a significant negative impact on the quality of life. , The selection of an orthopedic, orthodontic, or orthosurgical protocol depends on the severity of skeletal discrepancy and the craniofacial growth pattern.

In children, the most common treatment approach has been rapid maxillary expansion combined with anterior traction on the maxillary arch using a facemask. , Currently, the use of skeletal anchorage with miniplates has attracted supporters. At the end of or after the pubertal growth spurt, it is possible to use dental compensation in patients with milder skeletal discrepancies. In patients with more severe skeletal and dental deformities, for which neither changes in growth nor compensation are a solution, orthognathic surgery appears to be the alternative.

Although Class III correction is common in clinical practice—despite debatable predictability —the stability of this treatment is a major concern, regardless of the treatment protocol used. Patients with Class III malocclusion subjected to early facemask therapy have an anterior crossbite relapse rate of around 25%, which is associated with delayed mandibular growth, facial hyperdivergence, pronounced intermaxillary discrepancies, vertical facial growth, mandibular prognathism, and increased axial inclination of the maxillary incisors before treatment. The relapse rate among surgically treated adult patients seems to be as high as that observed among orthopedically treated children and is associated with inappropriate positioning of the condyles during surgery, the activity of soft tissues and muscles after surgery, ongoing mandibular growth, the extent of mandibular setback, , clockwise rotation of the mandible during surgery, excessive posterior displacement of the condyle at the articular eminence, and intermaxillary discrepancies >7 mm.

Orthodontic compensation is a routine approach for treating adolescents and adults with Class III malocclusion or with a mild or moderate skeletal discrepancy. In these patients, the treatment is based on increasing preexisting sagittal dental compensation by elastic mechanics or reducing mandibular dental mass associated with fixed orthodontic appliances. Although significant dental and soft-tissue changes can be expected in younger patients with Class III malocclusion treated with camouflage orthodontic tooth movement, the scientific literature lacks data on the potential relapse of this treatment protocol, as well as on the possible factors associated with the clinical prediction of treatment stability. A case series analysis of 12 females with Class III malocclusion treated with isolated extraction of mandibular premolars showed a clinically acceptable level over 11.8 years, whereas postretention findings after a nonextraction treatment approach showed that although still in the growth stage, relapse would occur because of horizontal growth of the mandible.

Although several studies have analyzed the stability of Class III treatment in children treated orthopedically or in adults treated with orthognathic surgery, studies evaluating the stability of camouflage treatment among patients with Class III malocclusion are scarce. Therefore, the objective of this study was to evaluate the stability of Class III compensatory orthodontic treatment in the permanent dentition and to examine possible factors that may explain the risk of relapse.

Material and methods

This retrospective study was approved by the Research Ethics Committee of the Center for Biological and Health Sciences of the Federal University of Pará, Belém, PA, Brazil (no. 63814816.8.0000.5168). All patients received verbal and written information about the study characteristics and signed an informed written consent form.

Patients were evaluated at baseline (T1), at the end of orthodontic treatment (T2), and at least 3 years after orthodontic treatment (T3). The following inclusion criteria were used: at T1, with unilateral or bilateral canine Class III malocclusion or with mild or moderate skeletal deformities, without clinical skeletal asymmetry, overjet <1 mm, and subjected to compensatory treatment with a fixed orthodontic straight-wire appliance for alignment of permanent dentition with follow-up at T3. Patients with craniofacial syndromes or cleft lip and/or palate were previously excluded from the study.

The data were collected by a single researcher (M.N), who also performed all measurements at T1 and T2. The dental models at T3 were blindly assessed by another researcher (D.N), who evaluated canine sagittal relation and overjet. By using the databases of 2 orthodontic clinics, the records of 106 consecutively treated patients were analyzed. Six of these were excluded because of missing data at T1 and/or T2. Among the 100 patients who were initially selected, 51 could not be contacted because of having moved away or changed addresses and/or telephone numbers. Of the 49 contacted patients, 36 (73.6%) were examined. Of the 13 patients (26.4%) not included in the study, 10 refused to participate, 2 were traveling at the time of the study, and 1 had died (as informed by his family). Among the included patients, 2 were being re-treated by another orthodontist, who provided the initial re-treatment data. These data were included in the T3 records.

All of the included patients (n = 36) had their permanent dentition treated with preadjusted brackets, 0.022 × 0.028-in slot, with (n = 14) or without (n = 22) previous orthopedic treatment, using rapid maxillary expansion and anterior traction of the maxilla on the deciduous or mixed dentition. The patients had been treated satisfactorily, obtaining a normal sagittal relationship in the anterior region at T2. All patients’ treatments were concluded with a canine Class I relationship and having a positive overjet (≥1 mm).

Information about patients’ sex, age at T1 and T2, treatment time (T2 − T1), posttreatment time (T3 − T2), whether the patient had undergone previous orthopedic treatment, tooth extractions for orthodontic reasons, and length of use of intermaxillary elastic bands during treatment was obtained from the patients’ clinical records ( Table I ).

Table I
Clinical, cephalometric, and dental cast variables associated with the dependent variable: clinical relapse (T3)
Independent variables Time
Sex T1
Age T1 and T2
Length of treatment T2 − T1
Posttreatment time T3 − T2
Number of treatment phases T2
Number of tooth extractions T2
Elastic band use in months T2 − T1
Maxillary retention T3
Mandibular retention T3
SNA T1 and T2
SNB T1 and T2
ANB T1 and T2
Wits appraisal T1 and T2
SNGoGn T1 and T2
IMPA T1 and T2
1.NA T1 and T2
PAR index T1, T2, and T2 − T1
Maxillary intercanine distance T1, T2, and T2 − T1
Maxillary intermolar distance T1, T2, and T2 − T1
Mandibular intercanine distance T1, T2, and T2 − T1
Mandibular intermolar distance T1, T2, and T2 − T1

The variables SNA, SNB, ANB, Wits appraisal, SNGoGn, IMPA, and 1.NA were obtained from lateral cephalometric radiographs of the head at T1 and orthodontic finishing at T2. The radiographs were traced and measured manually ( Table I ).

The dental models were assessed for peer assessment rating (PAR) index estimation, , overjet, intercanine distances (measured at the cusp tip of canines), and intermolar distances (measured from the mesiobuccal cusp tip at T1 and T2). These variables were measured using a digital caliper (model 530-102; Mitutoyo, São Paulo, Brazil).

Sagittal correction was the main objective of the evaluation of the orthodontic treatment of Class III malocclusion. The dependent variable was the clinical relapse of the sagittal relationship, determined from the analysis of dental cast at T3. Patients with relapse were defined when evaluated edge-to-edge or incisor crossbite (overjet <1 mm) and/or Class III canine relationship. This variable is not related to the loss of stability of the dental alignment because sagittal correction is the main objective of Class III treatment, and any change of tooth alignment would occur in any type of malocclusion similarly. The presence and type of retention were assessed at T2 and T3.

Because the cephalometric data collected at T3 would not be able to predict factors associated with the stability of the compensatory treatment of Class III malocclusion, we explored, for ethical reasons, only predictors for those variables obtained at T1 and T2.

Statistical analysis

For the analysis of error, the data obtained from lateral radiographs and from the models were reassessed in all 36 patients. The kappa coefficient was used to analyze the reliability of the diagnosis of clinical relapse, and the intraclass correlation coefficient was estimated for other dental plaster models and cephalometric variables. The statistical analysis of method error was performed using BioEstat software (version 5.3; Mamirauá Institute, Manaus, Brazil), with significance set at P <0.05. Random error was calculated using the Dahlberg formula.

Multivariate Poisson regression was used to determine the factors that influenced the clinical stability of Class III malocclusion treatment. Initially, the association of each independent variable with clinical relapse (dependent variable) was assessed using the univariate model. Subsequently, only those variables significantly associated with clinical relapse ( P <0.05) were included in the multivariate model. The analysis was performed with Stata software (version 12.0; StataCorp, College Station, Tex), and the significance level was set at 5%.

Results

The replicability of clinical relapse assessed by the kappa coefficient was 0.94 (95% confidence interval [CI], 0.81-1.0). The diagnosis was modified in only 1 patient among all (n = 36) that were reevaluated. The second assessment was considered for statistical analysis.

In the reassessment of cephalometric variables, intraclass correlation coefficients ranged from 0.85 mm for Wits appraisal to 0.97° for 1.NA ( P <0.001), with the random error between 1.22 mm (Wits appraisal) and 0.43° (ANB). The analysis of the variables obtained from the dental cast models showed that the correlation coefficient ranged from 0.97 for the PAR index to 0.99 mm for dental arch widths ( P <0.001), with the random error between 0.15 and 0.20 ( Table II ).

Table II
Analysis of method error by the intraclass correlation coefficient and random error by Dahlberg formula
Variable Method error Dahlberg
ICC P value
SNA 0.96 <0.001 0.75
SNB 0.96 <0.001 0.86
ANB 0.86 <0.001 0.43
Wits appraisal 0.85 <0.001 1.22
SNGoGn 0.97 <0.001 1.03
IMPA 0.94 <0.001 1.14
1.NA 0.97 <0.001 1.03
PAR index 0.97 <0.001 0.15
Maxillary intercanine distance 0.99 <0.001 0.15
Maxillary intermolar distance 0.99 <0.001 0.20

ICC , intraclass correlation coefficient.

The sample comprised 15 male patients (41.6%) and 21 female patients (58.4%). The mean age at T1 was 20 years (range, 9.5-40 years). A total of 22 patients (61.1%) were subjected to 1 phase of orthodontic treatment and 14 (38.9%) to 2 phases of treatment, which included the first phase with anterior traction on the maxilla in deciduous or mixed dentition. The mean corrective treatment time was 31.2 months (standard deviation [SD] = 15.36), and the mean length of posttreatment (T3 − T2) was 10.22 years (SD, 4.77). Class III elastic bands were used, on average, for 5.36 months (SD, 6.93) ( Table III ). Seven patients (19.45%) required tooth extractions—4 of which involved 2 mandibular premolars, and 3 of which involved 4 premolars, 1 per hemiarch. Extractions were performed to obtain space for anterior retraction. At T3, fixed retainers were used by 21 patients (58.34%) in the mandibular arch and 12 (33.34%) in the maxillary dental arch. All patients had clinically good periodontal health.

Table III
Descriptive statistics of clinical data on patients with relapse, patients without relapse, and total number of patients
Clinical data With relapse, n = 11 Without relapse, n = 25 Total, n = 36
Sex
Male 6 (54.55) 9 (36) 15 (41.6)
Female 5 (45.45) 16 (64) 21 (58.4)
Age, y
T1 23.1 (10-40) 18.6 (9.5-39) 20 (9.5-40)
T2 25.3 (12.9-42.4) 21.4 (12.4-40.7) 22.6 (12.4-42.4)
Treatment time-phase 2, mo 26.4 (12-42) 33.6 (13.2-47.2) 31.2 (12-47.2)
Posttreatment time, y 11.3 (3-23) 9.7 (3.2-18) 10.2 (3-23)
Two phases treatment, n 4.0 (36.4%) 10 (40) 14 (38.9)
Tooth extraction treatment, n 0 (0) 7 (28) 7 (19.45)
Elastic band use, mo 4.3 (2-9) 5.8 (0-40) 5.4 (0-40)
Maxillary retention at T3, n 4 (36.4%) 8 (32%) 12 (33.3%)
Mandibular retention∗ at T3, n 4 (36.4%) 17 (68%) 21 (58.3%)

Note. Data presented as mean (minimum-maximum) or mean (percentage).

During the treatment period, ANB changed from −0.21° (SD, 2.99) at T1 to −0.04° (SD, 2.5) at T2, and Wits appraisal decreased from −4.44 mm (SD, 3.2) to −3.8 mm (SD, 2.4) at T2. The mean SNGoGn value was 33.5° (SD, 6.1) at T1, decreasing to 32.3° (SD, 5.8). Regarding incisor inclination, the mandibular incisor (IMPA) revealed a slight lingual inclination from T1 (mean, 85.4; SD, 6.7) to T2 (mean, 84.8; SD, 7.1), and the maxillary incisor (1.NA) increased its inclination by an average of 2.7°, from 28.5° (SD, 7.1) to 31.2° (SD, 6.9). Large variability was observed for all these variables ( Table IV ).

Table IV
Comparative descriptive statistics of cephalometric data in patients with relapse, patients without relapse, and total number of patients
Cephalometric data With relapse, n = 11 Without relapse, n = 25 Total, n = 36
T1 T2 T1 T2 T1 T2
SNA (°) 82.5 (3.9) 83.0 (3.4) 81.9 (3.5) 83.1 (3.6) 82.0 (3.5) 83.0 (3.5)
SNB (°) 84.4 (4.6) 84.2 (4.0) 81.3 (3.9) 82.7 (4.1) 82.3 (4.3) 83.1 (4.1)
ANB (°) −1.9 (2.5) −1.2 (2.6) 0.5 (2.9) 0.4 (2.3) −0.2 (3.0) 0.0 (2.5)
Wits appraisal (mm) −4.7 (3.0) −4.1 (2.1) −4.3 (3.4) −3.7 (2.5) −4.4 (3.2) −3.8 (2.4)
SNGoGn (°) 31.6 (6.8) 31.2 (6.7) 34.4 (5.7) 32.7 (5.4) 33.5 (6.1) 32.3 (5.8)
IMPA (°) 84.5 (4.9) 84.5 (4.0) 85.8 (7.4) 84.9 (8.2) 85.4 (6.7) 84.8 (7.1)
1.NA (°) 32.4 (6.0) 33.6 (7.1) 26.8 (6.9) 30.1 (6.7) 28.5 (7.1) 31.2 (6.9)
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Jan 9, 2021 | Posted by in Orthodontics | Comments Off on Factors associated with the stability of compensatory orthodontic treatment of Class III malocclusion in the permanent dentition
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