Effect of Class II camouflage treatment on anterior arch length ratio and canine relationship

Introduction

To evaluate the influence of compensatory tipping of maxillary and mandibular incisors on the anterior arch length ratio and canine relationship in skeletal Class II malocclusion.

Methods

The study was based on posttreatment lateral head films and dental casts of 88 patients. The sample was divided into a Class II malocclusion group (32 patients; ANB ≥5° and mean [± standard deviation] age, 20.82 ± 7.67 years) and a Class I malocclusion group (56 patients; 1° ≤ ANB ≤ 2.5° and mean [± standard deviation] age, 19.20 ± 5.04 years). Measurements obtained for anterior arch length and width, Bolton discrepancy, canine relationship, growth pattern, and incisor position were compared between the groups. The canine relationship was correlated with dental and skeletal variables ( P <0.05).

Results

The mean ANB angles were 6.21° and 1.78° for the Class II and Class I malocclusion groups, respectively. The skeletal Class II group presented significantly larger mandibular anterior arch length, producing an unbalanced anterior arch length ratio. The canine relationship was more displaced toward Class II in this group. Anterior arch length ratio was the most influential variable in the canine relationship. The mandibular incisors had a higher compensation degree than the maxillary incisors. The groups were similar regarding overjet, overbite, and growth pattern.

Conclusions

Class II malocclusion camouflage treatment with excessive proclination of the mandibular incisors was associated with an increase in mandibular arch length, negatively influencing the anterior arch length ratio and the final canine relationship. Mandibular anterior arch length reduction by interproximal stripping may be necessary in moderate to severe skeletal Class II malocclusion orthodontic treatment.

Highlights

  • Patients with skeletal Class II malocclusion had camouflage treatment.

  • Anterior arch length ratio and canine relationship were affected.

  • Increase in mandibular anterior arch length deteriorated the anterior arch length ratio.

  • Anterior arch length ratio was the most influential variable in the canine relationship.

  • Stripping of mandibular incisors may be required for Class II camouflage treatments.

Class I canine relationship is one of the most sought orthodontic goal of malocclusion treatment, whereas molar relationship may vary according to treatment planning and extraction protocol. Class I canine relationship has a relevant esthetic and functional role because normal overjet, overbite, and anterior guidance are strongly associated with this occlusal relationship. , During the finishing phase of orthodontic treatment, Class I canine relationship is frequently associated with normal overjet and overbite, provided that the maxillary and mandibular anterior arch lengths are not compromised by incisors torque; dental anomalies of number, size, and shape; and unbalanced Bolton tooth-size ratio.

Skeletal Class II malocclusions can be treated with or without orthognathic surgery. It has been suggested that anteroposterior maxillomandibular discrepancies should have an ANB angle greater than 6° to indicate the need for orthodontic-surgical correction, otherwise profile esthetic improvement may become unpredictable. , When an orthodontic-surgical treatment protocol is indicated, mandibular premolar extraction may be required to decompensate labial tipping of the mandibular incisors and allow satisfactory mandibular advancement. , Patients with moderate to severe skeletal Class II malocclusions frequently present compensated mandibular incisors. When an orthodontic-surgical treatment of skeletal discrepancy is not accepted by the patient, orthodontic camouflage becomes the only way to achieve a good occlusion. However, this treatment option may become even more challenging if the mandibular premolar extraction is planned to align and upright the mandibular incisors, especially if the Class II anteroposterior discrepancy is more severe than a cusp-to-cusp relationship, and the patient has no remaining growth. By contrast, if the mandibular premolars are not extracted to benefit Class II anteroposterior malocclusion correction, excessive labial tipping of the mandibular incisors may become a hard obstacle to overcome to normalize the anteroposterior relationship, , just as it is for mandibular surgical advancement.

Several studies have evaluated the influence of maxillary incisor tipping on the maxillary arch length and molar relationship. Only a few studies have evaluated the impact of mandibular incisor tipping on the occlusal results of Class II camouflage treatment. , However, excessive labial tipping of the mandibular incisors is a common occurrence in patients with skeletal Class II malocclusions, and it cannot be easily corrected during Class II camouflage treatment, , especially because mandibular premolar extraction for incisor uprighting is frequently avoided owing to its negative impact on the occlusal results. , In addition, the orthodontic mechanics required to correct deepbite, which is frequently associated with Class II overjet, has a proclination effect on the incisors. Finally, all studies that correlated incisor tipping and occlusal results were based on laboratory models, lacking clinical support. Thus, the present clinical study evaluated the influence of skeletal Class II camouflage treatment on the final anterior arch length ratio and canine relationship. The null hypothesis was that there is no difference in the final anterior arch length ratio and canine relationship between skeletal Class II camouflage and skeletal Class I treatments.

Material and methods

This investigation was based on retrospective data obtained from orthodontic records of patients treated at the Faculty of Dentistry, Federal University of Rio Grande do Sul. It was approved by the corresponding institutional review board, under number 2.659.451. The sample was selected from a pool of 1050 treated patients from 1976 to 2017 in the Department of Orthodontics. Posttreatment lateral headfilms and dental casts from patients with skeletal Class I and skeletal Class II malocclusions were evaluated. Sample size calculation was performed assuming values of 5% and 20% for α (type I error) and for β (type II error), respectively. The minimum difference to be detected in dental arch length for patients with skeletal Class I and skeletal Class II malocclusions was 0.2 mm. Standard deviation was taken from a previous study, and sample calculation indicated that a minimum of 28 patients in each group were needed.

Sample selection was based on the following inclusion criteria: patients having a good quality of orthodontic records, patients with permanent dentition, straight profile and skeletal Class I (1° ≤ ANB ≤ 2.5°, Class I group), convex profile and skeletal Class II (ANB ≥5°, Class II group), and normal overjet and overbite ( Fig 1 ). These dentoskeletal characteristics were evaluated on posttreatment lateral head films. Exclusion criteria included dental anomalies of size, number, shape, or structure; extensive dental restorations involving proximal surfaces of the anterior teeth; permanent tooth loss; and incisor irregularity at the end of treatment. Orthodontic treatment protocols used to treat the patients with and without skeletal imbalance, as well as final molar relationships, were not a selection or allocation criterion in this study because skeletal and dental relationships are not always in agreement , ; for example, Class I occlusal relationships can occur in patients with skeletal Class II malocclusions and Class II occlusal relationships in patients with skeletal Class I malocclusions. Treatment protocols to correct the Class II malocclusions included maxillary premolar extractions, maxillary molar distalization, or Class II elastics, whereas the Class I malocclusions were treated without extraction or with 4 premolar extractions. Taking into account the selection criteria, 88 patients were selected from the total number of consecutive orthodontic records in our files. The skeletal Class II malocclusion group consisted of 32 patients (15 males, 17 females) with a mean age (± standard deviation) of 20.82 (± 7.67) years. The skeletal Class I malocclusion group consisted of 56 patients (16 males, 40 females) with a mean age (± standard deviation) of 19.20 (± 5.04) years. Patients with skeletal Class II and Class I malocclusions treated without and with interproximal stripping were allocated a posteriori into 2 subgroups to exclude any influence of this procedure on the results.

Fig 1
A, Class I skeletal pattern; B, Class II skeletal pattern.

Posttreatment dental casts were measured using a 0.01-mm precision digital caliper (Mitutoyo America, Aurora, Ill). The following dental cast measurements were performed in both arches by an experienced and trained orthodontist (J.F), who was blinded to the patient group: (1) the widest mesiodistal crown width of the incisors and the canines, (2) intercanine distance (distance between the cusp tips of the canines), and (3) distance between the cusp tips of the canines and the dental midline. Measurements 2 and 3 formed a triangle ( Fig 2 ). A trigonometric calculation based on Heron formula was used to determine the height of the triangle when the length of all 3 sides are known, allowing determination of the maxillary and mandibular anterior arch lengths. Afterward, the mandibular anterior arch length was divided by the maxillary arch length to determine the anterior arch length ratio. The ratio of the sum of the widths of the maxillary and mandibular anterior teeth was used to evaluate the anterior tooth-size disharmony (3-3, Bolton ratio). The canine relationship was determined by the arithmetic mean of the horizontal distance between the cusp tip of the maxillary canine and the embrasure between the mandibular canine and the first premolar measured on the right and left sides ( Fig 2 ).

Fig 2
Dental cast measurements: A, trigonometric calculation based on Heron formula and used to determine the anterior arch length; B, measurement of canine anteroposterior relationship. ML , midline; RC , right canine; LC , left canine; AAL , anterior arch length.

The lateral headfilms were obtained in centric occlusion. The posttreatment lateral head films from both groups were digitized by 1 investigator (L.M) and checked for landmark identification by a second examiner (K.C). Any disagreements between the examiners were resolved by a weighted reevaluation to the satisfaction of both examiners. The data were analyzed with Radiocef Studio 2 software (version 2.0, release 12.82; Radiomemory, Belo Horizonte, Brazil). A customized cephalometric analysis including dental and skeletal measurements from Steiner, Tweed, Wits, and McNamara analyses was used, totaling 11 variables (7 angular, 4 linear). The lateral headfilms were obtained using an x-ray machine (Orthophos CD; Siemens Sirona, Bensheim, Germany), which produced an image magnification of the order of 9.8%. This enlargement was corrected on the cephalometric software to match a 0% magnification factor. Posttreatment orthodontic records were obtained during the retention period, within 1 year after the fixed appliances were removed.

To evaluate the error of the method, 22 posttreatment dental casts and lateral headfilms were randomly selected and remeasured by the same examiners. Intraclass correlation coefficient (ICC) was used to assess intraexaminer reliability and reproducibility for all linear and angular measurements.

Statistical analysis

The ICC indicated that the measurements reliability and reproducibility degree ranged from satisfactory to excellent (ICC, 0.78-0.99). Descriptive statistics for dental cast and radiographic measurements were calculated for each group. Because several variables did not show normal distribution in both groups, the comparisons and the correlations were performed using parametric or nonparametric statistical tests according to the results of the Shapiro-Wilk normality tests. Categorical variables were compared with chi-square tests.

Intergroup comparability for final age, sex, and interproximal stripping was investigated with t and chi-square tests.

Dental and skeletal variables at posttreatment were compared between the groups with t and Mann-Whitney U tests. An investigation of the correlation between canine relationship with dental and skeletal variables was performed using Pearson and Spearman correlation tests.

All statistical tests were performed with Statistica software (version 7.0; StatSoft Inc, Tulsa, Okla). Results were considered statistically significant at P <0.05.

Results

The groups were similar regarding age, sex distribution, and percentage of patients with interproximal stripping ( Table I ). Patients with skeletal Class II malocclusions presented significantly greater mandibular anterior arch length and intermaxillary anterior arch length ratios ( Table I ). Class II canine relationship was significantly greater in the skeletal Class II malocclusion group at the end of treatment ( Table I ).

Table I
Comparison between the groups with and without skeletal Class II discrepancy
Variables Skeletal Class II
n = 32
Skeletal Class I
n = 56
P
Age, y, mean (SD) 20.82 (7.67) 19.20 (5.04) 0.184∗
Sex (%) M (46.87) M (28.57) 0.083
F (53.13) F (71.43)
Interproximal stripping (%) Yes (46.88) Yes (42.86) 0.715
No (53.12) No (57.14)
Dental cast measurements
MxAAL, mm 9.30 1.11 8.85 1.40 0.119
MdAAL, mm 6.11 1.07 5.16 1.25 <0.001∗
MdAAL/MxAAL 0.66 0.12 0.58 0.10 0.019∗
Mx3-3, mm 36.16 1.83 35.64 2.04 0.235
Md3-3, mm 27.63 1.57 27.57 1.62 0.869
TSD 3-3, Bolton ratio 0.77 0.02 0.78 0.02 0.109
Canine relationships, mm 1.74 0.91 1.03 0.56 <0.001 ‡,§
Cephalometric measurements
ANB, ° 6.21 1.12 1.78 0.52 <0.001∗
Wits appraisal, mm 3.39 1.08 −0.40 1.58 <0.001∗
Convexity (NAP), ° 11.25 4.15 1.16 3.01 <0.001 ‡,§
FH.MP, ° 28.07 5.26 26.66 5.53 0.245
SN.GoGn, ° 35.58 5.31 33.79 6.06 0.165
NSGn, ° 70.62 3.37 69.07 4.26 0.082
LAFH, mm 66.58 7.08 65.15 5.47 0.291
Mx1.PP, ° 107.75 6.98 111.40 6.57 0.016 ‡,§
Md1.MP, ° 100.24 7.24 92.76 7.68 <0.001 ‡,§
Overjet, mm 2.31 0.64 2.52 0.54 0.056∗
Overbite, mm 1.71 0.67 1.76 0.88 0.818

MxAAL , maxillary anterior arch length; MdAAL , mandibular anterior arch length; Mx , maxillary; Md , mandibular; TSD , tooth-size disharmony; NAP , skeletal profile convexity angle; LAFH , lower anterior facial height.
∗Mann-Whitney U test; †Chi-square test; ‡ t test; §Statistically significant at P <0.05.

The Class II maxillomandibular anteroposterior relationship was significantly greater in the Class II malocclusion group ( Table I ). The maxillary and mandibular incisor inclinations were significantly compensated in the skeletal Class II group ( Table I ). Although the skeletal Class II group showed a slight excess of vertical development, no statistically significant difference was found ( Table I ).

The skeletal Class II and Class I malocclusion subgroups composed of patients treated without any interproximal stripping were compared ( Table II ). The mandibular anterior arch length and the intermaxillary anterior arch length ratio were significantly greater in the skeletal Class II subgroup ( Table II ). The Bolton tooth-size ratio was significantly smaller in the skeletal Class II subgroup ( Table II ). The Class II canine relationship was significantly greater in the skeletal Class II malocclusion group at the end of treatment ( Table II ).

Table II
Comparison between nonstripped subgroups with and without skeletal Class II discrepancy
Variables Skeletal Class II
n = 17
Skeletal Class I
n = 32
P
Age, y 20.15 (5.99) 19.43 (4.80) 0.488∗
Sex (%) M (52.94) M (31.25) 0.137
F (47.06) F (68.75)
Dental cast measurements
MxAAL, mm 9.29 1.30 8.60 1.37 0.096
MdAAL, mm 6.47 1.24 5.08 1.19 <0.001∗
MdAAL/MxAAL 0.70 0.13 0.59 0.12 0.011∗
Mx3-3, mm 36.60 1.76 35.46 2.09 0.061
Md3-3, mm 27.74 1.54 27.45 1.56 0.540
TSD 3-3, Bolton ratio 0.77 0.02 0.79 0.02 0.033 ‡,§
Canine relationships, mm 2.09 1.1 1.08 0.55 <0.001 ‡,§
Cephalometric measurements
ANB, ° 6.07 1.00 1.72 0.52 <0.001∗
Wits appraisal, mm 3.12 1.15 −0.57 1.59 <0.001∗
Convexity (NAP), ° 10.88 4.58 0.53 2.94 <0.001 ‡,§
FH.MP, ° 27.55 6.10 26.28 5.45 0.463
SN.GoGn, ° 34.54 5.96 33.10 5.87 0.421
NSGn, ° 69.49 3.54 68.23 4.07 0.286
LAFH, mm 67.27 6.34 64.26 5.89 0.092∗
Mx1.PP, ° 107.51 5.96 111.01 7.18 0.092
Md1.MP, ° 99.27 8.06 91.39 7.91 0.001 ‡,§
Overjet, mm 2.25 0.63 2.50 0.54 0.037∗
Overbite, mm 1.72 0.55 1.68 0.88 0.366∗
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Jan 30, 2021 | Posted by in Orthodontics | Comments Off on Effect of Class II camouflage treatment on anterior arch length ratio and canine relationship
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