Introduction
The aims of this study were to investigate whether there is a different transverse morphologic pattern of dental arches among patients with different manifestations of Class II Division 2 incisor retroclination and to evaluate to what extent the pattern of smaller-than-average teeth in Class II Division 2 malocclusion is common to all groups studied. This information might clarify whether different Class II Division 2 phenotypes represent a single etiology or multiple etiologies.
Methods
The sample comprised 108 subjects with Class II Division 2 malocclusions, divided into 2 groups according to the type of incisor retroclination: group I included 43 Class II Division 2 subjects with retroclination exclusively of the maxillary central incisors, and group II included 65 Class II Division 2 subjects with retroclination of the 4 maxillary incisors. Maxillary and mandibular intercanine and intermolar widths as well as mesiodistal crown dimensions of the 4 maxillary and mandibular incisors were determined from the patients’ initial study models. Mean values of all variables were compared between the 2 groups by sex with analysis of variance.
Results
From the comparison between these 2 groups, no statistically significant differences were found for all transverse measurements ( P >0.05). For all mesiodistal measurements analyzed, statistically significant differences between the groups were only found for the mean value of both maxillary lateral incisors’ mesiodistal dimensions in both sexes ( P <0.05).
Conclusions
It is not possible to attribute a characteristic pattern of dental arch-width and incisor mesiodistal dimensions to the different manifestations of incisor retroclination in Class II Division 2 malocclusion.
The morphologic characterization has proved to be an important aid in determining the way certain genetic factors are expressed and also the extent to which malocclusion phenotype can be influenced by environmental factors. The similarity of morphologic features is often used as the main criterion for classification and grouping of malocclusion; consequently, it is decisive for diagnosing and addressing orthodontic treatment.
Class II Division 2 malocclusion has been described as having a phenotype resulting from multiple morphologic features that are not always present or that express themselves in variable degrees. Maxillary incisor retroclination is clearly the most peculiar feature and the main distinctive sign of this singular malocclusion, which, however, does not always manifest in the same way, with different forms of maxillary incisor retroclination being described in the literature. The diverse morphologic characteristics attributed to Class II Division 2 malocclusion have been interpreted as different manifestations of the same clinical entity, with no related studies to support this view. When we consider the diversity of characteristics associated with Class II Division 2, some are not always present or, when they are, occur in different levels. Particularly for the different forms of incisor retroclination, it is fair to speculate whether we have different clinical entities or whether we have different degrees, or even different manifestations of the same clinical entity.
A reduced dental pattern in the mesiodistal direction has been consistently attributed to Class II Division 2 malocclusion, as first shown by Beresford, who, when determining the maxillary central incisor mesiodistal dimension in the different Angle classes, only found statistically significant differences in Class II Division 2, when he observed narrower incisors. In addition to the maxillary central incisors, Milicic et al also analyzed the mesiodistal dimension of the maxillary lateral incisors and the 4 mandibular incisors and, by comparing a Class II Division 2 malocclusion group and a Class II Division 1 malocclusion group with a control group in normocclusion, concluded that subjects with Angle Division 2 had smaller incisors in the mesiodistal direction. Also, Peck et al observed a pattern of smaller-than-average anterior teeth associated with Class II Division 2 malocclusion, when comparing 23 severe manifestations of this malocclusion with a reference group. A reduced dental pattern has also been observed in the labiopalatal direction, associated with Class II Division 2 malocclusion.
Whereas there is significant scientific evidence regarding a pattern of smaller-than-average teeth associated with Class II Division 2 malocclusion, little consensus can be found in the literature concerning a transverse morphologic pattern of arch width, characteristic of this malocclusion. These studies on tooth morphology, however, failed to mention the constitution of the samples regarding the different manifestations of incisor retroclination and did not investigate the different Class II Division 2 phenotypes separately.
Some authors explain the different manifestations of maxillary incisor retroclination in Class II Division 2 malocclusion as the consequence of maxillary arch space conditions: ie, the different manifestations result from space availability in the anterior region during incisor eruption. This view might presuppose distinctive transverse dental arch features as well as different anterior dental dimension patterns associated with the various incisor retroclination manifestations.
The aim of this study was to investigate whether there is a distinctive transverse morphologic pattern of the arches among the different incisor retroclination manifestations. We also evaluated whether the pattern of smaller-than-average teeth in Class II Division 2 malocclusion is common to all groups studied. This information might aid in understanding the different clinical presentations of Class II Division 2 patients as a single clinical entity or as etiologically diverse entities.
This research could open the way for future studies that can contribute a better understanding of the etiopathogenic mechanisms involved in the different Class II Division 2 phenotypes in terms of incisor retroclination. A deep knowledge of malocclusion etiology will be paramount for the prevention and treatment of orthodontic disorders. Without a clear understanding of the etiologic factors responsible for this malocclusion, we run the risk of using empirical or exclusively symptomatic therapies.
Material and methods
This retrospective study was approved by the ethics commission of the Faculty of Dental Medicine of the University of Porto in Portugal. The sample was collected from the private practice of the first 2 authors. From the consecutive analysis of the initial orthodontic records of 4364 patients seeking treatment between 2002 and 2010, 215 patients were diagnosed with Class II Division 2 malocclusions. They were all nonsyndromic white patients, distributed into 2 groups on the basis of the type of maxillary incisor retroclination, after we applied the following inclusion criteria: (1) molar distocclusion, at least unilateral in centric occlusion; (2) all 4 maxillary incisors present; (3) no history of orthodontic treatment, of maxillofacial or plastic surgery, and of trauma to the maxillary anterior teeth; (4) no prosthetic crowns or extensive restorations in the 6 maxillary anterior teeth; (5) the angle between the maxillary incisor long axis and the palatal plane less than or equal to 100°; (6) overbite equal to or greater than 50%; and (7) previous eruption of the maxillary and mandibular second permanent molars. Patients with retroclination involving 3 incisors were excluded. The total sample thus included 108 subjects (66 female, 42 male) with a mean age of 22.6 years (SD, 9.1; range, 12-50 years) distributed into the 2 groups as follows.
Group I was composed of 43 subjects with Class II Division 2 malocclusion (27 female, 16 male) with retroclination exclusively of both maxillary central incisors, with a mean age of 22.3 years (SD, 9.3; range, 12-50 years).
Group II was composed of 65 subjects with Class II Division 2 malocclusion (39 female, 26 male) with retroclination of all 4 maxillary incisors, with a mean age of 22.9 years (SD, 9.1; range, 12-43 years).
For this morphologic study, the initial orthodontic study models were used. Of the 108 subjects studied, there were 75 plaster models available in good condition, and the remaining 33 had digital models obtained from the initial plaster models by using the Bibliocast system (Bibliocast Ibérica, Porto, Portugal) ( Table I ).
| Group | Digital models | Plaster models | Total | Digital proportion (%) | Plaster proportion (%) |
|---|---|---|---|---|---|
| I | 13 | 30 | 43 | 30.2 | 69.8 |
| II | 20 | 45 | 65 | 30.7 | 69.3 |
Four variables representing the dental arch widths were evaluated, and the mesiodistal dimensions of the 4 mandibular and maxillary anterior teeth were determined. The criteria defined for each variable were the following.
- 1.
Maxillary intercanine width: linear measurement between the tip of the maxillary right canine cusp and the tip of the maxillary left canine cusp or the center of the wear facet, when attrition of the cusp tip was evident.
- 2.
Mandibular intercanine width: linear measurement between the tip of the mandibular right canine cusp and the tip of the mandibular left canine cusp or the center of the wear facet, when attrition of the cusp tip was evident.
- 3.
Maxillary intermolar width: linear measurement between the central fossae of the maxillary right and left first permanent molars.
- 4.
Mandibular intermolar width: linear measurement between the tip of the mandibular right first permanent molar centrobuccal cusp and the tip of the mandibular left first permanent molar centrobuccal cusp. When the cusp tip had attrition, the center of the wear facet was used.
- 5.
Maximum mesiodistal crown diameter of the maxillary right lateral incisor.
- 6.
Maximum mesiodistal crown diameter of the maxillary right central incisor.
- 7.
Maximum mesiodistal crown diameter of the maxillary left central incisor.
- 8.
Maximum mesiodistal crown diameter of the maxillary left lateral incisor.
- 9.
Maximum mesiodistal crown diameter of the mandibular right lateral incisor.
- 10.
Maximum mesiodistal crown diameter of the mandibular right central incisor.
- 11.
Maximum mesiodistal crown diameter of the mandibular left central incisor.
- 12.
Maximum mesiodistal crown diameter of the mandibular left lateral incisor.
All measurements were rounded to the nearest 0.1 mm and taken by using a digital odontometric caliper (Mestra, Bilbao, Spain) on the plaster models and with the Cecile 3 tool (Bibliocast SARL, Paris, France) on the digital models. All variables were determined by the same examiner (P.M.P.).
The focus of this study was to compare groups with regard to dental arch-width and dental mesiodistal dimensions. There is scientific evidence of sexual dimorphism in tooth sizes as well as in maxillary arch widths (on average, males have wider teeth and wider arches than females). Because we knew that sexual dimorphism exists for the variables considered, the comparisons between groups formed in a sample with significantly more female subjects than males had to consider sex.
Estimates of measurement error were determined for 4 variables by using the double determination method. For the variables maxillary intercanine width, mandibular intermolar width, and the maximum mesiodistal crown diameters of the maxillary central and lateral incisors, second measurements were made by the same examiner on 20 subjects randomly selected, 30 days after the first measurements. After checking the assumption of normality (Kolmogorov-Smirnov test with values of P >0.05), a paired-sample t test was performed, but it showed no statistically significant differences ( P >0.05) in the mean values obtained through double determinations of each variable studied. This low method error shows high consistency and reproducibility of the measurement technique and the references used ( Table II ).
| Dimension measured twice | Mean difference | SD | P value ∗ |
|---|---|---|---|
| Maxillary intercanine width (mm) | 0.03000 | 0.28303 | 0.641 |
| Mandibular intermolar width (mm) | −0.31000 | 1.36532 | 0.323 |
| MD maxillary right lateral incisor (mm) | 0.02000 | 0.16092 | 0.585 |
| MD maxillary left lateral incisor (mm) | −0.02500 | 0.12085 | 0.367 |
Statistical analysis
The statistical analysis was performed by using statistical software (version 20.0; IBM SPSS, Armonk, NY). Since the measurements were evaluated in a quantitative scale, the most suitable procedures for comparison involved comparison of mean values in terms of groups. Because there were 2 fixed factors (sex and group), each with 2 levels, the most suitable procedure was the analysis of variance (ANOVA) test, which allowed comparison of mean values between the 2 levels of factors. The decision rule consists of detecting statistically significant evidence for probability values (value of the proof test) less than 0.05.
Results
Missing or impacted teeth essential to determine the transverse variables studied did not allow the evaluation of all 4 arch-width measurements in the 108 subjects. Table III shows the descriptive statistics for the 4 transverse measurements analyzed. We confirmed that the transverse measurements resulted from a normal distribution ( P >0.05), and, considering the assumption of independence between groups and the verified homogeneity of variance, ANOVA showed no statistically significant differences for all transverse measurements by comparing the 2 groups. Arch-width mean values proved to be significantly higher in males than in females ( Table III ).
| Group | Female | Male | P value ∗ | |||||
|---|---|---|---|---|---|---|---|---|
| n | Mean | SD | n | Mean | SD | |||
| Maxillary intercanine (mm) | I | 27 | 31.581 | 2.0692 | 16 | 33.331 | 2.4939 | 0.200 |
| P value † | II | 29 | 32.466 | 2.1978 0.007 ‡ |
15 | 33.460 | 2.2481 | |
| Mandibular intercanine (mm) | I | 27 | 24.893 | 1.8437 | 16 | 25.756 | 1.9664 | 0.107 |
| P value † | II | 37 | 24.430 | 1.7261 0.042 ‡ |
26 | 25.042 | 1.5308 | |
| Maxillary intermolar (mm) | I | 24 | 43.625 | 2.0283 | 16 | 45.956 | 3.0142 | 0.787 |
| P value † | II | 35 | 43.700 | 2.2326 <0.0001 ‡ |
24 | 45.504 | 2.8483 | |
| Mandibular intermolar (mm) | I | 24 | 45.608 | 2.1413 | 16 | 47.425 | 3.2980 | 0.999 |
| P value † | II | 27 | 45.770 | 2.2659 0.005 ‡ |
20 | 47.195 | 2.7558 | |
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