Mandibular First Molar Relation to Variable Lower Face Skeletal Components

Molar heights and incisor inclinations in adults with Class II and Class III skeletal open-bite malocclusions

INTRODUCTION

The aim of this research was to compare maxillary and mandibular molar heights and incisor inclinations in patients with skeletal open-bite Class II, patients with skeletal open-bite Class III, and an untreated control group.

METHODS

Pretreatment lateral cephalograms of 70 orthodontic patients (34 men, 36 women) between 16 and 40 years of age were examined. The sample was divided into 3 groups according to facial growth pattern and overbite. The control group (n = 25) included normodivergent Class I subjects with adequate overbite; the skeletal open-bite Class II group (n = 25) and the skeletal open-bite Class III group (n = 20) included hyperdivergent Class II or Class III subjects with negative overbite. Measurements considered were ANB angle, palatal and mandibular plane angles, maxillary incisor palatal plane angulation, and mandibular incisor mandibular plane angulation, as well as the distance from the palatal or the mandibular plane to the mesial cusp of the molars. Multivariate analysis of covariance and multivariate analysis of variance tests were used to determine the differences between the groups, followed by the Tukey post-hoc test. Additionally, the Mann-Whitney U test and Kruskall-Wallis test were performed.

RESULTS

Significant differences in molar height were found (P <0.001). A 4-mm difference in maxillary molar height between the skeletal open-bite and control groups was found. Mandibular molar height was greater in the skeletal open-bite Class II group (P <0.001). Maxillary incisor palatal plane angulation was greater in the skeletal open-bite Class III group by approximately 6°. Mandibular incisor to mandibular plane angulation was 10° more lingual in the skeletal open-bite Class III group (P <0.001).

CONCLUSIONS

The skeletal open-bite groups had greater molar heights than did the control group. The skeletal open-bite Class II group had more eruption of the mandibular molars. The maxillary incisors were more proclined and the mandibular incisors were more lingual in the skeletal open-bite Class III group.

Dento-facial relationships in individuals with normal occlusion

The aim of this study was to evaluate the relationships of selected facial measurements with mesio-distal crown widths and dental arch dimensions in individuals with normal occlusions. A cross-sectional study was conducted on 276 subjects with Angle's Class I normal occlusions. Three-dimensional images of the face and dental casts were captured and analyzed using stereophotogrammetric systems. Significant correlations were found between the sagittal facial variables and both upper and lower dental arch dimensions and to lesser degree with the horizontal and vertical variables. The values of correlation coefficients calculated between facial and dental crown measurements ranged from .01 to .50 for upper teeth and .01 to .49 for lower teeth. The values of correlation coefficients between facial and upper dental arch dimensions ranged from .01 to .55 and those between facial and lower dental arch dimensions ranged from .01 to .60. A principal components analysis showed that the sagittal dimensions, face height, nose, labial fissure, binocular widths were positively associated with dental arch dimensions and mesio-distal crown diameters in males. On the other hand, only the sagittal variables were associated with dental dimensions in females. The results of this study confirm that positive associations exist between facial and dental arch dimensions. These relationships should be taken into consideration when attempts are made to modify dental arch size as part of orthodontic treatment. Moreover, these relationships are also relevant to prosthodontists involved with selecting tooth sizes that display optimal functional balance with the craniofacial structures.