Components of adult Class III open-bite malocclusion.

In an effort to identify the frequency and differences in the dental and skeletal components of a large sample of adults with Class III malocclusion, with and without open bite, 176 subjects, one half of whom had an anterior open bite, were evaluated. These subjects were chosen by looking at the lateral cephalometric radiographs that were taken of 302 adults (128 men and 174 women) who exhibited at least an end-to-end Class III molar and canine relationship. The dental overbite was calculated for all subjects, and those with a negative overbite were placed in the open-bite (OB) group. Those with a positive overbite were placed in the non-open-bite (non-OB) group. The dental overbite was the only criterion used to define the open-bite and non-open-bite groups. The open-bite subjects were paired with a non-open-bite subject by sex, presence of presurgical orthodontic treatment, and anterior cranial base length. Eighty-eight subjects in each group (43 men and 45 women) were obtained. Various measures of craniofacial structure were calculated and analyzed by comparing the OB and non-OB groups with the paired t test. The areas that showed significant differences (p less than 0.05) between the OB and non-OB groups were as follows: the posterior maxilla exhibited vertical excess in the OB group; the maxillary occlusal plane was less steep in the OB group; the mandibular occlusal plane was more steep in the OB group; the gonial angle was higher in the OB group; the mandibular plane angle was higher in the OB group; the mandibular ramus was positioned in a more downward and backward location in the OB group; the total anterior facial height and lower facial height were increased in the OB group; the vertical height of the anterior maxilla was increased in the OB group; and the mandible was less protrusive in the OB group. No significant intergroup differences were noted in the cranial base, the anteroposterior position of the maxilla or the upper and lower incisors, the palatal plane, posterior facial height, mandibular ramus height, or mandibular body height. The results of this analysis indicate that the average Class III open-bite malocclusion is characterized by aberrations in both the maxilla and the mandible. Surgical therapy may, therefore, require intervention in both jaws to correct this deformity successfully.