Abstract
The purpose of this study was to clarify molar dental compensation and its longitudinal changes following orthognathic surgery in facial asymmetry patients.
Eleven adult patients with facial asymmetry, who underwent surgical orthodontic treatment, formed the basis of this study. Serial sets of gnathostatic model, frontal and lateral cephalogram were used for analysis. Materials were taken at the stages of first examination, the end of active treatment, and during retention (more than two years after the end of active treatment). Buccolingual tooth inclinations of the upper and lower first molars at each stage were measured on the three-dimensional graphics of the dental model generated by a noncontact threedimensional measuring unit. First, craniofacial deformity of the subjects at the first examination was evaluated, using lateral and frontal cephalometric analysis. Second, a characteristic molar dental compensation, and its correlation to the skeletal deformity, were examined. Third, longitudinal changes of molar dental compensation following orthognathic surgery were analyzed.
The results were as follows:
1. Skeletal deformity of the subjects was characterized by remarkable protrusion and asymmetry of the mandible, coupled with a small amount of asymmetry of the midface.
2. Distinguishing transverse dental compensations were found in the upper and lower molars. The upper molar on the shifted mandibular side showed significantly greater buccal inclination than that of the nonshifted mandibular side (p<0.05), while the lower molar on the shifted mandibular side showed greater lingual inclination than that on the non-shifted mandibular side (p<0.05). There was a significantly high correlation between the tooth inclination of the upper molar on the non-shifted mandibular side and the amount of mandibular deviation (r=0.75, p<0.05).
3. At the end of active treatment, molar dental decompensation was achieved. There were no significant differences in the amount of tooth inclination change between the upper and lower molar on both the shifted and the non-shifted mandibular sides. In retention, however, the amount of tooth inclination change in the upper molar was small, while that in the lower molar was great. The lower molar on the shifted mandibular side showed a significantly greater amount of tooth inclination change than that of the upper molar on both the shifted and the non-shifted mandibular sides (p<0.05). A tendency of lingual tooth inclination following mandibular relapse was found in the lower molar on the shifted mandibular side.
