Abstract
The purpose of this study was to examine molar occlusal changes in the frontal dimension and their effects on the anterior overjet and overbite following surgical orthodontic treatment.
The subjects were 14 adult patients with mandibular protrusion treated with sagittal splitting ramus osteotomy. Serial sets of gnathostatic models and lateral cephalograms were used for analysis. Materials were taken at the stages of first examination, end of active treatment, and in retention (more than two years after the end of active treatment).
Buccolingual inclination of the upper and lower first molar, lateral overjet and overbite, and inter molar distance in both arches were measured on the three-dimensional graphics of the dental model produced by the noncontact three-dimensional measuring unit. The anterior overjet and overbite were also measured on the lateral cephalometric radiographs. Changes of molar inclination, inter molar distance and molar occlusion during the treatment period and the retention period were analyzed, and a correlation between changes of molar occlusion and those of anterior overjet and overbite in the retention period was examined.
The results were as follows:
1. There was a significant correlation between the changes of molar inclination during the treatment period and those in the retention period (upper lst molar; r=-0.71, p<0.01, lower lst molar; r=-0.58, p<0.05). These results suggested a relapse tendency of molar inclination in the retention period. However, no significant correlation was found in the changes of upper and lower inter molar distance between treatment period and retention period, and lateral overjet and overbite on both sides remained stable in most of the cases in the retention period. It was suggested that the molar occlusion in the retention period was characterized by the relapse tendency of the molar inclination without the changes of the inter molar distance.
2. In the retention period, the changes of the anterior overbite had significant correlations with the lateral overjet (r=0.65, p<0.05) and the lateral overbite (r=0.64, p<0.05).
It was concluded that the change of the molar occlusion played an important role for long-term stability of the occlusion after surgical orthodontic treatment.
