Condylar Position in Adult Patients with Mandibular Prognathism before Orthognathic Surgery

Abstract

The present study was designed to evaluate three-dimensional position of the mandibular condyle relative to the glenoid fossa in adult patients with mandibular prognathism before orthognathic surgery.
Eight adult patients (four females and four males), who were indicated for orthognathic surgery with sagittal splitting ramus osteotomy, were selected as subjects. Seven-layered tomograms of the TMJs were taken from the subjects before treatment.
For evaluating three-dimensional position of the condyle to the glenoid fossa, an analytic method for tomograms of the TMJ was used. In this method, the condyle and glenoid fossa represented a three-dimensional surface model and the shortest distance between the condyle and the glenoid fossa (CGFD) was measured. Before the measurement, the influences of horizontal rotation and vertical inclination of condylar long axis on the CGFDs were investigated in a simulated model of the TMJ.
The CGFDs of the subjects were obtained for five areas on the condyle, i. e. anterior, middle, posterior, lateral and medial regions.Based on these values, the ratio of anterior CGFD to posterior one (A/P ratio) and that of lateral CGFD to medial one (L/M ratio) were calculated in order to evaluate condylar position in the TMJ in the anteroposterior and mediolateral directions, respectively.
The following results were obtained.: 1. The CGFDs obtained by the present technique were very accurate irrespective of horizontal rotation and vertical inclination of the condylar long axis.
2. The CGFDs in the anterior, middle and posterior regions were 2.46±0.43mm, 2.16±0.40mm and 3.36±0.58mm, respectively. Significant difference between the anterior and posterior CGFDs was found at 1% level of confidence. Meanwhile, the CGFDs in the lateral and medial areas were 2.06±0.39mm and 2.26±0.54mm, respectively, and no significant difference can be observed between both values.
3. The A/P and L/M ratios were 0.75±0.16 and 0.94±0.15, respectively.
It is shown that the condyles occupy more anterior position in the TMJ space in this particular subjects before orthognathic surgery.