[Relationship between an inclination of mandibular plane and a morphology of symphysis].

In order to investigate the relationship between inclination of mandibular plane and morphology of symphysis, 225 adult subjects' cephalograms were measured. Measurements of the mandibular and facial morphology were: SN-MP, gonial angle, SNA, SNB, SNP, ramus angle, SN-GN, L1 to MP, U1 to L1 angle, overbite, and overjet. Measurements of the symphysis were: thickness of symphysis, length of symphysis, height of symphysis, grade of mental protrusion, inclination of symphysis, curve of symphysis, and sectional area of symphysis. From these measurements, the inclination of mandibular plane and morphology of symphysis were compared. Then the following results were found: 1. There is negative correlation between mandibular plane angle (SN-MP angle) and thickness of symphysis at point B. There is more negative correlation between mandibular plane angle and thickness of symphysis at the apex. 2. There are no correlations between mandibular plane angle and thickness of symphysis at the base. 3. There is positive correlation between mandibular plane angle and height of symphysis. There is positive correlation between mandibular plane angle and length of symphysis. 4. There is positive correlation between mandibular plane angle and grade of mental protrusion. 5. There is a slightly positive correlation between mandibular plane angle and inclination of symphysis. There is a slightly positive correlation between mandibular plane angle and curve of symphysis. 6. There are no correlations between mandibular plane angle and sectional area of symphysis (bone volume of symphysis).