The growth changes of the mandibular symphysis were examined longitudinally in fourteen female patients with severe skeletal class III malocclusion.
The materials were lateral cephalograms of the patients when they were 10-16 years old. Detailed angular and linear measurements of the symphysis were taken. The resu ts were as follows:
1. Mandibular symphysis tipped lingually, in accordance with the increase of skeletal discrepancy, but the extent of lingual tipping varied from individual to individual.
2. In holizontal linear measurement, point B moved lingually with reduction of the symphyseal thickness at point B. The dislocation of pointB was larger than those of the points Is and Id. The changes of symphyseal thickness at pogonion was relatively small.
3. In vertical liner measurement, the symphysis elongated vertically, which depended mainly on the vertical increase in the height of MP-B.
4. The basal bone at point B showed the most conspicuous changes in both measurements.
The results suggested that mandibular symphysis shows an adaptive mechanism by inclining itself lingually to adjust for the increase of the skeletal disharmony and so the chin becomes more prominent.
