Masseter muscle cross-sectional images obtained by X-Ray CT Scanning were studied to assist in diagnosis of the stomatognathic function and evaluation of various prosthetic treatments.
The cross-sectional images of the masseter muscle of the subjects at rest and clenching at the level of subnasal point (subnasasion) and the basis of the cranium (basis craniiexterna) were obtained with computed tomography. For the analysis, the masseter muscle images were divided into two parts, an anterior part and a posterior part by a line drawn through the most forward point of the mandible (ramus). The area and length of each part were measured for all the subjects. Differences between the young and the older subjects were assessed with Student's t-test for unpaired data, and the Paired t-test for paired data at rest and clenching.
The results were as follows.
1) The bucco-lingual width of the masseter muscle and the cross-sectional area was smaller (53-54%) in the older than in the young subjects (p<0.01).
2) At clenching, there were very few morphological changes in the masseter muscle in older subjects.
3) Compared to the rest state, the cross-sectional area of the masseter muscle decreased at clenching (p<0.01), especially in the posterior part of the masseter muscle in young subjects.