Relationship between the physiological cross-section of the human jaw muscles and their cross-sectional area in computer tomograms.

Physiological cross-section (PCS) and cross-sectional area in computer tomograms made at right angles to the mean fibre direction were compared in the masseter, temporalis and pterygoid muscles of six human cadavers. PCS was determined as (1) total cross-section of teased fibre bundles (2) total fibre weight divided by mean fibre length. The two measures correlated strongly, but the first was always 25% lower than the second, irrespective of the muscle concerned. The cross-sections in the tomograms (SCS) were smaller than the PCS, except in the lateral pterygoid. In all muscles, a statistically significant correlation was found between SCS and PCS. The SCS can be used to predict PCS, with an error of 0.3-1.0 cm2. In our material, cross-sections were about 20% higher than reported in the literature. It is suggested, that this discrepancy is caused by the loss of natural teeth.