The purpose of this study was to develop a three-dimensional finite element model
of the mandible including the temporomandibular joint (TMJ) and further to investigate
stress distributions in the TMJ during clenching. The model consisted of 2088 nodes
and 1105 elements, comprising cortical and cancellous bones, articular disc, articular
cartilage layer and periodontal ligament. For loading condition, a resultant force
of 500 N derived from the cross-sectional areas of the muscles was applied to the
model. Compressive stresses were induced in the anterior, middle and lateral areas
of the TMJ during clenching, whereas the tensile stresses were induced in the posterior
and medial areas. The mean principal stresses on the surface of condyle were -1.642,
-0.543, 0.664, -1.017, 0.521 MPa in the anterior, middle, posterior, lateral and medial
areas, respectively. The mean stresses on the surface of glenoid fossa were approximately
1/5 to 4/5 those on the surface of condyle, although the patterns of stress distributions
were almost similar. In both the articular disc and cartilage layer, the stress distributions
were very approximate in qualitative and quantitative aspects. Thus, it is shown that
stresses during clenching vary substantially in different structures and areas of
the TMJ and that the stresses are reduced by the articular disc and cartilage layer
in comparison with actual biting forces exerted by the masticatory muscles, if anatomic
relation between various TMJ components is well maintained.