RESULTS

Stress Distribution

Figure 4 documents that large stresses appear in the jaws when subject to a quasi-functional feeding load. Warm colours (red, orange and yellow) indicate regions of high stress; blue indicates little or no stress. All models are shown to the same stress scale. Areas of unusually high stress were always observed at the condyle where the model was constrained from movement, an issue familiar to engineers as Saint-Venant's Principle (Cook 1995).

These stresses are artificially inflated by the constraints, but occur at a reasonable distance from our region of interest (mid-point of the tooth row) to not significantly influence the outcome of our analysis. Similarly high stresses were commonly observed around the base of the coronoid process (Figure 4). This area is the attachment point of two muscle groups with differently orientated force vectors, which may be at least partly responsible for this observed pattern. Again, however, the region of interest appeared unaffected.

Within the ramus of the jaw, a typical bending pattern was observed in which the highest stress values were recorded from the dorsal and ventral edges of the jaws, whilst the central jaw experienced little stress (akin to the neutral axis of a beam). As the load is applied, material of the upper margin undergoes tension, and the lowermost margin is compressed. As the model is two dimensional, this represents purely parasaggital bending. On average the dorsal and ventral jaw margins exhibited 2.84 MPa greater Von Mises stress than the centre.

The distal portions of the mandible, including most of the diastema, tended to exhibit very little if any stress. Such low stresses were also observed in the mandibular angle, where two patterns of stress could be differentiated. In species where this area was discordantly bulbous in relation to the thickness of the mandible corpus, stress tended to concentrate in exterior borders immediately surrounding it. In mandibular angles with wider curves and less protuberance, stress was generally distributed further from this area (Figure 4).