3.4. Finite element analysis
The three tooth models used in finite element analysis are shown in Fig. 13. Forces of 0.1 and 1.0 N were applied to the tip of the tooth in a direction perpendicular to the general elongation of the cusp, as will naturally occur during grazing. In the P. vulgata tooth model with heterogeneous material characteristics, the highest stresses appeared to occur in a narrow zone in the lower half of the tooth adjacent to the leading edge; lowest stresses were located in the core of the tooth with the core being surrounded by moderate stresses that extended even to positions that were very close to the tip of the tooth where the force was applied ( Fig. 14A). To appreciate the function of shape in distributing the stresses, the same force was also applied to the tip of a hypothetical radular tooth with the same material characteristics as the previous one, but with a straight leading surface and a trailing side which was only slightly curved (Fig. 14B). It appeared that maximum stresses were generated (1) in a narrow zone adjacent to the leading edge almost along the entire length of the tooth and (2) in an isolated patch in the trailing part close to the tip. The stresses recorded in the upper part of the tooth were higher in comparison with those recorded in the curved tooth.