RAFFERTY, Katherine L.; University of Washington: Mandibular Strain Patterns in the Isognatic versus Anisognathic Jaw

Strains in the mandible are caused by muscle contraction and occlusal force. The conditions of isognathy versus anisognathy are expected to produce different patterns of mandibular strain during mastication. Pigs and goats were compared to investigate the impact of these anatomical differences on strain patterns. Rosette strain gauges were applied to the lateral condylar neck and the lateral mandibular corpus in individuals of both species. In addition, rosette strain gauges were applied to the medial condylar neck and medial corpus in pigs so as to attain a picture of three-dimensional loading of the mandible. Goats had magnitudes of lateral condylar neck strain that were similar to those of pigs, but with a tendency toward larger strains on the balancing side condyle. In pigs, the medial side of the condylar neck experienced higher shear strains than the lateral side, but neither location differed in terms of working and balancing side strains. The pig condyle was compressed but did not show evidence of bending or twisting during the power stroke of mastication. In the corpus, pigs again had similar working and balancing side strains, whereas goats had larger and differently oriented strains on the working side compared to the balancing side. Comparisons between medial and lateral sides of the corpus in pigs revealed similar magnitudes but very different orientations, suggesting bending in the horizontal plane. The differences in working versus balancing side strains in goats are largely explained by their unilateral occlusion. Because only one tooth row can occlude at a time in goats, the bite point acts as a fulcrum, leading to larger strains on the working side corpus and the balancing side condyle. In contrast, the isognathic jaws of pigs and probable bilateral occlusion mean that, effectively, there are two working sides in terms of strain patterns. Supported by PHS awards DE 14457 and DE 08513