The relationship between split-line orientation and in vivo bone strain in galago (G crassicaudatus) and macaque (Macaca mulatta and M. fascicularis) mandibles.

There is still disagreement concerning the functional significance of split-line patterns in bone. This study was undertaken to reexamine the mechanical forces hypothesis for split-line formation by comparing split-line patterns with in vivo mandibular bone strain patterns. The relationship between split-line orientation and in vivo stress and strain patterns on macaque and galago mandibles was examined during jaw opening and the power stroke of mastication and incision. An attempt was made to relate split-line orientation to the direction of tensile stress and strain along the primate mandible. In addition, we also investigated the alternative possibility that split-line orientation is related to the direction of low stresses (and strains) on the primate mandible. The results of this study showed that there was no consistent relationship between split-line orientation and the principal strains or stresses. Thus, split-lines did not run consistently in the direction of high or low stress and strain. Therefore, we have concluded that split-line orientation provides little useful information for inferring patterns of stress and strain in bone.