Influence of teeth, alveoli, and periodontal ligaments on torsional rigidity in human mandibles

We investigated the influence of teeth, periodontal ligaments, and alveoli on the structural integrity of human mandibles loaded in torsion. Surface bone strain was recorded from the mandibular corpus below the first molar on each of four specimens. These specimens were loaded by an external force that caused primarily torsion about the long axis of the corpus, and bone strain was recorded under the following conditions: 1) all supporting structures intact, 2) all supporting structures intact and the M₁ loaded by a simulated bite force, 3) M₁ removed and 4) alveolar bone of the M₁ removed. For comparative purposes, experiments were also designed to investigate the effects of intermittent holes on the torsional rigidity of a baboon femur. This permitted comparison of the mechanical behavior of the mandibles with that of a more homogeneous bony member. These experiments suggest that the presence of teeth within alveoli has a measurable role in the maintenance of torsional rigidity. The condition of the periodontal ligament also appears to influence these stress‐bearing capabilities. Moreover, the alveolar bone supporting the teeth also provides structural support for countering torsional loads. For the specific case of corpus twisting, the mandible does not behave as a member with open or closed sections as predicted by theoretical models. The observed magnitudes of bone strain, however, conform more closely to the Predictions generated by a closed‐section model. © 1992 Wiley‐Liss, Inc.