Biomechanics of the mandible.

In this review the biomechanical behavior of the mandibular bone tissue, and of the mandibular bone as a whole, in response to external loading is discussed. A survey is given of the determinants of mandibular stiffness and strength, including the mechanical properties and distribution of bone tissue and the size and shape of the mandible. Mandibular deformations, stresses, and strains that occur during static biting and chewing are reviewed. During biting and the powerstroke of mastication, a combination of sagittal bending, corpus rotation, and transverse bending occurs. The result is a complex pattern of stresses and strains (compressive, tensile, shear, torsional) in the mandible. To be able to resist forces and bending and torsional moments, not only the material properties of the mandible but also its geometrical design is of importance. This is reflected by variables like polar and maximum and minimum moments of inertia and the relative amount and distribution of bone tissue. In the longitudinal direction, the mandible is stiffer than in transverse directions, and the vertical cross-sectional dimension of the mandible is larger than its transverse dimension. These features enhance the resistance of the mandible to the relatively large vertical shear forces and bending moments that come into play in the sagittal plane.