Regional Variation of Mechanical Properties in Human Mandibular Subchondral Bone Tissue

Introduction: The temporomandibular joint (TMJ) is a synovial joint that has a fibrocartilaginous articular disc located between the articular cartilage of the articular eminence of the temporal bone and the mandibular condyle. As masticatory muscles maintain the integrity of the TMJ, the components of the TMJ are constantly compressed during occlusion. During mastication, muscle contractions associated with TMJ movement can provide combinations of cyclic loading in various directions on the articular surface of the joint [1]. Degeneration of the TMJ can develop when these applied loads surpass the adaptive capacity of the TMJ. As such, it has been suggested that the mechanical properties of the mandibular condyles of the TMJ are the most important factors in determining TMJ osteoarthritis [2]. However, a lack of knowledge exists about characteristics of the bones contributing to the TMJ including subchondral cortical and trabecular bone. In this study, we hypothesized that the local mechanical properties of subchondral bone tissues may develop differently in response to the various types of loading at the TMJ. Nanoindentation has been widely used to assess elastic modulus and plastic hardness of bone at the tissue level. Recently, it has been indicated that this technology can be applied to measure viscoelastic properties of bone tissue at various anatomical locations of different species [3,4]. Thus, the objective of this study was to examine a regional variation of the elastic, plastic, and viscoelastic mechanical properties of human mandibular subchondral bone tissue using nanoindentation.