Biological responses induced by mechanical stresses-bone metabolism by bone scintigraphy at residual alveolar bone beneath the denture and TMJs

Stomatognathic functions, like the ingestion, mastication, swallowing and articulation, are achieved with the muscle contraction of the jaw and facial muscles as power sources. Forces exerted by the muscles load on the components of masticatory system, which may cause biomechanical-biological effects on the tissues. Significance of the mechanical factors is that they would affect tissue responses including metabolic turnover of the bone. They can lead to adaptive remodelling of these tissues or cause maladaptive, degenerative changes. However, biological changes including bone turnover by the mechanical stresses have not been fully elucidated. This review deals with in vivo biological reactions including the bone turnover with bone scintigraphy, induced by the mechanical stresses, which is least well understood in the biomechanical-biological interface. A few studies have revealed the bone changes of the temporomandibular joint (TMJ), following the mechanical loading with the loss of occlusal support, morphologically and histologically in animal experiments. In these studies, the resorption of cartilage and bone was observed and resulted in the deformation of TMJ. Bone changes beneath the denture base, which applied various loading, were reported in a series of the experiments. Bone resorption was observed histologically, and the level of bone resorption was dependent on the amount of load applied. The dynamic changes of bone metabolism at residual ridge beneath the denture base and TMJs were revealed with bone scintigraphy in the rats with the different mechanical conditions by means of the tooth extraction and the insertion of the experimental dentures. The results showed that mechanical force conducted with the denture increased the bone turnover beneath the denture base. Furthermore, the occlusal support with the denture influenced the remodelling of TMJs. The biological reactions induced by mechanical stresses are less well understood in the biomechanical-biological interface. These are the important topics in the future.