The in vivo and in vitro studies for the effect of mechanical loads on the temporomandibular joint disc

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Information about the viscoelastic behavior of the temporomandibular joint (TMJ) disc is required for its function to be understood and, for instance, for its tissue engineering. The aim of this research was, thus, to examine the dynamic viscoelastic properties of the TMJ discs and the lubricating ability in the TMJ. Using the porcine TMJ discs, the dynamic viscoelastic properties in tension, compression and shear were examined. The dynamic moduli increased as the loading frequency increased. Of the components constructing TMJ disc, the proteoglycans play an important role in determining the viscoelastic properties of the disc and, therefore, give the disc a greater capacity for distributing and reducing stresses. With respect to the TMJ lubrication, we conducted the first investigation for clarifying the lubricating ability of the intact TMJ. The mean frictional coefficient of porcine intact TMJ was 0.0145 after a constant load of 50 N during 5 s. The frictional coefficient increased with the length of the preceding load duration and 0.022 after 1 hr. Furthermore, the reduced lubricating ability by OA-like structure could be restored by the addition of hyaluronic acid with high molecular weight to a certain extent. Considering these findings, we started to do the tissue engineering, of the TMJ disc. Considering the composition of extracellular matrix and the cell types, Platelet derived growth factor (PDGF) may be effective for TMJ disc cell proliferation and metabolism. Thus, we investigate the effect of additive PDGF on the TMJ disc cell proliferation and synthesis of extracellular matrix. As the result, high doses of PDGF had the major effects on cultured disc cell proliferation, collagen and hyaluronic acid syntheses. This implies that the administration of PDGF may have future therapeutic potential in the treatment of disc degeneration, especially in tissue engineering of TMJ disc