Characterization and tissue engineering of the temporomandibular joint disc
Detamore, Michael Scott
Athanasiou, Kyriacos A.
Doctor of Philosophy
The temporomandibular joint (TMJ), commonly known as the jaw joint, can cause a great deal of suffering for those afflicted with TMJ disorders. Everyday activities like chewing, yawning, and sometimes even talking and laughing, can be agonizing, and personal life and work life often suffer. Approximately 3--4% of the population seek treatment for TMJ disorders, and almost 70% of these patients suffer from displacement of the TMJ disc. The TMJ disc is a poorly understood and scarcely studied structure in comparison to other musculoskeletal tissues. Prior to this thesis, a gap existed between the tissue engineering community and the TMJ characterization community. The objective of this work was therefore to perform the characterization studies vital to tissue engineering efforts, and to provide the initial steps toward an engineered TMJ disc construct. An argument was formed that provides a rationale for tissue engineering the TMJ disc, citing deficiencies in the current treatments for advanced stages of internal derangement. The TMJ disc has been shown to be mechanically non-homogeneous and highly anisotropic, which has been attributed to non-homogeneous extracellular matrix and cell sub-population distribution and anisotropic collagen orientation. The greatest variation by region in the TMJ disc is between the intermediate zone and the bands (anterior and posterior). The intermediate zone contains a higher proportion of fibrochondrocytes and higher quantities of type II collagen, chondroitin sulfate, keratan sulfate and dermatan sulfate proteoglycan compared to the anterior and posterior bands. Moreover, the intermediate zone is over an order of magnitude softer and weaker under mediolateral tension compared to these bands. Pioneering efforts in TMJ disc tissue engineering have been made, exploring growth factor effects and exploiting bioreactor technology. Insulin-like growth factor-I was selected from a group of four growth factors as the most promising for TMJ disc tissue engineering, most notably for its benefits associated with collagen synthesis. Moreover, a rotating bioreactor was shown to influence morphology and structure of engineered constructs, accelerating scaffold contraction and producing a much more heterogeneous matrix distribution compared to static culture.