Over 10 million people in the United States suffer from temporomandibular joint problems at any given time (NIDCR). The most common cause of TMJ dysfunction is anterior and/or medial displacement of the articular disc. Disc displacement are strongly associated with pain. Proposed etiological events include trauma, joint laxity, over loading (e.g., clenchin, bruxism), and changes in joint lubrication.
Normal and Displaced Discs
The disc is an avascular, negatively charged tissue and experiences mechanical load at all times. These features lead disc cells facing a complex physicochemical environment, which includes mechanical signals, such as strain, stress and fluid pressure, chemical signals, such as concentrations of nutrients and growth factors, and electrical signals which refer to ionic environment. Both in vivo and in vitro studies have shown that such changes of the physicochemical environment have strong influence on the disc cell activity. Most are dose dependent. The cellular response can alter the matrix, and initiate structure remodeling. These process are important for disc homeostasis. But they can also lead to disorganization and dysfunction, such as disc degeneration. Therefore, one of the key points to clarify the mechanism of the disc degeneration is to understand the cell response to the change of physicochemical environment induced by mechanical loading or induced by the change of the tissue composition durin g the tissue remodeling. As a first step, it is necessary to quantitatively determine the physicochemical environment within the disc under different mechanical loading condition. Currently, in vivo direct measurement of all these signals seems impossible. However, it might be possible to predict these signal by appropriate, biomechanical models with realistic material properties. This is the motivation of this study.
The general objectives of the study were to first, to develop function constitutive relationship between hydraulic permeability and tissue composition for disc tissues. Second to develop constitutive relation of solute diffusivity. Last to develop a 3D triphasic finite element model for analyzing physical signals and nutrient transport in the disc. The specific aims are summarized below.
The long-term goals of the study include developing novel, less-invasive diagnostic tools, strategies for restoring tissue function, and deliniating the biomechanical etiology of disc derangement and degeneration. This research is important for understanding the mechanism of disc degeneration, and will be useful to develop strategies either for restoring tissue function or retarding further disc degeneration. Also, the quantified physical signals may be used as an indicator for the diagnosis of disc degeneration.
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