TMJ FUNCTION AND MECHANICS--EXPERIMENTAL MODELS

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DESCRIPTION: The long-range goal of this work is to understand the biomechanical environment of the temporomandibular joint (TMJ) and to elucidate how alterations in that environment lead to remodeling or degeneration. The present project is prerequisite to further work, and aims to address the need of the research community for validated animal and biomechanical models of TMJ function. A double-pronged, coordinated attack is proposed. First, the miniature pig will be established as an animal model for functional studies. Second, this experimental system with be linked with the strengths of computer simulation. If the simulations are successful in reproducing joint loading and movement patterns in the pig, and predicting changes resulting from perturbations, then use of such simulations in humans would gain substantial credibility. Four specific aims will be addressed. Specific aim 1 is to characterize the loads and movements of the bony and soft tissue components of the pig TMJ during normal function. These studies will involve physiological measurement of internal pressures and surface strains from the bones, tensions in ligamentous tissues, and muscle activity. Age and gender effects will be examined. Compressive loads on the TMJ bony components during chewing movements will be quantified. The specific hypothesis to be tested is that the capsule and its attachments to bone are under tension during asymmetric jaw movements. Specific aim 2 is to determine the mechanical properties of the bony and soft tissue components of the pig TMJ. In vitro testing will be used to determine stiffness and strength of each tissue. Bone-soft tissue preparations will serve to assess viscoelastic properties of the soft tissues and their attachments. It is expected that the weakest points of the system are the attachments of ligamentous tissue into bone, specifically the attachments of the disc and capsule into the lateral pole of the condyle. It also is expected that the strength and stiffness of the ligaments and attachments of the disc is greater in postpubertal males than females, and will increase with age in both genders. Specific aim 3 is to construct dynamic and static computer simulation of pig TMJ movements and loads using information gained from the above studies. Validation tests will determine the acceptability of model performances for the entire range of experimental conditions. The models are expected to make valid predictions of disc motions, ligament stretch, and condylar strains. They will provide additional, unrecordable physical data, explain mechanical events, and indicate the potential value of the future computer simulations of the human TMJ. Specific aim 4 is to investigate cellular responses to the mechanical environment. Following interruption of the lateral attachments, longer-term studies will be conducted to allow joint tissues to adapt (remodel) or fail. Cell turnover, highly sulfated glycosaminoglycan (GAG) content and collagen composition will be compared to controls. Ligamentous tissues under increased tension are expected to show increased cell replication and type I collagen synthesis but decreased sulfated GAG content; decreased tension is expected to have the opposite results. Further, remodeling attachments are expected to have more type III collagen, particularly in postpubertal female animals. Remodeling is expected to be most effective in the younger age group.