1734 TMJ Disc Stresses During Stress-Field Translation
J.C. NICKEL, L.E. ROTHE, L.R. IWASAKI, and M.W. BEATTY, UNMC College of Dentistry, Lincoln, NE, USA

It has been hypothesized that fatigue failure of the TMJ disc may be due to asymmetric distribution of compressive and shear stresses during movement of stress-fields. Objective: To test if asymmetric stress distribution occurs. Method: 10 porcine TMJ discs were used in a laboratory apparatus to measure the pressure distribution beneath the disc during movement of an acrylic indenter over the condylar surface of the disc. Each disc was statically loaded with 11 N for 60 s, after which the loaded indenter was translated mediolaterally over the condylar surface at 104 16 mm/s. Stress distribution under each disc was measured using a linear array of nine transducers which had 3 mm between pressure sensitive areas and an accuracy of 6% full scale. All experiments were performed twice, with 2 h intervening between experiments to allow for disc rehydration. Pressure data under the leading and following edges of the stress-fields were plotted, and shear stresses and normalized pressure gradients were calculated. Results: Peak compressive stresses in excess of 80 Pa were recorded. The first pass of the indenter over the disc caused leading edge compressive stress gradients to be nearly twice that of the following gradients (p<0.001). After the third pass of the indenter there were no significant differences in gradients (p > 0.05). For all cycles, average shear stresses were 2.2 times greater for the lateral half compared to the medial half of the disc (range: 0.6 - 6.3, p < .01). Conclusion: Asymmetry in pressure distribution and shear stresses occurred during movement of a stress-field, and may explain why the lateral half of the disc is more prone to failure. L.E.R. was supported by a UNMC College of Dentistry Student Research Scholarship.

Seq #166 - TMJ - Structure and Function I
9:00 AM-11:00 AM, Friday, 8 March 2002 San Diego Convention Center Room 16A (Mezzanine Level)

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