Tractional forces on the temporomandibular joint (TMJ) disc predispose tissue fatigue. This study tested the hypotheses that tractional forces: (1) increased with stress-field velocity (V) and aspect ratio (AR, contact area diameter/cartilage thickness), and compressive strain (epsilon); and (2) varied depending on cartilage thickness. Porcine TMJ discs (n = 187) received a 10-N vertical static load via an acrylic indenter for 1, 5, 10, 30, or 60 sec, followed by movement. Physical data were recorded and analyzed by quadratic regression relations and a likelihood ratio test. Results showed non-linear increases in tractional forces that were positively correlated with increased V, AR, and epsilon when the stress-field moved onto relatively thicker (R(2) = 0.83) and thinner cartilage (R(2) = 0.86). When V was > 27 mm/sec and AR.epsilon(3), was > 0.09, tractional forces were significantly higher (< or = 12% of peak) when the stress-field moved onto thicker cartilage. Stress-field dynamic mechanics and cartilage thickness significantly affected TMJ disc tractional forces.