Summary After more than 75 years of study, general understanding of TMJ biomechanics is good. The notion of compression-free joints has been discredited, and the principles that influence the magnitude of joint forces are well understood: • For a given bite position, joint force increases with increasing bite force. • For a given bite force magnitude, joint force increases as bite position moves posteriorly. • During unilateral bites, balancing side joint force is higher than working side joint force. Because the forces in each joint may differ, and because so many of the factors that contribute to joint forces are not easily measured, the magnitudes of TMJ forces have not been established. Without this important information, design of optimal total joint prostheses continues to rely on trial and error.