Three-dimensional observation of the temporomandibular joint disk in the rhesus monkey.

The three-dimensional ultrastructure of the TMJ disk of two normal rhesus monkeys was investigated using the SEM. The upper and under surface of the TMJ disk consists of a close network of delicate collagen fibrils. On the undersurface, they have an undulating configuration, with the elevations running in one direction. On the upper surface, irregular and gentle waves can be observed. The matrix of the TMJ disk is composed of two main parts: one is the collagen fibrils that run in a sagittal direction making up the central fibrous core, and the other consists of the collagen fibrils that enclose the fibrous core. The collagen fibrils running in a sagittal direction show a wavy, winding appearance, and these structures are more numerous on the side of the TMJ disk facing the condyle. It is concluded that the wavy, winding structure and undulated configuration of the collagen fibers results in an elastic quality, opposes stress, and functions to absorb shock.