Biomechanical properties and collagen fiber orientation of TMJ discs in dogs: Part 1. Gross anatomy and collagen fiber orientation of the discs.

The present study investigated the gross anatomy and collagen fiber orientation of TMJ discs in dogs using macroscopic, stereomicroscopic, light microscopic, and scanning electron microscopic techniques. Results showed that (1) the surface of the disc has an undulated configuration (a "fingerprint pattern" under stereomicroscope), which appears to aid in storing synovial fluid and providing lubrication to the joint; (2) the fine fibrils in the middle part are twisted together tightly, presenting a wavy, winding, lamina layer structure anteroposteriorly that works to absorb shock; (3) the mediolateral fibers are composed of loose and less wavy bundles, and they are crossed perpendicularly by anteroposterior fibers in anterior and posterior bands. In fact, a fibrous anulus in the periphery of the disc is composed of the mediolateral fibers of anterior and posterior bands and the anteroposterior fibers of the medial and lateral portions of the middle band, which suggests a stabilizing function.