Anterior disc displacement without reduction refers to an abnormal forward, bunched-up position of the articular disc which does not reduce. In this latter scenario, the disc is not intermediary between the condyle and the articular fossa as it should be, and hence the articular surfaces of the bones themselves are exposed to a greater degree of wear (which may predispose to osteoarthritis in later life). Degenerative joint disease
The general term "degenerative joint disease" refers to arthritis (both osteoarthritis and rheumatoid arthritis) and arthrosis. The term arthrosis may cause confusion since in the specialized TMD literature it means something slightly different from in the wider medical literature. In medicine generally, arthrosis can be a nonspecific term for a joint, any disease of a joint (or specifically degenerative joint disease), and is also used as a synonym for osteoarthritis. In the specialized literature that has evolved around TMD research, arthrosis is differentiated from arthritis by the presence of low and no inflammation respectively. Both are however equally degenerative. The TMJs are sometimes described as one of the most used joints in the body. Over time, either with normal use or with parafunctional use of the joint, wear and degeneration can occur, termed osteoarthritis. Rheumatoid arthritis, an autoimmune joint disease, can also affect the TMJs. Degenerative joint diseases may lead to defects in the shape of the tissues of the joint, limitation of function (e.g. restricted mandibular movements), and joint pain.
The function of the articular eminence is to limit the forwards movement of the condyle. The ligament directly associated with the TMJ is the temporomandibular ligament, also termed the lateral ligament, which really is a thickening of the lateral aspect of the fibrous capsule. The stylomandibular ligament and the sphenomandibular ligament are not directly associated with the joint capsule. Together, these ligaments act to restrict the extreme movements of the joint. Muscles of mastication
The muscles of mastication are paired on each side and work together to produce the movements of the mandible. The main muscles involved are the masseter, temporalis and medial and lateral pterygoid muscles. They can be thought of in terms of the directions they move the mandible, with most being involved in more than one type of movement due to the variation in the orientation of muscle fibers within some of these muscles. Protrusion – Lateral and medial pterygoid. Retraction – Posterior fibers of temporalis (and the digastric and geniohyoid muscles to a lesser extent). Elevation – Anterior and middle fibers of temporalis, the superficial and deep fibers of masseter and the medial pterygoid. Lateral movements – Medial and lateral pterygoid (the ipsilateral temporalis and the pterygoid muscles of the contralateral side pull the mandible to the ipsilateral side).Each lateral pterygoid muscle is composed of 2 heads, the upper or superior head and the lower or inferior head.