This occurs when the there is more stress put on the jaw joint than the adaptive capacity of the joint is able to handle. This can occur because of a structural problem within the jaw (i.e. trauma, disk displacements or certain bad bites) or due to excessive loading forces on the jaw joint (i.e. jaw clenching or gum chewing).
The cells which make synovial fluid and the cartilage surrounding the bone are damaged before there is damage to the bone. The cartilage helps bring fluid in and out of the joint thereby eliminating waste products and bringing in nutrients. Typical symptoms include crackling or crepitation when opening and closing, pain in and around the ear, ear stuffiness, and bite shifting.
This can lead to shifting of the chin to the affected side and increased bite contact on the back tooth of the affected side. When the changes are more severe there can be a noticeable facial asymmetry from the chin shifting. When disk displacements without reduction are not properly treated, unwanted osteoarthritic changes have a greater chance of occurring.