Trauma is describe as any force to the masticatory structures that exceeds that of normal functional loading. Both intensity and duration are important. There have been many studies that have demonstrated the detrimental effects of trauma, particularly direct trauma. These have shown that the effect of trauma is more profound regarding intracapsular structures, as compared to muscular disorders.

Trauma must be sub-divided into macrotrauma and and microtrauma. Macrotrauma would be any sudden force to the face or jaw that could potentially cause structural alterations. Microtrauma refers to repeated small forces to the jaw structures over a long period of time.

Macrotrauma can be further divided into direct trauma, represented by trauma directly to the jaw, and indirect trauma, as possibly represented by a flexion-extension (whiplash) injury to the cervical spine that has been theorized as having an indirect effect of rapid movement of the condyle within the fossa, leading to an intracapsular inflammatory response.

As stated previously, there is ample evidence that direct macrotrauma to the head or jaw can have a significant effect on the development of a TMJ disorder, especially an intracapsular disorder. In spite of many reported cases of the development of TMD symptoms post-whiplash injury, the available research does not support the idea that this is the result of an indirect traumatic effect on intracapsular structures. The explanation that is offered to explain the resulting symptoms is heterotopic pain in response to injury to cervical structures. To the experienced clinician, this seems to be an inadequate explanation why these patients often develop a profound intracapsular inflammatory response to such injury.

Microtrauma to the temporomandibular joints is usually associated with prolonged clenching and bruxism. A great deal of research has been done on this phenomenon and the process is much too involved to attempt to explain here. However, as Okeson has pointed out, most studies that have been done have looked only at static occlusal relationships and TMD symptoms. There is a need to study the effects of eccentric occlusal relationships, as well as the effect of bruxism in instances of orthopedic instability of the TM joints.