MANDIBULAR HYPER-EXTENSION

In motor vehicle accidents, particularly in a rear end collision, the suddenness of the impact, snapping the head backward, happens so quickly that the anterior neck muscles do not have a chance to relax.

As a result, they act as an anchor on the mandible holding it still and forcing the mouth excessively open, as the head continues to move backward into hyper-extension.

This action, the whipping excessively open of the mouth and its subsequent closure into normal position, results in self-reducing dislocation of the temporomandibular joint.  The masticatory and cervical musculature, ligaments, and the synovial tissues of the temporomandibular joint are simultaneously injured.  A frequent result of this type of injury is the anterior displacement of the TMJ disc and posteriorization of the mandible as seen in Fig. 19.

This injury is particularly important because it has been well documented that 60% of the people involved in motor vehicle accidents do not fully recover.  The same studies also clearly demonstrated that many of the people who do not fully recover continue to suffer from a temporomandibular joint dysfunction that is directly related to the accident, but in fact, HAS GONE UNDIAGNOSED.

The anterior displacement of the TMJ disc has been demonstrated to be the primary etiology of progressive disease, which results in degenerative arthritis.

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