Are occlusal dysfunctions a risk factor for orofacial muscular parafunctions?

Occlusal dysfunctions are considered as a risk factor for orofacial parafunctional activity. It is assumed that occlusal disorders intensify the normal activation of the masticatory musculature, which has been observed as a response to stressors. In order to verify this hypothesis, test subjects with and without occlusal dysfunctions were compared under stress conditions with regard to their masseter muscle activity and further psychophysiological stress indicators. Out of 168 students of dentistry, 25 test subjects were each selected for the risk group (test subjects with occlusal dysfunctions) and the control group (test subjects without occlusal dysfunctions). The test subjects showed no acute symptoms of pain or dysfunction, and no such symptoms were known from their respective case histories. After a period of rest, the test subjects performed a mental arithmetic test (MAT), with a subsequent phase of recovery. The activity of the masticatory and frontalis musculature, skin conductivity and pulse frequency were recorded. Thetest subjects answered questionnaires on mood, personality variables and habitual stress management. The groups showed no differences either in the rest phase, the MAT phase or the recovery phase with regard to the medium activation level of the masseter muscle. With regard to the MAT phase, however, the masseter muscle activity of the control group was found to decrease, whereas the test subjects with occlusal disorders even showed a tendential increase. We interpreted this as an indication that occlusal dysfunctions can play the role of "latent dysfunctional factors" within the context of the aetiology of orofacial myoarthropathic disorders. Keywords: Occlusal dysfunction, bruxism, TMD aetiology, stress responses, stress induction, electromyogram, skin conductivity, cardiac frequency, dimensions of personality