Electromyographic study of activity of the masseter and anterior temporalis muscles in patients with temporomandibular joint (TMJ) dysfunction: comparison with the clinical dysfunction index.

Objectives: A comparison was made between the electromyographic patterns specific to patient with temporomandibular disorders and that of normal healthy patients. Study design: Electromyographic tests were carried out during rest and function of the masseter muscles and anterior temporalis muscles in a homogeneous group consisting of 95 patients for whom such pathology and its different degree of severity had been previously studied by means of a Helkimo Test. The electromyographic exploration results were compared to those of a control group consisting of 31 healthy subjects. Results: There were significant differences among patients with a different degree of clinical dysfunction, as well as between these and the control group. These differences were more important during maximum effort clenching and mastication. During maximum effort clenching, differences in masseteric activity were observed between control group and group III, between groups I and II and between groups I and III. Meanwhile, differences in temporalis activity were significant among all groups except between groups I and II. The multiple comparison analysis demonstrated the existence of significant statistical differences between healthy subjects and patients with severe TMD. However, the linear combination of these electromyographic (EMG) variables led us to elaborate four linear functions that classify all subjects into four well defined groups. Once extreme cases were eliminated, our EMG classification revealed an 80% match with that of the Helkimo Test. We thus conclude that in many cases, classification using electromyographic criteria matches that established by the Helkimo Test.