Relationship of electromyographic parameters in jaw dysfunction patients classified according to Helkimo's index.

Forty-two jaw pain-dysfunction syndrome patients (PDS) were divided into three groups depending on the severity of their condition using the Helkimo clinical dysfunction index. For both the left and right masseter and anterior temporal muscles three parameters of their electromyographic activity were measured, the silent period (SP), the root mean square value (RMS) and the mean power frequency (MPF). During the experiments the patients were instructed to clench as hard as possible in the intercuspal position. No statistically significant differences could be found between the values for any of the muscles measured between the different Helkimo clinical dysfunction groups. However, when the affected side was compared with the unaffected side in this patient material, statistically significant longer silent period durations and greater RMS values were found in the masseter muscles of the affected side group.