Pilot study of the heterogeneous patterns of masticatory muscle coordination in nonpatient population

This pilot study characterized coordination patterns of the muscles of mastication during voluntary chewing in a nonclinical population. Dental students (n = 177) who did not exhibit symptoms of temporomandibular disorder were screened by a comprehensive muscle and temporomandibular joint palpation examination. A group of 44 students was identified on the basis of the presence of four or more tender points indicated during palpation. This group was further subgrouped by the absence (group A-1) and presence (group A-2) of temporomandibular joint clicking. Five volunteers from groups A-1 and A-2 and five volunteers without any palpation tenderness and joint clicking (control group) were examined by simultaneous recordings of electromyography of bilateral masseter and posterior one third of the temporalis muscles and by mandibular kinesiography. The electromyographic coordination pattern for the control group demonstrated predominantly working masseter muscle activity. This "predominant working masseter" pattern was not observed in groups A-1 or A-2. Additional analyses of the recordings indicated that a hypoactive tendency of the working side masseter muscle particularly outlasting the tooth contact was present in group A-1, whereas significant hyperactivity of the posterior one third of the temporalis was present in group A-2. The data suggested that an asymptomatic nonpatient population may be functionally diverse.