RESUMEN
OBJECTIVES: The primary aim of this work was to determine the duration of ultra-low-frequency transcutaneous electrical nerve stimulation (ULF-TENS) application necessary to achieve sufficient relaxation of the masticatory muscles. A secondary aim was to analyze the influence of stimulation on muscle relaxation in pathological subjects and determine whether ULF-TENS has a noteworthy impact on muscle relaxation. METHODS: Sixteen adult subjects with temporomandibular disorders (TMD) and muscle pain and a group of four control subjects were included in this study. ULF-TENS was applied, and muscular activities of the masseter, temporal, and sternocleidomastoid muscles (SCM) were recorded for 60 min. RESULTS: Significant relaxation was achieved in the TMD group from 20, 40, and 60 min for the temporal, masseter, and SCM muscles (p < 0.05), respectively. Maximum relaxation was achieved in 12.5% of the subjects after 20 min, in a further 12.5% after 40 min, and in the remaining 75% after 60 min. Significant relaxation was achieved in the control group from 20 to 40 min for the masseter and temporal muscles, respectively (p < 0.05). DISCUSSION: Taken together, the results suggest that an ideal ULF-TENS application would last 40 min to obtain sufficient muscle relaxation both in patients with masticatory system disorders and healthy subjects, a time constraint that is consistent with everyday clinical practice.