Biomechanical properties of masseter muscle assessed through myotonometry in patients with temporomandibular disorder treated with ultrasound therapy: a randomized comparative study.

Background: The aim of the study was to make an objective quantitative assessment of effectiveness of procedures with the use of a therapeutic dose of ultrasounds in this nosological entity, in connection with improved biomechanical properties and alleviation of pain experienced in masseter muscles.

Methods: The study included 40 patients with temporomandibular disorder. In group 1 (N.=20) ultrasound therapy (1.2 W/cm²) was carried out, while in group 2 (N.=20) sham therapy was applied. A total of 10 procedures were performed. Myotonometric measurements and assessment of pain intensity were carried out before treatment and after the completion of procedures.

Results: The analysis revealed a significant difference (P=0.011) between the values of decrement (D) measured on day 0 (2.08±0.45 [log]) and day 4 (1.80±0.55 [log]) in group 1. In group 2 no statistically significant differences were noted between the results obtained on consecutive days of the therapeutic cycle. A statistically significant difference in values of decrement (D) between group 1 (1.80±0.55 [log]) and group 2 (2.23±0.51 [log]) was noted on day 4 of the experiment (P=0.021). Both in group 1 and in group 2, a statistically significant reduction of pain intensity (VAS Scale) was obtained.

Conclusions: The masseter muscle was more elastic during ultrasound therapy. However, the effect was transient. The analgesic effect was also observed in the control group; therefore, a placebo effect cannot be excluded.