Evaluation of Strain Values for Masseter Muscle Activity of Dentofacial Deformities Using Ultrasound Elastography.

Background/Objective: This study aimed to evaluate the strain values (SVs) of masseter muscle activity in dentofacial deformities (DDs) using ultrasound elastography. Methods: The DD group consisted of 60 patients with dentofacial deformities with skeletal class II or III malocclusion, and the control group consisted of 26 volunteers with normal occlusion. The SVs and the cross-sectional area of the masseter muscle were measured using an ultrasonic elastography. These were measured at three functional positions: resting, mouth opening, and clenching. The SVs were statistically compared with the DD and control groups. Changes in the cross-sectional area and factors (patient status, skeletal morphology, and oral function) related to the SVs in the study group were statistically analyzed. Results: The SVs were significantly higher during clenching than in resting and mouth opening in both groups, although there was no correlation between the DD group and the control group. The cross-sectional area was larger during clenching, resting, and mouth opening. The resting SVs decreased as the masseter muscle cross-sectional area increased. The SVs of clenching increased with higher resting SVs and decreased with greater maximum mouth opening. Conclusions: The SVs measured by ultrasound elastography changed depending on functional mandibular movement and have the potential to evaluate the masseter muscle activity of dentofacial deformities.