Comparison of Mouth Opening Length and Masseter Thickness in Subjects with and without Temporomandibular Joint Pain

Abstract

Background Although the temporomandibular joint (TMJ) is a bilateral joint, it is often used asymmetrically during active daily living. When there is a biomechanical or physiological imbalance in the masseter muscle, which is used to chew and close the mouth, a TMJ disorder can be occurred. Purpose The purpose of our study was to compare the extent to which subjects with and without TMJ pain could open their mouths and the asymmetry of masseter thickness. Study design A cross-sectional study Methods This study included 15 subjects with TMJ pain and 15 subjects without TMJ pain (control group). The maximum mouth opening and rotation mouth movement were measured using Image J, and masseter thickness was measured using ultrasonography. Results The results showed that there were significant differences in the maximum mouth opening and the rotation mouth movement between the groups (<italic>p</italic>&lt;0.05). However, no significant difference was found in the asymmetry of the masseter thickness (<italic>p</italic>&gt;0.05). Conclusions The pain felt in the TMJ was not related to the asymmetry of the masseter thickness; however, the maximum mouth opening and reduction of the rotation mouth movement were closely related to the pain level. Therefore, we recommend increasing the rotation mouth movement of the jaw to improve TMJ pain and solve the asymmetry of the rotation mouth movement of the jaw.