Background: Temporomandibular disorder (TMD) is characterized by pain and limited range of motion in the jaw. TMD patients generally prefer to chew on the unaffected or less-affected side, and this tendency often results in asymmetries in masseter muscle thickness and range of mandibular motion.
Objects: The purpose of this study was to compare the asymmetries in masseter muscle thickness and range of mandibular motion in subjects with and without temporomandibular disorders.
Methods: Thirty-nine subjects were divided into two groups: A TMD group (n1=19) and a control group (n2=20). The jaw opening range and laterotrusion were measured using a digital vernier caliper. The masseter muscle thickness was examined in both the resting state and the maximal clenching state using ultrasonography. The absolute asymmetry indices calculated based on the laterotrusion and masseter muscle thickness of the respective right and left sides. A two-way ANOVA and a Mann-Whitney U test were used for statistical analysis.
Results: No significant different was found in the masseter muscle thickness between the TMD and control group. A significant difference was found in the absolute asymmetry indices of mandibular laterotrusion between the TMD and control groups (p<.05). Furthermore, the ranges of jaw opening were significantly different between males and females (p<.05). The absolute asymmetry index values of masseter muscle thickness at rest and during maximal clenching were also significantly different between males and females (p<.05).
Conclusion: These results demonstrated that the subjects with TMD had a larger degree of asymmetry in laterotrusion than those without TMD. Therefore, a physiotherapy program needs to be designed to restore normal laterotrusion capacities for TMD subjects. These results also showed that female subjects had greater absolute asymmetry indices in masseter muscle thickness than male subjects. Therefore, more training is needed to promote bilaterally balanced chewing among women.

Abstract
 Ⅰ. 서론
 Ⅱ. 연구방법
  1. 연구대상자
  2. 실험 기기 및 도구
  3. 실험방법
  4. 분석방법
 Ⅲ. 결과
  1. 연구대상자의 일반적인 특성
  2. 개구범위와 턱관절가동범위의 비대칭지수 비교
  3. 교근 두께의 비대칭지수 비교
 Ⅳ. 고찰
 Ⅴ. 결론
 References

• 이지원(아산충무병원 물리치료실) | Ji-won Lee (Dept. of Physical Therapy, Asan Chungmu Hospital)
• 양연주(플러스병원 물리치료실) | Yeon-ju Yang (Dept. of Physical Therapy, Plus Hospital)
• 원종임(전주대학교 의과학대학 물리치료학과) | Jong-im Won (Dept. of Physical Therapy, College of Medical Science, Jeonju University) Corresponding author