Mandibular movement asymmetry and masticatory muscles incoordination in patients with temporomandibular disorders

AIM: Temporomandibular disorders (TMD) consist of a number of clinical problems involving the masticatory system, particularly in women. The aim of the current study was to quantitatively investigate the asymmetry of jaw kinematics and the incoordination of muscles’ activity during maximum voluntary contraction (MVC), in patients with moderate TMD and patients with severe TMD versus TMD-free subjects. METHODS: Fifteen patients with moderate-TMD (13f, 2m; 19-45y), 15 severe-TMD women (14-45y) and 15 healthy volunteers (12f, 3m; 21-30y) were analyzed in this study. To be recruited in the pathologic group, patients had to present TMD according to the Research Diagnostic Criteria for TMD (RDC/TMD), then they were assigned to the moderate or the severe TMD group according to the level of perceived signs and symptoms (ProTMDmulti protocol). Free movements of mouth opening and mandibular laterotrusions were non-invasively recorded using an infrared optoelectronic 3D-motion analyzer (BTS SMART System). Temporalis and masseter muscles’ EMG activity was recorded by a wireless device (BTS FreeEMG) during 5s of MVC. All signals were standardized as percentages of the potentials obtained during 5s of MVC with cotton rolls interposed between posterior teeth. RESULTS: TMD patients showed larger jaw lateral displacement during mouth opening (healthy, 2.7±1.1mm; modTMD, 4.1±2.3mm; sevTMD, 4.3±2.2; 1-way ANOVA, p=0.071), and larger laterotrusion asymmetry (healthy, 0.7±0.7mm; modTMD, 1.6±0.9mm; sevTMD, 1.4±1.1mm; p=0.040). As shown in table 1, TMD patients also presented a pattern of muscular incoordination during MVC, with both asymmetry (POC, percent of overlapping coefficient, and Asymmetry) and latero-deviating couple (TORS and Torque) indices increasing with the severity degree. CONCLUSION: Overall, TMD patients presented jaw movement asymmetry, incoordination between right and left muscle pairs, with a resultant latero-deviating moment on the mandible, all increasing with the severity degree. ACKNOWLEDGEMENTS: Provost’s Office for Research of the University of São Paulo, and Conselho Nacional de Pesquisa (CNPq), Brazil. Table 1: EMG indices in MVC, mean±SD, 1-way ANOVA. Measure Healthy Moderate-TMD Severe-TMD p-value POC_temporalis [%] 87.7±2.4 * 84.5±6.2 82.0±7.1 * 0.029 POC masseter [%] 87.1±3.0 * 83.5±7.7 78.3±14.2 * 0.049 Asymmetry [%] 5.9±3.8 * 7.2±7.8 # 13.0±5.1 *# 0.004 TORS [%] 91.9±0.9 * 88.1±6.3 86.2±7.1 * 0.021 Torque [%] 3.1±1.8 * 8.5±8.0 10.7±9.1 * 0.015 *, # = Bonferroni post-hoc significant test.