Standardized mastication increases the coordination in masticatory activity in women with chronic temporomandibular joint disorders: a case control study.

Background: The effects of jaw movement pattern on masticatory activity during chewing remains unclear in chronic temporomandibular joint disorders individuals. Objective: to assess the effect of habitual and non-habitual mastication patterns based upon the activation of the masseter and temporalis muscles in individuals with or without temporomandibular joint disorder (TMJD). Methods: Fifty-four participants (age: 18–44 years) were divided into two groups: the TMJD (n=27) and control (n=27) groups. TMJD was identified using the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD). Electromyographic activity of the masticatory muscles was measured during 2 tasks: habitual mastication with parafilm (HM) and non-habitual mastication with parafilm (NHM). MATLAB software was used to process electromyography (EMG) signals. The root mean square, symmetry index (SI%), anteroposterior coefficient (APC%) and torque coefficient (TC%) were determined from the processed EMG signal. Results: Reduced right masseter activation was observed for the TMJD group (p<0.05) during jaw agonist phase. During the jaw agonist phase, all muscles presented with more activation during NHM. Symmetry of temporalis (ST%) and APC% were the lowest for HM. TC% was increased for HM. Conclusion: Habitual and non-habitual mastication differ in masticatory activity during jaw agonist and antagonist phase and TMJD individuals presented a different way to recruit muscles under these circumstances. Non-habitual mastication has a more coordinating and stable motor pattern in masticatory activity and has less variability than habitual mastication to assess masticatory activity.