Maximum Muscle Output and Electromyographic Activity of Masticatory Muscles in Persons With Parkinson's Disease. A Case-Control Study

Background: Parkinson's disease (PD) affects the motor system of the body; however, there is limited understanding of how the disease impacts the complex interaction of the masticatory muscles. Objective: The purpose of this study is to investigate the maximum muscle output of the masticatory muscles during natural functions. Methods: This clinical case-control study included persons with PD and age- and gender-matched controls without PD. The masticatory muscle output was evaluated by bite force and bilateral surface electromyography. Electromyographic recordings were conducted from the anterior temporal, masseter and digastric muscles during chewing and maximum voluntary contraction (MVC) during maximal intercuspal biting (MVC biting) and maximal jaw opening (MVC opening). Statistical analyses included chi 2-test, Mann-Whitney U test and Spearman's rank correlation analysis (significance level p < 0.05). Results: The study included 20 persons with PD (median age: 68.5 years) and 20 persons without PD (median age: 67 years). No significant differences were found between the groups in terms of demographics, teeth present, or bite force measurements. The activity in the masseter muscle was significantly lower in the PD group during MVC biting. The PD group utilised 82% of their masseter muscle MVC during chewing, whereas the control group used 49% of theirs. Additionally, a negative correlation was observed between the severity of PD and the bite force and digastric muscle activity during MVC opening. Conclusion: These findings indicate that PD may alter the activity patterns of the masticatory muscles during function. This new understanding can be utilised to design targeted interventions aimed at improving orofacial function for this patient group.