Effect of Occlusal Appliances on Masseter Activity in Symptomatic Subjects

Objectives: Despite extensive use of oral splints in bruxism and TMD treatment, their mechanism of action remains unclear. In asymptomatic subjects, a biomechanical change in the TMJ was shown, sensitive to individual anatomies and partially neutralized by teeth clenching. Thus, other effects are being investigated. Aim of this study was to elucidate how occlusal appliances influence masseter activity in bruxers as well as in patients with myogenous pain
Methods: Fourteen pain-free bruxers (7 m and 7 f) as well as fourteen subjects with myogenous pain (7 m and 7 f) between 18 and 45 years participated in the study. Occlusal Michigan type appliances (3 mm thick in the first molar area) were fabricated in acrylic resin. Nocturnal EMG signals of the masseter on preferred chewing sides were recorded by means of portable devices at 2 kHz sampling frequency during five nights without appliance and five nights while wearing it. Activity periods (AP) were analyzed relative to maximum voluntary contraction (MVC) according to previously defined criteria. Statistical differences were assessed by Wilcoxon tests at a significance level of alpha=0.05 (median and IQR: interquartile range below).
Results: In bruxers, the number of AP per hour (13.4 – IQR 5.1 to 7.1 – IQR 4.7), their maximum amplitude (29.5 – IQR 18.8 to 19.3 – IQR 11.4 %MVC) as well as their duration (3.2 – IQR 1.4 to 1.7 – IQR 1.5 sec) decreased significantly when wearing the splint. In patients with myogenous pain, only the number of AP per hour (10.6 – IQR 4.2 to 7.0 – IQR 4.7) and their average amplitude (12.5 – IQR 3.5 to 10.0 – IQR 4.5 %MVC) decreased significantly when wearing the splint.
Conclusions: Within the limits of the experiment, the results suggest that occlusal appliances cause a behavioral change that appears stronger in bruxers than in patients with myogenous pain.