Association Between Contact from an Overerupted Third Molar and Bilaterally Redistributed Electromyographic Activity of the Jaw Closing Muscles

Aims: To determine whether the facial side of an overerupted third molar and/ or the side exhibiting symptoms of temporomandibular disorders (TMD) has an association with the bilateral distribution of occlusal contact number, occlusal force, or surface electromyographic (SEMG) activity of the anterior temporalis (TA) and masseter muscles. Methods: Nineteen patients with unilateral TMD symptoms and one overerupted mandibular third molar were enrolled. Occlusal contacts and the SEMG activity of the anterior temporalis and masseter muscles were recorded simultaneously during maximal voluntary clenching (MVC) in the intercuspal position (ICP-MVC) and in the protrusive edge-to-edge position (Pro-MVC). The associations between the side of overeruption/TMD symptoms and the Δvalues of the differences between the right- and left-side values for the number of occlusal contacts, sectional force value (defined as the ratio of the anterior or posterior sectional arch bite force of the right or left side to the total arch force {SFV]), and SEMG activity of the temporalis and masseter muscles were analyzed. Results: The overeruption side (P .050), but not the symptomatic side (P > .050), showed an association with the Δvalues, with higher SFVs of the posterior arch and lower values for temporalis SEMG activity in the 100%, 75%, and 50% protrusive clenching positions and larger numbers of occlusal contacts in the posterior arch in the 100% and 75% protrusive clenching positions than the non-overeruption side. Conclusion: The pattern of occlusion, but not TMD symptoms, had an association with the number and distribution of the occlusal contacts, occlusal force, and temporalis SEMG activity. Keywords: bite force, electromyography, jaw-closing muscle, occlusal contact, third molar overeruption