Objective: This study evaluated the effect of a natural mediotrusive contact on the electromyographic (EMG) activity of the anterior temporalis and sternocleidomastoid muscles during chewing in healthy subjects.
Materials and methods: The study sample included two groups of 15 subjects each (Group 1: with natural mediotrusive contact; Group 2: without natural mediotrusive contact). Bilateral surface EMG activity was recorded on anterior temporalis and sternocleidomastoid muscles during unilateral chewing of a half cookie and unilateral chewing of a piece of apple. Anterior temporalis and sternocleidomastoid muscle activity was normalized against activity recorded during maximal voluntary clenching in intercuspal position and maximal intentional isometric head-neck rotation to each side, respectively. The partial and total asymmetry indexes were also calculated. Data were analyzed using Mann-Whitney, Wilcoxon and unpaired t-test.
Results: EMG activity of anterior temporalis and sternocleidomastoid muscles showed no significant difference between the groups. EMG activity of anterior temporalis was similar between working and non-working sides during chewing in both groups. EMG activity of sternocleidomastoid muscle was higher in the working side than in the non-working side in Group 2 subjects. Asymmetry indexes were not significantly different between groups.
Conclusions: The similar EMG pattern and asymmetry indexes observed suggest the predominance of central nervous control over peripheral inputs on anterior temporalis and sternocleidomastoid motor neuron pools.
Keywords: Electromyography; mastication; masticatory muscles; neck muscles.