Objectives: Various designs of occlusal splints have been applied to treat symptoms related to the parafunctional habits such as nocturnal clenching. The purpose of this study was to reveal the effects of two different types of splint on bilateral electromyographic activities of temporalis, masseter, and sternocleidomastoid in the decubitus position.

Methods: Subjects were composed of ten healthy volunteers. Two types of interocclusal splints were fabricated for each subject; 1) incisal splint that covered the upper central incisors and had a point contacted with lower incisors only at any mandibular position, and 2) stabilization splint. The surface electromyographic activities were bilaterally recorded from the anterior belly of the temporalis, masseter, and sternocleidomastoid without a splint, with an incisal splint, and with a stabilization splint. Subjects were instructed to clench as hard as possible at the intercuspal position and bilateral eccentric positions while keeping the dorsal, right lateral, and left lateral decubitus position. Using the Friedman's test, the integrated electromyographic activities of each muscle were compared among without a splint, with an incisal splint, and with a stabilization splint.

Results: In the dorsal decubitus position, all muscles except left sternocleidomastoid showed significantly smaller activities with an incisal splint (p<0.05). In the right decubitus position, all muscles showed significantly smaller activities with an incisal splint (p<0.05). In the left decubitus position, bilateral temporalis and right masseter showed significantly smaller activities with an incisal splint (p<0.05).

Conclusion: It was concluded that the incisal splint can significantly reduce the muscle activities during clenching in the decubitus position and might be suitable for the treatment of symptoms related to nocturnal clenching.

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