Which muscles are typically most active during clenching in EMG studies?

• A. The bilateral masseter and temporalis muscles.
• B. Frontalis and orbicularis oculi.
• C. Digastric and sternocleidomastoid.
• D. Orbicularis oris and buccinator.

Answer: (C)

When clenching, the muscles that close the jaw are the most active. The primary jaw-closing muscles, especially the bilateral masseter and temporalis, generate the bulk of the bite force and show the highest EMG activity during a clench. These muscles work together to elevate the mandible and, in the case of the temporalis, contribute to jaw elevation and some lateral movement. In contrast, the digastric and sternocleidomastoid are more involved in opening the jaw and stabilizing the head, so their activity is comparatively lower during a pure clench. The remaining facial muscles, like the orbicularis oris, buccinator, frontalis, and orbicularis oculi, aren’t primary contributors to clenching and show minimal activation for generating bite force.