The two muscles of mastication that that are involved in closing of the mandible are the masseter and muscles.

The two muscles of mastication that that are involved in closing of the mandible are the masseter and pterygoid muscles.

Actually, three muscles that work together are involved in movement of the mandible: Temporalis, Masseter and Pterygoid Muscles.

Temporalis muscle - assists in closing the mouth and moving the mouth from side to side during the chewing.

Masseter muscle- the main chewing muscle and one of the strongest muscles in the body.

Pterygoid muscles- with the Masseter muscle to assist in  the chewing action and jaw rotation.  

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.