Muscles of mastication in small children: an electromyographic analysis.

The temporalis, masseter, and depressor muscles of fifteen normal children were studied electromyographically to determine their activities during the position of resting tonus, during various movements of the mandible, and during the act of swallowing. Analysis of our results led to the following conclusions: 1. Resting tonus of the mandible does not depend on neuromuscular activity in the three portions of the temporalis, masseter, and depressor muscle group; they were inactive bilaterally. 2. Opening of the jaw either slowly or maximally, and against resistance, is brought about by the contraction of the depressor muscle group. 3. Closing of the jaw quickly is brought about mainly by greater contraction of the masseter muscle, and slightly by contraction of the temporalis. 4. Closing the jaw quickly with occlusal contact of the teeth is effected by the temporalis and masseter muscles. 5. Protraction of the jaw is performed by contraction of the masseter muscles. The depressor muscle group contracts to maintain the slight depression followed by the protraction. 6. Swallowing saliva and water is accompanied by contractions of the depressor muscle group. 7. Incisor chewing of gum and peanuts mainly recruits marked contraction of the masseter muscle. Some slight-to-moderate activity is achieved by the temporalis. The depressor muscle group acts in antagonism with the elevator muscles. 8. Chewing gum on the right and left molar sides and normal mastication are effected by the contraction of the temporal and masseter muscles. The suprahyoid muscle group acts in antagonism with the elevator muscles. 9. Normal children with deciduous teeth have patterns that are similar to those of normal adults.