Introduction
Two muscle groups shape what happens in the mouth. The masticatory muscles move the mandible and produce the force of the bite. The mimic (facial) muscles move the lips and cheeks; they don't chew, but they hold food over the teeth and press on every denture border.
Masticatory muscles
All four main masticatory muscles are supplied by the mandibular division of the trigeminal nerve (V3).
The two heads of the lateral pterygoid
- Lower head: works when the jaw opens or moves forward, and pulls the condyle down the eminence toward the other side.
- Upper head: works when the jaw closes, clenches or swallows, and holds the condyle and disc against the eminence.
The temporalis in three parts
The front, middle and back fibres act almost like separate muscles. The front part works with the masseter when the teeth are clenched; the back part works against it, pulling the mandible backward.
Suprahyoid muscles: the openers
When the hyoid bone is held still, these muscles pull the mandible down and open the mouth; when the mandible is held still, they lift the hyoid in swallowing.