1 Lesson 5 Relevant Muscle Anatomy (Please fill in the blanks with either “elevates” or “depresses”.)

Masseter: ______the mandible (closes the mouth) Can cause facial pain and ear pain if overused with bruxism or with excessive biting on the back teeth

Temporalis: ______the mandible (closes the mouth) Can cause temporal headaches if overused with bruxism or with excessive biting on the back teeth

Medial Pterygoid: ______the mandible (closes the mouth) Protrudes the mandible Contra-laterally deviates the mandible Can cause facial pain and TMJ pain if overused with bruxism

Superior Lateral Pterygoid: Eccentrically controls the backward movement of the disc Often in increased tone, hence keeps the disc too far forward and does not allow it to go back when closing

Inferior Lateral Pterygoid: ______the mandible (opens the mouth) by assisting the anterior translation of the condyle / mandibular protrusion Contra-laterally deviates the mandible

Digastrics: Retrudes the mandible ______the mandible (opens the mouth) Often lengthened and weak due to forward head posture If weak, during mouth opening there is excessive forward translation of the mandible

Genioglossus: Depresses the tongue and often overused due to habitual tongue position resting at bottom of the mouth

© APTEI 2003 -2020 2 Muscles of Mastication Summary (Clue: Answers are all summarized below, but try to do it by memory :o)

Elevators (Close the mouth) Depressors (Open the mouth) 1) 1)

2) 2)

3)

Protractors (Protrude the chin) Retractors (Retrude the chin) 1) 1)

2)

3)

Lateral Deviators (Side-to-side) 1)

2)

3)

4)

In summary… The Temporalis, Masseter and the Medial Pterygoid muscles are powerful muscles that help forcefully close the mouth when chewing.

The Digastric and the Lateral Pterygoid muscles are relatively small muscles that help actively open the mouth. Their relative small size makes sense as high power and force is not functionally required for opening of the mouth.

The Masseter, Medial and Lateral Pterygoids all assist in jaw protrusion, and excessive protrusion is a common clinical problem.

The only muscle that assists in active jaw retrusion is the Digastric. This muscle is especially needed when opening the mouth wide to bite into a big apple or to yawn. The good thing about the Digastric muscle is that during maximal opening, it also retrudes the jaw (which is a good thing!).

The lateral deviators are the powerful Temporalis, Masseter, medial and lateral Pterygoid muscles. Lateral deviation or side-to-side movement is functionally essential for chewing and grinding of food.

© APTEI 2003 -2020