Chewing

Bones of Mastication

Muscles of Mastication

Temporalis: arises from the temporal fossa and inserts onto the coronoid process of the mandible
Masseter: arises from the zygomatic process of the maxilla and inserts into the angle and ramus of the mandible
- These two contract to lose the mouth

Lateral pterygoid: arises from the sphenoid and inserts into the condyloid process of the mandible
Digastric (posterior): arises from the mastoid notch, anterior arises from the lower border of the mandible. Insert onto the hyoid.
Infrahyoid: (4 pairs of muscles) arise from the hyoid and insert onto clavicle
- These contracts to open the mouth

All of the muscles of mastication are innervated by the mandibular branch of the trigeminal nerve.

Control of mastication:

Voluntary
Reflexes: jaw unloading, reflex, jaw jerk reflex
Brain stem pattern generator
Fine tuning via sensory feedback through periodontal ligaments and proprioceptors (when teeth touch)
A change in occlusion (e.g. following dentistry) will affect the chewing pattern
There are 3 main movements of mastication
- Hinge opening and closing
- Side-to-side lateral
- Protrusion and retraction

The temporomandibular joint (TMJ) allows for these movements

TMJ

Bilateral joint. Both joints must work together
Synovial joint (diarthrosis). Articular capsule and synovial membrane
- Can get both rheumatoid and osteoarthritis
Articular disc: divides the upper and lower synovial compartments
- Lower: rotational movement (ginglymus)
- Upper: sliding movement (arthrodial)
Ginglymoarthrodial joint
TMD: multifactorial and very common

Movement of the mandible