Masseter
- A powerful elevator of the mandible that is covered by parotid
and muscles of facial expression and composed of superficial and
deep portions. This muscle is supplied by the masseteric
artery (off maxillary) and nerve (primarily
seen in infratemporal fossa dissection).
Temporalis
- A large, fan-shaped muscle composed of a anterior, middle and posterior
portion which is an elevator of the mandible. Deep
temporal nerves from V3 of CNV innervate the muscle and it receives
its bloodflow from the anterior and posterior deep
temporal arteries (branches of the maxillary artery) and the superficial
temporal artery (branch from the external carotid). Covered
by a tough fascia that extends from just posterior to the dentition to
the muscle (an important point for the spread of infections from the oral
cavity to other points in the head and especially important for dentists).
Lateral Pterygoid
- Muscle is composed of a superior head whose
origin is the roof of the infratemporal fossa and infratemporal crest of
the sphenoid bone and an inferior head whose
origin is the lateral surface of the lateral pterygoid plate. Both
heads insert on the pterygoid fovea of the
mandible (the superior head occasionally also inserts on the TMJ disk).
If both sides contract, the mandible protrudes and is depressed.
If the inferior head contracts on the right, the mandible moves to the
left and vice versa. The superior is an antagonist to the elevators.
The muscle is innervated by the lateral pterygoid
nerve and is covered laterally by the pterygoid plexus of veins
(often punctured during anesthesia of the superior posterior alveolar nerve
resulting in immediate swelling).
Medial Pterygoid
- The origin of the muscle is the maxillary tuberosity, the medial surface
of the lateral pterygoid plate and the pyramidal process of the palatine
bone and it inserts on the medial aspect of the ramus of the mandible forming
a “mandibular sling” with the masseter. It is primarily an elevator
of the mandible and alternate contraction causes the motion necessary for
grinding. It is supplied by the
medial pterygoid
nerve and artery.
Anterior Belly
of the Digastric, Mylohoid, and Geniohyoid
are all accessory muscles of mastication that aid in mandible motion and
food movement in the oral cavity.
TMJ:
Dissection:
1. Peel back the parotid gland
from its posterior attachment near the ear in an anterior direction exposing
the posterior edge of the masseter muscle. If the dissection is being
completed on the side of the face where the infratemporal fossa was dissected,
this step can be ignored.
2. Cut the masseter just below
its insertion on the zygomatic and temporal bones and reflect the muscle
inferiorly toward the angle of the mandible.
3. Expose and examine the lateral
TMJ ligament and the joint capsule which extend from the temporal bone
to the neck of the condylar process. It will be very difficult to
separate the two ligaments from one another.
4. Open the joint capsule and
locate the TMJ disk. Note that it is attached to the lateral (and
medial) pole of the head of the condyle.
5. Identify the superior and
inferior joint cavities located above and below the disk. Note that
the superior head of the lateral pterygoid may insert onto the anterior
portion of the disk.
6. Loosen the mandible and notice
the motion of the condyle and disk in relation to the articular eminence
of the temporal bone.
7. If desired, the condyle can
be loosened and the disk removed. The disk will have to be cut from
the medial and lateral poles for further examination. Note that the
disk is biconcave in shape and thicker posteriorly than anteriorly.
Also examine the head of the condyle and the articular eminence for the
presence of a synovial membrane which aids in lubricating the joint during
movement.
Pictorial Atlas:
Disabilities
Mandible
Ligaments
Osteology
Disk
Motion