maxresdefault

MUSCLES OF MASTICATION

  • While in the deep head, the fibers are more vertically oriented and inserted into the upper half of the lateral surface of the ramus.
  • Action of masseter is mainly to elevate the mandible (antigravity action) and also helps in protrusive movement.
  • It is the main muscle involved in the elevation of the mandible
  • Nerve supply: by the mandibular branch of the trigeminal nerve, from the anterior division(massetric nerve).
  • Blood supply is from the maxillary artery which is a terminal branch from external carotid artery.
  • One of the interesting properties of this muscle is that, internally, the muscle has many tendinous septa that greatly increase the area for muscle attachment and so increase its power.

Masseteric Hypertrophy

  • Masseteric Hypertrophy was first described by Legg in 1880.
  • A hypertrophied muscle will alter facial symmetry, generating discomfort and negative cosmetic impact in many patients.
  • It may also produce functional  alterations like bruxism, mandibular prognathism and trismus.
  • It can be treated by using Botulinum toxin, RF  Electrocoagulation and surgical methods.
  • Botulinum toxin can reduce upto one third where as surgical methods can reduce upto two third of the muscle mass.

MEDIAL PTERYGOID

  • It is also called as the Pterygoideus internus (Internal pterygoid muscle).
  • It consist of 2 heads which differ in origin:

Origin:

The deep head originates from the medial surface of lateral pterygoid plate of the sphenoid bone.

While the superficial head originates from the maxillary tuberosity.

The muscle inserts into the inner surface of the angle of the mandible.

  • Nerve supply  of the muscle comes from the main trunk of the mandibular nerve.
  • Blood supply is chiefly from the maxillary artery.

Action:

  1. Elevate the mandible .
  2. Protrusion of the mandible (lateral & medial pterygoid on one side protrude the mandible to the opposite side).
  3. Side to side movement (these lateral movements are achieved by lateral & medial pterygoid on both sides acting together to produce side to side movements).

LATERAL PTERYGOID

  • Also called as the Pterygoideus externus (External pterygoid muscle).
  • It is a short conical muscle, having 2 heads:

upper and lower.

  • Upper head:

–     Origin: infra-temporal surface & crest of the greater wing of sphenoid

–     Insertion: enters the TMJ & inserted into:

a) Pterygoid fovea of the neck of the mandible

b) Articular disc

c) Capsule of TMJ (anterior aspect)

  • Lower head:

–     Origin: Lateral surface of the lateral pterygoid plate

–     Insertion:  its insertion is same as that of the upper head, it enters the TMJ & gets inserted into:

a) Pterygoid fovea of the neck of the mandible

b) Articular disc

c) Capsule of TMJ (anterior aspect)

  • The insertion of the lateral pterygoid in the articular disc occurs in the medial aspect of the anterior border of the disc and thus it plays a role in the T.M.J. diseases especially internal derangement.