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MUSCLES OF MASTICATION

    • Some of the T.M.J. diseases have been due to an attributed variation of the function and attachment of the superior head as an etiological factor in T.M.J. diseases.
    • Nerve supply is from the anterior division of the mandibular branch of trigeminal nerve(nerve to lateral pterygoid).
    • Blood supply of lateral pterygoid muscle is from maxillary artery .
    • Actions of lateral pterygoid:
    • If the Pterygoid muscles of one side act, the other side of the mandible is drawn forward while the same condyle remains comparatively fixed.
    1. Depression of the mandible .
    2. Side to side movement (lateral movement) .
    3. Protrusion of the mandible.

    ACCESSORY MUSCLES OF MASTICATION

    1. BUCCINATOR:
    • It is an accessory muscle of mastication, occupying the gap between mandible and maxilla forming important part of the cheek.
    • Its origin is from buccal plate of bone of the sockets of the upper and lower three molars and pterygomandibular ligament.
    • Course and insertion

    Upper fibers gets inserted into upper lip,

    Lower fibers gets inserted into lower lip,

    Middle fibers decussate at the angle of the mouth, the upper fibers pass to lower lip while the lower fibers pass to the upper lip .

    • Nerve supply is from buccal branch of facial nerve.
    • Blood supply is from facial artery.
    • The main action of buccinator is to prevent the accumulation of food in the vestibule of mouth.

    2. ANTERIOR BELLY OF DIGASTRIC:

    • Origin; it arises from the digastric fossa on the lower border of mandible on both sides of symphysis menti.
    • Insertion; into the intermediate tendon which is connected to the hyoid bone by a fibrous loop.
    • Nerve supply; is through anterior division of mandibular branch of trigeminal nerve.
    • Action; its main action is to depress the mandible .

    3. MYLOHYOID MUSCLE:

    • It form the floor of the mouth.
    • Origin is from mylohyoid line on the internal  aspect of mandible.
    • Insertion; The fibers slops downwards and forwards to inter-digitate with the fibers of the other side to form the median raphe.
    • This median raphe insert in the chin from above and the hyoid bone from below.
    •  Action; Elevates hyoid bone, supports and raises floor of mouth which aids in early stage of swallowing, depress the mandible.
    • Nerve  supply; by nerve to mylohyoid: which is a branch of Inferior alveolar branch of mandibular nerve, which originates before it  enters inferior alveolar canal.
    • Blood supply; by Facial artery and Lingual artery.
    • This muscle provides a separation between the submandibular and sublingual salivary glands.

    4. GENIOHYOID:

    •  Origin; from inferior genial tubercle (in the midline of inner surface of mandible).
    • Insertion; is into the hyoid bone.
    • Action; depresses the mandible.
    • Blood supply; is through lingual artery.
    • Nerve supply; is by hypoglossal nerve.

    5. ORBICULARIS ORIS:

    • It has two parts: intrinsic and extrinsic part.
    • Intrinsic part is a very thin sheet and originates from superior and inferior incisivus. It inserts into the angle of mouth.
    • The extrinsic part is actually formed by elevator and depressor muscles of the lips and their angles, and inserts into the angle of the mouth.