Facial Expression Muscles

Facial Expression Muscles

Eight paired muscles of expression in coordination with the single orbicularis oris muscle, control the movements of the lips and cheeks . The teeth and alveolar processes of the jaws support this group of muscles against collapse into the oral cavity. The muscles of facial expression also play an important part in forming the anterior and lateral portions of maxillary and mandibular impression borders.

Depressor Anguli Oris Muscle

Shaped flat and triangular, the depressor anguli oris muscle covers the depressor labii inferioris muscle. It also has an origin along the lower border of the mandible just beneath the mental foramen. With an insertion at the angle of the mouth, it acts to draw the angle upward.

Levator Anguli Oris Muscle.

The levator anguli oris muscle is flat and triangular. Its position is in the levator anguli oris fossa of the maxilla, covered by the levator labii superioris muscle. The levator anguli oris originates in the canine fossa and inserts at the angle of the mouth. It has three actions; it lifts the angle of the mouth upward, lifts the lower lip, and helps close the mouth.

Mentalis Muscle

The mentalis is a short, thick, cylindrical muscle positioned on the boney prominence of the chin, deep to the depressor labii inferioris muscle. Its origin on the mandible is also deep to the depressor labii inferioris. When contracting, it lifts and wrinkles the skin of the chin and pulls tissue below the lips towards the lower anterior teeth.

Intraoral Soft Tissue Anatomy

The muscles that form the sides, entrance, and floor of the oral cavity are the buccinators, orbicularis oris, and mylohyoids (in that order)

Platysma Muscle.

The platysma is a thin broad band of muscle that originates over the pectoralis major and deltoid muscles. Its insertion is the inferior border of the mandible and the skin of the lower face. The platysma acts to draw the corners of the mouth down and aids in depression of the mandible.

Risorius Muscle

The risorius muscle is flat and triangular. With a position lateral to the angle of the mouth, it originates in tissue over the masseter muscle and parotid gland. The risorius has an insertion at the angle of the mouth with the depressor anguli oris muscle. Its action is to draw the angle of the mouth laterally causing a smile and dimple.

Zygomaticus Major Muscle.

The zygomaticus major muscle is oblong, flat, and cylindrical. It is positioned lateral to and above the angle of the mouth. It originates at the zygomatic bone, lateral to the levator labii superioris muscle, and inserts in skin just superior to and at the angle of the mouth. The muscle's action is to draw the angle of the mouth laterally and upward.

Levator Labii Superioris Muscle

This facial expression muscle is flat and triangular. It is positioned lateral to the nose and has an origin by two heads; the frontal process of the maxilla and the inferior margin of the orbit. These unite at one insertion point in the fibers of the obicularis oris beneath the nostrils. The levator labii superioris muscle acts to elevate the upper lip, widen the nasal opening, and raise the corner of the nose

Orbicularis Oris

This ring-like muscle lies within the upper and lower lips and completely surrounds the opening to the mouth. When the orbicularis oris contracts, it causes the lips to close. The orbicularis oris has no real bony origin. Instead, it is entirely rimmed by the insertions of other muscles of facial expression, most of which do originate on bone. Certain muscles of expression that insert into the orbicularis oris act to draw the corners of the mouth backward, while some depress the lower lip and others elevate the upper lip.

Depressor Labii Inferioris Muscle.

With a flat and quadrangular shape, this muscle covers the mental foramen. It has an origin along the lower border of the mandible and inserts into the skin of the lower lip. When contracted, it acts to depress and invert the lower lip.

Buccinator Muscle

buccinator muscle is a thin, broad band of muscle tissue that forms the innermost muscle wall of a cheek. A buccinator muscle has three sites of origin. They are the pterygomandibular raphe (ligament), which originates behind the maxillary tuberosity and inserts at the posterior end of the mandible's mylohyoid line; the buccal surface of the alveolar process in the maxilla immediately above the root tips of the molar teeth; and the external oblique ridge of the mandible. The muscle fibers of the buccinator run parallel to the occlusal plane of the teeth and have a broad zone of insertion into the orbicularis oris at the corner of the mouth. Besides being muscles of facial expression, some anatomists classify the buccinators as accessory muscles of mastication. The primary functions of these muscles are to pull the corners of the mouth laterally and hold food between the teeth while chewing.