The lateral pterygoid (also called the external pterygoid) is a deep muscle located in the face. It is part of the muscle group that has a primary role in chewing (mastication). It is short, flat, thick and somewhat conical in shape. It can be found at the sides of the head, a little below the temples. The action of the lateral pterygoid results in the movement of the jaw. It’s why you can move your lower jaw forward, drop the lower jaw to help open your mouth and move the jaw from side to side. These actions are called protrusion, depression, and unilateral movement, respectively.
While initiating this action, several other muscles assist the lateral pterygoid. Very few muscles in the body have more than one head or parts and the lateral pterygoid is one of them. It has two heads inserting into a bulge called the condyloid process of the mandible bone. The mandible is actually the lower jaw bone which is the strongest and the largest bone in the face.
Each of the heads originates in a different location. The superior head begins in what is called the great wing of the sphenoid bone. This small bone can be found at the temples on both sides of the skull. The great wing protrudes from the sphenoid bone. The second head is the inferior head. This begins at the outside of the lateral pterygoid plate. The latter is a protrusion at the bottom of the sphenoid bone which is shaped like a hook.
Both the superior and inferior heads go horizontally towards the back of the head. From this position in the skull, they attach to different parts of the jaw. The superior head attaches to the temporomandibular joint. This is the joint where the skull and mandible meet. Meanwhile, the inferior head attaches to the condyloid process. This can be found at the back of the lower jaws.
Contraction of lateral pterygoid causes depression of the mandible which results in opening of the jaw. It can also cause the forward and side movements of the mandible. All of these movements are essential in chewing food (mastication).
Clinical Importance – Associated Diseases/Conditions
Lateral pterygoid muscle is prone to tenderness resulting in the derangement of temporomandibular joint (TMJ) and playing a role in some other conditions that briefly described below.
Temporomandibular Joint (TMJ) Dysfunction:
Lateral pterygoid muscle has been a point of focus in some cases of TMJ impairment. The superior head of the muscle is often involved triggering pain around the joint that can radiate to maxilla bone. Hyperactivity or spasm of the muscle has been established as the origins of this condition and can lead to displacement of the anterior disk of the joint. It can be very painful during chewing when the tongue and food is pressed against the muscle. Usually, treatment may include only pain killers.
Lateral Pterygoid Dystonia (Neuromuscular Dysfunction):
Sustained or repetitive use of the lateral pterygoid can cause the concerned mandible pushed off to one side, giving an asymmetrical facial structure. Other reasons of this dysfunction include myositis (inflammation), spasms or nutritional imbalances. Common symptoms of Lateral pterygoid dystonia include abnormal posture and pain, and can cause functional impairments in speech, chewing and swallowing of the patient. Treatment may include muscle relaxants, physiotherapy, Botox injections, and so on.
Myofacial Syndrome of Lateral Pterygoid:
This condition is rare and comprises of pain and tenderness of the concerned side, particularly anterior to the ear and occasionally into the temple. Dry needling technique is available, which according to one study is very effective in treating this condition. However, conventional treatment employs injecting local anesthetics or corticosteroids to suppress or reduce the pain.
Muscles Which Assist the Lateral Pterygoid
Three of the other muscles involved in chewing are the masseter, temporalis and medial pterygoid. The masseter looks somewhat like a parallelogram. It connects the mandible and the cheekbone. It is divided into superficial and deep sections. The superficial portion is the thick part that connects to the cheekbone while the deep portion is smaller and connects to the mandible. The superficial portion is tendon-line while the deep portion is more muscular. Parts of the masseter often get removed during jaw reduction surgery since it’s so bulky. The masseter tends to be larger in people who grind their teeth during sleep. The constant exercise causes them to develop square jaws.
The temporalis or temporal muscle is broad and shaped like a fan. It is located at the side of the head and fills a depression in the skull called the temporal fossa. The temporalis originates from the temporal fascia and fossa and passes the cheekbone. It then inserts into the coronoid process of the mandible. The is a bony part of the lower jaw. The temporalis muscle is beneath the temporal fascia. It is near the temples and its frequent use could be linked to what are called tension headaches.
The medial pterygoid is also known as the internal pterygoid muscle. It is a thick muscle with two heads. The bulky part of the medial pterygoid surfaces as a deep head from slightly above the medial surface of the lateral pterygoid plate. The smaller head, the superficial head originates from the maxillary tuberosity (the hindmost aspect of the upper jaw) and the pyramidal process of the palatine bone.