Anatomy of the Masseter Muscle
This Is How Your Jaw Moves
By Brett Sears, PT Medically reviewed by Mohamad Hassan, PT, DPT on December 21, 2020
From http://www.verywellhealth.com
The masseter is a rectangular-shaped muscle in your face and jaw and is one of the primary muscles of mastication, or chewing. It consists of three distinct layers and works with nearby muscles to move your temporomandibular joint and jaw bone. Injury to the masseter muscle may cause pain, difficulty chewing, or swelling around your jaw and face.
Anatomy
The masseter muscle arises from three distinct layers in each side of your face. (You have two masseter muscles, one on the left and one on the right.) The three layers of the masseter are the superficial layer, the intermediate layer, and the deep layer.
The muscle fibers originate from the zygomatic arch of your skull, also known as your cheek bone. The muscle layers then converge and insert onto the ramus of your mandible, or jaw bone.
Nerve innervation to the masseter muscle is via the mandibular division of trigeminal nerve, the fifth cranial nerve. It receives blood supply from the masseteric artery that emerges from the maxillary artery in your skull.
Function
The major function of the masseter muscle is to elevate your jaw bone. This brings your teeth together, as in the chewing motion. It works with the temporalis and lateral and medial pterygoid muscles to perform this function.
The deep and intermediate fibers of the masseter muscle work to retract your jaw bone, pulling your teeth into an overbite position. The superficial fibers of the muscle protrude your jaw, bringing it forward into an underbite position.
The deep fibers of the masseter muscle also serve as a major stabilizer of your temporomandibular joint (TMJ). When you are clenching your teeth together, it contracts to keep your TMJ in the correct position.
Associated Conditions
Since the masseter is one of the major muscles of mastication, it is often injured or implicated in a variety of conditions around the face and jaw. These may include:
Temporomandibular joint disorder (TMD)
Jaw fracture
Trigeminal neuralgia
Hypertrophy due to bruxism (teeth grinding)
The most common condition affecting the masseter muscle is temporomandibular joint dysfunction (TMD). Symptoms of TMD may include:1
Jaw pain
Swelling in one or both sides of your jaw and face
Difficulty chewing food
Clicking or catching sensations in your jaw
If you suspect you have TMD, see your dentist or physician right away. They can assess your condition and make recommendations for proper treatment for TMD.
Trauma to your face or jaw may result in injury to the masseter muscle. A sudden force to your jaw may cause the bone to fracture, leading to severe pain and swelling of your face and jaw, including the masseter muscle.
Trigeminal neuralgia is a condition causing pain in the face due to irritation of your fifth cranial nerve. This condition typically affects the sensory aspect of the nerve, preserving the motor function of the nerve (and masseter muscle).
If you notice any symptoms of pain or difficulty chewing, this may be a sign of masseter and TMJ dysfunction. Visit your physician to get the right treatment for your condition.
Rehabilitation
If you have a jaw condition that affects your masseter muscle, you may benefit from rehabilitation to regain normal pain free mobility. Rehab considerations for a jaw injury depends upon the cause of your condition.
Trauma to your jaw and masseter muscle may require a period of immobilization and rest to allow things to heal properly. A jaw fracture is often treated with surgical fixation of the jaw; you will not be able to move it for a few weeks while things are healing. Once healed, gentle motion should be started to slowly stretch and strengthen the jaw muscles.
Temporomandibular joint disorders may require a multi-faceted approach to care. You may benefit from physical therapy to help alleviate your symptoms and restore normal jaw motion and function. Treatments may include:2
Heat: Hot packs may be applied to the masseter and jaw to increase circulation, relax the muscle, and decrease pain.
Massage: Gentle massage to the masseter may help relax a hypertonic muscle and decrease pain. It may also help improve muscle flexibility.
Range of motion exercises: Gently working on pain-free range of motion of your jaw may help restore normal opening and closing of the joint.
Neuromuscular strengthening exercises: Many people with TMD benefit from restoring normal mobility of the joint in various directions. Rocabado exercises are a specific program to restore normal neuromuscular movement around your TMJ.
Ice: Application of cold packs to your sore masseter and jaw may be done to relieve pain, decrease circulation, and reduce swelling.
Postural control exercise: There is a connection between your jaw motion and posture. Your masseter muscle and other muscles of mastication work best when you are in optimum posture. Learning to attain and maintain proper sitting and standing posture may be a part of your rehab for TMD.
You may also benefit from using a mouth guard to properly position your TMJ.3 The night guard is worn while sleeping and keeps your TMJ in a neutral position while you sleep. It can also help prevent grinding of your teeth.
Biofeedback, relaxation training, and stress management may also be used to alleviate jaw and masseter pain due to TMD.2 It is a good idea to work closely with your dentist to ensure that your TMD rehab includes all the necessary components to restore normal, pain-free motion.
If TMD pain persists, you may benefit from diagnostic studies to examine your jaw joint.2 Magnetic resonance imaging (MRI) may be done to examine the muscles and structures around your TMJ. If a severe problem is found within the joint space, surgery may be performed to correct the joint structures.
If you are experiencing masseter and facial pain due to trigeminal neuralgia, you should consult with a neurologist who specializes in the condition. The correct treatment for you may be medication, and a surgical procedure called a microvascular decompression (MVD) may be done to correct the problem.
A Word From Verywell
The masseter muscle courses from your cheek bone to your jaw and is the main muscle of chewing. It works with other muscles to move and stabilize your jaw and temporomandibular joint. Injury to the masseter can cause pain and difficulty with jaw movement. Understanding the anatomy and function of the masseter can help you regain normal mobility after an injury to the muscle or jaw.
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