The masseter is a rectangular-shaped muscle in your face and jaw and is one of the primary muscles of mastication, or chewing. It has three distinct layers and works with nearby muscles to move your temporomandibular joint (TMJ) and jaw bone. Injury to the masseter muscle may cause pain, difficulty chewing, or swelling around your jaw and face.
This article will describe the anatomy of the masseter muscle, its function, and associated health conditions.
The masseter muscle arises from three distinct layers on 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 cheekbone. The muscle layers then converge and insert into the ramus of your mandible (jaw bone).
Nerve innervation to the masseter muscle is via the mandibular division of the trigeminal nerve , the fifth cranial nerve. The trigeminal nerve, the largest of the cranial nerves, consists of three main branches.
In addition to its role in chewing, the mandibular branch is also involved in several other facial functions, such as tongue and lip movement, facial sensations, and movement of other fine facial muscles.
The masseter muscles receive blood supply from the masseteric artery that emerges from the maxillary artery in your skull. The maxillary artery is divided into three parts: mandibular, pterygoid , and pterygopalatine .
Of these, the pterygoid is further divided into four sections and the masseteric artery is one of these branches. The masseteric artery goes deep into the masseter muscles and also connects with branches of the facial and transverse facial arteries.
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 from your jaw, bringing it forward into an underbite position.
The deep fibers of the masseter muscle also serve as a major stabilizer of the temporomandibular joint. When you clench your teeth together, the muscle contracts to keep the TMJ in the correct position.
Since the masseter is one of the major muscles of mastication, it is often injured or implicated in various conditions involving the face and jaw. These may include:
The most common condition affecting the masseter muscle is temporomandibular joint dysfunction (TMD). There are over 30 different TMD disorders. TMDs are divided into three different groups including:
While the condition is broad and encompasses several different types of TMD disorders, many of the symptoms can overlap. Pain in the jaw or with chewing are the most common symptoms. Symptoms of TMD may include:
If you suspect you have TMD, contact a healthcare provider for advice and treatment options. TMD is often self-limiting and may go away with appropriate treatment. Surgical options do not typically produce effective outcomes. Instead, treatment is highly individualistic and may include interventions such as learning to break habits such as jaw clenching, eating softer foods for some time, and taking over-the-counter medications to reduce pain.
Trauma to the face or jaw may injure the masseter muscle. For example, a sudden force to the jaw may fracture the bone, leading to severe pain and swelling of the face and jaw, including the masseter muscle. Other obvious signs of trauma, such as broken teeth or bleeding in the mouth, may occur.
Symptoms of a jaw fracture may include:
The treatment of a jaw fracture depends on its severity. If the fracture is small, the only treatment may be pain medications and a modified diet of soft foods and liquids. If the fracture is moderate to severe, you may need surgery. Surgical repair may also include wiring the jaw to help it heal correctly.
Trauma to the jaw can also cause a dislocated jaw. A dislocated jaw occurs when it moves out of its normal connecting points at one of the two temporomandibular joints (where the jaw connects to the skull). Symptoms of a dislocated jaw include:
Treatment for a dislocated jaw involves moving it back into the proper position. This procedure can be painful, so healthcare providers typically use numbing medications along with muscle relaxers to reduce the pain.
To help stabilize the jaw, patients are generally instructed not to open their mouths widely for six weeks. They may also have a bandage placed that goes under the jaw and up and over the head for support.
It is important to seek medical care immediately for trauma to the jaw. This is because a broken or dislocated jaw may cause a blocked airway or other breathing difficulties.
Trigeminal neuralgia affects the trigeminal nerve, the fifth cranial nerve. The trigeminal nerve has three branches: ophthalmic , maxillary, and mandibular branches. The ophthalmic branch affects the scalp and the front of the head. The maxillary and mandibular branches supply nerves to various face parts, including the upper and lower jaw, respectively.
Symptoms of trigeminal neuralgia typically include intense, debilitating pain attacks. The pain may last seconds to minutes and is usually one-sided. It is sudden and intense and is usually triggered by some contact or vibration on the cheek. Everyday activities such as putting on makeup, washing your face, shaving, or being exposed to wind can trigger an episode.
In between acute pain attacks, individuals may experience burning, throbbing, numbness, tingling, or other uncomfortable facial sensations.
Treatment includes medications to manage the pain, surgical interventions, and alternative therapies such as acupuncture or chiropractic care.
Masseter muscle hypertrophy is a rare condition in which the masseter muscle is enlarged on one or both sides of the face. There is no apparent cause, although factors such as chewing gum, grinding teeth, clenching the jaw, and temporomandibular joint disorders can all contribute to the development of the condition.
The condition is benign, and the main complaint is its aesthetic changes to the face. Patients may experience facial asymmetry, changes to the lines in the face, and a more prominent jawbone.
There are several treatment options. Noninvasive measures such as counseling may be effective if stress contributes to teeth grinding or clenching and subsequent enlargement of the masseter muscle. Mouthguards, medication for anxiety, muscle relaxers, and physical therapy may also be utilized.
Another option is the use of botox, or botulinum toxin type A, injections in the masseter. The injections work by paralyzing the muscle, which eventually shrinks after disuse. The main disadvantage of this treatment option is that it must be repeated to remain effective and is costly.
Lastly, various surgical interventions are utilized to reduce muscle size.
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 depend upon the cause of your condition.
Trauma to your jaw and masseter muscles may require a period of immobilization and rest to allow the muscles to heal properly. A jaw fracture is often treated with surgical fixation; you will not be able to move your jaw for a few weeks while it heals. Once healed, gentle motion should be started to stretch and strengthen the jaw muscles slowly.
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:
You may also benefit from using a mouth guard to properly position your TMJ. Work with your healthcare provider to ensure the right fit, and let them know if you experience any increased pain while using one.
Your provider may also use biofeedback, relaxation training, and stress management to alleviate jaw and masseter pain caused by TMD. 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. Your healthcare provider may order magnetic resonance imaging (MRI) to examine the muscles and structures around your TMJ. Your healthcare provider may recommend surgery to correct the joint structures if there is a severe problem within the joint space.
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 microvascular decompression (MVD) to correct the problem.
The masseter muscle plays an essential role in jaw function, stability, and chewing. Several conditions can affect the masseter muscle, causing pain, difficulty with chewing and eating, and facial aesthetics. If you're experiencing pain in your face or jaw, difficulty chewing, jaw stiffness, or other symptoms, reach out to a healthcare provider for advice.
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By Brett Sears, PT
Brett Sears, PT, MDT, is a physical therapist with over 20 years of experience in orthopedic and hospital-based therapy.
