Causes of Limited Jaw Opening (Trismus)

Limited jaw opening can occur for a number of reasons. The onset of limited jaw opening may relate to a history that helps explain why limitation has occurred. At other times limited jaw opening occurs slowly and requires careful assessment to arrive at the correct diagnosis. The following are the most common reasons for limited jaw opening

1- Fatigue of Jaw Muscles Leading to Spasm When the muscles of the jaw are subjected to overuse (heavy gum chewing, nail and cuticle biting, clenching) they can fatigue and at times go into a state of spasm. If this occurs, jaw opening will be markedly limited and accompanied by pain. Cessation of the overuse activity and time often resolves the problem. At times medications and exercises along with other home remedies may be required.

2- Infection Most often associated with problematic erupting wisdom teeth, infections in the jawbones can lead to extreme limitations of jaw motion. Infections can cause limited jaw motion as a result of their impact on muscle function and their association with inflammation and pain. Infections associated with salivary glands can also lead to restricted jaw motion. Jaw and/or intramural swelling is often seen as a result of these infection problems.

3- Dental/Surgical Treatment? Although the vast majority of all dental/surgical treatments proceed without concern, problems at times occur. One such problem is limited jaw motion that can be short-lived or persistent.

• Post-Injection Trismus: Following a lower jaw nerve block used routinely to make lower teeth numb, limited jaw opening may occur 72-96 hours after the injection took place. The limited jaw opening usually occurs in situations where multiple injections were given before the patient felt numb. The end result is a delayed onset of limited jaw opening due to muscle trauma, inflammation and sometimes infection. These problems can linger 3-8 weeks. Supportive antibiotics and anti- inflammatory medications are often used along with gentle jaw stretching. Though very upsetting to the patient, these problems always resolve, but slowly.
• Sprains and Traumas to the TM Joints:?At times when the jaw is kept open for extended periods of time, injuries can occur to the jaw muscles, TMJs and associated ligaments. Inflammation can occur leading to pain and limited jaw motion for several days. At other times the integrity of the TM joints can be upset, leading to restricted jaw motion as the shock absorbing disc slips out of place limiting motion. These are more complex problems and need expert evaluation and treatment. Many of these problems do not get better by themselves.

It is important to understand that these types of joint injuries occur most commonly unrelated to dental/surgical treatment. The origin can be due to an athletic or motor vehicle trauma or the result of long-standing small injuries associated with night clenching and grinding of the teeth, daytime overuse behaviors that strain the joint ligaments or medical conditions that predispose to?inflammation and unstable joint ligaments. When the TM joint ligaments are unstable, the shock absorbing disc and slip out of place leading to decreased jaw motion.

4- Changes in Bone Shape and Size There are a number of benign problems that lead to an increase in the size and shape of bones that can influence jaw motion.

• Coronoid Hyperplasia: A painless, progressive limitation in jaw motion that occurs as a result of the elongation of the coronoid process. When this occurs, a bony obstruction develops, limiting the motion of the lower jaw. Imaging is required to confirm this diagnosis and surgery required to restore motion. The origins of this problem may be traumatic or a result of abnormal tension of the temporal muscle.
• Osteoma of the Mandibular Condyle: A slow-growing and painless neoplasm of bone. The enlargement that occurs leads to reduced jaw opening.
• Bone Ankylosis: Fusion of bones caused by increased calcifications after trauma or infection.

As you can see the origins of limited jaw motion are multiple. Some situations are easy to diagnose, while others are very challenging. The history or medical status of the patient often provides clues for making an accurate diagnosis.