Lock jaw, medically known as trismus, is a condition characterized by the reduced ability to open the mouth fully. It occurs when the muscles of mastication (chewing) go into spasm or become stiff, restricting movement of the jaw joint. Normal mouth opening typically measures between 35 to 55 millimeters. Trismus is not a disease but a symptom indicating an underlying problem, such as muscle injury, infection, or a joint disorder. Addressing this restriction through immediate relief or professional treatment is the first step toward regaining full jaw function.
Quick Techniques for Immediate Relief
Applying gentle heat helps relax contracted jaw muscles by increasing blood flow. A moist heat pack, such as a warm, damp towel, should be placed on the affected side of the face for 15 to 20 minutes per hour. This warmth temporarily soothes muscle spasms and reduces stiffness.
Adjusting your diet prevents further strain on the jaw joint and muscles. Temporarily switch to soft foods, such as mashed vegetables, yogurt, or soup, that do not require extensive chewing. Avoiding hard, chewy, or tough foods allows the muscles to rest and minimizes irritation.
Over-the-counter non-steroidal anti-inflammatory drugs (NSAIDs), like ibuprofen or aspirin, manage pain and reduce inflammation in the short term. These analgesics are effective for temporary relief in cases of uncomplicated trismus, such as stiffness following a dental procedure. Additionally, gentle massage of the painful muscles around the jaw and temple can help loosen the tissues.
You can attempt gentle, non-painful stretching exercises to maintain mobility, but these must be done with caution. A common technique involves slowly opening the mouth as wide as possible without causing sharp pain and holding the position for ten seconds, repeating this several times. Another exercise is to gently press upward on the lower front teeth with stacked fingers to increase the opening slightly, holding the stretch for about 30 seconds.
Common Reasons for Jaw Restriction
The most frequent cause of jaw restriction is an issue with the temporomandibular joint (TMJ) or the surrounding muscles, known as temporomandibular disorders (TMD). This can involve joint inflammation or displacement of the cartilage disc, which mechanically blocks the jaw from opening fully. Muscle spasms in the masseter and temporalis muscles, often caused by stress, teeth grinding (bruxism), or clenching, are also common contributors.
Trismus often develops following dental procedures, particularly wisdom teeth extraction, due to trauma or inflammation near the injection site or joint. Keeping the mouth open for a long period during the procedure can also strain the muscles and lead to post-operative stiffness. Infections within the mouth, such as an untreated dental abscess or pericoronitis, cause swelling that spreads to the jaw muscles, triggering a protective spasm.
Trauma to the jaw from an accident or injury can lead to fractures or internal bleeding near the joint. Head and neck cancer treatments, especially radiation therapy, can lead to scar tissue formation (fibrosis) in the muscles, resulting in chronic and severe trismus. In rare instances, trismus can be an early symptom of tetanus, a severe bacterial infection that causes widespread muscle spasms.
Definitive Treatments from Medical Professionals
A medical professional will first determine the underlying cause of the trismus to formulate a long-term treatment plan. If an infection is suspected, antibiotics will be prescribed to resolve the source of inflammation and muscle irritation. For muscle-related pain, prescription-strength NSAIDs or muscle relaxants, such as benzodiazepines, may be used to quickly reduce spasms and improve mouth opening.
Physical therapy is a cornerstone of definitive treatment for chronic trismus and involves specialized exercises to restore jaw mobility. A physical therapist will prescribe a regimen of stretching and range-of-motion exercises, often utilizing manual therapy to gently increase movement. They may also recommend jaw-stretching devices, which fit between the upper and lower jaws and apply controlled force to gradually increase the opening.
For trismus related to TMD or chronic teeth clenching, a custom-fitted oral splint or night guard may be recommended. These appliances stabilize the jaw joint, prevent grinding, and alleviate strain on the masticatory muscles during sleep. In cases where muscle tension is severe and unresponsive to conservative methods, an oral surgeon may suggest localized injections of botulinum toxin (Botox) to temporarily relax the overactive muscles.
Surgical intervention is reserved for severe, chronic trismus that results from structural problems, such as advanced TMJ damage or significant scar tissue following radiation treatment. Procedures can range from removing scar tissue to reconstructing damaged joint components to allow for a greater range of motion. Restoring the jaw’s function to a normal range is important for maintaining proper nutrition and oral hygiene.
Warning Signs Requiring Emergency Attention
While many cases of trismus are temporary and managed with conservative care, certain symptoms indicate a medical emergency requiring immediate professional evaluation. The inability to swallow liquids or solids, or sudden difficulty breathing, suggests swelling or spasm is obstructing the throat and airway. This situation necessitates immediate medical intervention to ensure the airway remains open.
A high fever accompanying jaw stiffness is a significant warning sign, pointing to a serious, spreading infection, such as a deep abscess. Rapidly increasing facial or neck swelling also signals a potentially life-threatening progression of an underlying infection. Any severe, sudden-onset pain that is unresponsive to typical over-the-counter pain relievers and prevents sleep should prompt an urgent consultation.
Seek immediate care if trismus develops following any recent deep puncture wound. Although rare due to vaccination, this combination of symptoms could indicate tetanus, which requires prompt hospital treatment. Ignoring these acute signs can lead to severe complications, including systemic infection or permanent jaw dysfunction.