Mouth Opening

Trismus is defined in Taber's Cyclopedic Medical Dictionary as a tonic contraction of the muscles of mastication. In the past, this word was often used to describe the effects of tetanus, also called 'lock-jaw'. More recently, the term 'trismus' has been used to describe any restriction to mouth opening, including restrictions caused by trauma, surgery or radiation. This limitation in the ability to open the mouth can have serious health implications, including reduced nutrition due to impaired mastication, difficulty in speaking, and compromised oral hygiene. In persons who have received radiation to the head and neck, the condition is often observed in conjunction with difficulty in swallowing.

Quality of life

Trismus can dramatically affect quality of life in a variety of ways. Communication is more difficult when one is suffering from trismus. Not only is it difficult to speak with the mouth partly closed, thus impairing articulation, but trismus can decrease the size of the resonating oral cavity and thus diminish vocal quality. Severe trismus makes it difficult or impossible to insert dentures. It may make physical re-examination difficult, if limited mouth opening precludes adequate visualization of the site. Oral hygiene is compromised, chewing and swallowing is more difficult, and there is an increased risk of aspiration

Some causes of trismus

Limited jaw mobility can result from trauma, surgery, radiation treatment, or even TMJ problems. The limitation in opening may be a result of muscle damage, joint damage, rapid growth of connective tissue (i.e. scarring) or a combination of these factors. Limitations caused by factors external to the joint include neoplasms, acute infection, myositis, systemic diseases (lupus, scleroderma, and others) pseudoankylosis, burn injuries or other trauma to the musculature surrounding the joint.

Limitations caused by factors internal to the joint include bony ankylosis (bony in growth within the joint), fibrous ankylosis, arthritis, infections, trauma and (perhaps) micro-trauma that may include brusixm.

Central Nervous System disorders can also cause limitations to mouth opening. Tetanus, lesions that affect the trigeminal nerve and drug toxicity may all be suspects in this condition.

Finally, there are iatrogenic causes, such as third molar extraction (in which the muscles of mastication may be torn, or the joint hyperextended) hematomas secondary to dental injection and late effects of intermaxillary fixation after mandibular fracture or other trauma.

The muscles of mastication (also called the 'elevator muscles') consist of the Temporalis, Masseter, Medial pterygoid and Lateral pterygoid. Each muscle plays an important role in mastication, and when damaged, each can cause limitations in opening. When any muscle is damaged, a pain reflex may be stimulated. This condition, called "muscle guarding" results when muscle fibers engender pain when they are stretched. This pain causes the muscles to contract, resulting in loss or range of motion. This contraction is truly a reflex; it cannot be controlled by the patient. Thus, in treating this condition it is important to recall that rapid motion, or the use of powerful forces may be self-defeating. Rapid motion may create the reflex that causes muscles to contract, thereby making stretching of connective tissue difficult or even impossible. Gentle, passive motion has been shown to be efficacious in treating the condition.

Treatment options

If the examination reveals the presence of limited mouth opening, and diagnosis determines the condition to be trismus, treatment should begin as soon as is practical. As restriction becomes more severe, the need for treatment becomes more urgent. If treatment is delayed, the difficulty in reversing the condition increases.

Over the years, there have been a wide array of apparatus that have attempted to treat limited movement of the jaw. These devices range from a variety of cages that fit over the head, to heavy springs that fit between the teeth, screws that are placed between the central incisors, and hydraulic bulbs placed between the teeth. The most commonly used treatment appears to be tongue depressors. These are stacked, forced and held between the teeth in an attempt to push the mouth open over time.

Devices range widely in cost. Many devices must be custom made for each patient, thus increasing the cost of treatment. Others, such as continuous passive motion devices are rented on a daily or weekly basis, at rates of up to several hundred dollars per week. The least expensive option is the use of tongue depressors. This low-cost alternative has been used for many years to attempt to mobilize the jaw. However, low cost should not be confused with cost effective. In order to be cost effective, a treatment must be effective. A search of the literature failed to reveal any studies that could demonstrate significant improvement in treating trismus with tongue depressors.

A number of studies have demonstrated the efficacy of one particular product; the Therabite Jaw Motion Rehabilitation System. Buchbinder studied a population of patients with radiation-induced trismus. Over a ten-week period, the researchers compared the effectiveness of three different protocols to improve mandibular mobility. At the end of ten weeks, the group using the Therabite System had improved an average of more than 13mm, while the group using tongue depressors improved less than 5mm. A third group, using their fingers to force their mouth open, showed even less improvement.

In another study, researchers at NYU found significant improvement in persons suffering from trismus. This study, which lasted 16 weeks, also found that the use of tongue depressors was not helpful in improving the condition.

One of the benefits of the Therabite System is that it not only stretches the connective tissue that causes trismus, but also allows for proper mobilization of the temporomandibular joint, thus addressing a secondary cause of pain and tightness. This device is generally covered by medical insurance and Medicare, and is well tolerated by the patients. We have found that early use of this device helps to improve mobility of the mandible and also to improve speech and swallowing in a patient population that is at risk of having difficulties with these functions.

Expected Results

A typical patient will gain from 1-4 mm of opening in the first session (about one minute). However, most, if not all, of this gain will be lost within the next two hours. Only by continuing to stretch and mobilize for many sessions per day will any lasting benefit be achieved.

In most studies, patients using the Therabite system gain between 1-1.5mm of sustainable gains per week. Thus, to gain 10 mm of 'permanent gain', a patient may need to exercise from six to ten weeks.

Most patients will continue to need to mobilize and stretch at least once per day for the rest of their lives.

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