The prevalence of trismus increases with increasing doses of radiation, and levels in excess of 60 Gy are more likely to cause trismus. Patients who have been previously irradiated and who are being treated for a recurrence appear to be at higher risk of trismus than those who are receiving their first treatment.[32,33] This suggests that the effects of radiation are cumulative, even over many years. Radiation-induced trismus may begin toward the end of radiation therapy or at any time during the subsequent 24 months. Limitations in opening the mouth often increase slowly over several weeks or months. The condition may worsen over time or remain the same, or the symptoms may reduce over time, even in the absence of treatment.
Limited mouth opening frequently results in reduced nutritional status. These patients may experience significant weight loss and nutritional deficits. It is generally accepted that weight loss of more than 10% of initial body weight is considered significant. This is of particular importance at a time when the patient is recovering from surgery, chemotherapy, and/or radiation therapy. Additionally, it lowers the ability for social eating and thereby increases the risk of social isolation and decrease in quality of life in patients with HNC.
Finally, limited mouth opening can result in compromised oral hygiene. Patients who have undergone radiation therapy involving the salivary glands must maintain excellent oral hygiene to prevent dental caries. Deficits in oral hygiene can aggravate mucosal and dental problems, with the subsequent risk of mandibular ORN. Also, dental work and other professional oral care measures such as surgery can be made more difficult, which might even result in compromised oncologic follow-up.
The weighted prevalence of trismus with conventional radiation is estimated to be 25%, but 5% with IMRT only. Trismus prevalence in studies of chemoradiation is approximately 30%.
Early treatment of trismus has the potential to prevent or minimize many of the consequences of this condition. If the clinical 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 and likely irreversible, the need for treatment becomes more urgent.
Over the years, clinicians have attempted to prevent or treat trismus with a wide array of appliances. These devices include the following:
- Cages that fit over the head.
- Heavy springs that fit between the teeth.
- Screws that are placed between the central incisors.
- Hydraulic bulbs placed between the teeth.
These devices range widely in cost. Some devices, such as continuous passive motion devices, must be custom made for each patient; others 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, which has been used for many years to mobilize the jaw. A search of the literature, however, failed to reveal any studies that demonstrated significant improvement in treating trismus with tongue depressors.