A Comprehensive Review of the Pros and Cons of Definitions of Radiation-Induced Trismus

Radiation therapy is the most common cause of cancer-related trismus. Radiation therapy can lead to fibrosis and hypoxia in the temporomandibular joint ligaments, synovial fluid, and masticatory muscles. This makes it difficult for patients to move their jaws and eventually leads to restricted mouth opening. This devastating complication is called radiation-induced trismus, which occurs after radiation therapy in patients with head and neck cancers and affects their daily routine functions such as eating, speaking, chewing, swallowing, and oral hygiene habits, as well as impairs their psychosocial communication and decreases their quality of life. The evaluation in radiation-induced trismus determination is basically performed by measuring the maximum mouth opening. Previous studies evaluating radiation-induced trismus have used many maximum mouth opening cut-off values such as 40 mm, 35 mm, 30 mm, and 20 mm. The fact that no common and valid language is used to establish cut-off values means that the impact and prevalence of this serious complication are not fully revealed. In the absence of a widely accepted maximum mouth opening cutoff value or range for radiation-induced trismus definition that applies to all patients with head and neck cancers, a patient may be labeled as trismus in some studies but non-trismus in others. Preventative and therapeutic treatments may be disregarded in certain patients as a result of such ambiguity, which may cause severe declines in affected patients’ medical, psychological, social, sexual, and financial status. With a focus on the detrimental effects of such competing definitions on patient management, the current review aims to carefully compare and evaluate the pros and cons of each definition of radiation-induced trismus.