BACKGROUND: Trismus indicates severely restricted mouth opening of any 
aetiology. A mouth opening of 35 mm or less should be regarded as trismus. Aim 
of this study was to review the etiopathogenesis, incidence, treatment and 
prevention of trismus in patients with head and neck cancer.
OBJECTIVE OF REVIEW: Trismus is frequently seen in patients suffering from 
malignant tumours of the head and neck. The reported prevalence of trismus in 
those patients varies considerably in the literature and ranges from 0 to 100% 
depending on the tumour site and extension. Trismus may worsen or remain the 
same over time, or the symptoms may reduce, even in the absence of treatment. 
When a patient presents with trismus after tumour treatment, it is important to 
determine whether the trismus is the result of the treatment, or is the first 
sign of a recurrence. Restricted mouth opening may impede inspection of the oral 
cavity as needed for dental care, and particularly for oncologic follow-up.
CONCLUSIONS: Mouth opening after radiotherapy (RT) decreases on average by 
approximately 20% compared to mouth opening prior to RT. The prevalence of 
trismus increases with increasing doses of RT to mastication structures. The use 
of intensity-modulated RT seems to lower the percentage and severity of 
RT-induced trismus. Treatment of trismus can be conservative (with either 
medical or physical therapy) or surgical. Exercise therapy is the mainstay of 
treatment and exercise should start as soon as possible after treatment. The 
prevention of trismus, rather than its treatment, is the most important 
objective.