Trismus, a restricted mouth opening, is a well known complication following treatment of head and neck cancer. Many different methods to treat trismus have been proposed, exercise therapy with a TheraBite ^® seems to be superior to other therapies.

This study aims to analyze factors influencing the effects of TheraBite ^® -exercises on change in mouth opening in 69 head and neck cancer patients in a historical cohort.

Included were patients with trismus, treated between 2004 and 2011 for head and neck cancer in the University Medical Centers of Nijmegen and Groningen, the Netherlands. Mouth opening was assessed before TheraBite ^® -exercises and during last follow-up appointment.

Patient, tumor, and treatment characteristics were analyzed for their relationship with change in mouth opening. Variables univariately associated with change in mouth opening ( p ≤ 0.05) were entered in the multivariate linear regression analysis as independent variables.

Mean initial mouth opening was 22.0 mm (sd 6.4), mean increase in mouth opening 5.4 mm (sd 5.7). Variables significantly associated with change in mouth opening were: ‘chemotherapy’, ‘medical center’, and ‘interval between last oncological treatment and start TheraBite ^® -exercises’. Interval was dichotomized in early start (≤3 months) and late start (>3 months). In the regression analysis, the dichotomized variable ‘interval’ was the only variable that predicted change in mouth opening (explained variance: R ² = 0.24). Mouth opening increased averagely with 7.9 mm if TheraBite ^® -exercises were started early, and 2.4 mm if started late.

In conclusion, in order to have larger effects of TheraBite ^® exercise therapy, exercising should be started within 3 months after oncological treatment.

Conflict of interest: None declared.