Effect of Jaw Exercise on Mouth Opening and Trismus in Head and Neck Cancer Patients Undergoing Radiotherapy: A Randomised Controlled Trial

Background/Objectives: We aimed to assess the efficacy of a simple intervention by comparing changes in mouth opening and trismus status among HNC patients during radiotherapy treatment. It also explored its effect on the patient’s mandibular function impairment. Methods: This is a Randomised Controlled Trial in which subjects were divided into groups undergoing jaw exercise with a wooden tongue depressor versus a basic jaw exercise group. The primary outcome of this study was changes in maximal mouth opening (MMO)/maximal interincisal distance (MID) measured at baseline (before treatment), at the 10th and 20th week after initiation of radiotherapy. The secondary outcome included trismus prevalence and mandibular functionality, which were assessed in relation to trismus severity and the effectiveness of the intervention. Results: A total of 38 subjects were recruited, comprising 19 (50.0%) in the control group and 19 (50.0%) in the intervention group. There were 22 (57.9%) males and 16 (42.1%) females. Overall, the mean age of the patients was 52.5 years (22 to 74 years). Our clinical assessment showed no statistically significant differences (p = 0.835) in mouth opening among the groups, with an overall median of 0mm (IQR 7.0). Conclusions: Mouth opening did not worsen from baseline to 20 weeks after initiation of radiotherapy, and the addition of wooden tongue depressors did not confer a statistically significant benefit over basic jaw exercise alone. Trial Registration: ISRCTN96737564, registered on 26 August 2026, retrospectively registered.