Ultrasound of the masseteric muscle to evaluate the thickness and rigidity of the masseteric muscle before and after oral cancer treatment. There will be no invasive investigation of the muscle.

A first endpoint would be to compare the effect of the epidemiological and surgical variables on the maximal mouth opening in millimeters over time.

This research group would like to obtain a detailed image of the impact of trismus and oral cancer resections in general on the quality of life. Results will be based on validated and commonly used questionnaires addressing the different aspects of quality of life for this specific population. More specific the Washington questionnaire.

Investigation of the relation between the muscles of mastication and the tumour and how this correlation influences the incidence of postsurgical trismus. Therefore, the distance between the tumor and the muscles of mastication will be evaluated in millimeters, based on 3D preoperative radiological imaging (CT or MRI).

The final endpoint will be the evaluation of masseter alterations on ultrasound, which will lead to an improved understanding of muscular changes due to oncological resections, radiotherapy, and trismus. Even though newer (IMRT or intensity-modulated radiation therapy) techniques in radiotherapy protect vital structures as much as possible, the masseter is still often involved in the radiated area and muscular alterations are anyhow to be expected. The endpoints will be alterations in masseter muscle thickness (millimeter) in all oral oncology cases, trismus patients secondary to oral oncology resections, and in adjuvant radiotherapy cases.