The structures in the oral cavity and the oropharynx serve vital functions in mastication, deglutition and articulation of speech. Hence, patients with oral and oropharyngeal tumors often present with complaints of difficulty eating and speaking. While these tumors themselves can create functional deficits, treatment (including surgical resection and radiation with or without chemotherapy) often results in additional functional impairment. The magnitude of these post-treatment functional deficits is related to several factors, including (1–6):

Soft tissue volume loss

. Sensory loss

Motor function loss

. Post-treatment limitations in mobility of the tongue and pharyngeal musculature secondary to scar contracture and fibrosis

Alteration in the volume and viscosity of saliva