Some head and neck cancer survivors develop velopharyngeal dysfunction (VPD), a problem with closure between the soft palate and throat that can cause nasal-sounding speech, food or liquid leaking into the nose, difficulty swallowing, and reduced quality of life. This study aims to better understand VPD in this population and to evaluate whether pharyngeal wall augmentation (plumping up the back wall of the throat) can improve speech and swallowing. Participants will undergo a multidisciplinary assessment including physical examination, flexible nasolaryngoscopy, speech recording and acoustic analysis, nasometry, clinical swallowing evaluation, and fiberoptic endoscopic evaluation of swallowing (FEES). Aim 1: Determine the prevalence, severity, and functional impact of VPD in head and neck cancer survivors. Aim 2: Assess the feasibility and usefulness of advanced diagnostic tools for VPD. The investigators hypothesize that high nasalance scores (\>1 SD above normal) will accurately predict VPD with at least 75% positive predictive value and will correlate with worse communication-related quality of life (CPIB). The investigators also hypothesize that participants with VPD will have more pharyngeal residue or nasal regurgitation on FEES, and that these findings will be associated with lower swallowing-related quality of life (SWAL-QOL). Aim 3: Evaluate the effectiveness of pharyngeal wall augmentation injections for improving speech intelligibility and swallowing function. The investigators expect that this treatment will lead to measurable changes in both objective assessments and patient-reported outcomes. The results will help improve diagnosis and management of VPD in head and neck cancer survivors.