Abstract Purpose Prior to radiotherapy combined with chemotherapy (CRT) or biotherapy (BRT) for oropharyngeal squamous cell carcinoma (OPSCC), teeth with poor prognosis that pose a risk for post-RT osteoradionecrosis (ORN) are removed. The effect of tooth loss on body weight loss and tube feeding (TF) dependency during CRT/BRT is unknown. This study aimed to evaluate the effect of incomplete dentition, tooth extractions prior to CRT/BRT, and the subsequent loss of functional units on (1) weight loss during CRT/BRT and (2) the need for TF during CRT/BRT for OPSCC. Methods OPSCC patients treated with CRT/BRT between 2013 and 2016 were included in this retrospective cohort study. Dental status was determined during the dental assessment at first visit and after tooth extractions prior to the start of CRT/BRT. Weight loss during CRT/BRT was scored dichotomously, comparing weight loss > 5% to stable or increased weight. Potential factors associated with weight loss were identified, including patient, tumor, and treatment characteristics. Results Seventy-seven OPSCC patients were included. Forty patients (52%) experienced weight loss > 5% during CRT/BRT. Extractions were performed in 66% of the OPSCC patients. The mean number of extracted teeth was 4.1 ± 5.6 per patient. Tooth extractions prior to CRT/BRT were associated with weight loss > 5% during CRT/BRT (HR 1.130 (95% CI 1.011–1.262), p = 0.031). None of the dental status-related parameters showed any significant associative value for TF during CRT/BRT. Conclusions Pre-CRT/BRT tooth extractions intended to reduce the risk of ORN, are a risk factor for weight loss during CRT/BRT for OPSCC. Trial registration number This study was approved by the medical ethics committee of the MUMC + (METC 2020–1589) on July 28, 2020.