The purpose of this study is to determine if Hyperbaric Oxygen (HBO) therapy improves salivary gland function in previously head-and-neck irradiated patients. The following will be evaluated: salivary a-amylase, IGF-1, Thrombospondin-1, and VEGF-A concentrations, resting and stimulated salivary flow rate and pH, and salivary buffering capacity. Demographic data, past medical/surgical histories, social history and habits, risk factors, medication list, nutritional status, stage and location of tumor treated, dose/duration of radiation, and time elapsed since radiation treatment will be reviewed and recorded. Subjects will complete a quality of life questionnaire, describe (presence/absence) dry mouth symptoms prior to HBO therapy, and provide current A1c level, or submit to a finger stick. The following groups will be evaluated: 1. Head-and-neck irradiated subjects with ORN (indicating HBO therapy) 2. Subjects with other conditions indicating HBO therapy (positive control), and 3. Head-and-neck irradiated subjects without ORN (negative control). Subjects will include 78 males or females, 18 years old and over. In total, participation will last 22 weeks.