A case is presented in which a mucous retention cyst that obliterated the right maxillary sinus caused symptoms due to pressure on two separate branches of the second branch of the fifth cranial nerve during a chamber dive to 112 feet. The symptoms of pain and numbness occurred at different times during and after the dive. Referred pain to the maxillary teeth was due to pressure on the posterior superior alveolar branch and paresthesia with numbness and tingling of the lip and cheek was caused from pressure on the infraorbital nerve prior to its emergence through the infraorbital foramen. The symptoms resolved promptly on recompression treatment. The underlying mechanisms for the production of sinus barotrauma and the causes of tooth and sinus pain are differentiated, and a differential diagnosis of maxillary sinus opacities is schematized.