 This project examines experimental pain and chronic pain in the mouth, specifically the condition called atypical odontalgia AO:atypical toothpain. In 16 patients with AO and 16 healthy persons, capsaicin chili-pepper is applied to the gingiva to cause pain. This pain is evaluated by the participants. In three sessions, 3 different medications are tested for effect on the pain. The medications are fentanyl, S-ketamine and placebo-treatment saline. The aim is to know more about pain mechanisms in AO in order to develop an effective treatment. 