There is a great article in ODE magazine about Replacing Pain Killers with Hypnosis. They look specifically at a person having a tooth removed with only hypnosis. They then go on to explain how hypnosis works for people to stay comfortable without medication.
Increasingly, dentists, physicians and surgeons are using hypnosis to replace, or at least reduce, the use of painkillers as well as general and local anesthetics. Hypnosis may not be the method of choice for major operations, but for a growing number of procedures ranging from kidney stone fragmentation to minor surgery to childbirth it has proved an effective alternative to conventional sedatives and analgesics. Hypnosis is real, says psychiatrist David Spiegel, a professor in the Department of Psychiatry and Behavioral Sciences at the Stanford University School of Medicine. It’s no less palpable an analgesic than medication.