Two studies (1981-1990 retrospective, and 1989-1993 prospective) were performed to determine the optimal methods in preprosthetic surgery. The first study deals with four different types of grafts (split-thickness skin, mucosal, mesh mucosal, palatal) in combination with vestibuloplasties and lowering of the floor of the mouth. The parameters, vestibular depth, mobility and resilience of the transplants were examined. Keratinized grafts (split-thickness skin and palatal) showed advantages. On the basis of a high rate of complications at the site of harvesting of palatal mucosa and the limited amount of palatal mucosa available for grafting, we prefer a split-thickness skin graft. A second prospective study to compare the Edlan- and Kazanjian-plasty showed the disadvantages of both methods. The Edlan-plasty, in combination with implants, showed a small amount of bone resorption; the Kazanjian-plasty showed a significant loss of attached mucosa. Both methods were therefore abandoned in our clinic. For cases with insufficient width of attached mucosa, we recommend a vestibuloplasty secondarily, with keratinized grafts. If there is a deep palatal vault and the need for a large amount of graft material, a split-thickness skin graft should be harvested. In cases of limited need and flat palatal vault, the graft can be harvested from the palate.