Sintered ceramic, nonresorbable hydroxylapatite (HA) is a calcium phosphate biomaterial widely employed alone for augmentation or maintenance of the mandibular ridge and for filling alveolar bony defects. The small particles used for ridge augmentation or periodontal defects tend to scatter and the larger blocks used for extraction sockets don't fit well. Our recent studies suggest that these problems can be circumvented by composite plaster of Paris/HA implants. In addition to binding the HA particles, the plaster makes the implants easier to shape. Plaster is not only very biocompatible but may actually help prevent infection. It appears to act as a scaffold for incorporation of the HA particles into osseous tissue. In several days the plaster is resorbed but it is replaced at the same rate by infiltrating fibrovascular tissue; plaster definitely promotes the filling of osseous defects initially by connective tissue. This tissue not only maintains the form and integrity of the implant, but its vascular and collagen components promote healing and contribute to subsequent filling of the defects and approximation of the HA particles by new cancellous bone. These composite implants can be preformed on casts prior to surgery or tailored during the surgical procedure. Their use precludes the difficulties encountered when plaster alone is implanted (resorption) or when HA alone is used (particle scatter or nonpenetration of the material by host vascular and connective tissues). By having a resorbable component which permits penetration by fibrovascular tissue and a nonresorbable component which can act as a nidus for new cancellous bone formation, these composite alloplasts act like artificial bone. Their use to support a denture, or for immobilizing teeth and reducing pocket depths in advanced periodontal disease, gives better results than HA alone.