B one defects may result from a variety of causes, including bone loss from open fractures, infections, and tumors. According to Bick [1], the filling of defects with various substances, including animal bone, was, at least, vaguely described in Hindu, Egyptian, and Greek sources. Perhaps one of the earliest descriptions in modern times was that by Jobi Meekren, a Dutch surgeon, who, in 1682, attempted to fill the skull defect of a soldier using fragments of a dog’s skull [2]. (Davison and Smith commented, ‘‘In those early days of superstition when the Church ruled all it surveyed, Jobi Meekren was forced to remove the implanted bone under the ban of excommunication from the Church which refused to recognize such a monumental work and referred to it as ‘an unchristian’ method of treatment.’’) Many others, including Ollier, Duhamel, and Syme experimented with various sorts of grafts to fill defects, but according to Sir Arthur Keith [4], ‘‘The modern practice of bone grafting was invented by Macewen in the Infirmary of Glasgow in 1880.’’ While most authors used autografts (bone from the patients) or allografts (bone from other humans), surgeons attempted to fill defects with other materials quite early on. In 1961, Peltier [5] described his many animal and clinical experiments using plaster of Paris (a hemihydrate of calcium sulfate) to fill bone defects. According to him, several dozen individuals had experimented with this material to fill defects in experimental animals or humans, beginning with Dreesmann in 1892 [3]. Based on his animal experiments, Peltier concluded that plaster of Paris was easily