Particulate Hydroxylapatite has been used to augment mandibular and maxillary atrophic ridges for over 12,000 patients in the United States. The Hydroxylapatite particles are ultimately held in position by the development of dense fibrous tissue. The results have been most encouraging. The technique suffers from two distinct drawbacks; (1) ridge stability is unpredictable and shearing strength is about a third of normal bone. To overcome the latter difficulty Hydroxylapatite has been combined with autogenous cancellous bone. This has resulted in an in-growth of bone into Hydroxylapatite ridge with satisfactory results. Unfortunately harvesting and autograft increases pain, morbidity, as well as hospital expense. Numerous studies have shown a direct electrical current of 1-30 microamperes are capable of eliciting an osteogenic response. Such an effect has been reported in actively repairing systems such as fresh fractures where it potentiates the osteogenic response associated with the injury stimulus. Electrical stimulation also elicits an osteogenic response in quiescent bone systems and this property forms the basis of its use in clinical orthopedics with the treatment of non-union and pseudoarthrosis. The ability of electricity to stimulate bone growth may be useful to augment Hydroxylapatite treatment of atrophic mandibular and maxillary ridges by fostering bony ingrowth into the Hydroxylapatite. Extraction of posterior mandibular teeth will allow ten weeks later, the creation of a subperiosteal tunnel on the mandibular ridge. This tunnel will be filled with Hydroxylapatite and maintained in position by means of a prefabricated splint. Electrical stimulation by means of an embedded silver wire will commence immediately. Half the animals will receive 30 bouts and half 10 bouts of electrical stimulation. A bout being three hours of continued stimulation at 20 microamperes, negative polarity. The contralateral side of the mandible will act as the control and will be prepared in the identical manner but will not undergo electrical stimulation. Half the animals will be sacrificed at three and six months following augmentation. Bone formation will be identified by oxytetracycline florescence and histological examination will examine cellular detail. Mechaniucal testing will also be utilized to compare the ultimate mechanical strength of the electrically stimulated Hydroxylapatite and the contralateral sham. The mechanical data will be evaluated using a paired t-test.
