Synthesis of Dahllite: the Mineral Phase of Bone

Abstract

Apatites are of substantial interest in medicine since dahllite, an apatite containing 4% to 6% carbonate by weight, is a major constituent in bone, teeth, and some invertebrate skeletons. While apatitic preforms, powders, and cements are currently being considered and used in a number of dental and orthopedic applications, carbonated apatites have been largely overlooked or ignored. Carbonated apatites may be promising in dental and medical applications as bioactive materials due to enhanced dissolution and increased osteoclast mediated resorption. Apatitic solids may be produced by several different processes, and the amount of carbonate that may be incorporated into the solid lattice varies depending upon its processing history. In this study, various formulations were processed as low temperature cementitious reactions of acidic and basic calcium phosphates. Formulations without calcite acquired less than 1 percent carbonate from the curing environment while those containing calcite were found to incorporate more than 3 percent carbonate by weight in the final product. Only the cements with the unique formulations incorporating both a reactive acid and calcite were found to contain greater than 4 percent carbonate by weight in the final product thus qualifying the product as dahllite. The crystallinity of this synthetic dahllite was found to resemble bone mineral more closely than did sintered hydroxyapatite. Calcium phosphates, particularly thermally processed ceramic hydroxyapatites, have found very limited application in orthopedics because of their low fatigue properties relative to bone. Implants constructed of dahllite facilitate bone remodeling thus replacing the implant with living bone and creating an implant/bone composite. Replacement of dahllite implants by living bone may result in a more durable weight-bearing construct.