The purpose of this study was to evaluate the action of
hydroxyapatite (HA) (
Osteogen HA Resorb, GBD Marketing Group Inc., Valley Stream, N.Y.) on the dental pulp of rats. Four upper molar pulps in 45 rats were exposed and capped with synthetic HA (
Osteogen) with a stereoscopic microscope. Pulps capped with
calcium hydroxide (
Dycal, L.D. Caulk Co., Milford, Del.) served as controls. The cavities were filled with amalgam, and the molars on each side of the maxilla were protected by the placement of a pedodontic steel crown. Pulp
inflammation and dentin repair were compared by histologic observations and computer image analysis after 7, 14, and 28 days. After 7 days a partial acute
pulpitis were observed in specimens treated with
Osteogen or
Dycal. Reparative dentin formation along the pulp walls was also seen. After 14 days the
pulpitis was more extensive in the
Osteogen-treated teeth than in the control teeth. Dentin formation as measured by morphometric analysis was more pronounced in
Osteogen-treated teeth. Neo-odontoblasts were observed after the use of both materials. After 28 days an acute inflammatory reaction was still evident in the
Osteogen-treated group. A complete dentinal bridge was observed more frequently with
Dycal than with
Osteogen. Despite the putative abilities of HA to be osteoconductive, osteogenic, and dentinogenic, the results of this study indicate that it should not be used as a
pulp-capping agent because of its tendency to cause scattered dystrophic calcification in the dental pulp, which could interfere with future endodontic treatment.