Ultrastructure of durapatite-periodontal tissue interface in human intrabony defects

The ultrastructure of the interface between Durapatite (hydroxylapatite) and human periodontal tissues was examined. Durapatite was implanted into the intrabony periodontal defects during periodontal surgery. Reentry procedures were performed after 1 year and the tissues in the defects were biopsied and processed for transmission electron microscopy. Nineteen tissue blocks from four patients were examined, 17 contained Durapatite particles embedded in fibrous tissue and two contained particles encased in bone, all without inflammation. The fibrous connective tissue consisted of densely packed collagen fibrils surrounding the implant particles. The bone surrounding the Durapatite consisted in one case of relatively mature bone, and in the other of osteoid tissue. A granular, amorphous, collagen-free, electron-dense layer was routinely observed between implant and tissue. This layer was thicker in the bone-encased samples than in those surrounded by fibrous connective tissue. Except for the particle surrounded by mature bone, this layer was continuous with an organic meshwork located on the periphery of the implant spaces. The ultrastructural features of the interface are consistent with the existence of a mucopolysaccharide "bonding zone" described by other investigators. The organic meshwork appears to outline areas similar in size and shape to the individual crystallites of hydroxylapatite. This may indicate that the reactive surface of hydroxylapatite is much larger than merely the exterior surface of the implant, a finding which may explain the apparently good tissue adhesion to the implant.