An ultrastructural study of the process of hard tissue formation in amputated dental pulp dressed with alpha-tricalcium phosphate

This study was undertaken to determine the reaction of amputated dental pulp to the capping agent, alpha-tricalcium phosphate (alpha TCP), and to reveal the exact nature of the processes involved in both the healing of, and new hard tissue formation in the pulp when dressed with alpha TCP. The dental pulps of the anterior teeth of Macaca fuscata were dressed with alpha TCP ceramic 4-10 microns in diameter. The teeth were fixed by perfusion, then observed with light and electron microscopes. At 10 and 14 days postoperatively, the phagocytosis of the alpha TCP layer by the many macrophages and multinucleated giant cells, both of which had emerged beneath it, was seen. The synthesis of collagenous matrix underlying the alpha TCP layer began at 14 or 21 days, the cells involved exhibiting morphologic characteristics similar to those seen in osteoblasts. By the 90th day, only a bone-like hard tissue remained. No inflammation was observed in the residual dental pulp at any time during the experimental period. At 14 days, needle-like crystals were seen to have formed on the surface of alpha TCP particles, and by the 21st day, these crystals had extended to the newly synthesized matrix, with the result that calcification of the matrix was initiated, a calcified layer being superficially produced in the matrix. In the region of the matrix adjacent to the superficial calcified layer, a number of matrix vesicles were also found to function as another mechanism of matrix mineralization. Thus, it was concluded that the bone-like hard tissue was induced in the pulp capped with alpha TCP, and its potential for clinical application to exposed dental pulp was confirmed.