Remineralization of dentin in vitro

Mineralization and calcium fixation within a porous apatitic ceramic material after implantation in the femur of rabbits

Cylinders (0.8 cm long, 1.0 cm of diameter and with an axial hole), constituted, after firing, of a ceramic mixture of hydroxylapatite (HA) and beta-tricalciumphosphate (beta-TCP) in a 10:1 ratio, were implanted into mid-diaphyseal defects of one femur of 20 rabbits and stabilized with intramedullary rods. The implantation sites were checked radiographically every month, and after 3 months (3 animals) and 6 months (17 animals) the rabbits were sacrificed and the implants with the surrounding tissue were embedded in methylmethacrylate, cut to thick sections and analyzed by scanning electron microscopy (SEM). Porosimetric and x-rays diffraction analyses were carried out before and after implantation of the cylinders, and the state of mineralization at the bone-implant interface was determined by EDAX microprobe analysis. Bony callus formation started at 1 month at the osteotomy sites, as judged by radiography, but after 3 months a not-mineralized zone had still been demonstrated between bone and the implants. At 6 months, 13 implants showed themselves firmly fixed in their implantations beds, while 4 implants were only incorporated at their proximal ends. In bone contact zones, an enrichment of Ca2+ was displayed by microanalytical techniques in the outer zone of the implanted samples which may be explained by an apparent additional phase transformation of HA into TCP, thanks to the change of the Ca/P ratio, that takes place in vivo.

The kinetics of mineralization of human dentin in vitro

The prospect of restoration of damaged dental tissues has recently attracted great interest. An understanding of the remineralization of human dentin in vitro was attempted by using super-saturated calcium phosphate solutions at sustained supersaturation by means of a constant solution composition method. The direct growth of HAP from solutions of low supersaturation on powdered whole human dentin was confirmed. Moreover, it was found that the kinetics were similar to those of the seeded growth at synthetic HAP. A high apparent activation energy pointed to a surface-controlled mechanism.