The kinetics of mineralization and demineralization of biologically relevant calcium phosphates.

摘要

Calcium phosphate phases such as hydroxyapatite (HAP) are utilized in many dental and orthopaedic applications such as implant coatings and bone substitutes (BS). Although for many years it has been considered that HAP is the model calcium phosphate system for the study of biological minerals such as bone and teeth, it is now recognized that a calcium deficient carbonated apatite (CAP) may be a better model. The following work was performed in an effort to better understand the mineralization and demineralization behavior of implants and BS in vitro.; The dissolution kinetics of plasma sprayed (PS) and pulsed laser deposited (PLD) calcium phosphate coated implants was investigated. Surface impurities consisting of calcium containing phases in the PS coatings led to a wide range of dissolution rates from sample to sample, even though conventional physical analytical methods of characterization (e.g. X-ray Diffraction and FTIR) indicated the exclusive presence of HAP. PLD implants proved to have much less impurities in their coatings, in addition to having dissolution rates 1-2 orders of magnitude lower.; The mineralization kinetics of various titanium surfaces was also studied. Under the conditions utilized, no mineralization on uncoated titanium surfaces occurred unless the protein human serum albumin was present in solution. The protein that binds to the surface of an implant may be the initial event that occurs when a calcium phosphate has nucleated onto the implant surface. The mineral phase nucleated onto these surfaces was either OCP-like or ACP-like, rather than HAP-like.; Mineralization and demineralization kinetics of bone substitutes were examined. Depending upon the pore size, some of the bone substitutes tested (e.g. Endobon and Cancellous Bio-Oss) tended to disintegrate into smaller granules, indicating that they may not withstand enough load after biological implantation. The rate of mineralization of carbonated apatite, which is the calcium phosphate phase said to most resemble bone, was approximately 3 orders of magnitude faster than Cortical Bio-Oss.