J de Blieck | PubMed Health

PubMed1997

Degradable bisphosphonate-alkaline phosphatase-complexed hydroxyapatite implants in vitro.

Degradable hydroxyapatite (HA) implants complexed with the resorption inhibiting agent bisphosphonate (PCP) and the mineralizing agent alkaline phosphatase (ALP) can theoretically maintain alveolar bone mass directly after extraction of teeth. The present in vitro study investigated the surface properties of PCP-ALP-complexed HA implants in relation to the requirements of implant behavior and action. Adsorbed PCP (pH 3.49) resulted in a flattening and broadening of the phosphate peaks and the formation of carbonate peaks in the HA pattern of the implant indicating a chemical alteration of the HA surface. Adsorption of ALP onto PCP-altered HA surfaces was 26% lower than onto HA implant blank surfaces. PCP-ALP-complexed HA implants released the PCP and ALP steadily and continuously over observation periods of, respectively, 75 and 14 days. During these observation periods, the ceramic grains of the HA implant became smaller and intergrain boundaries became broader. These morphologic characteristics suggested preconditioning of the HA implant surface for future bonding and degradation in vivo. Individual grains were no longer bonded to other grains and detached from the implant which had become rounded in shape. From in vitro mice experiments we found that PCP concentrations between 10(-4) and 10(-3) M resulted in 45Ca-release from the bone HA. Our calculations showed, however, that only a total concentration of 1.4 x 10(-4) M PCP was gradually released over the whole observation period. In another experiment, it appeared that a PCP concentration in solution < 10(-3) M did not reduce ALP activity. It is concluded that release of PCP by the PCP-ALP-complexed implants is maintained at levels in the range to impair osteoclast bone resorption but not high enough to block osteoblast activity. The amount of ALP released can lead to induction of bone formation onto implant surfaces. pH-induced alterations in the microstructure and chemistry of the HA surface allow for controlled degradation of the HA implants in vitro. A PCP-ALP-complexed HA implant acting as temporary scaffolding for alveolar bone growth enhancement, mineralization, and maintenance seems to be a reasonable concept for preservation of the edentulous alveolus.

Absorption↗

PubMed1996

Dual X-ray absorptiometry for alveolar bone: precision of peri-implant mineral measurements ex vivo.

The precision of measurements of minor mineral changes in alveolar bone mineral content (ABMC) and alveolar bone mineral density (ABMD) on implant surfaces was determined in small regions (0.03 +/- 0.005 cm2) using dual X-ray absorptiometry (DXA). Dog hemimandibles with alveolar processes containing 17 implants were studied ex vivo. The precision was expressed as the coefficient of variation in percent (c.v. %). The ultra-high resolution protocol was applied to the mesial, distal and apical subregions of each implant. The line spacing was 0.0254 cm and the point resolution was 0.0127 cm. The mean c.v. (%) +/- s.d. for the ABMC in the mesial, distal and apical regions were 0.42 +/- 17, 0.47 +/- 0.21 and 0.48 +/- 0.18, respectively. For the ABMD these values were 0.42 +/- 0.16, 0.47 +/- 0.19 and 0.48 +/- 0.16. For each region approximately 68% of the 17 c.v. values were distributed within 1 s.d. from the mean c.v. These results indicate that measurements are highly reproducible (better than 0.48%) and that there are no differences in precision between several peri-implant regions. Changes as small as 0.85% in ABMC and ABMD in small areas adjacent to implant surfaces are measurable with a confidence level of 95%. Therefore the DXA technique will be expedient for our research evaluating the efficacy of the ceramic hydroxyapatite implant releasing agents affecting or inducing alveolar bone- and root cementum-like materials on its surface.

Absorptiometry, Photon↗