Failure of a hydroxyapatite-coated endosteal dental implant: a clinical report

Spectroscopic analyses on sonocatalytic damage to bovine serum albumin (BSA) induced by ZnO/hydroxylapatite (ZnO/HA) composite under ultrasonic irradiation

ZnO/hydroxylapatite (ZnO/HA) composite with HA molar content of 6.0% was prepared by the method of precipitation and heat-treated at 500°C for 40min and was characterized by powder X-ray diffraction (XRD). The sonocatalytic activities of ZnO/HA composite was carried out through the damage of bovine serum albumin (BSA) in aqueous solution. Furthermore, the effects of several factors on the damage of BSA molecules were evaluated by means of UV-vis and fluorescence spectra. Experimental results indicated that the damage degree of BSA aggravated with the increase of ultrasonic irradiation time, irradiation power and ZnO/HA addition amount, but weakened with the increase of solution acidity and ionic strength. In addition, the damage site to BSA was also studied by synchronous fluorescence technology and the damage site was mainly at tryptophan (Trp) residue. This paper provides a valuable reference for driving sonocatalytic method to treat tumor in clinic application.

Survival of hydroxyapatite-coated implants: a meta-analytic review

PURPOSE

Some reports show a benefit of coating dental implants with hydroxyapatite (HA), and others assert that resorption of the HA coating compromises long-term implant survival. This study examined this controversy by systematically reviewing all the current literature that reports the outcomes of HA-coated implants in human clinical trials.

MATERIALS AND METHODS

A systematic Medline computer search of the English literature yielded 45 human clinical trials that reported on the outcome of HA-coated implants. Eleven studies that met specific inclusion criteria were selected for detailed analysis. The studies were divided into 2 groups. One group of 5 studies reported implant survival using overall percentage, and another group of 6 studies reported implant survival using life-table analysis.

RESULTS

The overall percentage survival rates ranged from 93.2% to 98.5%, with 4 to 8 years of follow-up. The cumulative survival rates for studies that used life-table analysis ranged from 79.2% to 98.5%, with 5 to 8 years of follow-up. The yearly interval survival rates reported for the studies using life-tables were variable but remained above 90% and did not show a progressive or precipitous decrease with increasing years of follow-up.

CONCLUSIONS

The survival rates reported for HA-coated implants were similar to the survival rates reported for uncoated titanium implants. If resorption of the HA coating causes late failure of implants, the yearly interval survival rates should have decreased with increased years of follow-up. This decrease was not observed in the longitudinal human clinical trials that met the selection criteria for this study. Detailed analysis of these clinical trials did not show that HA-coating compromises the long-term survival of dental implants.

Diverse mechanisms of osteoblast spreading on hydroxyapatite and titanium

Hydroxyapatite (HA) is an osteoconductive implant material. We previously demonstrated that RGD peptides regulate the spreading of HOS cells on HA but not on titanium, speculating that the osteoconductivity of HA might be attributed to this RGD domain-dependent spreading of osteoblasts. To confirm this hypothesis, the molecules which regulate the spreading of HOS cells on HA and on titanium were investigated. The 50% effective dose (ED50) of RGD peptide for the spreading on HA was five fold lower comparing to titanium. Anti-alphaV integrin antibody, vitronectin, and fibronectin inhibited the spreading on HA but not on titanium. In Western blot analysis, vitronectin and fibronectin were found in components adsorbed to HA but not to titanium. Taken together, the spreading of HOS cells on HA but not on titanium requires the interaction of alphaV integrin and its ligands. The ED50 of the RGD peptides on titanium but not on HA was remarkably reduced by neuraminidase treatment, that by itself could not inhibit the spreading on both materials. This phenomenon suggests that RGD domain and sialic acid cooperatively but not independently mediate the spreading of HOS cells on titanium. Collectively, the molecules regulating the spreading on HA are apparently different from those on titanium. The spreading of osteoblasts mediated by RGD domain of vitronectin and fibronectin might contribute to the osteoconductive ability of HA.

In vivo dissolution behavior of various RF magnetron sputtered Ca-P coatings

Radiofrequency magnetron sputter deposition was used to deposit Ca-P sputter coatings on titanium discs, and these coatings were implanted subcutaneously into the backs of rabbits. Half of the as-sputtered coatings were subjected to additional heat treatment for 2 h at 500 degrees C. X-ray diffraction (XRD) demonstrated that annealing at 500 degrees C changed the amorphous sputtered coating into an amorphous-crystalline apatite structure. Scanning electron microscopic (SEM) examination of the sputtered coatings showed excellent coverage of the substrate surface. Annealing of the 4-microm-thick coatings resulted in the appearance of small cracks. SEM demonstrated that until 4 weeks of implantation, all heat-treated coatings were present and all amorphous coatings were completely or mostly dissolved. Fourier transform infrared spectroscopy showed the formation of carbonate apatite (CO3-AP) on these specimens. Furthermore, XRD analysis showed that these CO3-AP precipitated coatings disappeared after 8 weeks of implantation. On the other hand, SEM inspection of these specimens revealed that the 4-microm heat-treated coating was still partially maintained and that small Ca-P crystals were present on the titanium substrate. On the basis of these results, we conclude that apparently 0.1 microm heat-treated Ca-P sputter coating is of sufficient thicknesses to stimulate carbonate apatite deposition under in vivo conditions.

RGD peptides regulate the specific adhesion scheme of osteoblasts to hydroxyapatite but not to titanium

Hydroxyapatite (HA) is a bioactive dental implant material which accelerates bone formation on its surface. The mechanism of this acceleration is not clear. The elucidation of the cell adhesion might be the key to the understanding of the bioactive mechanism of HA. In this study, we analyzed the adhesion of HOS human osteoblasts onto HA and titanium to find the particular adhesion to HA. In short-term cultures in fetal bovine serum-pre-coated materials, a significantly higher number of cells adhered to HA than to titanium. In addition, serum-free conditions with phosphate-buffered saline pre-coating or bovine serum albumin pre-coating materials were tested. The results were nearly the same among all pre-coating conditions, suggesting that the quantity of cell adhesion was not affected by serum components. However, in the morphological observations by SEM, the form of adhesion was found to differ among pre-coating conditions. The osteoblasts tightly adhered and spread onto both HA and titanium with serum pre-coating, whereas the cells loosely adhered and did not spread without serum. To evaluate the Arg-Gly-Asp (RGD) sequence-specific adhesion, we used synthetic RGD peptides for a competitive inhibition test. The results showed that RGD peptides remarkably inhibited the tight adhesion and spreading of osteoblasts onto HA, whereas they did not strongly inhibit adhesion and spreading onto titanium. These results demonstrate that the regulation of cell adhesion to HA is different from that to titanium. Our study suggests that the RGD-containing serum proteins might have a major role in regulating the specific adhesion of osteoblasts to HA, and in inducing enhanced cell growth and differentiation.