Properties of calcium phosphate coatings before and after exposure to simulated biological fluid.

The surface qualities of calcium phosphate (CaP) implants are important factors determining the nature and degree of cellular behaviour, especially cellular attachment, proliferation and differentiation. Thus, in this study, the chemical composition and crystallographic properties of radiofrequency sputter-deposited CaP coatings prior to and after in vitro immersion in a physiological solution were characterized. Significant differences in crystallite size were observed with different heat treatments, with coatings heat treated at 850 degrees C (CA8) having larger crystallites compared to coatings heat treated at 700 degrees C (CA7). However, no statistical difference in the Ca/P ratio, carbon concentration and surface energy were observed with different heat treatments. After immersion in a physiological solution, the crystallite size was significantly increased. The crystallite size for the CA8 and CA7 coatings remained statistically different after 1-week immersion in solution. An increase in carbon concentration was also observed for both samples after 1-week immersion in solution. However, no significant differences in the Ca/P ratio and surface energy were indicated between the two coatings after 1-week immersion in solution. In addition, no statistical difference in surface energy was observed for both samples initially and after 1 week.

Cleaning and heat-treatment effects on unalloyed titanium implant surfaces.

This study tested the following hypotheses: (1) acid-cleaned and passivated unalloyed titanium implants have higher surface energies (which are considered desirable for bone implants) than ethanol-cleaned titanium; (2) higher temperatures of heat treatment of unalloyed titanium result in higher surface energies; and (3) these changes can be related to changes in surface composition and roughness. Thus, unalloyed titanium specimens were either acid-cleaned and passivated (CP) or ethanol-cleaned (Et). Each set was then divided into 3 groups and heat-treated for 1 hour at 316 degrees C (600 degrees F), 427 degrees C (800 degrees F), and 538 degrees C (1,000 degrees F), respectively. Surface roughness values for each of these groups were determined using atomic force microscopy, while surface compositions were determined using Auger electron, x-ray photoelectron, and Raman spectroscopic techniques. Surface energies were estimated using a 2-liquid geometric mean technique and correlated with surface roughness, elemental composition, and elemental thickness. The CP surfaces were slightly rougher than the Et specimens, which had greater oxide thickness and hydrocarbon presence. The surface oxides were composed of TiO2, Ti2O3, and possibly titanium peroxide; those heat-treated at 427 degrees C or above were crystalline. The CP specimens had carbonaceous coverage that was of a different composition from that on Et specimens. The CP specimens had significantly higher surface energies, which showed statistically significant correlations with oxide thickness and carbonaceous presence. In conclusion, ethanol cleaning of unalloyed titanium dental implants may not provide optimal surface properties when compared to cleaning with phosphoric acid followed by nitric acid passivation.

Surface characterization of radio-frequency glow discharged and autoclaved titanium surfaces.

To characterize titanium surfaces treated with radio-frequency glow discharge (RFGD) after media exposure, surface chemical analyses were performed using x-ray photoelectron spectroscopy. Auger electron spectroscopy, and Fourier transform infrared-reflection absorption spectroscopy (FTIR-RAS). The RFGD treatments resulted in a cleaner surface as compared to as-sputtered or as-autoclaved titanium specimens. The oxide thickness of RFGD-treated titanium specimens was not statistically different from the as-autoclaved and as-sputter cleaned titanium specimens. Exposure to a phosphate-buffered saline solution revealed a greater deposition of calcium and phosphorous on the RFGD-treated surfaces. Auger electron spectroscopy depth profiles showed that calcium and phosphorous ions diffused into the titanium oxide layer. The calcium and phosphorous deposits were identified as amorphous calcium phosphate compounds using FTIR-RAS. These results suggest that RFGD treatments of titanium enhance calcium and/or phosphate affinity because of an increase in elemental interactions at the surface, thereby resulting in the formation of amorphous calcium phosphate compounds.

Effect of surface topography of titanium on surface chemistry and cellular response.

Surface topography plays a critical role in the interaction of dental implants with adjacent tissues. It has been hypothesized that an increase in surface roughness will result in an increase in calcium and phosphorus deposition after immersion in a simulated physiological solution and will increase protein production and calcium uptake by osteoblast-like cells. With the use of a profilometer, titanium samples ground with 600 grit silicon carbide paper were observed to have an average roughness (Ra) value of 0.28 +/- 0.03 micron, whereas titanium samples polished with 0.3 micron Al2O3 exhibited a Ra value of 0.11 +/- 0.01 micron. X-ray photoelectron spectroscopy analyses indicated the presence of calcium, phosphorus, sodium, and chlorine on both surface conditions after immersion in a protein-free physiologic solution. No significant difference in calcium and phosphorus concentrations were observed between the 600 grit or Al2O3 polished titanium samples after immersion in solution. The Ca/P ratio for both 600 grit and Al2O3 polished titanium was in the range of 0.8 to 1.1 after 12 days in solution. The percent protein retained by the rat bone marrow cell layer on both the Al2O3 polished and 600 grit titanium surfaces increased dramatically during the initial 3 days of the study. The 45Ca assays revealed no significant difference in cellular calcification on Al2O3 polished and 600 grit titanium surfaces. For both the Al2O3 polished and 600 grit surfaces, a sharp increase in 45Ca incorporation was observed after 9 days incubation.

Effect of surface treatment on unalloyed titanium implants: spectroscopic analyses.

Surgical implant finishing and sterilization procedures were investigated to determine surface characteristics of unalloyed titanium (Ti). All specimens initially were cleaned with phosphoric acid and divided into five groups for comparisons of different surface treatments (C = cleaned as above, no further treatment; CP = C and passivated in nitric acid; CPS = CP and dry-heat sterilized; CPSS = CPS and resterilized; CS = C and dry-heat sterilized). Auger (AES), X-ray photoelectron (XPS), and Raman spectroscopic methods were used to examine surface compositions. The surface oxides formed by all treatments primarily were TiO2, with some Ti2O3 and possibly TiO. Significant concentrations of carbonaceous substances also were observed. The cleaning procedure alone resulted in residual phosphorus, primarily as phosphate groups along with some hydrogen phosphates. A higher percentage of physisorbed water appeared to be associated with the phosphorus. Passivation (with HNO3) alone removed phosphorus from the surface; specimens sterilized without prior passivation showed the thickest oxide and phosphorus profiles, suggesting that passivation alters the oxide characteristics either directly by altering the oxide structure or indirectly by removing moieties that alter the oxide. Raman spectroscopy showed no crystalline order in the oxide. Carbon, oxygen, phosphorus, and nitrogen presence were found to correlate with previously determined surface energy.

Osteoblast precursor cell activity on HA surfaces of different treatments.

The clinical success of dental implants is governed by implant surfaces and bone cell responses that promote rapid osseointegration and long-term stability. The specific objective of this study was to investigate osteoblast precursor cell responses to hydroxyapatite (HA) surfaces of different treatments. Since the nature of bone cell responses in vitro is influenced by the properties of HA ceramics, this study was divided into two components: a chemical and crystallographic characterization of the HA ceramics and an in vitro cell culture study. The sintered HA samples were observed to have the highest crystallite size as compared to the as-received HA and calcined HA samples. No differences in the surface roughness and chemical composition were observed among the sintered, calcined, and as-received HA surfaces. In concurrence with the X-ray diffraction, high resolution XPS resolution of Ca 2p also indicated a higher crystallinity on sintered HA samples as compared to the calcined and as-received HA samples. As indicated by increased alkaline phosphatase-specific activity, increased cell-surface and matrix-associated protein, and 1.25 (OH2) vitamin D3-stimulated osteocalcin production, a more differentiated osteoblast-like phenotype was observed on the sintered HA surfaces compared to the as-received HA and calcined HA surfaces. An increased osteoblast-like cell activity on the sintered HA surfaces suggested that the crystallite size of HA surfaces may play an important role in governing cellular response.