The aim of this study was to evaluate surface character¬istics and biological properties of the dentin -derived hydroxyapatite (HA) coating on titanium substrate. Dentin-derived HA was obtained from extracted human teeth using a calcination method at 850℃. The commercially pure titanium (cp-Ti, ASTM Grade II) was used as a metallic substrate and a radio frequency magnetron sputtering method was employed as a coating method. Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) were utilized to investigate the coating aspects and composition. Atomic forced microscopy (AFM) and a surface profiler were used to assess the surface morphology and roughness. Corrosion tests were performed in phosphate- buffered saline at a 36.5 ± 1℃ in order to determine the corrosion behavior of the uncoated and coated specimens. The biocompatibility of dentin-derived HA coated specimens with fetal rat calvarial cells and human gingival fibroblasts was assessed by SEM and cell prolif¬eration analysis. The results showed that the dentin-derived HA coatings appeared to cover thinly and homogeneously the surfaces without changing of the titanium substrate. The EDX analysis of this the coating surface indicated the presence of Ca and P elements. The mean surface roughness of cp-Ti and dentin-derived coating specimens was 0.27 µm and, 1.7 µm, respectively. Corrosion tests indicated a stable passive film of the dentin-derived HA coating specimens. SEM observations of fetal rat calvarial cells and human fibroblast cells on coated surfaces showed that the cells proliferated and developed a network of dense interconnections. The cells on all specimens proliferated actively within the culture period, showing good cell viability. At day 1 and 3, dentin-derived coating specimens showed 89% and 93% cell viability, respectively, when normalized to cp-Ti specimens. These results suggest that dentin-derived HA coating using the RF magnetron sputtering method has good surface characteristics and biocompatibility.

In the previous study it was demonstrated that most of sialolith contained bacterial colonies in their center of calcified laminated capsules1). Although it is still not determined whether the bacterial infection is a major pathogenic cause or not, many authors reported that the bacterial vegetation in sialolith can cause chronic suppurative inflammation in salivary gland. Actually a lot of different bacteria were found in oral cavity, most of them are non-pathogenic as normal flora, and only some of them are pathogenic for different mucosal infectious diseases. However, this study was aimed to identify a causative bacterial strain for the sialolith formation in human salivary gland. A strain of Bacillus subtilis (B. subtilis ) was found in the culture of sialolith, which was known to be a normal flora related to the fermentation of various Korean bean foods. In vitro culture experiment of B. subtilis it abundantly produced the thick biofilm aggregated around their cells and colony structure, which were subsequently attached on the surface of hydroxyapatite( HA) beads in scanning electronmicroscope(SEM) observation. The bacterial adherence on HA beads was strongest in the culture of B. subtilis, followed by Streptococcus mutans (Str. mutans ), oral mixed bacteria, and lactobacillus. Therefore, B. subtilis might be an important causative microorganism for the sialolithiasis in Korean people, and it is suggested that postmeal oral hygiene care should be required to reduce the number of normal flora, B. subtilis, after eating of fermented bean foods.

Hydroxyapatite (HAp) powders with different crystallinities were synthesized at various calcination temperatures through the co-precipitation of Ca(OH)2 and H3PO4. The degradation behavior of these HAp powders with different crystallinities was assessed in a simulated body fluid solution (SBF) for 8 weeks. Below 800˚C, the powders were nonstochiometric HAp, and the single HAp phase was successfully synthesized at 800˚C. The degree of crystallinity of the HAp powders increased with an increasing calcination temperature and varied in a range from 39.6% to 92.5%. In the low crystallinity HAp powders, the Ca and P ion concentrations of the SBF solution increased with an increasing soaking time, which indicated that the low crystallinity HAp degraded in the SBF solution. The mass of the HAp powders linearly decreased with respect to the soaking time, and the mass loss was higher at lower crystallinities. The mass loss ranged from 0.8% to 13.2% after 8 weeks. The crystallinity of the HAp powders increased with an increasing soaking time up to 4 weeks and then decreased because of HAp degradation. The pH of the SBF solution did not change much throughout the course of these experiments. These results suggested that the crystallinity of HAp can be used to control the degradation.

Using a polyurethane foam replica method, porous hydroxyapatite scaffolds (PHS) were fabricated using conventional and microwave sintering techniques. The microstructure and material properties of the PHS, such as pore size, grain size, relative density and compressive strength, were investigated at different sintering temperatures and holding times to determine the optimal sintering conditions. There were interconnected pores whose sizes ranged between about 300 μm and 700 μm. At a conventional sintering temperature of 1100˚C, the scaffold had a porous microstructure, which became denser and saw the occurrence of grain growth when the temperature was increased up to 1300˚C. In the case of microwave sintering, even at low sintering temperature and short holding time the microstructure was much denser and had smaller grains. As the holding time of the microwave sintering was increased, higher densification was observed and also the relative density and compressive strength increased. The compressive strength values of PHS were 2.3MPa and 1.8MPa when conventional and microwave sintering was applied at 1300˚C, respectively.

Nano-crystalline hydroxyapatite (HAp) films were formed at the Ti surface by a single-step microarc oxidation (MAO), and HAp-zirconia composite (HZC) films were obtained by subsequent chemical vapor deposition (CVD) of zirconia onto the HAp. Through the CVD process, zero- and one-dimensional zirconia nanostructures having tetragonal crystallinity (t-ZrO2) were uniformly distributed and well incorporated into the HAp crystal matrix to form nanoscale composites. In particular, (t-ZrO2) was synthesized at a very low temperature. The HZC films did not show secondary phases such as tricalcium phosphate (TCP) and tetracalcium phosphate (TTCP) at relatively high temperatures. The most likely mechanism for the formation of the t-ZrO2 and the pure HAp at the low processing temperature was proposed to be the diffusion of Ca2+ ions. The HZC films showed increasing micro-Vickers hardness values with increases in the t-ZrO2 content. The morphological features and phase compositions of the HZC films showed strong dependence on the time and temperature of the CVD process. Furthermore, they showed enhanced cell proliferation compared to the TiO2 and HAp films most likely due to the surface structure change.

It is necessary to improve the esthetic and function in the patient with oral and maxillofacial bone defects. Synthetic bone substitute materials and anorganic bovine bone mineral(ABBM) have been used for clinical restoration. The purpose of this study was to observe the biocompatibility and bone formation of synthetic hydroxyapatite(SHA) and ABBM in hole of rabbit's tibia. After specimens with SHA and ABBM at 8 weeks were fixed in 10% neutral formalin solution, dehydrated, and embedded with spurr low viscosity, they were cut by 500um with slow diamond wheel saw and grinded up to 200um in thickness. These specimens were coated with carbon and examined with r efraction microscope for bone density. Refraction microscopic features of 8 weeks in synthetic HA showed network-like new bone forming trabecular pattern attached to resorbed HA. Less well calcified trabecular bone surrounding conglomerated HAs showed irregular arrangement of numerous osteocytes. There was not completely filled in defected area by new bone trabecular. New trabecular bone formation by ABBM was more prominent and completely compacted in defect hole at 8 weeks. It suggested that although bone formation activity of AMMB might be superior to that on synthetic HA, both group would be the good biocompatibility in this experiment.

Hydroxyapatite (HAp) and biphasic calcium phosphate (BCP) nano powders were synthesized using the microwave-assisted synthesis process dependent on pH and microwave irradiation time. The average size of a powder was less than 100 nm in diameter. Through in-vitro cytotoxicity tests by an extract dilution method, the HAp and BCP nano powders have shown to be cytocompatible for L-929 fibroblast cells, osteoblastlike MG-63 cells and osteoclast-like Raw 264.7 cells. The activation of osteoblast was estimated by alkaline phosphatase (ALP) activity. When the HAp and BCP were treated to MG-63 cells, alkaline phosphatase activities increased on day 3, compared with those of the untreated cells. Also, the collagen fibers increased when the HAp and BCP powders suspension were treated to MG-63 cells, compared to those of the untreated cells. Quantitative alizarin red S mineralization assays showed a trend toward increasing mineralization in osteoblast cultured with powder suspension. In conclusion, hydroxyapatite and biphasic calcium phosphate appeared to be a bone graft substitute material with optimal biocompatibility and could be further applied to clinical use as an artificial bone graft substitute.

In this study, hydroxyapatite (HAp) and hydroxyapatite-yttria stabilized zirconia (HAp-3YSZ) with 20 vol. %– (ZrO2+3 %mol Y2O3) nanopowders were consolidated very rapidly to full density by High-frequency induction heat sintering (HFIHS). Effects of temperature and the addition of 3YSZ on the toughness, hardness and microstructure properties have been studied. 3YSZ second phase toughening HAp composites with higher toughness were successfully developed at relatively low temperatures through this technique. Compared with hardness and toughness obtained for pure HAp, the hardness and toughness for HAp-20vol. % 3YSZ were much higher.

The process of coprecipitation of biocomposite hydroxyapatite/chitosan from aqueous solution at low temperature in alkali environnement was examined. We have shown that initially we have the formation of amorphous octocalcium phosphates and the transferring from OCP to amorphous calcium phosphate , and then from TCP to calcium-deficient hydroxyapatite and hydroxyapatite . The transformation of ACP to HAP was inhibited in the presence of chitosan. The result suggests that there is an affinity binding between ACP and chitosan and subsequently blocking the active growth site of ACP.

In the present study, silver-doped antibacterial hydroxyapatites were successfully prepared by the sol-gel method. For the starting solution, the molar ratio of was set to 0.075:0.045:20:0.135; was added to a ratio of Ag to total cation concentration of . The prepared sol was dried at for 48h and heat-treated at for 2h to obtain particles in the 200-500nm size range. The product from the synthesis of silver-doped hydroxyapatite was investigated through X-ray diffraction experiments and scanning electron microscopy. The product showed high antibacterial properties, with a disinfection ratio of Staphylococcus aureus (ATCC 6538) and Escherichia coli (ATCC 25922) over as calculated from an antimicrobial effects evaluation by the shake flask method.