Key Engineering Materials Vols. 309-311

Abstract: Three-dimensionally ordered materials containing hydroxyapatite (HAp) as well as Bioglass® (BG) have been prepared in form of pellets and have been examined the effects of BG addition -in combination with a heat treatment process- on biological properties of composite HAp/BG. The investigation of the bioactive behavior of sintered and unheated biphasic mixtures and the deviations from pure HAp was performed by FTIR spectroscopy and Differential Thermal Analysis. It was observed the appearance of new phases on sintered composite pellets, while a faster biological HAp layer formation was detected, on the composite unheated pellets’ surface than on pure HAp and sintered composite pellets, currently leading to increased bioactivity.

Abstract: Ceramics of hydroxyapatite (Ca10(PO4)6(OH)2: HA) and β-tricalcium phosphate (β-Ca3(PO4)2: β-TCP), were prepared by spark plasma sintering (SPS) at the temperatures from 800 °C to 1000 °C for 10 min with a heating rate of 25 °C·min-1. The HA ceramics prepared at 900 °C and 1000 °C showed transparency. On the other hands, transparent β-TCP ceramics was obtained by SPS at 1000 °C. In analysis of the densification behavior during sintering of HA and β-TCP by SPS, dominant sintering mechanism was plastic flow in the early stage of densification. Transparent ceramics should be the most suitable materilas to investigate the interface between human cells and ceramics.

Abstract: Amorphous calcium phosphate (ACP) was prepared by a sol-gel method from Ca alkoxide synthesized with Ca metal and ethanol in N2 atmosphere. As-prepared products by sol-gel method were spherical ACP particles of approximately 3 to 10 nm in diameter before heat-treatments. The results from Ca-K edge of as-synthesized ACP showed only one peak around 0.2 nm, suggesting the presence of the first neighbor of Ca in Ca-PO4 cluster.

Abstract: Amorphous calcium carbonate (ACC) occurs with varying stabilities in different organisms. It is thought that the stability is influenced by certain ions and proteins. We describe here a study investigating the particular influence of phosphate ions on the stability of ACC. Synthesised ACC was treated with different concentrations of Na2HPO4 and molar ratios of PO4:Ca ≥ 12:1 were shown to be effective in preventing crystallisation of ACC to calcite. The nature of the resulting sample is discussed.

Abstract: The objective of this study was to evaluate the biocompatibility and effects of the particulated and surface modified Ostrich eggshell (OES) as bone graft substitutes in healing of calvarial defects in rats. Additionally we compared the bone forming ability of the surface modified OES to that of BioCoral (Inoteb, France), which has the same chemical compositions as OES, calcium carbonate (CaCO3). Surface modified OES particles were fabricated by alkaline etching (microroughened-OES) and biomimetic calcium phosphate coating (CaP coated-OES). 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay was performed to evaluate cell viability at 1, 4, and 7days using ROS 17/2.8 cells, a rat osteosarcoma cell line. To evaluate the bone forming ability, surface modified OES and BioCoral were filled in the calvarial defects of fourteen adult male Sprague-Dawley rats. After 4 weeks of healing, animals were sacrificed and evaluated histologically and histomorphometrically. The MTT assay indicated the increases in viable cell numbers of all groups according to the time, and significantly increased cell numbers were observed on CaP coated-OES and BioCoral at 7 day (P<0.01). The histomorphometric results showed that significantly increased amount of new bone formation in the microroughened-OES, CaP coated-OES, and BioCoral grafted defects compared with unfilled defects (P<0.0001). The degree of ossification was most prominent in CaP coated-OES grafted defects. The results of this study suggest that surface modified OES particles are biocompatible and yield favorable bone formation in rat calvarial defects. In conclusion, surface modified OES grafts may be considered as effective osteoconductive grafting materials, but further studies are needed to produce more optimal surface modification and confirm long-term results.

Abstract: This study evaluated periodontal repair and biomaterial reaction following implantation of a calcium carbonate and autogenous bone on the regeneration of 3-wall intrabony defects in the beagle dogs. The surgical control group received a flap operation only, while the experimental group I was treated with a calcium carbonate and the experimental group II was treated with autograft. The subjects were sacrificed 8 weeks after surgery and a comparative histometric analysis was done. No root resorption or ankylosis were observed in the experimental group. ANOVA post Hoc test showed that the experimental group II produced statistically significant higher gain in connective tissue adhesion, new cementum regeneration and new bone formation. These results suggest that the use of autograft in 3-wall intrabony defects has a significant effect on new cementum and new bone formation height.

Abstract: We have directly observed the transformation from octacalcium phosphate (OCP) to hydroxyapatite (HA) in transmission electron microscope (TEM). The phase transformation was induced by electron beam irradiation in TEM. Several TEM techniques were employed to examine the crystal structure change, including bright field images, electron diffraction, high resolution microscopy (HRTEM) and fast Fourier transformation pattern of HRTEM images. The examinations indicate possible hydrolysis reaction in solid state transformation and crystallographic orientation of OCP (010)//HA (010) and OCP (001)//HA (001) which has not been reported previously.

Abstract: Calcium phosphates are widely used in medicine and dentistry. However, synthesis of these substances through precipitation methods still presents problems regarding reproducibility. Alginate is a polymer extracted from brown algae, whose monomers are D-mannuronic and L-guluronic acids, and is suitable for biomedical applications. The aim of this paper is to investigate how the poly-ionic nature of alginate affects phase composition of calcium phosphate obtained through a precipitation method.

Abstract: Effects of pH on the transformation of gypsum to apatite in the presence of ammonium hydrogen phosphate was studied using NH4H2PO4, (NH4)2HPO4 and (NH4)3PO4. When set gypsum was immersed to ammonium hydrogen phosphate, pH of the solution decreased regardless of the solution. Although pH of the solution decreased, no significant compositional change was observed when gypsum was immersed in NH4H2PO4. On the other hand, apatite and small amount of dicalcium phosphate anhydrous (CaHPO4) was formed when gypsum was immersed in (NH4)2HPO4 solution. Only apatite was formed when gypsum was immersed in (NH4)3PO4 solution. Although the detailed mechanism for the pH dependent products has not been clarified, one of the causes may be the different thermodynamical difference between gypsum and apatite. We would like to recommend the use of (NH4)3PO4 solution since this provides higher pH and thus larger thermodynamical difference between apatite and gypsum and resulting pure apatite block.

Abstract: The purpose of this study is to evaluate the effect of paste type calcium sulfate on the epithelial migration, alveolar bone regeneration, cementum formation and gingival connective tissue attachment in intrabony defect in dogs. These results suggest that the use of paste type calcium sulfate in 3-wall intrabony defects has significant effect on new cementum formation , but doesn't have any significant effect on the prevention of junctional epithelium migration and new bone formation. As a result, the paste type calcium sulfate that is used in this study is suggested to be the material that can have a significant effect on the periodontal healing, if its biocompatibility is improved.