Nano-particles of pure single phase calcium aluminate (CA) were prepared via solid state reaction at high temperature. An ultra-pure nano-size hydroxyapatite (HA) prepared by sol-gel method was used to formulate a composite of 1:1 CA: HA. Setting times, micro-hardness, bulk density, calcium ion and phosphorus ion concentration, XRD, FTIR and scanning electron microscopy (SEM) were investigated. The results showed that the substitution of 50% by weight of pure calcium aluminate cement (CA) by nano-size hydroxyapatite (HA) has a retardation effect on setting process. The use of artificial saliva solution as hydration medium enhances the hydration process of both synthesized calcium aluminate based materials due to the formation of more hydrated compounds. Curing of calcium aluminate cement in hot and humid conditions, resulting in hardness loss and high porosity due to the conversion process, in which the compounds CAH 10 and C 2 AH 8 (hexagonal crystals) are converted into the more stable compound C 3 AH 6 (cubic crystals). The SEM studies indicated that the presence of nano-particles of hydroxyapatite in CA/ HA composite facilitated the precipitation of hydroxyapatite-like active layer, suggesting that pure CA cement has some distinctive physico-mechanical properties make it suitable for use as root end filling materials in dental applications.

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Nano particles made of pure single phase Mineral trioxide [tricalcium silicate (C 3 S)] and Tetracalcium phosphate (TTCP) bio ceramics were prepared via solid state reaction at high temperature. Setting times, compressive strength, pH, XRD, FTIR and scanning electron microscopy (SEM) were investigated. Cytotoxicity and antibacterial activity of both C 3 S and TTCP to human gingival fibroblasts were studied. Both C 3 S and TTCP compounds undergo hydration reaction when mixed with distilled water. A delayed setting time and very poor mechanical properties for TTCP were detected compared to those of C 3 S phase. The nano-structure C 3 S bio ceramic was found to be completely safe to BHK cells compared with TTCP. The prepared C 3 S and TTCP pastes were applied to the demineralized dentin specimens for seven days. The ultramorphology of dentin revealed that both C 3 S and TTCP are successful in dentinal tubules occlusion, thus they are beneficial for dental application in the treatment of teeth hypersensitivity.

Composites of nano-calcium aluminate 'CA' biocement, synthesized by a solid state reaction, were prepared with 5, 10 and 20 wt.% of nano-SiO 2 particles. The influence of nano-SiO 2 particle additions on the physico-mechanical properties and hydration characteristics of CA biocement was studied. Calcium ion concentrations and, pH values of the curing medium were measured. The hydration characteristics of pure and composite CA phase were studied by determining the X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). Evaluation of cytotoxicity against the skin normal human cell line BJ-1 was carried out. The results showed that the bulk density and micro-hardness of the composite CA containing 10 wt.% of nano-SiO 2 were better than those of pure CA and composite prepared with higher weight percentages of nano-SiO 2 . Both pure and composite CA bio-cements showed no cytotoxicity, making these materials suitable for medical applications.

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The influence of using simulated body fluid (SBF) as a curing medium on some characteristics of pure single tri-calcium silicate (C 3 S) bio-cement was investigated. CaCl 2 salt solution was used as an accelerating liquid for setting and hardening of C 3 S pastes in comparison with distilled water (DW). Solid state reaction was applied to synthesis C 3 S phase at elevated temperature followed by rapid cooling. The results showed that 10 wt.% CaCl 2 solution was the optimum concentration that showed the lowest setting time (106 min). C 3 S pastes prepared with CaCl 2 solution have better physical and mechanical properties than those mixed with DW even after curing under SBF solution for the different curing ages. However, SBF solution has an adverse effect on the hydrated compound C-S-H that results in a little decrease in strength and hardness values. The elemental analysis emphasized the presence of apatite layer on the surface of the hardened C 3 S paste. Scanning electron microscopy (SEM) photomicrographs and elemental analysis revealed reliable adaptation of the experimentally prepared C 3 S paste to the tooth structure, in addition to its bioactivity makes it a consistent material to be used as dentin substitute.

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