Silicon compounds are known as bioactive materials that are able to bond to the living bone tissue by inducing an osteogenic response through the stimulation and activation of osteoblasts. To improve the bioactive and mechanical properties of an α-Ca(3)PO(4)-based cement, the effects of the addition of Ca(3 SiO(5) (C(3)S) on physical, chemical, mechanical, and biological properties after soaking in simulated body fluid (SBF) were studied. The morphological and structural changes of the material during immersion were analyzed by X-ray diffraction and scanning electron microscopy. The results showed that it is possible to increase the compressive strength of the cement by adding 5% of C(3)S. Higher C(3)S contents enhance bioactivity and biocompatibility by the formation of a dense and homogeneous hydroxyapatite layer within 7 days; however, compressive strength decreases drastically as a consequence of delayed hydrolysis of α-Ca(3)(PO(4) (2). An increment in setting times and degradation rate of composites containing C(3)S was also observed.

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The addition of tricalcium silicate (C 3 S) to apatite cements results in an increase of bioactivity and improvement in the mechanical properties. However, adding large amounts raises the local pH at early stages, which retards the precipitation of hydroxyapatite and produces a loss of mechanical strength. The introduction of Pozzolanic materials in cement pastes could be an effective way to reduces basicity and enhance their mechanical resistance; thus, the effect of adding silica on the chemical, mechanical and biological properties of a-tricalcium phosphate/C 3 S cement was studied. Adding silica produces a reduction in the early pH and a decrease in setting times; nevertheless, the presence of more calcium silicate hydrate (C-S-H) delays the growth of hydroxyapatite crystals and consequently, reduces early compressive strength. The new formulations show a good bioactivity, but higher cytotoxicity than traditional cements and additions higher than 2.5% of SiO 2 cause a lack of mechanical strength and an elevated degradability.

The effect of the method of sterilization on the physical, chemical and mechanical properties of a new bone repairing material was studied. The material was obtained by thermal hydrolysis of beta-tricalcium phosphate/orthophosphoric acid cement and was composed of calcium deficient hydroxyapatite, octacalcium phosphate (OCP), and beta-tricalcium phosphate. Partial decomposition of the OCP was observed after sterilization for the three methods. Decomposition increased to the following sequence of sterilization methods: ethylene oxide; autoclaving; dry oven. On the other hand, mechanical strength decreased with regard to non sterilized material in the sterilization sequence: ethylene oxide; dry oven; autoclaving. The compressive strength was 8.5 ± 1.0; 9.0 ± 1.2; 8.2 ± 0.8 and 6.5 ± 1.0 MPa, whereas diametral tensile strength was 2.1 ± 0.3; 2.5 ± 0.1; 1.9 ± 0.9 and 1.6 ± 0.3 for the material sterilized by ethylene oxide, dry oven, and autoclaving, respectively. Several compositional and microstuctural changes were detected after dry heat and autoclave sterilization. Ethylene oxide sterilization had lesser effect on the chemical composition and strength than dry heat and autoclaving

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Calcium phosphate cements have received much attention in recent decades owing to their biocompatibility, <i>in situ</i> handling, and shaping abilities. However, their low initial mechanical strength is still a major limitation. On the other hand, calcium aluminate cements (CACs) set fast and have a high initial strength and good corrosion resistance in contact with body fluids, making them excellent dental restorative materials. Therefore, the chemical, mechanical and biological properties of new-TCP/CA cement after aging in simulated body fluid (SBF) were investigated. The results indicated that the composites have setting times not appropriated for immediate applications and have degradation rates higher than those of the traditional CPCs. Moreover, the compressive strength of composite was lower than 5MPa and did not increase with SBF immersion. However, the <i>α</i>-TCP/CA composites showed a higher bioactivity at early stages and were not only more biocompatible but also more noncytotoxic

The transformations that took place in a scaffold composed of CDHA/OCP/beta-TCP by ageing in SBF at 36.5 degrees during 14 days were studied. A carbonated-apatite layer was formed during immersion in SBF on the surface of the scaffold and part of the OCP present in the inner core of the material was also transformed into apatite. The precipitated apatite layer exhibited the typical globular morphology characteristic of bioactive materials. The content of CDHA increased from 14 to 29 wt % at the expense of the content of OCP that decreased from 39 to 29 wt %. beta-TCP content dropped slightly from 47 to 42 wt %. Total porosity (from 56.1% +/- 0.6% to 62.4% +/- 0.5%) and real density (from 2.58 +/- 0.01 to 2.79 +/- 0.01 g/cm(3)) increased, and diametral tensile (from 2.1 +/- 0.3 to 0.9 +/- 0.1 MPa) and compressive strengths (from 8.5 +/- 1.0 to 6.8 +/- 0.6 MPa) decreased during ageing. The in vitro results showed that the scaffold composed of CDHA, OCP, and beta-TCP is bioactive and partially resorbable. It seems to be suitable for in situ bone regeneration procedures.

The effect of using Na2HPO4 solution as mixing liquid in the physicochemical and mechanical properties of calcium aluminate cement (CAC), with a view to a possible reinforcement additive of conventional α-TCP-based CPC was studied. The results showed that the degree of the hydration reaction of CaAl2O4 (CA) increased when Na2HPO4 solution was used as mixing liquid. The porosity of cement was also lower (37.9 ± 1.3 %) than for H2O (33.2 ± 3.6 %). The values of compressive strength for cements prepared with both mixing liquids were lower than 3 MPa due to the excessive L/P ratio employed and large porosity. After immersion in SBF, only the Al(OH)3 hydrate is observed and no other crystalline hydrated calcium aluminate nor calcium phosphate was formed in any of the cements. Both cements released Ca ions to, and removed P ions from SBF, being this effect more remarkable when Na2HPO4 was used. As for other CAC, no Al was released to the SBF and no potential toxicity due to this ion should be expected.