Calcium phosphate cements have received much attention in recent decades owing to their biocompatibility, in situ 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 α-TCP/CA composites showed a higher bioactivity at early stages and were not only more biocompatible but also more noncytotoxic.
Calcium phosphate cements (CPCs) are a clinical alternative to traditional bioceramics because they are easy to handle and shape, they mold themselves well to the contours of defective surfaces, and set in situ in the bone cavity to form a solid restoration [
One of the most important formulations is based on α-tricalcium phosphate [α-Ca3(PO4)2; α-TCP], which sets in situ and forms a calcium-deficient hydroxyapatite [Ca9(HPO4)(PO4)5(OH); CDHA] when hydrated [
In view of the excellent bioresorbability of CDHA, researchers have focused their efforts on overcoming the mechanical weakness of calcium phosphate cements by using different fillers, fibers and reinforcing additives that lead to the formation of various multiphase composites, based on the idea that the filler in the matrix may eliminate crack propagation [
In the late 1990s, the Swedish company Doxa Certex AB proposed the use of calcium aluminate cements (CACs) as dental restorative materials in place of amalgam [
Although some calcium phosphates, as β-tricalcium phosphate, are used in combination with CACs in order to induce some biological activity in the resultant composites [
α-TCP was prepared through solid state reaction, heating the appropriate mixture of Ca2HPO4·2H2O (Extra Pure, DyneÒ) and CaCO3 (Extra Pure, Nuclear) at 1300˚C for 5 h followed by quenching in air [
CA was synthesized through Pechini technique [
Synthesized CA (7 µm; 11.88 m2/g) was mixed in powder ratios of 0, 5.0 and 10.0 mass % with α-TCP (10.71 µm; 5.52 m2/g). The liquid phase was a sodium phosphate buffer prepared from NaH2PO4 and Na2HPO4·12H2O and the liquid-to-powder ratios (L/P) employed were 0.4, 0.44 and 0.46 ml/g, respectively. Each powder sample was carefully weighed and mixed with the liquid phase in appropriate powder-to-liquid ratio, packed into silicon molds and aged at 36.5˚C with 100% humidity for 24 h.
The setting time of samples was measured according to ASTM C266-89 using a Gillmore Needles method [
To assess in vitro bioactivity, the 24h-set pastes were soaked in simulated body fluid (SBF) at 36.5˚C [
For degradation tests, the disks were accurately weighed before and after immersion in SBF. The weight loss (WL) was calculated according to
being W0 the initial weight of the specimen and Wd the weight of the specimen dried after different degradation times (7, 14 and 21 days). All the measurements were taken in triplicate and the average values were calculated.
The cell viability assay was performed by direct contact test according to ISO 10993-5 using peripheral blood mononuclear cells (PBMCs) and a procedure described elsewhere [
The phase composition of the samples was determined by X-ray diffraction (XRD) in a Philips® X’Pert MPD diffractometer equipped with a Cu-target. Diffractograms were recorded employing Ni-filtered radiation (λ = 1.5406 Å) with a step size of 0.05˚ and a time/step ratio of 1 second.
The powders’ specific surface area was determined by nitrogen gas sorption and obtained by five-point BET analysis using a Nova 1000 surface area analyzer, while the particle size distribution was determined in a CILAS 1180 particle size analyzer using isopropyl alcohol as dispersant.
The morphological variations of materials before and after soaking in SBF were characterized by Scanning Electron Microscopy (SEM) using a JEOL microscope (JSM-6060) on gold-coated samples.
Compressive strength (CS) was measured in a servohydraulic universal testing machine (MTS 810) equipped with a 10 kN load cell, at a loading rate of 1 mm/min. The number of replicas was n = 10 and Student’s Multiple Comparison Test was performed to compare mean values.
The pH value was measured during soaking in SBF and readings were taken in an mPA-210 pH meter at 36.5˚C.
Figures 3-5 show the powder XRD patterns of composites before and after soaking in SBF for 7 and 14 days. For all times and all formulations, the characteristic peaks of β-TCP (JCPDS 09-0169), which appears as a seconddary phase in a-TCP powder (JCPDS 29-0359), were detected. After 24 h setting (
After 7 days of soaking (
Fourteen days after, the hydration reaction seemed to be complete for a-TCP, whereas a great amount of unreacted a-TCP, in addition to CDHA, could be observed for
composites containing CA (
Some bacterial contamination by Bacillis and Cocci colonies, represented by spherical and rod-shaped holes, were also observed [
For 5CA and 10CA (Figures 6(B) and (C)) small round shaped particles, spherulites-like cristals, of hydroxyapatite, were beginning to deposit on top of the leaf-like intermediary structure since the early stages (about 1day of soaking). Evidence of the formation of a new product containing phosphorus was formed on the surface of composites was confirmed by EDS analysis (