Ilse Y. Pieters

Characterization of calcium phosphate cements modified by addition of amorphous calcium phosphate.

In this study the influence of amorphous calcium phosphate (ACP) on the setting of, and the formed apatite crystallite size in, a calcium phosphate cement (CPC) based on alpha-tricalcium phosphate (alpha-TCP) or tetracalcium phosphate (TTCP)/monocalcium phosphate monohydrate (MCPM) was investigated. Setting times at 22 degrees C were measured in air atmosphere; those at 37 degrees C were measured at 100% relative humidity. The phase composition of the set cements was investigated after 1 week using X-ray diffractometry and infrared spectroscopy and the morphology was investigated using scanning electron microscopy. The compressive strength (CS) of the set CPCs was measured after 1 day. Viability of MC3T3-E1 cells on the CPCs was analyzed after 7, 14 and 21 days of incubation using the CellTiter 96 Aqueous Non-Radioactive Cell Proliferation Assay. The alpha-TCP-based cement exhibited long setting times, a high CS and was converted to a calcium-deficient hydroxyapatite (CDHAp). The TTCP/MCPM-based CPC was only partly converted to CDHAp, produced acceptable setting times and had a low CS. Addition of ACP to these two CPCs resulted in cements that exhibited good setting times, CS suitable for non-load-bearing applications and a full conversion to nanocrystalline CDHAp. Moreover, the ACP containing CPCs demonstrated good cell viability, making them suitable candidates for bone substitute materials.

Carbonated apatites obtained by the hydrolysis of monetite: Influence of carbonate content on adhesion and proliferation of MC3T3-E1 osteoblastic cells

The influence of the carbonate content in apatites on the adhesion and the proliferation of MC3T3-E1 osteoblastic cells was investigated. B-type carbonated apatites (DCAps) were prepared by the hydrolysis of monetite (CaHPO(4), DCP) in solutions with a carbonate concentration ranging from 0.001 to 0.075 mol l(-1). Stoichiometric hydroxyapatite (DCAp0) was synthesized in carbonate-free solution. MC3T3-E1 cells were seeded on the compacted DCAps and cell adhesion and proliferation were analysed after 24h and 7 days, respectively, using a MTS assay and fluorescence microscopy. Cell adhesion tends to increase with increasing carbonate content for carbonate contents between 0 and 6.9 wt.% and levels out to an acceptable value (+ or - 50% compared to the control) for carbonate contents between 6.9 and 16.1 wt.%. Only DCAps with a carbonate content equal to or higher than 11% support high cell proliferation comparable to the control. On the latter DCAps, the cells have a spread morphology and form a near-confluent layer. A decrease in charge density and crystallinity at the apatite surface, as well as the formation of more spheroidal crystals with increasing carbonate content, might attribute to changes in composition and three-dimensional structure of the protein adsorption layer and hence to the observed cell behaviour. Consequently, only DCAps with a high carbonate content, mimicking early in vivo mineralization, are possible candidates for bone regeneration.

Fracture resistance and reinforcement of immature roots with gutta percha, mineral trioxide aggregate and calcium phosphate bone cement: a standardized in vitro model

Endodontic treatment of immature teeth is often complicated because of flaring root canals and open apices for which apexification is needed. Long-term prognosis for these teeth is surprisingly low because of cervical root fractures occurring after an impact of weak forces. In this study, an experimental model was developed to determine the fracture resistance of immature teeth and to test the hypothesis that endodontic materials succeed in reinforcing them. Compact and hollow bone cylinders from bovine femurs were used as standardized samples. In order to evaluate the experimental model, fracture resistance in both groups was evaluated by determining the ultimate force to fracture (UFF) under diametral tensile stress. Analysis of variance (ANOVA) revealed a statistically significant difference between the mean values of UFF for both groups, independently of the sampling location or subject. In a following setting, the hypothesis that obturation with gutta percha (GP), mineral trioxide aggregate (MTA), or calcium phosphate bone cement (CPBC) reinforces the hollow bone samples was investigated. Obturation resulted in a significant reinforcement for all materials, but the degree of reinforcement depended on the material. The experimental model appeared to be suitable for in vitro investigation of reinforcement and fracture resistance in a standardized way.

Influence of the solution composition on the stoichiometry of Na+- and of K+-containing carbonated apatites obtained by the hydrolysis of monetite

In this study, Na+- and CO2−3-containing hydroxyapatites (NCAps) and K+- and CO2−3-containing hydroxyapatites (KCAps) were prepared by the hydrolysis of monetite in solutions with independently varied CO2−3 and alkalimetal (M+) concentration. The chemical and physical analysis results show that both the CO2−3 and the M+ incorporation in apatite can affect the dimensions of the hexagonal lattice. From the composition of the unit cell of these apatites, the contributions of the substitution mechanisms for the incorporation of CO2−3 and M+ could be calculated. Generally, the contributions of the predominant mechanisms, (Ca2+ + PO3−4 + OH− ↔ VCa + CO2−3 + VOH) and (Ca2+ + PO3−4 ↔ M+ + CO2−3) with VX a vacancy on a regular X lattice site, vary as can be expected on the basis of the variation of the driving force in the hydrolysis solution. Their behavior seems to suppress the appearance of the less stable mechanisms: (Ca2+ + OH− ↔ M+ + VOH) for the NCAps and (Ca2+ + 2PO3−4 ↔ VCa + 2CO2−3) for the KCAps. This suggests that, although there is no intrinsic coupling between the fundamental substitution mechanisms, an indirect correlation can occur.

Apatite formation in composites of α-TCP and degradable polyesters

The objective of this study was to investigate the conversion of α-Ca3(PO4)2 (α-TCP) in composite bone cements based on a water-degradable polyester matrix as a function of the polymer formulation and the α-TCP filler content. Cross-linkable dimethacrylates of ε-caprolactone/D,L-lactide co-polymer or of ε-caprolactone/glycolide co-polymer were mixed with hydroxyethyl-methacrylate, a photo-initiator and α-TCP to obtain composites with a filler content of 80 or 40 wt% α-TCP. The disk shaped composite samples were set by visible light irradiation and immersed in HEPES at 37°C. At selected times the samples were removed from the solution and analysed with X-ray diffractometry and infrared spectroscopy. Conversion of α-TCP into calcium-deficient hydroxy-apatite (CDHAp) was observed for all composites, but the reaction was not completed after 8 weeks immersion. The conversion rate of α-TCP and the crystallinity of the formed apatite apparently were not affected by the type of polyester used, but significantly depended on the α-TCP content of the composites. An increase of the amount of α-TCP in the composite resulted in a slower formation of CDHAp with a higher crystallinity.