Mechanical properties of a permanent dental restorative material based on calcium aluminate

This paper deals with some important mechanical properties (hardness, dimensional stability, compressive and flexural strength) of an experimental version of a translucent calcium aluminate dental restorative material. All samples investigated have been made from pre-pressed tablets, with a compaction degree of approximately 60%, hydrated using a 0.15 wt % Li salt solution as an accelerator. The samples were stored in water at 37 degrees C between the measurements. As reference materials one composite, Tetric Ceram, and one glass ionomer, Fuji II, were used with specimens prepared according to the manufacturer's recommendations. For the reference materials some of the properties were published data. The results show that the calcium aluminate material has sufficient mechanical properties to be used as a permanent dental restorative taking as a reference the ISO 9917 and the ISO 4049 as well as the reference materials. In addition the results indicate that the mechanical properties are controlled by the microstructure, which is mainly determined by the grain size of the filler.     

Microstructure of rapidly-quenched ZrO2-SiO2 glass-ceramics fabricated by container-less aerodynamic levitation technology

In this work, an aerodynamic levitation technology (ALT) was utilized to prepare ZrO₂-SiO₂ glass-ceramics with two different ZrO₂ contents, that is, 35 mol% and 50 mol%. The glass-ceramics were partially melted at ∼2000°C or fully melted at ∼3000°C by ALT, followed by rapid quenching to obtain spherical glass-ceramic beads. The phase compositions and microstructures of the glass-ceramics were characterized. Crystallization of ZrO₂ occurred during the solidification process and ZrO₂ content, processing temperature, and the addition of yttrium (3 mol%) affected the crystalline phase of ZrO₂. No ZrSiO₄ or crystalline SiO₂ were formed during the solidification process and the glass-ceramics were away from thermodynamic equilibrium due to rapid quenching. The glass-ceramics showed a microstructure of irregular-shaped ZrO₂ micro-aggregates embedded in an amorphous SiO₂ matrix, with lamellar twins and lattice defects formed within ZrO₂ crystals. For samples prepared at ∼3000°C, a liquid-liquid phase separation occurred in the melt, which eventually resulted in the formation of large and irregular-shaped ZrO₂ aggregates. In comparison, for samples prepared at ∼2000°C, pre-existed ZrO₂ crystals formed during heating acted as nucleation sites during the cooling process, followed by grain growth to form large ZrO₂ aggregates. Solidification and microstructure formation mechanisms were proposed to elucidate the solidification process during rapid cooling and the microstructure of the glass-ceramics obtained.     

Effects of Boiling on Dietary Fiber Components in Fresh and Stored White Cabbage (Brassica oleracea var. capitata)

The effects of boiling (10 min) and how differences in cultivars (n= 6), maturity (n= 2), and storage (n= 3) may affect dietary fiber in white cabbage were studied. A great variation in total dietary fiber content between boiled cabbage samples was seen (17.7 to 31.7 g/100 g dry weight basis). Total and insoluble dietary fiber following boiling could be predicted from the initial amount. Average losses for early and late cultivars were similar (about 10%) and were mainly due to insoluble polymers consisting of glucose and partly of uronic acids. The early cultivar ‘Balbro’ was least affected by heat treatment: only 2% total dietary fiber was lost. Harvesting before physiological maturity and short‐term storage increased the loss of soluble polymers (pectic substances), whereas long‐term storage decreased the loss.     

Ion substitution induced formation of spherical ceramic particles

How to precipitate ceramic nano- and microspheres in water based solutions only using inorganic ions is a challenge. In this study, spherical particles of alkaline earth phosphates and fluorides were synthesized using a precipitation reaction. Substituting ions, through inhibition of crystal growth, was used to induce sphere formation and to alter the morphology, size and composition of the spheres. The difference in ionic radius between the substituting ion (Mg, Ca and Sr) and the main cation (Sr and Ba) influenced the critical concentration to allow for sphere formation as well as the crystallinity. The larger difference, the lower was the concentration needed to form spheres. Low concentrations of Mg was enough to generate amorphous spheres of Sr- and Ba-phosphates whereas higher concentrations were needed if the radius difference were smaller. An increasing degree of substitution leads to a decrease in crystallinity of precipitated particles. The degree of substitution was determined to 16–55% where a low degree of ion substitution in the phosphates resulted in the formation of spheres (500–800?nm) with rough surfaces composed of apatite like phases. A higher degree of substitution resulted in amorphous spheres (500?nm- 1?μm) with smooth surfaces.     

Photocatalytic activity of low temperature oxidized Ti–6Al–4V

Numerous advanced surface modification techniques exist to improve bone integration and antibacterial properties of titanium based implants and prostheses. A simple and straightforward method of obtaining uniform and controlled TiO₂ coatings of devices with complex shapes is H₂O₂-oxidation and hot water aging. Based on the photoactivated bactericidal properties of TiO₂, this study was aimed at optimizing the treatment to achieve high photocatalytic activity. Ti–6Al–4V samples were H₂O₂-oxidized and hot water aged for up to 24 and 72 h, respectively. Degradation measurements of rhodamine B during UV-A illumination of samples showed a near linear relationship between photocatalytic activity and total treatment time, and a nanoporous coating was observed by scanning electron microscopy. Grazing incidence X-ray diffraction showed a gradual decrease in crystallinity of the surface layer, suggesting that the increase in surface area rather than anatase formation was responsible for the increase in photocatalytic activity.     

Influence of water content on hardening and handling of a premixed calcium phosphate cement

Handling of calcium phosphate cements is difficult, where problems often arise during mixing, transferring to syringes, and subsequent injection. Via the use of premixed cements the risk of handling complications is reduced. However, for premixed cements to work in a clinical situation the setting time needs to be improved. The objective of this study is to investigate the influence of the addition of water on the properties of premixed cement. Monetite-forming premixed cements with small amounts of added water (less than 6.8 wt.%) were prepared and the influence on injectability, working time, setting time and mechanical strength was evaluated. The results showed that the addition of small amounts of water had significant influence on the properties of the premixed cement. With the addition of just 1.7 wt.% water, the force needed to extrude the cement from a syringe was reduced from 107 (± 15) N to 39 (± 9) N, the compression strength was almost doubled, and the setting time decreased from 29 (± 4) min to 19 (± 2) min, while the working time remained 5 to 6 h. This study demonstrates the importance of controlling the water content in premixed cement pastes and how water can be used to improve the properties of premixed cements.     

Particle erosion of cemented carbides with low Co content

Cemented carbides are well known for their high erosion resistance and are therefore used in many demanding applications involving erosion, such as grit blasting nozzles. A number of investigations on the erosive wear resistance of conventional cemented carbides have been published. The present paper is aimed at investigating the erosion resistance of a series of modern cemented carbides containing no or very small amounts of Co, so-called binderless carbides, and relating their performance to conventional sorts.

A series of binderless carbides with varying grain size (0.6, 2 and 5 μm) and binder content (0.25 and 1 wt.%) has been tested. The materials were eroded by SiC particles of three sizes (80, 200 and 600 μm) from four angles (90, 70, 50 and 30°) with a velocity of 70 m/s. Three conventional WC-Co grades of corresponding grain sizes were also tested, under identical test conditions.

The materials are ranked with respect to their erosion rate and scanning electron microscopy is used to analyse the worn surfaces. The influence of carbide grain size and binder amount on the wear behaviour is discussed.     

A novel rapid synthesis,characterization and applications of calcium phosphate nanospheres from Baltic seawater

Due to the considerable high bio-compatibility, calcium phosphate nanoparticles are widely used in biomedical applications. This study proposes a novel strategy for low-cost manufacturing calcium phosphate nanoporous spheres. The controlled reaction only took less than five minutes, when using Baltic seawater with the dissolved calcium concentration of 2.2?mM as the calcium resources. Porous nanospheres were obtained, with spheres ranging from 50 to 130?nm. The obtained nanospheres possess high drug-loading capacity and exhibit sustained release and pH-dependent properties. In addition, this method provides a general efficient strategy to synthesize other low-cost inorganic nanospheres from seawater.     

Simvastatin-doped pre-mixed calcium phosphate cement inhibits osteoclast differentiation and resorption

Simvastatin, a cholesterol lowering drug, has been shown to have positive effects on fracture healing and bone regeneration based on its dual effect; bone anabolic and anti-resorptive. In this study the focus has been on the anti-resorptive effect of the drug and its impact on the degradation of acidic calcium phosphate cement. The drug was added to the pre-mixed acidic cement in three different doses (0.1, 0.25 and 0.5 mg/g cement) and the release was measured. Furthermore the effect of the loaded cements on osteoclast differentiation and resorption was evaluated by TRAP activity, number of multinucleated cells, gene expression and calcium ion concentration in vitro using murine bone marrow macrophages. The simvastatin did not affect the cell proliferation while it clearly inhibited osteoclastic differentiation at all three doses as shown by TRAP staining, TRAP activity and gene expression. Consistent with these results, simvastatin also impaired resorption of cements by osteoclasts as indicated by reduced calcium ion concentrations. In conclusion, our findings suggest that simvastatin-doped pre-mixed acidic calcium phosphate cement inhibits the osteoclastic mediated resorption of the cement thus slowing down the degradation rate. In addition with simvastatin’s bone anabolic effect it makes the cement-drug combination a promising bone graft material, especially useful for sites with compromised bone formation.     

Cytotoxicity of modified glass ionomer cement on odontoblast cells

Recently a modified glass ionomer cement (GIC) with enhanced bioactivity due to the incorporation of wollastonite or mineral trioxide aggregate (MTA) has been reported. The aim of this study was to evaluate the cytotoxic effect of the modified GIC on odontoblast-like cells. The cytotoxicity of a conventional GIC, wollastonite modified GIC (W-mGIC), MTA modified GIC (M-mGIC) and MTA cement has been evaluated using cement extracts, a culture media modified by the cement. Ion concentration and pH of each material in the culture media were measured and correlated to the results of the cytotoxicity study. Among the four groups, conventional GIC showed the most cytotoxicity effect, followed by W-mGIC and M-mGIC. MTA showed the least toxic effect. GIC showed the lowest pH (6.36) while MTA showed the highest (8.62). In terms of ion concentration, MTA showed the largest Ca²⁺ concentration (467.3 mg/L) while GIC showed the highest concentration of Si⁴⁺ (19.9 mg/L), Al³⁺ (7.2 mg/L) and Sr²⁺ (100.3 mg/L). Concentration of F^? was under the detection limit (0.02 mg/L) for all samples. However the concentrations of these ions are considered too low to be toxic. Our study showed that the cytotoxicity of conventional GIC can be moderated by incorporating calcium silicate based ceramics. The modified GIC might be promising as novel dental restorative cements.