The objective of this work was to measure and correlate the degree of conversion (DC), mechanical properties and monomer elution from self-, dual- and light-cured core composites. Five samples of each of the following materials were prepared for each test: Clearfil (Core, Photo Core, Automix), Bisco (Core-Flo, Light-Core and Bis-Core). DC was determined using FTIR, compressive and flexural strength and modulus of elasticity using a universal testing machine and microhardness using Vickers hardness. Elution was measured using HPLC. One-way ANOVA with Tukey’s post-test and Pearson’s correlation were used to statistically analyze the data. DC of Clearfil-Dual (70.1%) and Clerafil-Photo (66.8%) were higher than Clearfil-Self (55.4%) and all Bisco materials (51.4–55.3%). Flexural strength of Clearfilwas higher than that of Bisco composites. The Microhardness of Clearfil-Dual (119.8VHN) and Clearfil-Photo (118.0VHN) were higher compared to other materials. The greatest elution was detected from self-cured materials. DC positively correlated to microhardness and compressive/flexural strength and negatively to BisGMA elution. Clearfil-Photo and Automix showed higher conversion, lower monomer elution and, generally, better mechanical properties. Self-cured composites should not be recommended for routine clinical use as their performance was inferior to dual- and light-cured composites. Microhardness may be used as an indicator of elution.
The aim of this study is to analyze viscoelastic properties of direct composite core (Lightcore, Build-it, Clearfil Photo Core, Rebilda). Experiments are preformed and mathematical models developed, based on derivatives of fractional order, to describe the viscoelastic properties of the studied materials. The basic assumption that materials are of memory type was proved to be correct. For each material, four fractional derivative models are used to fit experimental data and then one model, with smallest error between measured and calculated data for storage and loss modulus, is chosen. On the basis of mathematical model formulated here, it is possible to predict some viscoelastic properties of the materials that are important in clinical application. Central conclusion is that the four studied materials have different rheological properties although they are indicated for the same clinical procedure.
As a part of this study, a mathematical model based on two-compartment pharmacokinetic system with general fractional derivatives was developed. Its aim was to describe the release of BisGMA and TEGDMA monomers from composite core resin over three time periods. For this purpose, five Clearfil Photo Core resin samples were prepared and elution was measured using high performance liquid chromatography at 1, 7 and 28 days post-immersion in 75% ethanol. The findings confirmed good model fit to the data related to released monomer quantity.
The aim of this work was to find the influence of the addition of low amount of hydrophilic and hydrophobic TiO2 nanoparticles on compressive strength, microhardness and rheological properties of flowable dental composite material. Specimens were prepared by adding 0.05; 0.2 and 1 wt. % of hydrophilic and hydrophobic 20 nm TiO2 nanoparticles. These specimens were compared to non-modified control specimens in compressive strength and microhardness. Furthermore, their rheological properties were determined. The optimal nanoparticle loading was 0.2 % hydrophobic TiO2, resulting in significantly higher compressive strength and microhardness than those of the control specimen group. Mechanical properties of flowable composites reinforced with hydrophilic and hydrophobic TiO2 at higher loadings are lower than those of control specimens, which is the result of nanoparticle agglomeration. TiO2 nanoparticles addition resulted in the decrease in viscosity in all specimens except for the specimewn with 1% hydrophilic TiO2 nanoparticles. In accordance to the obtained results, hydrophobic nanoparticle addition results in a more resistant and durable material, combined with an increased flowability compared to a non-modified composite.
For many years, poly-methyl methacrylate has been used as a material of choice for making the denture base, thanks to its good and desirable performances, such as: simplicity in work, possibility of reparation, aesthetics and affordable price. Considering to its insufficient hardness and fracture resistance, there is a tendency to improve the mechanical properties of the material, by changing its basic composition. The aim of the research was to determine the fracture resistance of the heat-curing denture base acrylic resin materials. Materials and methods: For the research ,20 samples of the 2 heat-curing acrylics had been prepared, standard ones and reinforced acrylic resin material. After the storage in the saline for 15 days, measurements of the fracture resistance were performed by using the universal testing device. The data were statistically processed using the Student’s t-test for independent samples. Results: By measuring the flexural strength and deflection at breakage, it has been proven that there was, statistically, a significant difference of the flexural strength between reinforced (179.91-248.72MPa) and standard heat-curing acrylics (183.25- 200.74MPa). The deflection at breakage showed approximately the same values for both materials (1,0-1,4mm; 1.0-1.5mm). Conclusion: By enhancing the polymer, the mechanical properties of the denture base acrylic resin materials will be improved, primarily, higher fracture resistance, that means that these technologies need to be improved.
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