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This study had as its main objective to evaluate the flexural properties (strength and modulus) and degree of conversion of a dimethacrylate resin containing different amounts of nanoparticulated clay Montomorillonite (MMT) as filler. A series of composites containing similar amounts (in volume) of barium glass particles was also tested as control data. Eight formulations with polymeric matrix-based BisGMA/TEGDMA (Bisphenol A Bis(2-hydroxy-3 methacryloxypropyl)Ether/Triethyleneglycol Dimethacrylate), four added with MMT and four added with barium glass in the volume concentration of 20, 30, 40 and 50 vol% were studied. The degree of conversion was determined using near-IR spectroscopy. Elastic modulus and flexural strength were determined by the three-point bending test. The dispersion of MMT nanoparticles was determined by means of X-ray diffraction and transmission electron microscopy analysis. The fillers montomorillonite and barium glass interacted with polymer matrix-based BisGMA/TEGDMA in a distinct manner. Although the addition of montomorillonite nanoparticles resulted in similar degree of conversion and higher elastic modulus values at all concentrations tested, only at the 20 vol% the flexural strength was statistically higher, compared to the control groups filled with barium glass. This could be related to the need of concentration optimization of montomorillonite for each type of polymer matrix in order to adjust or improve mechanical properties. The addition of low concentrations (<l 20% vol) of montomorillonite nanoparticles in dental composites resins – such as additive or hybrid filler – should be studied, aiming to the reduction of polymerization shrinkage, better mechanical properties and improvement of a new technology for future applications.

This study evaluated the influence of formulation and thermal treatment on the degree of conversion, fracture toughness, flexural strength, and elastic modulus of experimental composites. Six composites were analyzed at BisGMA : TEGDMA molar ratios of 1 : 1 and 7 : 3 with filler at 30, 50, and 70 wt%. The degree of conversion was analyzed by Fourier transform infrared spectroscopy, fracture toughness was measured using the single-edge notched beam, and flexural strength and elastic modulus were measured with the 3-point bend test. For all tests, one-half of the specimens received thermal treatment at 170°C for 10 min. Data were analyzed by the Kruskal-Wallis or ANOVA/Tukey's test (α = 5%). The 1 : 1 BisGMA : TEGDMA ratio showed higher properties than the 7 : 3 ratio. Although the material with 70% filler had a conversion lower than the one with 50%, it showed higher mechanical properties. The thermal treatment improved all properties in all materials. Therefore, the use of an equimolar ratio of BisGMA : TEGDMA can be paired with 70 wt% filler to design dental composites that possess increased advantageous physical and chemical properties. Furthermore, the simple and low-cost method of thermal treatment proposed for use in clinical dentistry has been shown to effectively improve the properties of all evaluated materials.

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The effects of pre‐irradiation treatment (dose ranged from 25 to 50 kGy) of MMT (Montmorillonite) nanoclay added as filler (50 wt %) in experimental dental composites was studied; composites containing similar amounts of non‐irradiated MMT were also tested. The thermal stability of the resulting material was tested by thermogravimetric analysis ranging from 50 to 800 °C. Elastic modulus and flexural strength were determined by the three point bending test (n = 10). Data for elastic modulus was analyzed using two way ANOVA/Tukey's test. Data for flexural strength was analyzed using Kruskal–Wallis/Tukey's test. For all tests, the global significance level was 5%. The modifications in elastic modulus and flexural strength with applied dose were characterized. X‐ray diffraction analysis allows the depicting of intercalation phenomenon between base‐polymer and nanophase. The polymeric system modified with MMT nanoparticles showed higher thermal stability by delaying the thermal degradation, compared to the control group, and the radiation dose influenced this thermal behavior directly. However, the applied dose was not sufficient to improve the mechanical properties significantly, which is related to the interaction between MMT and polymeric matrix. The pre‐irradiation treatment of MMT nanoclay phase was useful for attaining efficient interaction between the two constitutive phases of the polymeric systems based bis‐GMA/TEGDMA [bisphenol A bis(2‐hydroxy‐3‐methacryloxypropyl)ether/triethyleneglycol dimethacrylate], modified with MMT nanoparticles, because the polymer component was not affected. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45063.

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O objetivo do presente estudo foi avaliar o grau de conversão, contração volumétrica pós-gel e citotoxicidade de seis compósitos comerciais “bulk-fill” de consistência regular e fluida. Foram testados seis compósitos do tipo bulk-fill, e dois compósitos restauradores convencionais, foram testados como controles. O grau de conversão foi determinado por espectroscopia FTIR, determinou-se a contração volumétrica pós-gel utilizando o método de strain-gage e a avaliação da citotoxicidade em fibroblastos humanos foi determinada indiretamente por ensaio de MTT. Os dados foram submetidos ao teste ANOVA / Tukey unidirecional. Todos  os materiais, incluindo bulk-fill e convencionais, foram classificados como não tóxicos, com viabilidade celular superior     a 70%. Os compósitos bulk-fill apresentaram contração volumétrica semelhante ou inferior (1,4 a 0,4%) em comparação com os compósitos convencionais (1,7- 2,1%). No entanto, apenas três dos compósitos bulk-fill foram capazes de manter uma conversão homogénea ao longo da profundidade de 4 mm. Sendo assim, o clínico deve prestar especial atenção na seleção de um material que realmente atinja o desempenho proposto de um material bulk-filll.Palavras-chave: Compósitos. Contração.

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