Effect of Electron Beam Irradiation or Flexural Strength of two Nanocomposites-an In vitro Study.

Aim: The aim of this study is to investigate whether dental nanocomposite Filtek Z350 XT and Ceram X-duo can benefit from electron beam irradiation in order to achieve increased flexural strength Place and Duration of Study: Department of Conservative Dentistry and Endodontics, A. B. Shetty Memorial Institute of Dental Sciences, Nitte University, Deralakatte, Mangalore, India and Microtron Centre; Department of Physics Mangalore University; Mangalore, India between May 2011 to March 2014. Materials and Methods: Materials were prepared on rectangular bar shaped specimens of 25-×2-×2-mm according to ISO standard -4049. Electron beam irradiation dose selected for the study were 1KGy, 3KGy and 5KGy. In total, 48 specimens were fabricated and divided into 4 groups based on radiation dose group I (non-radiated), group II (1KGy), group III (3KGy), group IV (5KGy) with 12 specimens in each. After 24 hours, specimens were subjected to 3-point bend test on a universal uniaxial servo mechanical testing machine. Statistical Analysis: Performed using one way ANOVA and inter group comparisons were done using tukeys multiple comparision. ‘P’ value<0.05 was considered statistically significant. Results: Flexural strength of Filtex Z350 XT before radiation was170.89±9.07.Flexural strength of Filtex Z350 XT after irradiation with 1KGy, 3KGy and 5KGy was found to be 269.06±94.91, 326.53±54.74 and 377.64±74.5 respectively. P value statistically significant (P<0.0001). Flexural strength of Ceram X duo before radiation was120.14±7.12.Flexural strength of Ceram X duo after irradiation with 1KGy, 3KGy and 5KGy was found to be 206.27±76.38, 177.31±67.35 and 229.33±59.15 respectively. P value statistically significant (P<0.0001). Conclusion: It can be concluded that electron beam irradiation can be used as a tool to modify the present day dental materials for enhancing their mechanical properties.

Identification and quantification of monomers released from dental composites using HPLC

The aim of this study was to detect and quantify the main residual monomers released from composites, using high performance liquid chromatography (HPLC). Discs were made with dental composites (Herculite XRV, Tetric Ceram and Filtek Z250) and immersed in deionized water at 37ºC for 28 days, with water changes in 1, 7, 14 and 21 days. The mean concentration of residual monomers were subject to the Kruskal-Wallis test (p<0.05). Tetric Ceram exhibited significantly higher concentrations of leached monomers. Bis-GMA was the monomer released in lower concentrations for all the materials. There was no statistical difference between the amounts of TEGDMA and UDMA. Most of the monomers demonstrated maximal concentration at the 7-day period. The HPLC analysis identified Bis-GMA, TEGDMA and UDMA in detectable quantities for all the tested composites.

A liberação de monômeros residuais pode afetar o comportamento clínico e a biocompatibilidade dos materiais resinosos. O objetivo deste estudo foi detectar e quantificar os principais monômeros residuais liberados de resinas compostas, usando cromatografia líquida de alta performance (HPLC). Discos foram construídos de resinas compostas de uso odontológico (Herculite XRV, Tetric Ceram and Filtek Z250) e imersos em água deionizada a 37ºC durante 28 dias, com mudanças de água em 24 horas, 7, 14 e 21 dias. As concentrações médias dos monômeros residuais foram submetidas ao teste de Kruskal-Wallis (p<0,05). Tetric Ceram apresentou as maiores concentrações de monômeros lixiviados. Bis-GMA foi o monômero liberado em menores concentrações para todos os materiais. Não houve diferença estatística significante entre TEGDMA e UDMA. A maioria dos monômeros demonstrou máxima concentração no período de 7 dias. A análise por meio de HPLC identificou Bis-GMA, TEGDMA e UDMA em quantidades detectáveis para todas as resinas compostas testadas.

Effect of instrument compliance on the polymerization shrinkage stress measurements of dental resin composites / 대한치과보존학회지

The purpose of this study was to evaluate the effect of instrument compliance on the polymerization shrinkage stress measurements of dental composites. The contraction strain and stress of composites during light curing were measured by a custom made stress-strain analyzer, which consisted of a displacement sensor, a cantilever load cell and a negative feedback mechanism. The instrument can measure the polymerization stress by two modes: with compliance mode in which the instrument compliance is allowed, or without compliance mode in which the instrument compliance is not allowed. A flowable (Filtek Flow: FF) and two universal hybrid (Z100: Z1 and Z250: Z2) composites were studied. A silane treated metal rod with a diameter of 3.0 mm was fixed at free end of the load cell, and other metal rod was fixed on the base plate. Composite of 1.0 mm thickness was placed between the two rods and light cured. The axial shrinkage strain and stress of the composite were recorded for 10 minutes during polymerization, and the tensile modulus of the materials was also determined with the instrument. The statistical analysis was conducted by ANOVA, paired t-test and Tukey's test (alpha<0.05). There were significant differences between the two measurement modes and among materials. With compliance mode, the contraction stress of FF was the highest: 3.11 (0.13), followed by Z1: 2.91 (0.10) and Z2: 1.94 (0.09) MPa. When the instrument compliance is not allowed, the contraction stress of Z1 was the highest: 17.08 (0.89), followed by FF: 10.11 (0.29) and Z2: 9.46 (1.63) MPa. The tensile modulus for Z1, Z2 and FF was 2.31 (0.18), 2.05 (0.20), 1.41 (0.11) GPa, respectively. With compliance mode, the measured stress correlated with the axial shrinkage strain of composite; while without compliance the elastic modulus of materials played a significant role in the stress measurement.

Infrared spectroscopy: a tool for determination of the degree of conversion in dental composites

Infrared spectroscopy is one of the most widely used techniques for measurement of conversion degree in dental composites. However, to obtain good quality spectra and quantitative analysis from spectral data, appropriate expertise and knowledge of the technique are mandatory. This paper presents important details to use infrared spectroscopy for determination of the conversion degree.