UV-Vis spectrophotometric analysis and light irradiance through hot-pressed and hot-pressed-veneered glass ceramics

This study evaluated the irradiance of curing units through core and veneered hot-pressed ceramics as well as the transmittance of these materials. Discs of 0.7, 1.4 and 2 mm in thickness of Empress (EMP) and Empress Esthetic (EST), and 0.8 (n=5) and 1.1 mm (n=5) thickness of Empress 2 (E2) were obtained. For E2, two of the 0.8-mm-thick discs were covered with dentin (1.2- and 1.4-mm-thick) and two with dentin + enamel (1.5-mm-thick). The 1.1-mm-thick specimens were submitted to the same veneering procedures. Specimens were evaluated by UV-Vis transmittance analysis and the percentage of transmittance was recorded. Irradiance through each specimen was evaluated with a quartz-tungsten-halogen (QTH), used in continuous or intermittent exposure modes, or a blue light-emitting diode (LED). Data were analyzed by Dunnett's test, ANOVA and Tukey's test at 5 percent significance level. Exposure through ceramic decreased the irradiance for all ceramics. Irradiance through EST was significantly higher than through EMP. For E2, reduction in irradiance depended on the core and/or veneer thickness. The QTH intermittent mode showed higher irradiance than the continuous mode, and both showed higher irradiance than LED. The ceramic significantly influenced irradiance and transmittance, which were found to decrease with the increase in thickness.

Este estudo avaliou a irradiância de unidades de fotoativação através de cerâmicas para subestrutura com e sem cobertura, e a transmitância desses materiais. Discos de 0,7, 1,4 e 2 mm de espessura de Empress (EMP) e Empress Esthetic (EST), e de 0,8 (n=5) e 1,1 mm (n=5) de espessura de Empress 2 (E2) foram obtidos. Para E2, dois discos de 0,8 mm foram cobertos com dentina (1,2 e 1,4 mm de espessura) e dois com dentina + esmalte (1,5 mm de espessura). Os discos de 1,1 mm de espessura foram submetidos aos mesmos procedimentos de cobertura. Os espécimes foram avaliados por análise de transmitância UV-Vis e o percentual de transmitância foi registrado. A irradiância através dos discos foi avaliada com fonte de luz de lâmpada halógena de quartzo-tungstênio (QTH), utilizada nos modos contínuo ou intermitente, e diodo emissor de luz (LED). Os dados foram analisados com testes de Dunnett, ANOVA e Tukey com nível de significância de 5 por cento. A exposição através da cerâmica reduziu a irradiância para todas as cerâmicas. A irradiância através de EST foi maior que EMP. Para E2, a redução dependeu da espessura da subestrutura e/ou cobertura. O modo intermitente para QTH mostrou maior irradiância que o modo contínuo; ambos apresentaram maior irradiância que o LED. A cerâmica influenciou significativamente a irradiância e transmitância, que diminuíram com o aumento da espessura.

Effect of alkaline-earth oxides on the structure of lithium silicate glasses and their glass-ceramic derivatives by ultrasonic and X-Ray diffraction techniques

Lithium silicate glasses of the composition [65% SiO[2] + 30%Li[2]O + 5% RO [mol%]]; where RO is one of the divalent oxide: MgO, CaO, SrO or BaO, and their glass ceramic derivatives were examined using ultrasonic technique and x-ray diffraction for studying their structures. Also, the density of the samples was measured. Ultrasonic velocity measurements were carried out using 4 MHz longitudinal and shear wave probes at room temperature. The elastic moduli, Poisson's ratio, Debye temperature and softening temperature of the prepared samples were calculated. The results show that, the ultrasonic velocities [longitudinal and shear], the shear and Young's elastic moduli decrease as the divalent oxide is changed from MgO, CaO, SrO or BaO, respectively. Meanwhile, the density, the molar volume, Debye temperature, softening temperature and Poisson's ratio increase. The variations in the different physical parameters were correlated and discussed in relation to composition and compactness of the respective glass

Preparation and structural investigations of titanium substituted Li-Zn ferriets

The mixed ferrites Li0.35 Zn0.30 Tix Fe2.35-x O4 [where x 0.0 to 1.0] were prepared using standard ceramic methods and were sintered at 1150 in static air atmosphere. The formation of ferrite spinel structure was investigated using X-ray diffraction and IR techniques. It was found, that samples with Ti content [x <0.2] have a spinel cubic structure. With increasing titanium content, bulk density and diameter shrinkage were found to decrease, while apparent porosity and grain size increased. Samples with x >0.2 were found to have more than one structural phase