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.

Infrared absorption spectra of gamma irradiated glasses of the system Li20-B2o3-Al2o3

Spectroscopic studies on alkali metal borate glasses have revealed that the structure of alkali metal borate glasses is dependent not only upon the content of the alkali metal ion but also upon the difference in the alkali metal ion [1] Basic characteristics of borate glass structures are generally agreed upon. The fundamental building block in vitreous B[2]O[3]- is the BO[3] groups either as a random network of boroxol rings beside some fraction of BO[3] triangles [2] connected by B-O-B linkages [bridging atoms][2] The boroxol group is composed of three corner-sharing BO[3] triangles which form a very highly planar ring. Recent studies concluded that any model which attempts to give a full description of the structure of B[2]O[3] must include a high concentration of boroxol group. The addition of alkali oxides modifies the boroxol rings; complex borate groups with one or two four-coordinated boron atoms are formed[4]. Alkali oxide is usually incorporated into B[2]O[3] glass ionically. The initial effect upon the introduction of alkali oxide into B[2]O[3] is the conversion of Sp [2] planar BO[3] units into more stable Sp3 tetrahedral BO[4]. units thereby preserving the B-O bonding without the creation of non bridging oxygen [NBO] ions. Early NMR studies [5] indicated that the conversion of 3-to-4 coordinated boron extends for levels of alkali oxide up to about 30 mol percent and that the NBO ions should be created in large numbers at alkali oxide concentrations above the 30 mol percent level The alkali borate glasses will be composed of structural groupings [boroxol, tetraborate, diborate, metaborate, pyroborate, and orthoborate] present in the various crystal structures of the alkali borate compounds. The abundance and type of structural units present depend upon the amount of alkali oxide incorporated into the glass. Detailed recent investigations of the infrared spectra of borate glasses and their corresponding crystalline derivatives have been carried by Kamitsos et al[6]'. The interpretation of the results is believed to be tough task, due to the complexity originating from the glassy nature of the materials and to the large number of possible structural groups found in borate glasses. In a previous investigation [7] the effect of progressive increasing gamma rays dose on the infrared spectra of ternary borosilicate glasses of the system BaO-B[2]O[3]-SiO[2] was studied Experimental results indicate that the intensities of the characteristic absorption bands generally decrease with radiation, the frequencies of all the observed bands remain unchanged, and new bands are formed. In this paper, the work is continued to make a vibrational analysis by comparing the spectra obtained before and after gamma-ray irradiation to search for a further support to the previous published work and emphasizing to the role of changing glass composition on the infrared spectra of the. ternary Li[2]O-B[2]O[3]-Al[2]O[3] glasses