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Showing 2 results for Opacity
Evaluation of opacity in polyethylene fiber reinforced composites
M. Hasani Tabatabaie, Z Hassani, S Arami,
Volume 23, Issue 1 (6-2010)
Abstract

Background and Aims: The main objective of this study was to determine the effect of polyethylene fibers and veneering composites in fiber-reinforced resin systems on the opacity (contrast ratio).

Materials and Methods: The specimens were divided into four groups. Two groups were used as the control groups, with no reinforcement. The fibers of polyethylene (Fibre-Braid) with special basement composites were used as the reinforced framework materials. Filtek Z250 and GRADIA (shade A2) were used as veneering materials. The total thickness of samples was 3 mm with 13 mm diameter. Specimens were prepared in disk shaped metal mold. The composite materials were light-cured according to their manufacturers' instructions. The contrast ratio (CR) of each specimen was determined on black and white backgrounds using reflection spectrophotometer. Reflectance was measured at intervals of 10 nm between 400 nm and 750 nm. Data were analyzed by two-way ANOVA and Tukey HSD test.

Results: When contrast ratio were compared among the different types of materials statistically significant differences were observed in both veneering composites (P<0.05). The Z250 resin composite had the lowest CR. It was shown that CR tended to decrease as the wavelength of incident light increased from 400 nm to 750 nm. On the other hand, the most differences in CR between groups were found in longer wavelengths.

Conclusion: It was found that polyethylene fibers reduced the amount of the translucency in FRC samples. The results of this study indicate that light reflectance characteristics, including the wavelength dependence, play an important role for the CR of a fiber-reinforced composite.


Radiopacity investigation of two types of bases and liners in comparison with dental structure, using a digital radiography system
Ehsan Tavakoli Hosseini, Abdolrahim Davari, Mahsa Asemi Esfahani,
Volume 30, Issue 3 (10-2017)
Abstract
Background and Aims: Radiopacity is an essential requirement for all restorative materials. Radiopaque materials allow the dentist to diagnose and assess radiographically the restoration, primary caries, assessment of contours, overhang and secondary caries. The aim of this study was to evaluate the radiopacity of two types of dental bases and liners in comparison whit dental structure using a digital radiography system.
Materials and Methods: Two classes of materials were prepared: 1 mm and 2 mm thickness disks for glass inomer and 1 mm and 0.5 mm thicknesses for dycal. Specimens of enamel and dentine with the same thicknesses were obtained. As a control, an aluminum step wedge was used. Samples were positioned over a phosphor-ray, plate of min ray soredex system, exposed, and the images were analyzed using the contour dent software. ANOVA analysis was used to investigate the significance of differences among the groups. For pairwise comparisons, the Bonferroni test was applied (P<0.005).
Results: 0.5 mm diameter of self-cure and light cure dycal and enamel, presented radio-opacity higher than that of dentine, except for the light cure dycal that had radiopacity lowers than enamel. 1 mm diameter of all the groups presented higher radiopacity than dentin. Light cure and self-cure glass inomer and self-cure dycal presented radiopacity higher than enamel. Enamel showed radipacity higher than light cure dycal in 2 mm diameter self-cure. Light cure glass inomer presented radiopacity higher than that of enamel and dentin.
Conclusion: The increased thickness of the materials evaluated increased their radio-opacity. It was concluded that all the materials had lower radiopaaty than dentin. Only enamel showed higher radiopacity than light-cured dycal.

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