Numerical Simulation of Thermo-Optic Effects in an Nd: Glass Slab with Low Thermally Induced Wavefront Distortion

A gain slab configuration with a low thermally induced wavefront distortion, which is based on heating the edge by the cladding layer, is proposed. The gain slab will be applied to a helium-cooled Nd: glass multislab laser amplifier with an output of 100 J at a repetition rate of 10 Hz. Additionally, a 3D numerical simulation model is developed to analyze the thermo-optic effects in the gain slab. Some parameters, including the absorption coefficient (α) of the cladding layer, the shape of the pump beam, and the gap between the pump area and absorbing cladding layer, are optimized to eliminate the thermo-optic effects. The results indicate that the peak-to-valley (P-V) of the thermally induced wavefront distortion of the specific gain slab can be reduced by 61% if other parameters remain constant.

Effect of Different Finishing and Polishing Techniques on Surface Roughness of Two Universal Nanohybrid Composite Resins

AIM: This study investigated the effect of different finishing and polishing systems on surface roughness of two types of universal nanohybrid composite resins. MATERIALS AND METHODS: A total number of 40 samples will be prepared to form two main equal groups of specimens (n = 20), according to the composite resin materials. Two universal nanohybrid resin composites were used in this study. First group (A1) is a universal nanohybrid composite resin (Mosaic) and the second group (A2) is a universal nanohybrid composite resin (Harmonize). Each group was subdivided equally into four equal subgroups (n = 5), according to the used finishing and polishing systems. Mold was made to prepare the specimens with a central hole of 4 mm in diameter and 4 mm in thickness. Light curing tip was placed touching the glass slab for 20 s then the cured specimens were removed from the mold and the specimens immediately and immersed in distilled water at 37°C for 24 h. Surface roughness (Ra) was measured using light sectioning vision system. SEM was done to support the results. RESULTS: The results showed that the lowest (Ra) values were recorded by the specimens under Myler strip followed by Polishing Discs treated specimens followed by Diacomp Plus specimens and the highest (Ra) values were recorded by white polishing stone specimens and regardless to finishing or polishing, it was found that mosaic resin composites group recorded statistically significant (p < 0.05) lower roughness mean value than Harmonize resin composites group. p ≤ 0.05 is statistically significant in all tests. CONCLUSION: Achieving long-lasting esthetics in resin composites restorations needs special attention for obtaining optimal resin polymerization and a perfect surface finish using the appropriate finishing and polishing system.

Degree of Conversion of Light Cured Resin Cements Polymerized under Two Thicknesses of Different Lithium Silicate Ceramics

Objective: To show the consequence of two thicknesses of ceramic on the polymerization of resin cement light cured when three different lithium silicate ceramics were used. Materials and Methods: 42 ceramic slices were prepared from three types of ceramics, Emax CAD, Celtra Duo CAD and Vita suprinity CAD (n=14). They were further divided into two subgroups according to thicknesses into sub group thickness 0.5mm and sub group thickness 1mm (n=7). Teflon moulds were fabricated with specific dimensions, where the ceramic disc was placed followed by light cured resin cement Bisco choice 2 veneer and a glass slab with finger pressure applied. Curing with Ascent® PX LED light cure unit for 20 seconds took place, where the tip placed over the ceramic sample directly. Cement film was then separated from the ceramic disk and subjected to analysis by Fourier Transform Infrared Spectroscope. Uncured cement samples were also subjected to analysis. Results: Celtra DUO CAD ceramic showed higher degree of polymerization that of Emax and Vita suprinity while the difference between Emax and Suprinity on the degree of polymerization was not significant. Also, ceramic thicknesses had a significant effect on the degree of polymerization of the resin cement. Conclusion: Thickness of ceramics up to 1mm affects the polymerization of resin cement significantly.

Comparison of Film Thickness of Two Commercial Brands of Glass Ionomer Cement and One Dual-cured Composite: An in vitro Study

ABSTRACT Aim The present study is undertaken to examine the film thickness of three most commonly used luting cements and to determine their usage as a luting agent. Materials and methods This study was carried out strictly according to the guidelines of American Dental Association (ADS) specification no. 8. Two glass slabs of 5 cm in length and 2 cm in width were used. One glass slab was kept over the other glass slab and the space between the two glass slabs was measured using metallurgical microscope at the power of 10×. Two brands of glass ionomer cement (GIC) and one dualcured resin cement were used in this study. The test cement is sandwiched between two glass slabs. A static load of 15 kg was applied using universal testing machine on the glass slabs for 1 hour and the space present between the two glass slabs was measured using metallurgical microscope at the power of 10×. Results Greatest film thickness was found in group III (Paracore) followed by group II (micron) and lowest in group I (GC luting and lining cement). All the tested samples can be used for luting purposes. Conclusion Greatest film thickness was observed in Paracore followed by micron and lowest in GC luting and lining cement. This suggests that the 25 to 27°C is ideal for mixing of the cement when used for luting consistency. The cement with film thickness more than 30 µm should never be used for luting purposes. Clinical significance The dentist should choose the luting cement with utmost care noting the film thickness and bond strength of the cement. The cement with low exothermic heat production and good bond strength should be encouraged. How to cite this article Khajuria RR, Singh R, Barua P, Hajira N, Gupta N, Thakkar RR. Comparison of Film Thickness of Two Commercial Brands of Glass Ionomer Cement and One Dualcured Composite: An in vitro Study. J Contemp Dent Pract 2017;18(8):670-674.