Evaluation and Comparison of Light Conducting Efficacy of CERANA Prefabricated Inlay with Inlays Made by Bioglass-Ceramic and Dental Porcelain in Increasing the Hardness of Posterior Composites

Statement of Problem: There are many techniques to overcome the light cured composite related problems including the depth, speed or rate and shrinkage patterns of polymerization. Among them, light transmitting and reflecting matrix, light conducting proximal wedges, incremental placement, use of glass-ceramic inserts and transparent cone, and application of different light exposure patterns could be referred. The goal of this study is evaluation and comparison of the light conducting ability and efficacy of prefabricated CERANA inlay with those made by dental porcelain and three new formulas of bioglass-ceramic and their effects in increasing the bottom hardness of posterior composite resin restorations. In this in vitro study, 90 molars were divided into nine groups of ten samples. Cavities similar to the medium size bur of CERANA kit were prepared in all samples. Forty inlays in the medium size and shape of CERANA with Vita 230 VMK dental porcelain and bioglass-ceramic with three new formulas with MOAZ4, MOAZ5, MOAZ6 codes were made. Four control groups including one bulk and incremental with two different light exposure distances ('0.0 mm to the tooth and 4.0 mm to the composite surface) were considered. All cavities in the control group were restored with A3 Colten® composite and 80 seconds light exposure time for one-bulk negative control and testing groups and 2x40 seconds for incremental positive control groups with Coltolux 2.5®. After epoxy resin embedding and diamond disk cutting, cooled with water and polishing with 1200 grit Sic paper, samples were tested with micro hardness tester from the top to the depth of four, one millimeter far from each other and 50 microns far from and along the inlays and also counterpart points in control groups. The data were tested with ANOVA and Duncan statistical tests. Along this study, dye penetration was done for all groups for statistical results confirmation. Statistical tests showed that tested groups with Vita 230 VMK, MOAZ6 and MOAZ4 inlays had 20%, 19% and 4% increase in a 4.0 mm depth. The group with CERANA inlays had 1% decrease in respect to the surface. The inlays made by MOAZ5 had the highest light conduction rate because they could cause a 41% increase at the deepest points (4.0mm depth). In relation to control groups including (C-0) one bulk 0.0 mm, (C+0) incremental 0.0 mm, (C-4) one-bulk 4.0 mm, (C+4) incremental 4.0 mm, a 2%, 22%, 50% and 21% reduction in hardness at 4.0 mm depth in respect to the surface were noticed respectively. Finally, the dye penetration in control and testing groups could support the microhardness testing. Placement of inlays made by MOAZ5 in composite restorations causes a better light conduction and a higher hardness in deeper points of restoration and with monotone and simultaneous curing in different depths of restoration and a higher polymerization and hardness at the flour of restoration causing higher possibility for elimination or reduction of microleakage.