The aim of this study was to assess the micro-hardness of treated enamel with 810 nm and 980 nm diode lasers and to compare it with a conventional bleaching process.A sample of 45 caries-free human premolar teeth were selected. The enamel surfaces were completely polished. The crown portion of each tooth was then sectioned with a diamond disk, at dimensions of 3 × 3 × 3 mm. These sections were embedded in acrylic resin. The initial micro-hardness was determined by Vickers hardness apparatus at a vertical load of 200 g for 15 s. The samples were then randomly assigned to three groups of 15 samples.-Study group 1 (SG1): bleaching with Heydent JW gel and an 810 nm diode.-Study group 2 (SG2): bleaching with Heydent JW gel and a 980 nm diode.-Control group (CG): bleaching with Opalescense Boost.After bleaching, the Vickers micro-hardness was again evaluated. An analysis of covariance (ANCOVA) was used to compare the micro-hardness between the groups after bleaching, considering the initial micro-hardness as a covariate. A paired samples t-test was also used to compare micro-hardness before and after bleaching in each group and between groups.There was a significant difference in micro-hardness after bleaching with a laser and without a laser. After bleaching, the Vickers micro-hardness in the CG was significantly higher than in SG1 and SG2. There was no significant difference between SG1 and SG2 after bleaching (p value > 0.05).According to this study, laser irradiation with 810 nm and 980 nm diode lasers during tooth bleaching could cause a significant decrease in enamel micro-hardness.

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Background: This study aimed to assess the color change of two amine-free dual-cure resin cements following aging in comparison with a light-cure resin cement. Materials and Methods: This in vitro , experimental study evaluated 6 groups ( n = 10), including three groups of cements bonded to feldspathic porcelain and three groups of resin cements alone. Panavia V5 (Kuraray) and G-CEM LinkForce (GC) dual-cure resin cements and Choice 2 (Bisco) light-cure resin cements were bonded to porcelain according to the manufacturers’ instructions. The color parameters of the groups were measured before and after 5000 thermal cycles by spectrophotometry. Data were analyzed using two-way ANOVA and Tukey's post hoc test (α =0.05). Results: The color change (ΔE) of the cement groups alone was significantly greater than that of porcelain-bonded cements. The ΔE of G-CEM LinkForce cement group was significantly higher than that of Panavia V5 group ( P = 0.020), and the ΔE of the latter group was significantly higher than that of Choice 2 cement group ( P = 0.021). Conclusion: Considering the color change of cements evaluated in this study, Choice 2 and Panavia V5 cements bonded to porcelain showed acceptable color change, which indicates that they are suitable for cementation of esthetic dental restorations. Ceramic laminates have become an ideal esthetic treatment for anterior restorations. The resin cement discoloration can affect final appearance of these restorations. Besides that, exposed resin cement line can lead to the esthetic problem over time.