Background. Repairing aged composite resin is a challenging process. Many surface treatment options have been proposed to this end. This study evaluated the effect of different surface treatments on the shear bond strength (SBS) of nano-filled composite resin repairs.Methods. Seventy-five cylindrical specimens of a Filtek Z350XT composite resin were fabricated and stored in 37°C distilled water for 24 hours. After thermocycling, the specimens were divided into 5 groups according to the following surface treatments: no treatment (group 1); air abrasion with 50-μm aluminum oxide particles (group 2); irradiation with Er:YAG laser beams (group 3); roughening with coarse-grit diamond bur + 35% phosphoric acid (group 4); and etching with 9% hydrofluoric acid for 120 s (group 5). Another group of Filtek Z350XT composite resin samples (4×6 mm) was fabricated for the measurement of cohesive strength (group 6). A silane coupling agent and an adhesive system were applied after each surface treatment. The specimens were restored with the same composite resin and thermocycled again. A shearing force was applied to the interface in a universal testing machine. Data were analyzed using one-way ANOVA and post hoc Tukey tests (P < 0.05).Results. One-way ANOVA indicated significant differences between the groups (P < 0.05). SBS of controls was significantly lower than the other groups; differences between groups 2, 3, 4, 5 and 6 were not significant. Surface treatment with diamond bur + 35% phosphoric acid resulted in the highest bond strength. Conclusion. All the surface treatments used in this study improved the shear bond strength of nanofilled composite resin used.

The effect of bleaching on the microhardness of restorative materials is material dependent. Before the application of bleaching systems on the glass ionomer materials, the application of a protective barrier should be considered.

Introduction: Discoloration of resin composites is a common reason for replacement of these restorations. The aim of this study was to evaluate the influence of different light curing devices on color stability of a microhybrid resin composite. Materials and Methods: 80 disc-shaped specimens (8 mm in diameter, 2-mm height) were fabricated from filtek Z250 resin composite. Specimens were divided into 4 groups (n=20) and cured with LED (Bluephase C5, Valo) or QTH (Astralis7 with two different light intensity) light curing devices. Baseline color of each specimen was measured with a spectrophotometer according to the CIE (L*a*b*) color scale. ( CIE L*a*b* is a color measurement system with dimension L for lightness and a and b for the color-opponent dimensions). Each subgroup (n=10) were immersed in tea or artificial saliva for 72h at 37°C. The color values of specimens were remeasured and the color change values (ΔE*ab) were calculated using One-Way ANOVA and Tukey test. A P value of <0.05 was considered significant. Results: In groups immersed in tea, specimens cured with high power mode of Astralis7 (750mW/cm2), showed the statistically significant lowest color change. There was no statistically significant difference between two types of Light Emitting Diode units. Conclusion: Conventional halogen light (QTH) with high power mode showed the maximum color stability in tea.

Context:Bleaching can affect the surface properties of resin composites.Aims:The aim of this study was to evaluate the effect of three regimens of carbamide peroxide (CP) on staining susceptibility of silorane and methacrylate-based resin composites.Methods:In this study, 80 composite disks were prepared from A2 shade of P90 and Z250 composite resins (40 each). Samples were divided into three test groups based on the CP concentration (10%, 16%, and 22%) and bleached for 14 days. Controls were kept in distilled water. Then, specimens were immersed in a tea solution for 14 consecutive days. A spectrophotometer was used to measure the specimen colors in CIE L*a*b system, initially and after staining. Data were analyzed using SPSS 16 software using two-way ANOVA, t-test, and Tukey honestly significant difference tests at α = 0.05.Results:The color susceptibility of Z250 samples were significantly affected in groups bleached with 22% CP compared to the controls (P = 0.001). The different concentrations of CP did not affect the staining susceptibility of the P90 samples (P > 0.05).Conclusions:Bleaching of the tested resin composites did not increase their susceptibility to extrinsic staining in vitro except for the Z250 samples bleached with 22% CP.

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