One of the most required esthetic measures for patients with teeth discoloration or those who strive to have a beautiful smile and appearance is bleaching. The objective of this study is to analyze enamel morphological changes, chemical composition and microhardness following the application of 35% hydrogen peroxide, utilizing two various protocols for laser activation and the application of 4 different remineralizing agents. Materials and methods:In this study, 40 extracted human lateral and central incisors were chosen where the researcher categorized teeth into 2 groups consisting of 20 incisors, using two different laser-activated bleaching protocols. The researcher then subdivided each group into 4 subsets consisting each of 5 incisors where 4 remineralizing agents were applied to each bleached subset. Enamel surface morphology was studied by ESEM. Calcium and Phosphorus content were measured by EDAX and microhardness Vicker's test was performed to study the alteration in enamel hardness. Pre-and post-demineralization (bleaching) investigations were conducted and then they were repeated following remineralization.Results: ESEM revealed the improvement of enamel surface morphology in the remineralized groups except in (HD) and (LD) groups. After remineralization, all groups had a higher weight percent of calcium (Ca) and phosphorus (P) levels than its levels after demineralization except in groups (HD) and Vicker's hardness number in all groups showed significant increase except (HD) and (LD). Conclusion:The use of remineralizing agents containing casein phosphopeptide-amorphous calcium phosphate, fluoride or hydroxyapatite nanoparticles could improve the enamel morphology, microhardness and chemical composition of laser bleached enamel.

Objectives To evaluate the micro‐shear bond strength of two resin cements to aged laser bleached enamel after the application of three different desensitizing agents. Materials and methods Forty extracted human central and lateral incisors were prepared and bleached using laser activation bleaching protocol. The teeth were assigned randomly into four groups for desensitization; G1: No post‐bleaching treatment, G2: GC MI Paste Plus, G3: Hydroxyapatite nanoparticles (n‐HAP) and G4: Flor‐Opal. Specimens were subjected to aging for 6 months. All groups were subdivided into two subgroups according to the resin cements used (dual‐curing resin cement and light‐curing resin cement). Results Flor‐Opal groups showed the highest statistically significant micro‐shear bond strength (MSBS), followed by GC MI Paste Plus and n‐HAP groups with no statistically significant difference between them. The light‐curing resin cement had statistically higher MSBS than dual‐curing resin cement in case of no‐post bleaching treatment and n‐HAP groups, and no statistical difference in case of GC MI Paste Plus and Flor‐Opal groups. Conclusion Usage of desensitizing agents containing, CPP‐ACP, n‐HAP or fluoride after laser bleaching can enhance the bond strength of the resin cements to enamel. Clinical significance The composition of the desensitizing agents applied after laser bleaching could interfere in bond strength values.

Objective: This study measured the color change of lithium disilicate (E. max CAD), microhybrid resin composite (Coltene C bright, Filtek Z250) and feldspathic ceramic (Vita Mark II) laminates after putting them in coffee, Cola and artificial saliva staining solutions for seven days.Materials and Methods: Sixty freshly extracted sound upper central incisors were randomly divided into four groups (n=15) according to the material used for laminate veneer fabrication; E. max CAD (Group I), VitaMark II (Group II), Coltene C Bright blocks (Group III) and Filtek Z250 composite resin (Group IV). Teeth were all prepared to receive a prepared sample of a squared-shaped laminate of different materials in a dimension of 7x7 mm. Cementation, finishing and polishing procedures were performed followed by color change measurement using a spectrophotometer. Measurements were all recorded before and after immersion for seven days.Results: Time, material type and immersion medium had a statistically significant effect on mean color change (p<0.001). Intra-group comparisons displayed that E. max CAD showed the lowest color change, whereas Coltene C bright blocks were the greatest to show color change. Vita Mark II showed a higher color change in artificial saliva than Filtek Z250, however, the latter demonstrated a surpassing change in color in the other solutions. Conclusion:Material type, external source of stain, and staining time are important factors that affect the degree of color change, which in turn could affect patient satisfaction. E. max showed the best results in all solutions regardless the exposure time.

Objective: To evaluate the effect of CAD/CAM surface treatments and different adhesives on the shear bond strength (SBS) of a CAD/CAM composite to dentin. Materials and Methods:In total, 120-flat dentin surfaces were prepared, and divided into 12 groups (n=10) according to: 1-CAD/CAM surface treatment, and 2: Type of adhesive. A total of 120 CAD/CAM composite rods (2mmx2mmx4mm) were prepared, and sandblasted. The rods were left without further treatment, ultrasonically cleaned in distilled water, or acid etched using 35% phosphoric acid. The dual-and self-cured adhesives were applied to dentin, in etch-and-rinse or self-etching modes and the rods were cemented using dual-cured resin cement. The SBS test was run at a crosshead speed of 0.5 mm/min until failure. Data were analyzed using Two-Way ANOVA/ Tukey test, P=0.05.Results: Factors "surface treatment", "adhesive" and "surface treatment x adhesive" had significant effect on SBS (P<0.05). Sandblasting had the highest significant SBS among surface treatments (P<0.05). Self-cured adhesive showed higher SBS compared to dual-cured adhesive in etch-and-rinse mode (P<0.05). Mixed failure was the predominate failure (59.2%). Conclusion:Sandblasting improved the SBS of a CAD/CAM composite to dentin. The use of dual-cured universal and self-cured adhesives in their simplified self-etching approach is preferrable.