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The aim of this study was to evaluate the effect of Er:YAG laser irradiation on the micro-shear bond strength of self-etch adhesives to the superficial dentin and the deep dentin before and after thermocycling. Superficial dentin and deep dentin surfaces were prepared by flattening of the occlusal surfaces of extracted human third molars. The deep or superficial dentin specimens were randomized into three groups according to the following surface treatments: group I (control group), group II (Er:YAG laser; 1.2 W), and group III (Er:YAG laser; 0.5 W). Clearfil SE Bond or Clearfil S 3 Bond was applied to each group's dentin surfaces. After construction of the composite blocks on the dentin surface, the micro-shear bond testing of each adhesive was performed at 24 h or after 15,000 thermal cycles. The data were analyzed using a univariate analysis of variance and Tukey's test (p < 0.05). Laser irradiation in superficial dentin did not significantly affect bond strength after thermocycling (p > 0.05). However, deep-dentin specimens irradiated with laser showed significantly higher bond strengths than did control specimens after thermocycling (p < 0.05). Thermocycling led to significant deterioration in the bond strengths of all deep-dentin groups. The stable bond strength after thermocycling was measured for all of the superficial-dentin groups. No significant difference was found between the 0.5 and 1.2 W output power settings. In conclusion, the effect of laser irradiation on the bond strength of self-etch adhesives may be altered by the dentin depth. Regardless of the applied surface treatment, deep dentin showed significant bond degradation.

Objective: The purpose of this study was to evaluate the effect of surface and heat treatments on the mechanical properties and phase transformation of yttria-stabilized tetragonal zirconia (Y-TZP) materials., Background Data: Zirconia is exposed to several treatments during dental application process. Knowing the effect of applied treatments on zirconia is essential for clinical success., Material and Methods: Forty disk specimens of Zirkonzahn (Z) and DC-Zirkon (DC) materials were fabricated. The specimens were randomly divided into four groups according to surface [control, sandblasting, Erbium: Yttrium Aluminum Garnet (Er:YAG) laser irradiation] and heat (firing) treatments. The surface roughness (Ra, μm) was measured using a surface profilometer. The relative amount of the transformed monoclinic (m) phase was analyzed by X-ray diffractometry (XRD). Biaxial flexural strength was tested using piston-on-three-ball technique. The data were analyzed with the Kruskal-Wallis H test with Bonferroni correction, and the Mann-Whitney U test was used for pairwise comparisons., Results: There were no significant differences in surface roughness among the treated groups (p > 0.05), whereas sandblasting showed higher surface roughness than other treatments for both materials. Scanning electron microscopic (SEM) analyses revealed changes in surface morphology after surface treatments, especially in laser groups with the formation of cracks, and in sandblasting groups with the formation of microretentive grooves. The greatest amount of the monoclinic phase was measured after sandblasting (8.13%) for Z and (19.8%) for DC. The monoclinic phase reverted to the tetragonal phase after heat treatment. Heat treatment groups showed significantly lower flexural strength than other treatments (p < 0.05)., Conclusions: Heat and surface treatments influenced the mechanical properties of zirconia ceramic. The biaxial flexural strength and crystalline phase of materials decreased after heat treatments.