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Effects of Er:YAG laser irradiation on the microtensile bond strength to bleached enamel
Eduardo dos Santos Leonetti1, José Augusto Rodrigues, André Figueiredo Reis
1Department of Restorative Dentistry, School of Dentistry, Guarulhos University, São Paulo, Brazil.
Objective:
The objective of this study was to evaluate the influence of different Er:YAG laser (λ = 2.94 μm) energy parameters on the microtensile bond strength (μTBS) and superficial morphology of bovine enamel bleached with 16% carbamide peroxide.
Background:
Laser irradiation could improve adhesion to bleached enamel surfaces.
Methods:
Sixty bovine enamel blocks (7 × 3 × 3 mm(3)) were randomly assigned to six groups according to enamel preparation procedures (n = 10): G1-bleaching and Er:YAG laser irradiation with 25.52 J/cm(2) (laser A, LA); G2-bleaching and Er:YAG laser irradiation with 4.42 J/cm(2) (laser B, LB); G3-bleaching; G4-Er:YAG laser irradiation with 25.52 J/cm(2); G5-Er:YAG laser irradiation with 4.42 J/cm(2); G6-control, no treatment. G1 to G3 were bleached for 6 h during 21 days. Afterwards, enamel surfaces in all groups were slightly abraded with 600-grit SiC papers and G1, G2, G4 and G5 were irradiated according to each protocol. Enamel blocks were then restored with an etch-and-rinse adhesive system and a 4-mm thick composite buildup was made in two increments (n = 9). After 24 h, restored blocks were serially sectioned with a cross-section area of ∼1 mm(2) at the bonded interface and tested in tension in a universal testing machine (1 mm/min). Failure mode was determined at a magnification of x100 using a stereomicroscope. One treated block of each group was selected for scanning electron microscopy (SEM) analysis. μTBS data were analyzed by two-way ANOVA and no statistical differences were observed among groups.
Results:
Mean bond strengths (SD) in MPa were: G1-30.4(6.2); G2-27.9(8.5); G3-32.3(3.9); G4-23.7(5.8); G5-29.3(6.0); G6-29.1(6.1). A large number of adhesive failures was recorded for bleached and irradiated enamel surfaces.
Conclusions:
Bleached enamel surfaces μTBS values were not significantly different from those of unbleached enamel. Even though Er:YAG laser irradiation with both parameters had no influence on μTBS for bleached and unbleached enamel, SEM analysis revealed that Er:YAG laser irradiation with 25.52 J/cm(2) should not be recommended, as enamel ablation was observed, whereas irradiation with 4.42 J/cm(2) did not promote any remarkable changes on enamel surface.