Influence of Preparation and Etching Time on the bond stregth

Objective: To evaluate, in vitro, the effect of acid etching time and surface preparation on the microtensile bond strength (MTBS) of a one-bottle two step total etch adhesive system to enamel. Method: Twenty human third molars were selected and mesio-distally sectioned for obtaining forty enamel surfaces. With half of them, the enamel surface was grounded using a high-speed diamond bur (P) under water irrigation. With the other half, the surface was not prepared (NP). A 35% phosphoric acid (3M ESPE) was applied for either 15 or 30 seconds, in both groups. After rinsing the acid etching, the enamel surface was air dried and the adhesive (Adper Single Bond 2, 3M ESPE) was applied, according to manufactures instructions. The adhesive was gently air dried and light cured. A hybrid resin composite (Filtek Z350, 3M ESPE) was applied in 3 increments of 2.0mm and light cured for 20 seconds each with a final polymerization of 60 seconds. After 24 hours in water, the specimens were sectioned into beams of 0.8mm2±0.2 cross sectional area with a low-speed diamond saw (Isomet 1000, Buehler), under water irrigation in X and Y directions. The MTBS of each beam was measured in an Instron machine at a crosshead speed of 0.5mm/min. The data was analyzed with two-way ANOVA and Duncan's post hoc (P<0.05). Results: MTBS in MPa (Mean±SD): 15NP=39.36(±9.03)a; 15P=38.68(±5,06)a; 30NP=38.55(±3.5)a; 30P=38.32(±4.02)a. Means with the same letter are not statistically different at P<0.05. There was no statistical difference between groups. Conclusions: Bonding to enamel seems to be predictable with a 15 or 30 seconds time of 35% phosphoric acid conditioning, with or without surface preparation.