Does Double-layer Application of a Universal Adhesive Affect Its Bonding to Different Tooth Substrates?

Abstract

Objective: evaluate the influence of single- or double-layer application of a universal adhesive on the bond strength to different tooth substrates. 
 Methods: To Seventy-two extracted sound human teeth were used for the study. The teeth were divided into three groups according to tooth substrates; enamel, coronal and radicular dentin (n=24). The roots of the teeth were separated from the crowns and then abraded to obtain flat surfaces. The specimens were randomly allocated into 2 groups in accordance with application layers of universal adhesive (n=12). The universal adhesive, Adhese Universal was applied in self-etch mode as single- or double-layer (without light-curing of the first layer) to different substrates. Following the adhesive application, enamel, coronal- and radicular dentin substrates were restored with a resin composite (Tetric N-Ceram). The specimens were subjected to shear bond strength (SBS) test after storage in distilled water (37℃,24 h). Representative fractured and interface samples from each group were examined by a scanning electron microscope. The data were analyzed using two-way ANOVA(α = 0.05). 
 Results: There was no statistically difference in SBS values between single- and double-layer applications of the tested universal adhesive on different dental substrates (p>0.05). Whilst no difference was occurred between the different dental substrates in the single-layer application (p>0.05), double-layer application on coronal dentin presented significantly higher bond strength than enamel (p