Adhesion to Dentin in Permanent Teeth - in vitro Study of the Border Zone and Bond Strength in Total-Etch Adhesives

The objective of this study was to analyze the thickness and characteristics of the hybrid layer (HL) in samples of permanent teeth by using the scanning electron microscopy (SEM) and to evaluate the strength of the adhesive bond after application of total-etch adhesive systems. Material and methods 50 samples of permanent teeth were studied by assigning into two groups, depending on the type of the tested adhesive systems. The tested adhesive systems were the three-step total-etch system OptiBondFL (Kerr) and the two-step total-etch system Exite (Ivoclar Vivadent). The adhesive systems were applied according to the manufacturer's instructions. The samples were restored with a composite resin (TeEconom, Ivoclar Vivadent). For the purposes of SEM examination of the border zone, 5 samples of each group were subjected to thermal stresses (1, 500 cycles at temperatures between 5?-55?C) and masticatory loads (150, 000 cycles over intervals of 0.4 seconds). Then, the samples were cut in the middle, demineralized, deproteinized and dried. The dentine-adhesive border zone was studied by using SEM to evaluate the thickness and micro-morphologic characteristics of the hybrid layer. The bond strength was assessed by performing the macrotensile test. The destructed surfaces were studied by SEM to determine the type of failure. For the purposes of data processing, the statistical software program SPSS v.17.0 was used. Results The SEM examination showed differences in the thickness and characteristics of the HL between the two generations of adhesive systems. The three-step adhesives provided reliably greater strength of adhesion to the dentin, compared to the two-step adhesives.