Microtensile bond strengths of one- and two-step self-etch adhesives to bur-cut enamel and dentin.

PURPOSE: To evaluate the bonding effectiveness of one- and two-step self-etch adhesives in comparison with a total-etch approach.

METHODS: From 55 non-carious human third molars, mid-coronal dentin and enamel bur-cut surfaces were prepared. The bonding surfaces were treated strictly following the manufacturers' instructions with three one-step self-etch (all-in-one) adhesives, AQ bond, Reactmer and Xeno CF Bond; two two-step self-etch adhesives, experimental ABF and Clearfil SE Bond, one two-step total-etch adhesive, Prime & Bond NT, and one three-step total-etch adhesive, OptiBond FL. Composite built-ups were made using Z100. After storage overnight in 37 degrees C water, the bonded specimens were sectioned into rectangular slabs of approximately 2x2 mm width and 9 mm length. They were then trimmed into a round cross-sectional shape resulting in an interface area of approximately 1 mm2, and subsequently subjected to microtensile bond strength (microTBS) testing with a cross-head speed of 1 mm/minute. Differences in microTBS were determined for enamel and dentin using the Kruskal-Wallis test at P < 0.05.

RESULTS: The microTBS to enamel varied from 10.3 MPa for the one-step self-etch adhesive AQ bond to 49.5 MPa for the total-etch adhesive Prime & Bond NT. The microTBS to dentin varied from 15.5 MPa for the one-step self-etch adhesive Reactmer to 59.6 for the three-step total-etch adhesive OptiBond FL. The microTBS of the total-etch adhesives to enamel was significantly higher than that of the one-step self-etch adhesives. Comparing the dentin microTBS, only OptiBond FL performed significantly better than the one-step self-etch adhesives. Specimen failure during preparation occurred with each one-step adhesive, but more frequently when bonding to enamel than to dentin. Most one-step self-etch adhesives failed predominantly adhesively between the tooth substrate and the bonding layer in contrast to the two- and three-step adhesives that revealed generally more mixed adhesive-cohesive failures.