Dentin and Enamel Bond Strength of a Self-Cured Universal Adhesive

Objectives: To compare the immediate bonding performance of a self-cured with a light-cured universal adhesive system in enamel and dentin. Moreover, bond strength to enamel was assessed using self-etching and selective etching modes.
Methods: Extracted intact human molars kept in distilled water for no longer than 6 months were used to test resin-enamel and resin-dentin shear bond strength (SBS) (n=10) and resin-dentin microtensile bond strength (µTBS) (n=30). For SBS, enamel and dentin surfaces were polished with 600-grit silicon carbide paper prior to adhesive application. For µTBS, the mid-coronal dentin surface was flattened with a diamond bur. Scotchbond Universal Adhesive (light-cured) (SBU, 3M Saint Paul, MN) and Tokuyama Universal Bond (self-cured) (TUB, Tokuyama Dental Corporation, Japan) adhesives were applied following the manufacturers’ recommendations. When used in the selective etching mode, enamel surfaces were acid-etched for 30 s prior to the bonding procedures. Teeth were restored with the resin composite from the same manufacturer (Filtek Supreme Ultra for SBU and Omnichroma for TUB) applied incrementally and light-cured. For the µTBS, the trimming technique was used to obtain dumbbell-shaped resin-dentin samples tested in tensile until failure. Statistical analysis consisted of a two-way ANOVA and a two-sample t-test (α=0.05).
Results: In dentin, the bond strength of SBU was higher than TUB (mean µTBS: 58.33 vs. 20.95 MPa; mean SBS: 41.95 vs. 26.10 MPa; p<0.001). In enamel, selective etching resulted in higher enamel bond strength than self-etching mode for both adhesive systems (p ≤ 0.001). TUB presented higher bond strength than SBU in the selective etching mode (40.99 vs. 35.17 MPa; p=0.048), while SBU displayed higher bond strength than TUB for the self-etching mode (26.70 vs. 19.24 MPa; p=0.006).
Conclusions: TUB presented lower bond strength than SBU when used in the self-etching mode in enamel and in dentin, but better bonding performance than SBU when used with selective enamel etching.