The aim of the study was to evaluate the efficacy of the microtensile bond test (μTBS) and the microshear bond test (μSBS) in ranking four dental adhesives according to bond strength to enamel and identify the modes of failure involved.

Forty-four caries-free human molars were randomly assigned to one of two bond strength testing methods: 20 teeth were used for μTBS test and 24 teeth for μSBS test. Flat enamel surfaces were created by wet grinding. Four adhesive systems were applied to the ground enamel surfaces; a two-step self-etch (Clearfil SE Bond, SEB), two all-in-one self-etch (Adper Prompt L-Pop, APL; Hybrid Bond, HB) and a two-step etch-and-rinse (Adper Single Bond, ASB). Resin composite (Z100) was applied over the adhesive. The μTBS and μSBS were determined after 24h of storage in water at 37°C. The mode of failure was determined by light microscope and SEM. Data was analyzed with ANOVA, Tukey's and Chi-square tests.

μTBS test ranked the adhesives as follows: SEB=ASB=APL>HB, while μSBS test ranked the adhesives as follows: ASB>SEB=APL>HB. The highest percentage failure mode with μTBS testing was cohesive in enamel or at the DEJ: SEB (95%), APL (65%) and ASB (65%). As for HB, adhesive failure (95%) was the common finding. The predominant failure mode in case of the μSBS was adhesive (APL 50%, SEB 58.3%, ASB 75% and HB 91.7%).

Ranking appears to be test-dependant and μSBS test appears to be more accurate in differentiating among the stronger adhesives.