Bonding effectiveness and interfacial characterization of a HEMA/TEGDMA-free three-step etch&rinse adhesive

Objectives: Small and hydrophilic monomers as HEMA and TEGDMA can easily penetrate human tissues. For biocompatibility issues it is therefore better to avoid such monomers in dental adhesive formulations. The purpose of this study was (1) to determine the micro-tensile bond strength (μTBS) to enamel/dentin of a HEMA/TEGDMA-free three-step etch&rinse adhesive (cmf Adhesive System, Saremco), and (2) to characterize it's interfacial interaction with enamel/dentin using transmission electron microscopy (TEM). Methods: Twelve intact freshly extracted human third molars were used for μTBS. The three-step etch&rinse adhesive OptiBond FL (Kerr) served as control adhesive. After bonding procedures and subsequent composite build-up (Z100, 3M ESPE), specimens were sectioned to sticks and trimmed at the interface to a cylindrical hour-glass shape. TEM section of non-demineralized and demineralized sections were prepared by ultra-microtomy and examined. Results: The μTBS of the cmf Adhesive System to enamel was not statistically significantly different from that of the control (OptiBond FL) adhesive (p = 0.3512); the μTBS to dentin was however significantly lower (p < 0.0001). TEM showed a tight interface at enamel for both adhesives. A relatively thick, completely demineralized and acid-resistant hybrid layer was formed at dentin. Some degree of spot- and cluster-like nano-leakage was observed with cmf Adhesive System, but did not differ in extent and form in comparison to that observed with the OptiBond FL control. Conclusions: The new three-step adhesive cmf Adhesive System showed indications of good bonding effectiveness, certainly to enamel and only significantly lower to dentin, when compared to the gold-standard adhesive. The latter may be related to the adapted HEMA/TEGDMA-free formulation and the somewhat lower mechanical properties.