Evaluation of the long-term bond strength of HEMA-free adhesives to caries-affected dentin

Objective: This in vitro study aimed to evaluate the bond strength of HEMA-containing and HEMA-free universal adhesives to sound and caries-affected dentin. Materials and Methods: A total of 120 sound human molars were prepared to expose mid-coronal dentin. Half were subjected to alternating demineralization and remineralization for 14 days to create caries-affected dentin. Specimens were randomly assigned into six groups (n = 10) according to the adhesive system (Gluma Bond Universal, Clearfil Bond Universal, G2 Bond Universal) and application mode (self-etch or etch&rinse). Each tooth was symmetrically sectioned before adhesive application. Composite blocks (Clearfil Majesty Flow) were built; one was tested after 24 h and the other after 10000 thermal cycles using a shear bond strength test (1 mm/min). Values were expressed in MPa. Failure modes were analyzed under a stereomicroscope, resin tags with SEM, and degree of conversion with ATR-FTIR. Results: Adhesive type and application mode significantly affected bond strength (p < 0,001), whereas substrate type and thermal cycling showed no effect (p > 0,05). The adhesive type–substrate type interaction was significant (p = 0,009). G2 Bond Universal and Gluma Bond Universal produced higher bond strength than Clearfil Bond Universal. Self-etch mode yielded greater values than etch&rinse. Mixed failures predominated in the G2 Bond Universal group, while Clearfil Bond Universal showed the highest adhesive failure rate. Clearfil Bond Universal exhibited a significantly higher degree of conversion than G2 Bond Universal and Gluma Bond Universal, with no significant difference between the latter two (p > 0,05). Conclusion: HEMA-free universal adhesives were effective in bonding to both sound and caries-affected dentin. Keywords: Caries-Affected, Degree of Conversion Dentin, Dentin Bonding, HEMA-Free Adhesive, Universal Adhesive.