The Effect of Bioactive Liner Materials on the Bond Strength of Universal Adhesives to Dentin

Objective: This in vitro study aims to investigate how different bioactive base materials influence the bond strength of two universal adhesive systems, Single Bond Universal and Prime&Bond Universal, when applied to dentin-liner complexes. Understanding the interaction between adhesives and base materials is critical to improving the longevity of restorations placed in deep cavities.Methods: Eighty extracted human molars were sectioned and standardized dentin surfaces were prepared. Four bioactive base materials (TheraCal LC, Riva LC, Riva SC, and BioMTA+) were applied, followed by one of the two universal adhesives. Composite build-ups were placed and specimens underwent 10,000 thermocycles to simulate oral aging. Shear bond strength (SBS) testing was performed, and failure modes were analyzed microscopically. A two-way ANOVA and Tukey's post hoc tests were used (α = 0.05).Results: The type of base material had a statistically significant effect on bond strength (p < 0.001), while the adhesive brand did not (p = 0.247). TheraCal LC yielded the highest mean bond strength (20.6 ± 2.1 MPa), whereas BioMTA+ showed the lowest (10.2–11.4 MPa). A failure mode analysis revealed that cohesive failures predominated in the BioMTA+ group, suggesting internal material weakness.Conclusions: The bond strength of universal adhesives is substantially affected by the choice of bioactive base material. TheraCal LC demonstrated superior performance, which is likely due to its resin-modified composition and light-curing capability. No significant differences were observed between the two adhesives tested.