Too Wet, Too Dry? Influence of Water Contamination and Overdrying on the Bond Strength of a Universal Adhesive to...

The aim of this in vitro study was to measure the microtensile bond strength (μTBS) and the contact angle of a universal adhesive (Prime & Bond Active) to overdried and water-contaminated human dentin.

After exposing flat dentin surfaces (5×5 mm2) of 60 caries- and restoration-free molars, test groups were either overdried or water-contaminated before adhesive application (self-etch) or after phosphoric acid etching (etch&rinse). In control groups, the adhesive was applied according to the manufacturer's instructions. μTBS (n = 45 samples) was analyzed (24 h/thermocycling: 15,000 cycles, 5/55°C). Fracture patterns were assessed microscopically. Contact angles were measured using the sessile drop method. Statistical analysis was performed using Tobit regression and Scheffé correction for bond strength data and Kruskal-Wallis test for contact angle measurements (α = 0.05).

Overall, µTBS was significantly higher after etch&rinse application compared to the self-etch mode before (P 0.001, Δ 11.04 MPa) and after aging (P 0.001, Δ 6.73 MPa). The highest μTBS (29.9 ± 10.4 MPa) was achieved by the etch&rinse control before aging. For etch&rinse application, water contamination and overdrying initially led to significantly lower µTBS compared to the control (P = 0.014/P = 0.007). Aging significantly decreased μTBS in both etch&rinse control and overdry groups (P 0.001/P = 0.036). Fracture modes were predominantly adhesive (90%). Contact angle on water-contaminated dentin was significantly lower for self-etch than for etch&rinse mode (P = 0.008).

The adhesive application mode significantly influenced bond strength. Dentin surface condition initially affected the µTBS solely in etch&rinse mode. Only on water-contaminated dentin, the contact angle was influenced by the adhesive application mode.