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

## TL;DR

This study found that overdrying or water contamination of dentin affects the bond strength of a universal adhesive, with etch&rinse application showing higher strength than self-etch.

## Contribution

The study reveals that dentin surface conditions and adhesive application mode significantly impact bond strength and contact angles in dental adhesion.

## Key findings

- Etch&rinse application resulted in significantly higher microtensile bond strength (μTBS) than self-etch mode.
- Water contamination and overdrying reduced μTBS in etch&rinse mode before aging.
- Contact angles on water-contaminated dentin were lower for self-etch compared to etch&rinse mode.

## Abstract

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.