The durability of adhesion to phosphoric acid etched, wet dentin substrates

Objective. The purpose of this study was to investigate the influence of remaining non-resin-impregnated, phosphoric acid demineralized dentin upon the long-term durability of specimens that were wet-bonded to bovine dentin substrates. Methods. Prepared bovine dentin samples were etched with 65% phosphoric acid then rinsed with water and kept wet during application of 5 wt% 4-methacryloyloxyethyl trimellitate anhydride (4-META) in acetone primer. This was followed by application of a photocured dentin-bonding agent consisting of 4-methacryloyloxyethyl trimellitate anhydride/triethyleneglycol dimethacrylate - camphorquinone/N-phenylglycine (4-META/TEGDMA-CQ/NPG). The tensile bond strength (TBS) of bonded specimens was determined after immersion in 37°C water for various time intervals. Generated data were analyzed for statistical significance by one-way ANOVA and Duncanʹs New Multiple Range Test (p<0.05). The dentin side of the tensile-load-fractured specimens was examined under optical and scanning electron microscopes (SEM). Results. TBS decreased from 6.6±1.0 MPa after 1-day water immersion to 3.4±1.7 MPa after 1 month of water immersion. After 6 months of water immersion, TBS was found to be 3.9±0.9 MPa and this decreased to 2.0±1.0 MPa for specimens immersed in water for 1 year, a statistically significant difference (p<0.05). Optical microscopic and SEM observations disclosed failure patterns within demineralized, non-resin-impregnated dentin that increased with the period of water immersion. Significance. The bond durability to wet dentin was poor when demineralized dentin was not resin-impregnated, resulting in exposure of collagen fibrils which hydrolyzed during long periods of water immersion.