Dentin bond durability after three years using a dentin bonding agent with and without priming.

Abstract

OBJECTIVES: This three-year study was conducted to evaluate the tensile bond strengths of a dual-cured bonding resin, with and without priming, to bovine dentin. METHODS: Superficial bovine dentin was conditioned with 37% phosphoric acid and left unprimed (control) or was primed with 5-NMSA. Clearfil Photobond (Kuraray Co., Japan) was placed and light-cured, a layer of Protect Liner (Kuraray Co.) was applied, cured, then covered with Photo Clearfil Bright (Kurary Co.) resin composite and cured. Bonds were stressed in tension to failure at 1 d, 1 mon, 3 mon, 6 mon, 1 y and 3 y after preparation. Ten specimens were made for each group. Results were analyzed using one-way ANOVA and Duncan's multiple range test. Visual and SEM observations determined mode of failure and were analyzed using the Mann-Whitney U-test. Separate 1 d and 3 y specimens were fractured across the bonded interface and observed using a Field Emission SEM. After observation, the photomicrographs were compared for visual qualitative changes between the two time periods. RESULTS: The control (non-primed) group showed only a small decrease in bond strengths over 3 y, but in the primed group, a significant decrease was observed (p < 0.05). The bond strength of the non-primed group (5.2 MPa) was less than the primed group (10.6 MPa) at 1 d (p < 0.01), but by 3 y, the bonds of both groups were similar, 4.3 MPa and 5.5 MPa, respectively. Fractography indicated that only adhesive failure occurred in the control group. Failure in the primed group was cohesive in dentin initially, but shifted to the base or top of the hybrid layer after 1 y. Field Emission SEM observations showed hybrid layer formation in the primed group, but minimal resin infiltration in the control group. SIGNIFICANCE: Initially greater bond strengths were obtained for the primed group compared to the unprimed group (p < 0.01). However, by 3 y, the bond strength had decreased markedly in the primed group (p < 0.01), being almost the same for both groups. It was concluded that priming may only be useful to achieve strong bonding in the short term. These results may have significant implications related to clinical longevity of restorations.