Fluoride-containing adhesive: Durability on dentin bonding

Objectives: To evaluate (1) the influence of fluoride-containing adhesive on microtensile bond strength (μTBS) and (2) in vitro secondary caries inhibition at the resin-dentin interface after 24 h and 3 months water-storage and (3) the degree of conversion of different adhesives after 24 h 1 month. Methods: Flat surfaces of human teeth were ground and randomly assigned to six groups: (SBMP-24) Scotchbond Multi-Purpose control [SBMP], 24 h; (SE-24) SBMP etch and primer + Clearfil SE Bond adhesive [SE], 24 h; (PB-24) SBMP etch and primer + Clearfil Protect Bond adhesive [PB], 24 h; (SBMP-3) SBMP, 3 months; (SE-3) SBMP + SE, 3 months; and (PB-3) SBMP + PB, 3 months. To evaluate the effect of the adhesive resin alone, all teeth were etched with 35% phosphoric acid and primed with SBMP primer prior to applying the adhesive resin. Bonded assemblies were prepared for μTBS and stored in distilled water at 37 °C for 24 h and 3 months. Sections of restored teeth of each group were exposed to an acid challenge. The specimens were sectioned, polished, and then observed with polarized light microscopy (PLM). Also, the degree of conversion (DC) of the adhesives was measured using Fourier Transform-Infrared spectroscopy (FTIR) at 24 h and 1 month, after polymerization. Results: μTBS values obtained in MPa (24 h/3 m) were: (MP) 61.5 ± 10.5/52.9 ± 8.9, (SE) 55.5 ± 11.8/55.6 ± 13, and (PB) 50.3 ± 9.9/61.0 ± 13.6. For interface analysis by PLM, an inhibition zone (IZ) adjacent to the hybrid layer was created only when the fluoride-containing adhesive (PB) was used. The DC in percentage (24 h, 1 month) were: (MP) 60.5 ± 2.8/61.3 ± 0.6, (SE) 69.6 ± 1.3/70.7 ± 0.05, and (PB) 53.1 ± 0.4/58.3 ± 1.6. Significance: The fluoride-containing adhesive demonstrated significant increase of bond strength values after water-storage. This material was also able to create an acid inhibition zone in dentin. There was a significant increase of degree of conversion after 1 month only for PB.