How Different Resin Applicators and Primer Systems Affect Dentin Adhesion

Objectives: Test the hypothesis that dentin adhesive applicators affect dentin bond strength, and that the effect is influenced by the solvent used in the primer. Methods: Third molars (n = 4x12) were cut perpendicularly to their long axes to expose occlusal dentin, then embedded into stone and polished with sandpaper under continuous water cooling. Each exposed dentin surface was etched with 35% phosphoric acid (15 s) and water rinsed (20 s). The etched surface was blotted dry and either HEMA/65vol% water(W) or HEMA/65% acetone(A) primer was placed onto spherical microbrushes(M) or cylindrical fiber brushes(F). Two coats of primer were brushed onto the tooth surface and air-thinned for 3 s. Then adhesive resin was placed using the prescribed applicator and air-thinned for 3 s, followed light activation for 10 s. Composite material, ~1 mm thick, was inserted into a metal ring (inner diameter=3.0 mm) on the dentin surface and light-cured for 40 s. Another 1 mm layer was added to fill the ring and light-cured for 40 s. The samples were then submerged in water and kept at 37°C for 24h. A shear force was applied to the metal ring surrounding the composite specimen, and the force at dislodgement was divided with the cross-sectional area of the composite sample to obtain bond strength. The bond strength values were analyzed using PROC NPAR1WAY to determine whether significant differences existed between primer systems or bristle types. Results: W+M=8.0±5.0 MPa, W+F=12.8±7.6 MPa, A+M=9.0±5.2 MPa, A+F=7.5±3.3 MPa. Comparing the two brushes independent of solvent medium and the two solvents independent of brush use revealed no significant differences (p=0.3341 vs. p=0.2023). When comparing the four groups, a non-significant difference with a p-value of 0.0914 was found. Conclusion: The results could not support the proposed hypothesis.