MMP-9 involvement in dentin-bond degradation

Many studies suggest that MMP-9 might be involved in degradation of resin-dentin interfaces. Objective: To determine the effect of an activated MMP-solution on the mechanical properties of the bond to dentin. If MMP-9 is involved in the bond-degradation process, the activated MMP-9 solution is expected to reduce the bond strength to dentin. Methods: Bur-cut dentin surfaces of 6 human molars were etched with 37% phosphoric acid (Scotchbond Etchant, 3M ESPE) for 15 sec and rinsed with water for 10 sec. Half of the surface was treated with either a 0.1 μM (MMP-LC) or 10 μM MMP-9 solution (MMP-HC) in TRIS-buffer for 60 seconds, while the other half (buffer treatment only) served as control. Then, the etch&rinse adhesive Scotchbond 1 XT (3M ESPE) was applied, followed by a composite (Z100, 3M ESPE) build-up. After storage in water for 7 days at 37°C, 1x1 mm resin-dentin sticks were prepared and the micro-tensile bond strength (µTBS) was determined. Results: One-way-ANOVA revealed no significant differences between the groups (p=0.8081). The mean µTBS values were 48.4 ± 8.6 MPa for group MMP-LC, 45.3 ± 15.3 MPa for group MMP-HC and 44.9 ± 14.3 MPa for the control. Failure analysis revealed predominantly mixed failures for all groups, including failures inside the dentin, at the resin-dentin interface and inside the resin (adhesive/composite) part. Conclusion: Application of a highly concentrated, activated MMP-9 solution did not affect the bonding effectiveness of a 2-step etch&rinse adhesive to dentin. Therefore, the role of this gelatinase in bond degradation appears limited, as before the gelatinase can be involved, collagen fibrils need first to be broken down by other degradation mechanisms.