Effects of EDC crosslinking on the stiffness of dentin hybrid layers evaluated by nanoDMA over time

Application of collagen cross-linkers to demineralized dentin improves bond durability. While the benefits of cross-linking treatments to bond strength and fatigue resistance have been explored, changes in hybrid layer stiffness with aging have not been examined. Objective To examine the influence of a cross-linking treatment using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) on hybrid layer stiffness of resin-dentin adhesive bonds, using spatially-resolved nanoscopic Dynamic Mechanical Analysis (nanoDMA). Methods Bonded interface specimens were prepared using a two-step (SB) or three-step (SBMP) etch-and-rinse adhesive. Adhesive bonding of the treated groups was preceded by a 1 min application of an experimental EDC conditioner to the acid-etched dentin. Control specimens did not receive EDC treatment. The bonded interfaces were evaluated using nanoDMA to determine the dynamic mechanical properties after storage in artificial saliva at 37 °C for 0, 3 and 6 months. Results The EDC treatment had no influence on the dynamic mechanical properties of the hybrid layer immediately after bonding. There was also no reduction in the hybrid layer stiffness after 3 and 6 months aging as defined by the complex modulus and storage modulus. However, there was a significant reduction in the loss modulus and tan δ components (i.e. viscous behavior) of the hybrid layers with aging. Degradation occurred to both adhesive systems with storage, but was greatest for SB. Without EDC treatment, the reduction in tan δ of the hybrid layer prepared with SB exceeded 80% in 6 months. Significance The application of EDC to acid-etched dentin helps maintain the viscoelasticity of hybrid layers.