Nanoindentation Mapping and Bond Strength Study of Adhesive–Dentin Interfaces

Abstract

AbstractA scanning probe microscopy (SPM) nanoindentation technique is employed in this work to relate structure of adhesive–dentin interfacial regions with in situ mechanical properties. Noncarious human third molars are sectioned to obtain superficial, middle, and deep dentin disks. Each dentin disk is divided into two parts for bonding with All‐Bond Universal in etch‐and‐rinse (E&R) and self‐etch (SE) modes. Nanoindentation arrays of a small‐scale region of 40 × 40 µm2 are configured, which include the whole adhesive interface area from the restorative composite across the adhesive interface to unaffected dentin. Micro‐shear bond strength (μSBS) is measured to evaluate the mechanical capability. By virtue of high‐resolution quantitative mapping of nano‐elastic modulus and nanohardness, the continuous hierarchical substructures of adhesive–dentin interfaces are visualized, including the composite, adhesive layer, hybrid layer, and unaffected dentin. A noticeable finding is the existence of a transition zone between the hybrid layer and unaffected dentin. The μSBS result indicates that mechanical interlocking between intertubular dentin and adhesives dominates the bond strength. SPM nanoindentation mapping can correlate surface structure with mechanical properties across adhesive interfaces. Even more, the present findings demonstrate that SPM‐mapping of combined structural and mechanical property data of adhesive interfaces can potentially be used to evaluate bonding performance.