Interfacial Chemomechanics of Bonding to Clinically Relevant Dentin Substrates

Dentists must often attempt to bond adhesive resins to caries-affected dentin substrates. However, to date there is little information available on the effect such substrates have on the bonding of adhesives. Objective: Using FTIR and Raman chemical imaging, high frequency scanning acoustic microscopy (SAM), and staining techniques we set out to examine the bond that exists between adhesive resins and caries-affected dentin. Methods: Normal and carious human molars (with occlusal dentin lesions) were sectioned longitudinally to remove enamel. After Raman and SAM were performed on bare specimens one of four adhesives (Peak SE, Adper Prompt, PQ1, Single Bond Plus) was applied. The specimens were then cut into 5-micron sections using a microtome, these sections were later used for staining and FTIR imaging. Raman and SAM were then repeated on the specimens which now contained adhesive. Results: The differences in structure and composition not only interfered with acid-etching process but also subsequent resin monomer penetration. At the interfaces, there were dramatic changes of Young's modulus, an area of about 5-20 microns of significantly lower values than those of adhesive or dentin was observed. As compared to normal dentin, there were striking differences in depth of demineralization, adhesive infiltration and micro-mechanical properties at the interface with caries-affected dentin. It was shown that the interface between the adhesive and caries-affected dentin was wider and more complicated than that of the adhesive and normal dentin. Distinct interfacial patterns also correlated to the type of adhesive applied. Among the adhesives tested, PQ1, marked by its high filler composition, yielded relatively enhanced interfacial structure and properties. Conclusions: The chemistry of resins and caries-affected dentin leads to highly uneven structure and property along the length and breadth of the interface. The interfacial variation and complexity could be readily visualized with the complementary techniques. Supported by NIH DE015281.