TEM characterization of a silorane composite bonded to enamel/dentin

ObjectivesThe low-shrinking composite composed of combined siloxane–oxirane technology (Filtek Silorane, 3M ESPE, Seefeld, Germany) required the development of a specific adhesive (Silorane System Adhesive, 3M ESPE), in particular because of the high hydrophobicity of the silorane composite. The purpose of this study was to characterize the interfacial ultra-structure at enamel and dentin using transmission electron microscopy (TEM).MethodsNon-demineralized/demineralized 70–90 nm sections were prepared following common TEM specimen processing procedures.ResultsTEM revealed a typical twofold build-up of the adhesive resin, resulting in a total adhesive layer thickness of 10–20 μm. At bur-cut enamel, a tight interface without distinct dissolution of hydroxyapatite was observed. At bur-cut dentin, a relatively thin hybrid layer of maximum a few hundreds of nanometer was formed without clear surface demineralization. No clear resin tags were formed. At fractured dentin, the interaction appeared very superficial (100–200 nm). Distinct resin tags were formed due to the absence of smear plugs. Silver-nitrate infiltration showed a varying pattern of both spot- and cluster-like appearance of nano-leakage. Traces of Ag were typically detected along some part of the enamel–adhesive interface and/or between the two adhesive resin layers. Substantially more Ag-infiltration was observed along the dentin–adhesive interface of bur-cut dentin, as compared to that of fractured dentin.ConclusionsThe nano-interaction of Silorane System Adhesive should be attributed to its relatively high pH of 2.7. The obtained tight interface at both enamel and dentin indicates that the two-step self-etch adhesive effectively bridged the hydrophilic tooth substrate with the hydrophobic silorane composite.