The purpose of this work was to study the adhesive interface created, with an universal adhesive system (Futurabond M+), between two types of dentin substrates and a restorative material. To fulfill this purpose, we evaluated both the degree of conversion (DC) of the adhesive system and the degree of demineralization (DD) of the dentin, using μ-Raman Spectroscopy, and the morphology of the adhesive interface under Scanning Electron Microscopy (SEM). Two types of dentin were used – sound, from a healthy tooth, and affected, collected from the deepest layer of a carious lesion, without bacteria, partially demineralized however physiologically remineralizable. The universal adhesive system was applied using two available modes - etch-and-rinse (ER) and self-etch (SE). Analyses were performed after 24 h and 6 months of the restorative procedure. Significant differences were found between adhesive modes in the DD of sound substrate specimens after 6 months aging and in the DD of affected substrate specimens, after 24 h and 6 months aging. Average DD values were, overall, higher with the ER mode. Average DC values were substantially high (DC ≥ 78%) overall, independently of the experimental group analised. DC values were on average lower closer to the dentin substrate and higher closer to the adhesive layer. The morphology of the interface was consistent with the results obtained by the μ-Raman Spectroscopy technique.