To observe the ultrastructure of the dentin-adhesive interface after in vitro sequential challenge by acidic and basic chemicals around adhesive restorations. Box-shaped cavities were prepared in bovine root dentin and restored as follows: Reactmer Bond and Reactmer Paste (RB/RP), Clearfil SE Bond and Clearfil AP-X (SE/APX), ABF (experimental) and APX (ABF/APX), Single Bond and APX (SB/APX). After the specimens were stored in water for 1 week, the integrity of the bonds tested by sequential immersion were placed in an artificial demineralizing solution (pH 4.5) for 20 min and in 5% NaOCl for 20 min. The specimens were sectioned, polished, then argon-ion etched for 7 min, and gold sputter coated for SEM examination of the dentin-adhesive interface. The morphological results indicated tight bonding between the cavity wall dentin and the adhesive. For the fluoride-releasing restoration, RB/RP, a thick acid-resistant zone was clearly observed adjacent to the restoration; however, the bonding resin, RB, was partially degraded by the acid-base challenge. For SE/APX, ABF/APX and SB/APX, the bonding resins were resistant to the acid-base challenge. With the self-etching adhesive systems, SE and ABF, a thin band of acid-base resistant dentin less than 1 µm thick was observed beneath the hybrid layer. With the wet bonding system, SB, the hybrid layer was partially degraded by the acid-base challenge. SEM observation is useful for observing the reactions of adhesives to acid-base challenge. Prevention of secondary caries around a restoration may be influenced by the physical properties of the restorative and adhesive materials, quality of the hybrid layer, and fluoride-release. Keywords: hybrid layer, secondary caries, dentin bonding, SEM