Micromorphological spectrum from overdrying to overwetting acid-conditioned dentin in water-free, acetone-based, single-bottle primer/adhesives

Objectives. The goal of this study was to illustrate and define the micromorphological spectrum which exists at the resin-dentin interface when two water-free, acetone-based, single-bottle primer/adhesive systems (One-Step, Bisco, and Prime & Bond, Dentsply/LD. Caulk) were applied to acid-conditioned dentin under different dry and wet bonding conditions. Methods. Forty-eight 1 mm dentin discs were each conditioned with 10% phosphoric acid and rinsed for 20 s. They were randomly divided into 4 groups based upon the status of the remaining surface moisture: Group I (30 s dry) ; Group II (3 s dry); Group III (blot dry) and Group IV (overwet). Bonded dentin disc pairs were then demineralized in EDTA and embedded in epoxy resin for transmission electron microscopic examination. Results. The micromorphological spectra of the two bonding systems were essentially similar. Both were affected by even mild desiccation (3 s), resulting in incomplete intertubular resin infiltration. Optimal intertubular resin infiltration was achieved when the collagen network was kept moist and appeared relatively unaffected by the presence of excess surface moisture. On the other hand, intratubular resin infiltration was severely compromised in the presence of excess water within the dentinal tubules and at their openings on the dentin surface. The continuity of the resin layer deteriorated; blister-like spaces formed on the dentin surface and resin globules were found around the tubular orifices and on the surface of the hybrid layer. In addition, a complex phase separation pattern was observed in Prime & Bond that was characterized by phase inversion in the presence of surface moisture. Significance. The "window of opportunity" for optimal interfacial integrity for both water-free systems appeared to depend upon keeping the demineralized collagen network moist, coupled with the complete evaporation of excess and "displaced" water from tissues prior to lightcuring the primer/adhesives.