Silicone oil emulsion

The dehydration process was followed by immersion of dentin beams in 50% solvent in the darkness (according to the solvent present in each adhesive)/ 50% adhesive system solution at room temperature for 30 min, and two immersions in 100% adhesive system for 30 min each. For the third immersion in 100% adhesive system, the beams were kept in the dark for 30 min at room temperature (23 ± 1 °C) or in an oven (Isotemp, Fisher Scientific, Pittsburgh, PA, USA) at 40 ± 1 °C to enable solvent evaporation. The macro-hybrid layers are thicker than hybrid layers created in clinical procedures [22 (link)], therefore, a passive volatilization of solvents was done (without the use of air jet) for 30 min but with the vial (containing the infiltrated beam) semi open to allow evaporation of solvents.
The resin-infiltrated dentin beams were placed between two mylar strips and immediately light cured as described for adhesive resin beams. The excess of adhesive around the dentin beams was removed using a scalpel blade and the margins and surface were hand-polished using 600-grit silicon carbide grinding paper with silicone oil emulsion (Sigma-Aldrich, St. Louis, MO, USA) [26 (link)].

One mL of each adhesive system was dispensed in a circular-plate and their initial mass was measured using an analytical balance (XP 504DR, Mettler Toledo Inc., Columbus, OH, USA). Each circular plate with the adhesive system was repeatedly weighed after 15, 30, 45 and 60 min until weight was stabilized. To keep traces of solvent in the adhesive, the time of volatilization was set at 30 min (based on pilot studies). The adhesive systems were kept in the dark for 30 min in an oven at 40 ± 1 °C or at room temperature (23 ± 1 °C). After time elaspsed, the adhesives were placed in polyvinyl siloxane molds (0.28 mm × 1.5 mm × 7.0 mm) and were immediately light-cured for 60 seconds on each side. Photo-activation was performed using a halogen-based unit (Optilux 501, Kerr Corp., Orange, CA, USA) with light intensity of 800 mW/cm². Then, all adhesive resin beams (n=12 per group) with final dimensions 0.28 mm thickness × 1.5 mm width × 7.0 mm length were hand-polished with 600-grit silicon carbide paper with a silicone oil emulsion (Sigma-Aldrich, St. Louis, MO, USA) [26 (link)].