Photodeveloping solution

30 specimens were utilized in this experiment. 10 teeth were randomly selected from each group. The selected specimens were vertically cross-sectioned with a diamond saw under water cooling through the dentin-resin interface. The bonded slabs were ground and polished using #1000 silicone carbide paper under wet conditions. The specimens were dried, then coated with two layers of fast-drying nail varnish applied up to 1 mm from the bonded interface. The specimens were exposed to ammoniacal silver nitrate in total darkness for 18 h, rinsed thoroughly, and immersed in photodeveloping solution (Kodak, NY, USA) for 6 h under fluorescent light to reduce silver ions into metallic silver [15 (link)]. The silver-stained resin-bonded specimens were lightly polished to remove the superficial silver remnants [2 (link), 5 (link), 15 (link), 16 (link)], followed by drying the specimens and preparing it for SEM observation. The specimens were examined using SEM/EDS (JCM-6000, NeoScope, JEOL, Tokyo, Japan), and line scans were examined across the resin-dentin interface [2 (link), 5 (link), 15 (link)]. The nanoleakage expression was observed and recorded in three areas: hybrid layer, hybrid layer-adhesive interface, and adhesive layer. All of the experimental steps are summarized in Figure 1.

For nanoleakage, the beams received two layers of nail varnish up to 1 mm from the bonding interface on both sides. Then, they were individually immersed in an aqueous ammoniacal silver nitrate solution (50% in weight; pH = 7.0) and kept in a dark environment for 24 h, thoroughly rinsed in running water, and immersed in a photo-developing solution (Kodak, Rochester, Nova York, USA) under fluorescent light for 8 h, in order to reduce silver ions into metallic silver grains at the bonding interface. Afterwards, the surfaces were wet polished with 600-grit, 1200-grit, and 4000-grit SiC paper, ultrasonically cleaned in water for 10 min (Ultrassom 750 USC, Quimis, Rio de Janeiro, Brazil), and dried for 48 hours in a desiccator with blue silica gel at 37°C.
The resin/dentin interfaces were observed using scanning electron microscopy (SEM) (Phenom ProX, Phenom-World, Eindhoven, Netherlands), at an accelerating voltage of 15 kV, backscattered mode, and using a charge reduction sample holder (low vacuum environment). Three images were registered for each beam: two from both ends (right and left sides) and one central, with a magnification of 2000x. The amount of silver nitrate uptake in the hybrid layer was registered as a percentage of the total area observed, using an Energy-dispersive X-ray spectroscopy (EDS) detector (Phenom ProX, Phenom-World, Eindhoven, Netherland).