Malacarne-Zanon et al position, batch number, and manufacturer of each in a photo-developing solution for 8 hours, while adhesive system are listed in Table 1. kept under a fluorescent light, so that the silver Three disk specimens were prepared for each ions could be reduced into metallic silver particles. adhesive system and for the primer+bond mixture. The silver-impregnated specimens were then em- The uncured adhesives (approximately 200 μL) bedded in epoxy resin for support. The prepared were directly poured into a brass mold (5.8 mm adhesive discs were cut along their diameter us- diameter, 0.8 mm thick).8 For the primer+bond ing a low-speed diamond saw (Isomet 1000 Preci- specimens, a single drop of the primer was dis- sion Saw, Buehler, Lake Bluff, IL, USA), in order pensed into the mold, which was left undisturbed to expose the innermost surface. The exposed for 20 s, and then the bonding resin was poured surfaces were dry-polished using a glass knife over the primer until the mold was completely attached to an ultra-microtome (Sorvall Porter- filled. A micro-brush was applied to actively mix Blum, MT2-B, Norwalk, USA). Several cuts were primer and bond agents. As primer solutions and made to the exposed surface of the specimens un- some bonding agents have a certain amount of til an adequate polish was obtained. The prepared solvent and/or water in their composition, a sol- surface was carbon-coated and analyzed at a va- vent evaporation procedure was performed for all riety of magnifications in an SEM (JEOL-5600 LV, materials by using an oil/water-free air-syringe Tokyo, Japan) under backscattered electrons at for 30 s. A glass cover slip was placed on the top 90 kV. After this first evaluation, specimens were of the resin to minimize atmospheric oxygen, and returned twice to the ultra-microtome in order to photo-activation was performed using a quartz- expose other regions of specimens that were then tungsten-halogen light source, operating at 650 prepared following the steps outlined above to be mW/cm2, for 40 s (Elipar TriLight, ESPE, Germany). observed under SEM. In this way, three different After removal from the mold, the bottom of each evaluations were performed for each specimen. disk was further photo-cured for another 40 s. Any rEsuLts uncured resin remaining on the disk surface was cleaned off with absorbent paper. Next, the disks Figures 1 to 8 depict the most characteris- were pre-dried in a sealed desiccator containing tic patterns of silver permeation observed along fresh silica gel (at 37ºC), over a three-day period. the inner exposed surfaces of the different adhe- This time was used to enhance the specimens’ po- sives. Observation of adhesive surfaces revealed lymerization and to permit better evaporation of the presence of silver deposits in all evaluated residual solvent incorporated into the materials.8 materials. The amount of silver deposition varied. Some were sparsely spread on the surface of the Nanoleakage tracing and scanning electron specimen and others were severely interspersed microscopy evaluation through the entire thickness of the specimen. When the drying process was complete, speci- The bonding resins of SE and MP (Figures 1 mens were immersed in a 50% ammoniac silver and 2, respectively) showed slight silver perme- nitrate solution following the diamine silver im- ation over the interface with the embedded epoxy pregnation protocol reported by Tay et al,2 except resin. No infiltration extending to the center of the for the period of immersion in the tracer solution, specimens was observed. which was extended for 48 hours. In a previous Images produced for SE-PB showed two dif- study,8 it was found that fewer hydrophilic adhe- ferent and separate phases: one poorly infiltrated sives took approximately 48 hours to reach water occupying the center of the specimen and another sorption equilibrium. As silver ions were carried greatly infiltrated sector restricted to the upper into polymerized adhesives by water, this period and lower edges of the exposed surfaces (Figure of immersion was used for all adhesives tested, 3). instead of the 24-hour-period used by Tay et al.2 SB presented two distinct types of silver depo- Thus, the specimens were placed in the silver ni- sition, one consisting of isolated and aggregated trate solution in total darkness for 48 hours to al- silver granules distributed along the interface low silver saturation of the specimens. Afterwards, with the epoxy resin and extending to the center they were rinsed in distilled water and immersed of the specimens and another observed in the the October 2010 - Vol.4 431 European Journal of Dentistry