Dark zones in fluorotic enamel after resin infiltration

Before application of resin infiltrant (Icon) enamel is dried. Figure 1 shows that dried fluorotic enamel appears opaque (no birefringenc) under polarizing microscopy with Red I filter (red background). After resin infiltration, the air volume is partially filled by resin infiltrant as can be evidenced by the formation of dark zones (arrows) in infiltrated fluorotic enamel.

Figure 1. Ground section of fluorotic enamel under polarizing microscopy with Red I filter (red background). Left, fluorotic enamel dried for 48 h (20º C and 50% of relative humidity), presenting opaque enamel (no birefirngence). Right, fluorotic enamle after resin infiltration for 10 min, showing elimination of opaque enamel, but formation of dark zones (arrows) in the previously opaque area. The dark zones (same red color as the background) are evidence of the partial occlusion of enamel pores by the resin.