Resin infiltration (ICON) is normally done to even out any white/brown/yellow spots on the enamel. These spots are areas of porous enamel.
If these spots are not very significant and are shallow, then the process of trimming the enamel to accomodate the veneer will remove these areas of porous enamel and eliminate any colour discrepancy which may show through.
If the spots are prominent and deep, then prior bleaching or use of ICON may not be effective and microabrasion of the enamel may be required prior to veneer placement.
Generally, when the masking material is thicker, the greater amount of colour correction can be achieved. Very significant colour changes can be difficult to achieve with composite as compared to porcelain.
