What is the correct sequence of steps in the resin infiltration technique (ICON) for a proximal lesion?

• A. Etch, infiltrate, apply hydrophilic resin, light cure, polish and monitor
• B. Etch, light cure, apply hydrophobic resin, infiltration, polishing
• C. Etch, apply hydrophilic resin, allow infiltration into lesion, light cure; follow with polishing and monitoring
• D. Apply resin, etch, light cure, polish, monitor

Answer: (C)

The main idea is that resin infiltration arrests early proximal caries by letting a low-viscosity, hydrophilic resin penetrate and fill the porous demineralized lesion before it is cured. First you prepare the lesion surface with an acid etch to create microporosities that the resin can enter. Then you apply a hydrophilic, low-viscosity resin so it can flow into the lesion; you allow enough time for the resin to infiltrate the porosities. After infiltration, you light-cure to polymerize and lock the resin in place. Finally, you polish the surface and schedule monitoring to check arrest or progression. This sequence—etch, apply hydrophilic resin, allow infiltration, light cure, then polish and monitor—follows the correct flow for ICON. The other orders are inconsistent with how resin infiltration works: curing before infiltration, using a hydrophobic resin, or omitting the infiltration step would not properly seal the lesion or would disrupt the expected penetration and arrest mechanism.