In minimally invasive dentistry, the aim is to preserve as much healthy tooth structure as possible, so the shapes used are designed to be conservative. A full crown requires substantial reduction of both enamel and dentin all around the tooth to fit the crown, which means removing a lot of sound tooth structure. That makes it non-conservative. The other shapes fit the MIS mindset. A tunnel prep lets you access and remove decay from beneath a tooth surface while keeping the cusps and marginal ridges largely intact, preserving strength. A slot or box prep provides access for proximal decay with minimal removal while maintaining much of the tooth’s structure. PRR, short for Preventive Resin Restoration (or partial caries removal and restoration), uses a resin restoration to seal and restore small lesions, again preserving more tooth structure than a full crown would. So the option that isn’t listed as a conservative prep shape is the full crown.

Topical fluoride therapy means applying fluoride directly to the tooth surface to enhance remineralization and prevent demineralization. Fluoride varnish is a professional topical product applied to teeth and left to release fluoride over time. Fluoride foam in lined trays is another topical method that coats all tooth surfaces for a period, delivering fluoride where it’s needed. Home fluoride products, like toothpaste and mouth rinses, provide daily topical exposure as they contact the tooth surfaces during regular brushing or rinsing. These approaches all deliver fluoride directly to the tooth surface rather than through ingestion and systemic distribution. Therefore, all of the listed options are methods of topical fluoride application.

Sealing is used to manage early proximal caries in patients at high caries risk, aiming to arrest progression while preserving tooth structure. When there are incipient proximal lesions or radiographic proximal radiolucencies without cavitation and the patient has high caries risk, sealing the area can halt further decay without drilling. If there are cavitated proximal lesions, sealing isn’t appropriate because a restoration is necessary to remove decay and restore form. No proximal lesions with low caries risk likewise doesn’t warrant sealing, and cosmetic appearance alone isn’t a driver for proximal risk management.

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.