Rank the following surfaces from MOST to LEAST susceptible to dental caries.

Correct answer: D. Occlusal → interproximal → buccal/lingual smooth surfaces

• A. Interproximal surfaces rank second, not first. Pits and fissures remain the highest-risk sites in the permanent dentition.
• B. Susceptibility varies markedly by surface anatomy — this is precisely why sealants are placed on occlusal surfaces and not on buccal smooth surfaces.
• C. Smooth surfaces are the LEAST susceptible, not the most — they are wiped by the tongue, cheek and brush and are bathed in saliva.
• D. CORRECT. Susceptibility follows PLAQUE STAGNATION and cleansability. OCCLUSAL pits and fissures are the most susceptible — the fissure is narrower than a toothbrush bristle, so plaque is mechanically protected and fluoride penetrates poorly. INTERPROXIMAL surfaces below the contact point come next: inaccessible to a brush and cleanable only with floss. BUCCAL and LINGUAL smooth surfaces are the least susceptible because they are self-cleansing under tongue and cheek movement and are directly reached by the brush.

Note: This ranking is the rationale for pit-and-fissure sealants: the highest-risk surface is also the one least protected by fluoride, since fluoride works best on smooth surfaces.