How do you check for interferences on the INTERNAL (fitting) surface of a crown before cementation?

Correct answer: C. A low-viscosity fit-checking silicone (e.g. vinyl polyether/polysiloxane fit checker)

• A. A shade guide addresses esthetics, not fit.
• B. Articulating paper marks OCCLUSAL contacts on the outer surface — it cannot evaluate the intaglio.
• C. Correct. A FIT CHECKER — a thin, low-viscosity silicone (vinyl polysiloxane/polyether) — is painted into the intaglio surface and the crown seated. Where the material is displaced to show-through or perforates, the casting is binding on the preparation. Those points are then relieved with a bur until the crown seats fully. Alternatives include disclosing wax or a pressure-indicating paste.
• D. A probe checks margins and periodontal parameters, not internal binding.