A single tooth appears as two crowns sharing a single pulp chamber, and the total tooth count in the arch is NORMAL. What is the diagnosis?

Correct answer: C. Gemination

• A. DENS INVAGINATUS ('dens in dente') is an infolding of enamel into the crown, most often in a maxillary lateral incisor. It does not produce two crowns.
• B. CONCRESCENCE is union of two adjacent teeth by CEMENTUM ONLY, after root formation. The crowns and pulps remain entirely separate.
• C. CORRECT (given a normal tooth count). GEMINATION is incomplete division of a SINGLE tooth germ, producing two crowns on one root with a shared pulp chamber. Because it began as one tooth, counting the affected structure as ONE tooth yields a NORMAL total count — that is the discriminating feature.
• D. FUSION is the union of TWO separate tooth germs. It also produces a shared crown/pulp appearance, but counting the fused structure as one gives a REDUCED total tooth count. Fusion and gemination are distinguished by the count, not by appearance.

Note: Note — the discriminator is the TOOTH COUNT. Two crowns with one pulp and a NORMAL count = gemination; the same appearance with a MISSING tooth from the count = fusion. The source states 'gemination' without giving the count, so read the stem carefully on exam day.