In dens invaginatus, the base of the invagination extending into the crown or root is lined by which tissue?

Correct answer: B. Dystrophic (malformed) enamel

• A. Cementum lines the external root surface, formed by cementoblasts of the dental follicle. It has no role in lining an internal invagination of the enamel organ.
• B. CORRECT. Dens invaginatus results from an infolding of the ENAMEL ORGAN into the dental papilla before mineralisation. Because it is the enamel organ that invaginates, the invagination is lined by ENAMEL — and because the ameloblasts in that folded region are distorted and function poorly, the enamel formed there is DYSTROPHIC, thin, hypomineralised and frequently discontinuous. Those defects communicate directly with the pulp, which is why these teeth develop pulp necrosis very early, often before any caries is clinically visible.
• C. Necrotic pulp is a consequence — the common sequela when bacteria track through the defective enamel — not the histologic lining of the invagination.
• D. Dentin lies deep to the invagination's enamel lining but does not form the lining itself.

Note: Practical implication: a maxillary lateral incisor with a deep lingual pit deserves prophylactic SEALING as soon as it erupts. Once necrosis occurs, the aberrant internal anatomy makes conventional endodontics difficult and MTA apexification or surgery may be needed.