What is the cause of the grey discolouration seen in a non-vital tooth?

Correct answer: B. Blood breakdown products within the dentinal tubules

• A. Canal calcification produces a YELLOW, opaque appearance from the bulk of reparative dentine, not grey.
• B. CORRECT. When the pulp dies following trauma or infection, erythrocytes lyse and haemoglobin degrades. Iron combines with hydrogen sulphide produced by bacteria to form IRON SULPHIDE — a black-grey pigment that diffuses into the DENTINAL TUBULES. Because the stain is within dentine and not on the surface, external bleaching is ineffective; internal (walking) bleach is required.
• C. External resorption occurs on the root surface and does not discolour the crown.
• D. Internal resorption classically produces a PINK spot (the pink tooth of Mummery) where vascular granulation tissue shows through thinned dentine.

Note: Discolouration colour code: grey-brown = necrosis and blood products; pink = internal resorption; yellow = pulp canal obliteration; blue-grey opalescent = dentinogenesis imperfecta.