Why does a traumatised primary incisor commonly become discoloured?

Correct answer: B. Intrapulpal haemorrhage with blood breakdown products entering the dentinal tubules, with or without subsequent necrosis

• A. Replacement resorption is a radiographic and percussion finding, not a cause of crown discolouration.
• B. CORRECT. The impact ruptures pulpal vessels and blood floods the pulp chamber. Haemoglobin degrades to iron sulphides which diffuse into the DENTINAL TUBULES, staining the crown grey-pink and then grey-brown. Notably, many of these teeth remain VITAL and the discolouration may fade over months; others progress to necrosis. Discolouration alone is therefore not an indication for treatment.
• C. Enamel hypoplasia in the traumatised primary tooth itself is not the mechanism; hypoplasia is what may appear later on the PERMANENT successor.
• D. Tetracycline staining is systemic and generalised, banding all teeth forming during the exposure period — it is not localised to one traumatised tooth.

Note: Monitor a discoloured but asymptomatic primary incisor. Intervene only for a sinus tract, abscess, pathological mobility or radiographic pathology.