A necrotic tooth with a 1-year history of trauma shows internal discoloration. The most likely cause of the discoloration is:

Correct answer: B. Breakdown of red blood cells (hemoglobin degradation products)

• A. Calcific metamorphosis (pulp canal obliteration) produces a yellow-orange discoloration from secondary dentin deposition, not from breakdown products.
• B. Correct. Traumatic dental injuries can cause pulpal hemorrhage. As the pulp necroses, hemoglobin from RBCs breaks down into hemosiderin and other iron-containing pigments that diffuse into dentinal tubules, causing gray-brown discoloration of the tooth.
• C. Bacterial endotoxins contribute to pulpal pathology but do not cause the characteristic gray-pink discoloration of post-traumatic pulp necrosis.
• D. WBC breakdown does not produce pigmented byproducts that stain dentin.