This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
The most common pre-eruptive staining is: 
Select and explain. 
A. Amelogenesis imperfecta., B. Dentinogenesis imperfecta., C. Endemic fluorosis., D. Pulp necrosis.
C: Endemic fluorosis.
Answer: C: Endemic fluorosis. 
Explanation: Intrinsic colors are determined by optical properties of enamel and dentin and their interaction with light. If incorporated into the dentin, they become visible because of the translucency of the enamel. They can be related to periods of tooth development, as in amelogenesis imperfecta  or dentinogenesis imperfecta or they may be acquired after completion of tooth development, as in pulp necrosis. The most common pre-eruptive staining is endemic fluorosis caused by excessive fluoride ingestion during tooth development.