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: Radiology
The minimum amount of tooth demineralization required for radiographic detection of dental caries is 
Select and explain. 
A. 20%, B. 40%, C. 60%, D. 80%
B: 40%
Answer: B: 40% 
Explanation: Lesions confined to enamel may not be evident until approximately 30% to 40% demineralization has occurred. For this reason, the actual depth of penetration of a carious lesion is often deeper than seen in the image.
 
Oral radiology by White & Pharaoh 7th ed. Page no 288