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
Which tooth is known as enigma to endodontist 
Select and explain. 
A. Mandibular canine, B. Maxillary 1st premolar, C. Mandibular 2nd premolar, D. Mandibular 1st premolar
D: Mandibular 1st premolar
Answer: D: Mandibular 1st premolar 
Explanation: None