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: Surgery
The maxillary tooth that is difficult to anaesthetize by infiltration is: 
Select and explain. 
A. Canine, B. 3rd molar, C. Incisors, D. 1st molar
D: 1st molar
Answer: D: 1st molar 
Explanation: The maxillary tooth that is difficult to anaesthetize by infiltration is First molar due to the presence of thick zygomatic buttress in this region.