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 muscle has an indirect effect on the extent of impression in labial vestibule (maxilla) 
Select and explain. 
A. Orbicularis oris, B. Buccinator, C. Masseter, D. Levator anguli oris
A: Orbicularis oris
Answer: A: Orbicularis oris 
Explanation: None