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
Fluoride recharging of a glass ionomer cement restoration is more effective by which of the following agents? 
Select and explain. 
A. 0.02% NaF solution for 2-3 minutes, B. 0.02% NaF solution for 2-5 minutes, C. 1.23% APF solution for 4-5 minutes, D. 1.23% APF solution for 2-3 minutes
C: 1.23% APF solution for 4-5 minutes
Answer: C: 1.23% APF solution for 4-5 minutes 
Explanation: The ability of a restorative material to be recharged and serve as a fluoride reservoir depends on the type and permeability of the material, the frequency of fluoride exposure, and the concentration of the fluoridating agent. For example, recharging is more effective by acidic fluoridating agents such as APF.
Ref: Phillip’s Science of Dental Materials ed 12 pg 334