Which of the following is a disadvantage of topically applied sodium fluoride solution?
Advantages of neutral sodium fluoride solution-
1. It is relatively stable when kept in a plastic container and there is no need to prepare a fresh solution for each patient. 
2. The taste is well accepted by patients. 
3. The  solution  is non-irritating  to the gingiva. 
4. It does not cause discoloration of tooth structure. 
5. Once applied to the teeth, the solution is allowed to dry for 3 minutes. Thus the clinician in public health programs can pursue a multiple-chair procedure. 
6. The series of treatments must be repeated only four times in the general age range of 3  to  13, rather than  at annual or semiannual intervals, therefore in a public health program, other groups of children can be treated in theJintervening years. 
Disadvantage of neutral sodium fluoride solution-
1. The major disadvantage of the use of sodium fluoride is that the patient must make four visits to the dentist within a relatively short period of time.
Need to prepare a fresh solution for each patient
Taste is not well accepted by patients
Patient must make four visits to the dentist within a relatively short period of time
The solution should be allowed to dry for 5 minutes