‘Choking off’ phenomenon takes place after application of:

 # ‘Choking off’ phenomenon takes place after application of:
B. NaF
C. SnF2
D. Amine Fluoride

The correct answer is B. NaF.

Choking off phenomenon is seen with the application of sodium fluoride varnish.

Neutral Sodium Fluoride 
• Fluoride concentration = 9200 ppm 
• Formed by dissolving 20 gms NaF in 1 Litre of water in a plastic bottle 
• Knutson technique: used for NaF application - Clean and dry teeth and isolate the field - Apply 2% NaF over teeth with cotton bud/applicator. Allow the solution to dry for 3-4 minutes - Application is repeated at 2nd, 3rd and 4th week at an interval of 1 week each. These applications are not preceded by Scaling. - The four-visit procedure is recommended for age groups 3, 7, 11, 13 years coinciding with eruption of different dentitions 

• Mechanism of action - NaF applied to tooth surface reacts with tooth calcium to form CaF2 - As CaF2 develops, it impedes further penetration of fluoride into hydroxyapatite. This is called "Choking off" phenomenon. It is because of this phenomenon, repeated application of NaF should be done only after 4 minutes. - The CaF2 reacts with hydroxyapatite to slowly release fluoride and thus is caries inhibitory. 

• Advantages: 
- NaF is stable when kept in plastic containers. NaF reacts with glass 
- Taste is well acceptable by patient 
- Does not discolour tooth structure 
- Procedure indicated only at specific ages and not every year application 

• Disadvantages: - At the index age, 4 visits to the dentist are mandatory in that year. 

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