Evaluation of Proposed Total Fluoride Method for Varnishes

Objectives:   Currently, there is no universally-accepted method to determine total fluoride in 5%NaF-varnishes.  A working group has drafted a test method, and here we share important modifications and share results for: A=Colgate®Duraphat®Varnish, B=3M™ESPE™Clinpro™WhiteVarnish, C=Premier®EnamelPro®Varnish, D=Colgate®PreviDent®Varnish, E= Kolorz®ClearShield®, F=Control 2% wt/wt NaF-Solution, G=Fluoride-Standard-1000ppm-RICCAChemicalCompany®.

Methods:   The draft method involves varnish (0.1-0.2mL) added to a mixture of chloroform (4.0mL) and TISAB (10.0mL) in a glass vial followed by vigorous shaking, stirring (1.5hrs), and settling (>30min).  Once settled, 1.0mL of the aqueous layer (top) is mixed with 1.0mL of DI water and 18.0mL of a 50/50 TISAB/Water solution.  The sample is measured using a calibrated fluoride-ion selective electrode (F-ISE) and NaF standards at 0.0001, 0.001, and 0.01 mol/L in an equal volume of TISAB solution. 

Results:   Modifications to the test method included: mix the varnish completely prior to adding to chloroform, and then add TISAB.  Vigorously shake the solution for >6 minutes by hand (with periodic venting) to ensure the fluoride is extracted to the aqueous layer, and settle for at least 24-hours.  Create a standard curve using five fluoride standards (1, 2, 10, 50, and 100ppm) in TISAB and determine F-concentration. 

Varnishes A,B,C,D,E were evaluated, n=5, using the modified method.  Controls F,G were also evaluated. Mean ppm values and standard deviations are shown in the figure below.  Varnish A is considered the industry standard, and labels state that each varnish contains 5%NaF (22624ppmF). 

Varnishes B, D, E exhibited fluoride content that was not statistically significantly different than A, and varnish C was statistically significantly different.  Varnish-C contains Amorphous-Calcium-Phosphate(ACP), which can react with fluoride. 

Conclusion:   The proposed method may not be a good tool to measure total fluoride, especially for varnishes that contain ACP.

Research supported by 3MESPE