Analysis of 1-minute Bioavailable Fluoride from Dentifrice

Previous reports found that some fluoride containing dentifrices do not release effective concentrations of fluoride during brushing.  Failure to release bioavailable fluoride can be due to dentifrice matrix components that interfere with the solubilization of the fluoride salts during brushing.

Objectives: Demonstrate the previously described filter paper absorption method to assess the 1-min bioavailable fluoride concentration. This method utilizes coiled filter paper which rapidly absorbs the aqueous phase of the dentifrice slurry followed by centrifugation to recover that fluid.

Methods: Bioavailable-F: vigorously mix 1.0g dentifrice and 3mL distilled water for 60s, submerge coil of filter paper into the slurry for 15s, place coil of wetted filter paper into the filter assembly, insert into centrifuge tube and centrifuge for 2min at >14,000rpm.  Total-F: recover 0.5mL aliquot of slurry for analysis of total fluoride. Hydrolyze all samples with HCl at least 1h followed by NaOH neutralization.  All-F: analyze using fluoride ion selective electrode (F-ISE). Six dentifrices containing NaF, MFP, SnF₂, or NaF+ACP were tested on at least two different days.

Results:

Dentifrice F source	Total F (S.D.)ppm	Bioavailable F (S.D.)ppm	% Bioavailable F
NaF-A (n=8)	1172(59)	1069(87)	91.2
NaF-B (n=8)	1148(35)	1039(69)	90.5
MFP-A (n=8)	960(45)	848(122)	88.3
MFP-B (n=4)	850(40)	409(34)	48.1
SnF2 (n=8)	1031(49)	535(14)	51.9
NaF+ACP (n=8)	1238(12)	999(19)	80.7

The variations between analyses were higher for the MFP samples where the hydrolysis of the solubilized MFP was necessary for the F-ISE measurements.

Conclusions: The filter paper absorption method yielded reproducible results for most products with MFP samples showing the largest variations.  This method is designed for the analysis of bioavailable-F in dentifrice samples that may have a kinetic limitation (delivers solubilized fluoride too slowly or the fluoride is quickly precipitated after release) and is not necessary for dentifrice that does not have a kinetic limitation.

 

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