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The goal of fluoride mouthwash is to deliver $\ce{F-}$ to the surface of the teeth to turn hydroxyapatite in the dental enamel into fluorapatite. Typically sodium fluoride or stannous fluoride are used.

ACT fluoride mouthwash also contains $\ce{Ca}$ in the form of $\ce{Ca-EDTA}$. https://www.drugs.com/otc/114080/act-total-care-anticavity-fluoride-rinse-fresh-min-01.jpg

$\ce{CaF2}$ has a very low solubiliy product of $3.9 × 10^{−11}$, I would expect the $\ce{F-}$ to precipitate as $\ce{CaF2}$ and become unavailable. This is in agreement with the literature where $\ce{EDTA}$ has been used in the determination of $\ce{F-}$ through backtitration of $\ce{Ca^2+}$. This shows that the complex is less stable than the fluoride. http://www.sciencedirect.com/science/article/pii/S0003267000876369

Note:

It was suggested in the comments to use 10x the concentration of $\ce{Ca-EDTA}$. I don't see how this could work, all it would do is depress the concentration of available fluoride even more.

I suspect $\ce{EDTA}$ is used as an anti biofilm agent or preservative, and the $\ce{Ca}$ is used so it doesn't chelate dental $\ce{Ca}$. I assume this use is unrelated to the process of fluoride delivery.

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  • $\begingroup$ Good observation but don't surprised by the fact a lot of food items have EDTA. A mouth-wash is no major exception. You will have read the patent in order to get the idea why EDTA is beneficial in oral rinses patents.google.com/patent/WO1988000044A1/en $\endgroup$ – M. Farooq May 9 at 20:34
  • $\begingroup$ Secondly you concern of NaF is not a . Ca-EDTA must be present in excess. $\endgroup$ – M. Farooq May 9 at 20:37
  • $\begingroup$ EDTA suppresses biofilm formation and it also has antimicrobial properties. I assume this is why it as added, or maybe it is used as a preservative. Na-EDTA will scavenge Ca from the teeth, so presumably the Ca-EDTA will leave the Ca in the teeth. What I don't understand is why it does not react with the fluoride. $\endgroup$ – vodona May 9 at 21:55
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    $\begingroup$ There is no $\ce{CaF}$. Presumably you mean $\ce{CaF2}$ $\endgroup$ – Buck Thorn May 11 at 7:53
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    $\begingroup$ @NilayGhosh Thanks. You learn something new every day, sometimes two things. $\endgroup$ – Buck Thorn May 11 at 14:00

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