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I'm having a discussion with somebody regarding Fluoride usage. I told him that even if he doesn't like the idea of ingesting it, brushing and spitting it out will do you no harm. He then said this:

You have missed the point of ingestion massively! Brushing with fluoridated paste is NOT fine.

The mouth, with its gum entry and under tongue glands are the PERFECT entry point to the blood, without even swallowing? What do you think oil pulling is all about? Fluoride passes those barriers as easy as the shit that resides in your blood can!"

Now I call BS on this, but I'd just like an expert opinion with cited sources if possible. Can Fluoride be absorbed purely by the mouth without ingestion?

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  • $\begingroup$ Absorption in the mouth doesn't happen, see this answer. But this will probably not persuade your friend. $\endgroup$ – Chris Aug 16 '17 at 13:31
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    $\begingroup$ @Chris definitely not a friend of mine, haha :) $\endgroup$ – Charlie Aug 16 '17 at 13:56
  • $\begingroup$ @Chris whilst that links explains remineralization very well, it doesn't really talk about gums or the tongue or digestion in the mouth and why fluoride can't be absorbed that way. That's more of the kind of thing I'm looking for $\endgroup$ – Charlie Aug 16 '17 at 13:58
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    $\begingroup$ If fluoride can't be absorbed through the mouth, then why do dentists recommend fluoride-containing dental rinses? $\endgroup$ – jamesqf Aug 17 '17 at 5:03
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    $\begingroup$ @jamesqf because it can be absorbed onto the teeth that way, but my question is can it enter the blood through the gums, tongue etc. I know it can be absorbed into the teeth through the mouth $\endgroup$ – Charlie Aug 17 '17 at 13:15
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Although I'm having a hard time finding a source that provides specific information on fluoride in toothpaste, this review explains that fluoride is most readily absorbed through intestinal epithelia and that fluoride absorption through other tissues, such as oral epithelia, depends strongly on other chemical properties of fluoride-containing compounds: their

"reactivity and structure, solubility, and ability to release fluoride ions."

This suggests that you would need additional information concerning the overall toothpaste formula.

This review shows the rates at which fluoride ions are released from various toothpaste formulations. Figures 2 and 3 show that the highest discharge rate is roughly 1.7ppm and the lowest was just under 0.5ppm, both occurring after a 24hr period. The authors note in the discussion that these measurements are likely higher than what would occur in the mouth, since they had to use deionized water for their experiments, in which fluoride is more soluble than in saliva.

Wikipedia lists fluoride toxicity levels as being between 0.5 and 1.0mg/L. Fluoride's molar mass is 18.9984 g/mol and this calculator shows that 0.5mg/L of fluoride translates to about 0.5ppm. While at first this makes the above results sound a dire, it's important to note that toothpaste remains on your teeth for far less than 24hrs and to remember that less fluoride is released into saliva than into deionized water.

Wish I could find better results on how much fluoride might be released during a typical toothbrushing session, but I'm inferring from the linked review that it would be small enough to not merit a health concern.

I emailed a dentist friend for more info and will update this post as I hear back from him.

As for the comment about glands, it's important to understand that the glands found in the mouth are secretory glands, which means that they are optimized for discharging fluids and not for accepting them.

--Update--

My dentist friend wrote back, confirming that no significant fluoride absorption occurs through the gums. From him:

the only significant absorption would be through swallowing fluoride. Any that was just in the mouth would not be well absorbed... that is why we do the high dose swish and spit treatments is to avoid fluorosis but deliver sufficient fluoride to the teeth.

In short, it looks like the answer to your question is: no, fluoride is not significantly absorbed into the blood from within the mouth without swallowing.

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    $\begingroup$ thanks for the info! I'll keep this open for now to allow time for you and others to find out more. $\endgroup$ – Charlie Aug 20 '17 at 15:33

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