# Fluoride Toothpaste vs Mouthwash
November 20, 2024

DISCLAIMER: I'm not a dentist or dental professional of any sort,
you should do whatever they recommend rather than following what I
spent five minutes guesstimating XD.

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A while ago I noticed that fluoride mouthwash has less than 25% the
fluoride that toothpaste has in it, and have been wondering if that
means it's less effective than using fluoridated toothpaste. I
think for maximum effiacy you're supposed to leave toothpaste in so
the fluoride stays, and while I'm fine with that in the morning
there is no way in hell I'm not washing all the loosened food bits
out of my mouth at night lol, especially after flossing which I do
after brushing my teeth. But then I still like the idea of getting
that fluoride action going. But then, from a superficial look, it
appears that fluoride in mouthwash may be so low as to not really
help, or perhaps actively get worse if it washes away the small
amount of fluoride left in your mouth from the toothpaste. So I
figured I'd spend five minutes calculating it lol.

These numbers are just using the seemingly standard for US
toothpaste and fluoride mouthwash, I'm sure there's specialty
fluoride therapy stuff out there as well as just different national
standards. And for this I'm using the stated concentration of
fluoride ions by % weight/volume, since the first percentage on the
label is the concentration of sodium fluoride as a whole rather
than solely the fluoride.

Based off of a standard toothpaste tube being 93 grams, and a few
random resources online which say that toothpaste tubes tend to
last for ~80 uses, which tracks with my anecodotal experience:
    93. g / 80. uses = 1.2 g/use

Amount used for a 1.5 cm line of toothpaste, linearly interpolated
from values given by Colgate. Done because, measuring random
toothbrushes and guessing from various places I've seen, most
people use a ~1.5 cm line of toothpaste rather than a rather small
1 cm or a long 2 cm:
    (1.7 g - 0.8 g)/2 + 0.8 g = 1.3 g
Source for those values:
https://www.colgateprofessional.com.au/content/dam/cp-sites/oral-care/professional/en-au/general/pdf/student-Fluoride-Conversions.pdf

And now for mouthwash, since dosages are given in volume but we
need mass to compare with. I'm just assuming that it has the
denssity of water, since according to the inactive ingredients it
is mostly water and propylene glycol. And in general, since it is
"water with some solids dissolved in it", it will most likely be
≥the density of water, and that means that the dose will only ever
be higher than what's calculated here.
    10. mL/use × 1.0 g/mL = 10. g/use
(Real shocker of a calculation lol)

And now actually calculating the amount of fluoride delivered with
each use. Using the typical fluoride concentration in US
toothpaste, and the lower of the two toothpaste usages I calculated:
    (93. g / 80. uses) × 0.15% F = 1.7 mg F/use

And just whatever is stated by Act mouthwash since that's what I
happen to use:
    10. mL/use × 1.0 g/mL × 0.020% F = 2.0 mg F/use

So surprisingly, mouthwash gives a similar but actually higher dose
of fluoride with every use! But makes sense beyond a superficial
look, since the amount of mouthwash you use is much higher than
toothpaste.

Note that I'm not really sure what these doses mean for the
concentration that ends up in your mouth, since that's what's
actually important. You definitely have a lot of saliva that
reduces the concentration for toothpaste, while probably less so
for mouthwash. According to Wikipedia, you really need ≥1000 PPM of
fluoride (in toothpaste) for it to be effective.

But also, does the thick gel of toothpaste leave the fluoride in
contact with your teeth better than the low viscosity mouthwash? I
have no clue and maybe mouthwash is still worse. And I remember
reading somewhere that more than one source of fluoride has no real
benefit, so this may not even matter if you drink fluoridated
water, or if you do leave toothpaste in instead of washing it out
in the morning? And fluoride isn't really that important compared
to just, actually brushing and flossing your teeth for an adequate
amount (or at all) every day lol.


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