So, lots of examples in medicine where something is given to a patient either buccally or sublingually , since the oral mucosa absorb many things well and directly into the bloodstream.
So a decent serving size of toothpaste when brushing contains about 1 mg of fluoride ion, exposed over what... 60 sq. cm of surface area ?
But you have to figure it affects most where it enters the body, on the gums because you are scrubbing it in with that little toothbrush.
I ponder whether chronic use of fluoridated toothpaste is responsible for causing teeth to die. I also ponder the chronic use of fluoridated toothpaste as it relates to causing gum recession.
What I like to remember to do is take about 50 ml of water, add 2-4 drops Lugol's to it, and hold it in my mouth a minute or two, swish it around. I bet this is really good for teeth and gums if I do it 2-3 times a week.