I have the dentist on Monday and he does not take any notice of my having a thyroid problem. I have to remind him each time not to include any adrenalin in the local, and each time he signs and rolls his eyes. Anyway, I was having a bit of an internet search and came across this which may be useful for those of us who cannot get the dose spot on - this could be a reason!
Many people are not aware that in the first half of the 20th century, fluoride was used medically as an anti-thyroid drug, to slow down thyroid function in patients with an overactive - hyperthyroid - gland. Fluoride was found to be effective at suppressing or reducing thyroid function, according to research, and the dose needed to reduce thyroid function was low -- 2 to 5 mg per day over a period of months. Some scientists estimate that people today who are living in communities with fluoridated water supplies have a range of exposure of 1.6 to 6.6 mg/day.
So I checked my toothpaste and it has flouride, as do most of them. I have no idea how much could be absorbed in the mouth, but I just thought it was interesting and maybe of help to someone here.