There are actually two different types of fluoride treatment. You are probably aware of both, but most people don’t understand the differences between them.
1 – The fluoride in the water (and prescription tablets/drops) is for developing teeth. It is ingested into your body when you drink the city water (Snoqualmie water is not fluoridated, thus the frequently recommended FL tablets). When it is in your body it will be used by your body to make the teeth as they are formed in the bone. Some of the fluoride will take the place of calcium. This results in stronger teeth that are harder and more resistant to cavities!
There is some controversy in placing this in the public water system. The main argument comes from the fact that not only does it make teeth stronger, but it also makes bones stronger. This can be a negative in that harder bones bend less. So, when someone falls (older people especially) and lands on their hip, it is more likely to break than bend, thus resulting in a fracture.
Idealy, the best scenario is to take fluoride pills as a child and not have fluoride in the city water. This is not usually done because the people most likely to not take their kids to the dentist and get the fluoride pills are the ones that are most likely to not take care of their children’s teeth. We do not recommend having your children take fluoride after the age of 8. At this age the crown portion of all teeth (except of wisdom teeth) has fully formed, see a chart here. Therefore, taking fluoride past this age is of no dental benefit.
2 – Fluoride in the dental office is a high concentration form. The amount in the water is usually only a couple parts per a million. This is such a low concentration that it will not do anything for your teeth that are already formed and in the mouth. When the in office treatment is done, the high concentration allows some fluoride to soak into the enamel and replace some calcium ions, thus creating a stronger enamel. Small cavities can actually remineralize and stop growing, thus eliminating the need for the future filling. Because of this fact, many insurance companies have started to pay for fluoride treatments on adults and not just children. They end up paying less because you get less cavities. You are happy because you get less cavities, a win-win situation for you and your insurance company.