Fluoride without a doubt makes teeth harder and hence more resistant to caries (decay). It is best when it is available to the body to be incorporated into a tooth as it develops which starts at about 13 weeks in utero for primary (baby) teeth and about 4 months after birth for permanent teeth. Even if you don’t count 3rd molars (wisdom teeth), tooth development is not complete until the mid teens. That is really the biggest reason it is found in so many municipal water systems. Unfortunately, over time the fluoride that was incorporated into the tooth during development leaches out, basically just an equilibrium trying to be established when there is more fluoride in a tooth than in the surrounding oral environment (saliva). That is where fluoride toothpastes and fluoride applications at the dental office come into play. When in contact with the teeth, there is now a higher concentration of fluoride around the tooth, helping to replenish that which has leached out, thereby keeping the tooth strong. While there are nay-sayers out there that claim fluoride causes cancer etc, the American Dental Association and Surgeon General still recommend it. Ever since fluoride was added to the water supply of Grand Rapids, MI in 1945 we have been able to document a decreasing incidence of childhood caries (decay) in communities that have followed suit. Having said that, can too much fluoride be bad? Yes. Fluoride occurs naturally in water, and in some areas of the country, parts of Texas and Colorado for instance, the fluoride is in concentrations that are too high resulting in enamel fluorosis, characterized in mild cases by white patches in the enamel, and in more severe cases with some darkening of the enamel. Since an infant can get too much fluoride a fluoride containing toothpaste should not be used until the child is old enough to be able to spit.
Be advised that if you use bottled water extensively or have a filtration system at home, you are most likely losing the benefits of fluoride.
Don’t know if your community fluoridates your water or not? Visit the CDC’s My Water’s Fluoride website at https://nccd.cdc.gov/DOH_MWF to find out. Most states participate in the program.