1. A study examined the effects of different levels of fluoride in water on dental health in several communities. 2. Fluoride levels between 0.7 to 1.2 parts per million were found to be optimal for reducing cavities compared to levels below 0.5 ppm or above 4.0 ppm. 3. Both too low and too high fluoride levels were found to increase risks of dental fluorosis, though the risks were greater at the higher levels above 4.0 ppm.

1. ............................................................................................ ........................ ...................... F .....................
F
F
1.
2. F F
3. F F F 0.5 F
4.
1. F F
2. F F F F F
F F
3. F F F
F F
4. F F F F F F
5. F F F FF F
1. F
2. F F F F F
3. F F F F
4. F F F
F F
5. F F F F