In my humble opinion the answer to that is, yes.
Below you will see an artistic rendering of the skull of a child
between the ages of 2-5. The baby teeth are fully
erupted into the mouth and are in white.
The adult teeth, that will erupt later, are in blue.
As you can see the adult teeth are still in the process of forming. At this time the body is looking for the building blocks needed to form strong healthy teeth and placing those building blocks in an appropriate configuration. If the body can not find the proper materials that does not mean that the teeth will not be formed. It simply means that the teeth will be formed in an inferior fashion. The teeth will be more prone to decay and fracture over time.
Fluoride is an important part of the forming tooth.
Whether or not you get enough fluoride naturally is up to you to find out.
Check you local city or county to find out where your water
comes from and what the natural concentrations of fluoride is.
Then check to see if they are adding fluoride to it.