Fluoride plays a great role in the prevention of tooth decay (dental caries).  Fluoride is a mineral that has been found in air, food and water. Foods that contain fluoride are: fish, cereals, black and green tea, egg yolk.

Fluoride performs the following functions:

• promotes remineralization of teeth
• increases resistance of  teeth to dental caries
• blocks the production of acid by bacteria

It has been found that some regions of the earth contain a lot of fluoride in spring water. In those regions tooth decay does not spread at all. Scientists have found that the sufficient amount of fluoride in water to prevent tooth decay is 0.7–1.2 mg l(–1) . But 70% of cities and countries do not have a high enough amount of fluoride.

It is possible to improve oral health by using tooth paste with fluoride. There is  also  some bottled mineral water that contains  fluoride( you can read this on its label).

But there is still a risk of getting fluorosis if you use more than one source of fluoride. Dental fluorosis is a health condition caused by receiving too much fluoride during tooth development.

My advice is to use toothpaste with fluoride and if you want to add another source of fluoride pre-check with your dentist.