Fluoride is a naturally occurring mineral that is very effective in protecting teeth against decay. When teeth first start to decay, minerals in saliva help mend the teeth, but the mending process requires fluoride to work properly. Most people do not get enough fluoride from the water supply, therefore fluoride is useful when added to toothpaste.
Most packs will tell you how many parts per million (ppm) of fluoride the toothpaste contains - 500ppm is a low level and 1000-1500ppm is high.Low fluoride toothpaste should be used for children under seven because it is important to avoid too much fluoride while permanent teeth are still forming as it can mark the teeth.