Fluoride helps protect teeth from decay and cavities. Teeth with fluoride in the enamel simply resist acids better than teeth that have not. When bacteria in the mouth combine with sugars, acid is produced that can dissolve tooth structure and cause cavities or erode away the enamel. It protects teeth from demineralization caused by the acid. It can also help with repairing enamel that has been mildly damaged by acids. Studies have shown water fluoridation continues to be effective in reducing tooth decay by 20- 40%, even with widespread availability of fluoride from other sources.