After you eat, the small food particles left behind in your mouth break down into carbohydrates and sugars, which in turn the bacteria break down into cavity causing acids. These acids dissolve minerals from the tooth enamel, a process called demineralization. These acids, thus, can make teeth weaker, and can result in tooth decay. That’s where fluoride comes in. When it reaches your teeth, fluoride is absorbed into the enamel. It helps to repair the enamel by replenishing the lost calcium and phosphorous to keep your teeth hard. This process is caused re-mineralization. When fluoride is present during re-mineralization, the minerals deposited into the tooth enamel help strengthen your teeth and prevent dissolution during the next demineralization phase. Thus, fluoride helps stop the decay process and prevent tooth decay.