Caries is another word for cavities or tooth decay. To get a cavity, you need three things: a tooth, bacteria, and sugar or carbohydrates. Everyone has bacteria in their mouth. When bacteria mix with sugar or carbohydrates, acid forms. The acid attacks the tooth and the enamel begins to weaken in a process known as demineralization. If the cavity has just started and is in the outermost layer of the enamel, it can be reversed in a process known as remineralization. Remineralization can occur through the application of fluoride. That is why a professionally applied fluoride treatment is so beneficial in the prevention of decay.