Fluoride is an important part of healthy tooth development and will help prevent cavities.
Fluoride can provide protection from tooth decay in a couple ways:
1) It helps to strengthen the tooth's enamel so it can repel the acid that is formed by plaque.
2) Teeth that have been damaged by plaque can repair and re-mineralize themselves with the help of fluoride.
Fluoride is incapable of repairing already formed cavities, but it does assist in reversing low levels of tooth decay and helps in preventing new cavities from forming.