How does fluoride strengthen teeth?

Fluoride strengthens teeth primarily through the process of remineralization and by inhibiting bacterial growth. Remineralization is the natural repair process where minerals, such as fluoride, calcium, and phosphate, are redeposited in the enamel of the teeth after being removed by acids produced by bacteria. When fluoride is present in the oral environment, it becomes incorporated into the crystalline structure of the enamel, making it more resistant to acid attacks that cause decay.

Moreover, fluoride has antimicrobial properties that help inhibit the growth of bacteria, particularly Streptococcus mutans, which is a key contributor to tooth decay. By reducing bacterial growth, fluoride not only helps to protect the teeth but also contributes to a healthier oral environment overall.

The other choices do not accurately reflect the mechanism by which fluoride strengthens teeth. Whitening treatments focus on cosmetic improvements rather than structural integrity, expanding tooth structure does not occur with fluoride application, and changing tooth color does not address the primary protective functions of fluoride which are remineralization and antibacterial action.