Final answer:
Fluoride stabilizes calcium in tooth enamel to promote a resistance to tooth decay.
Step-by-step explanation:
Fluoride promotes a resistance to tooth decay by stabilizing calcium in tooth enamel. When fluoride reacts with hydroxylapatite in the enamel, it forms fluorapatite, which is more resistant to acid attacks and less soluble. This helps protect the teeth from the corrosive acids produced by oral microbes that cause tooth decay. Fluoride can be found in toothpaste, mouthwashes, and is also commonly added to drinking water.