Your teeth are not made of fluoride. Fluoride makes bones brittle and more prone to facture. Your dentist may have told you enamel wears out and cannot be restored, however enamel is in fact always being replaced.

It was found that a toothpaste that had the ingredients of enamel, was utilized by the enamel building process and aids in rebuilding tooth enamel.

Enamel is so hard because it is composed primarily of inorganic materials: roughly 95% to 98% of it is calcium and phosphate ions that make up strong hydroxyapatite crystals. Yet, these are not pure crystals, because they are carbonated and contain trace minerals. Apatites are a group of calcium phosphate compounds, with the generic formula Ca5(PO4)3X. The identity of the X ion determines the specific type of apatite. For example, when X = F, you get fluorapatite, Ca5(PO4)3F, that comes in all kinds of colors while hydroxyapatite is usually colorless or white, is Ca5(PO4)3OH.

A mineralization toothpaste is composed of calcium and phosphate ions and trace minerals to provide mineralization to aid the system in enamel generation and maintenance. Certain foods, even healthy foods also affect the enamel.

https://cen.acs.org/materials/biomaterials/dental-enamel-does-protect-teeth/98/i41

Recent science suggests that cavities and tooth decay is 90% caused by the water / sugary environment of the mouth, which is dietary. The residue sugar feeds a bacterium that also feeds on your teeth. Sugary environments. Read more here... https://scitechdaily.com/90-reduction-scientists-discover-natural-molecule-that-eradicates-plaques-and-cavities/