Smile!

When they are about 10 cm (4 in) in length… the mouth of the (sand tiger shark) embyro becomes functional and teeth are formed [inside the mother shark].
Three rows of long needle-like front teeth protrude from their open mouth. The back teeth are molar-like. (Aquarium of the Pacific)
Shark teeth are covered in fluoride, making them cavity-resistant. One 2012 study published in the Journal of Structural Biology found that sharks’ enamel is made up of a chemical called fluoroapatite, which is resistant to acid produced by bacteria. (livescience)