It’s Shark Week, and while the Discovery Channel is apparently
kinda fucking it up, that shouldn’t keep us from bringing you a
weird science fact about the most terrifying sea creature to
probably pose you no threat whatsoever. And that fact is this:
Shark teeth have built-in natural toothpaste. The outside of a
shark’s tooth is made of fluoride, the same stuff that gets
added to toothpaste, mouthwash, and municipal water systems to
improve your dental health.  Though fluoride is a tougher
material than hydroxyapatite (the stuff our teeth are made of),
weirdly, shark teeth are not harder than human teeth:  “This
finding is surprising, because the mineral fluoroapatite is
harder than the mineral hydroxyapatite, so if a tooth were to
consist of the mineral alone, a shark tooth would be harder than
a human tooth,” Epple said. “It seems as if the human tooth
makes up for the less hard mineral by the special arrangement of
the enamel crystals and the protein matrix, and ends up being as
hard as a shark tooth.”  So