How to Whiten Your Teeth, 1607

labeled engraving of unicorn, narwhal, unicorn skeleton, unicorn horn That Unicornu fossile is definitely legit.
Michael Bernhard Valentini, Museum museorum (1714)

The horne of an Vnicorne being beaten and boyled in wine, hath a wonderful effect in making the teeth white or cleare, the mouth being well clensed therewith.

Edward Topsell, The Historie of Foure-Footed Beastes

Wine and unicorns really do make everything better, don’t they?