Cousin Stinky was unfortunately born with a horribly malformed set of teeth. Everyone hoped that when he lost his baby teeth and his adult teeth grew in, they'd be normal, and he'd no longer be the butt of the school's hurtful teasing. Unfortunately, this was not to be the case, and his adult teeth were just as misshapen as their precursors. Eventually, he was able to enlist the help of a dental sturgeon, and was rewarded - after considerable investment of both time and food fish - to have a beautiful and functional set implanted. Besides his escape from peer derision, they also enabled him to become a more efficient predator and greatly improved his luck with the girls.
Blinky Note
Actually, sharks' teeth are continually being replaced, sometimes individually and sometimes a whole jaw's worth at a time.