As we've previously reported, the prop was the real deal: those chompers were actually human! (Though we assume they weren't stolen off of a corpse...). And it turns out that's not the only fun fact about that necklace.
Recently, Brendan Robinson (Lucas Gottesman) tweeted this pic, along with this factoid: "Guess who made the creepy tooth necklace for #PLL? MY DENTIST!! And guess what, they were REAL HUMAN TEETH! Creepy!"
It looks like Brendan's dentist keeps a montage of his/her (it looks like her based on one of the photos) big TV moment at the office. Cool!