Joker Teeth, also known as Chattering Teeth, are mechanical gag teeth used by the Joker. The teeth are wind-up prank teeth that giggle and hop around in a small radius where they are left. The teeth, when broken, break in half and their laugh box detonates.
Throughout his takeover of Arkham Asylum, the Joker leaves teeth to show his presence. While the teeth are not hostile, Batman can easily walk by them and destroy them. The Riddler challenges Batman to destroy all the Joker teeth throughout the asylum in order to gain rewards.
When finally fighting the Joker, the villain launches multiple explosive Joker Teeth that actually persue Batman. These teeth are obviously hostile and more dangerous than their docile version before. 
Joker is shown to have Explosive Joker Teeth in his inventory at all times. Joker can remotely control these teeth whenever he launches them. The teeth are timed and will automatically explode when they run out of time. 
When Batman is trapped in the new super prison, Arkham City, the hero can find multiple Joker Teeth scattered around the subway station. Like in Arkham Asylum, these teeth are docile. Riddler again challenges Batman to destroy all of these teeth. 
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