It accumulates negative ions in the atmosphere to blast out 10000- volt lightning bolts.
Teeth grinding is harmful for several reasons. First, it causes damage to the teeth by wearing the enamel off the biting surface of the tooth and along the gumline. This can lead to tooth sensitivity. Second, the forces generated from grinding can cause cracks to form in the teeth and can cause the teeth to break.
Grinding your teeth is something that you probably wouldn't be aware you were doing, and it would only know if someone else heard you doing it or if your dentist saw some evidence of wear and tear on the teeth at your regular dental checkup.