What causes you to clinch yor teeth while sleeping?

Bruxism. Clenching or griiding of teeth during sleep is called bruxism. It is actually a clenching of the jaw muscles. It can cause abnormal wear of the teeth, and a dentist can make an oral device to separate the upper and lower teeth during sleep.
Cause of bruxism. Grinding/clenching the teeth during sleep (nocturnal bruxism) is frequently caused by obstructive sleep apnea. Indeed, many dental sleep specialists believe osa is the most frequent cause of nocturnal bruxism.