Bruxism sounds like a radical political philosophy, but here the proletariat is the citizenry of your mouth, being ground down by an oppressive reflex of the jaw.
A disorder that affects both children and adults, teeth-grinding wears the enamel off your hardworking bicuspids and can cause serious jaw pain and headaches. Most of us occasionally grind our teeth in both waking and sleeping hours, but the sleep disorder is linked to frequent episodes. One study reports that nocturnal bruxers suffer five to six grinding episodes an hour during sleep, compared to one or two episodes in the unaffected.
The cause seems to be related to anxiety and stress. Therapies that involve stress reduction help to control the behavior. Mouthguards can also help, and are doubly useful if your other nocturnal activities include contact sports.