Do you wake up with a stiff, tired jaw? Are your teeth sensitive to cold drinks? If you answered yes to either of these questions, you may be grinding or clenching your teeth during sleep. Grinding of the teeth is a medical condition called bruxism. Over time, bruxism will result in the wearing down of your natural tooth enamel. In fact, studies suggest that those who grind and clench their teeth experience up to 80 times the normal wear per day compared with those who do not.