It may just be frozen water, but chewing ice can be very hard on your teeth. People who chew ice end up with a lot of fracture lines in their teeth. These slight cracks make teeth painfully sensitive to cold and biting pressure. Sometimes a whole piece of tooth will break off and the only way to save the tooth may be to place a crown. If the fracture lines are deep enough to threaten the tooth nerve, that can mean a root canal or an extraction. In addition chewing ice will wear off the enamel on your teeth and over the long term put them at more risk to decay. Some people even end up with serious bite problems. So stop chewing ... it's better to break the ice habit!