Front teeth usually break due to a knock, an accident or during biting. Back teeth can also be fractured from a knock. They are much more likely than front teeth to crack from forces applied by the jaws slamming together rapidly. This is why sportspeople wear mouthguards to cushion the blow. Other forces occur during sleep because people grind their teeth with a much greater force than they would ever do while awake. The first sign of problems may be what we call “cracked tooth syndrome” –a sore or sensitive tooth somewhere in the mouth that is often hard for even the dentist to find. In some individuals the grinding, called bruxism, causes tooth wear rather than fracture.