A crossbite is a common tooth misalignment in which some of the lower teeth rest outside the upper teeth. Two different types of crossbite may occur. The first is an anterior crossbite in which the front upper teeth may rest behind the lower front teeth. The second is a posterior crossbite in which the back teeth in the upper jaw rest behind the back teeth in the lower jaw.
Many cases of crossbite are genetic and inherited from parents or other relatives. Some people are naturally born with a small upper jaw, and their adult teeth overlap, leading to a crossbite.
External factors that may contribute to a crossbite include mouth breathing and excessive thumb-sucking habits in childhood. If there is a delay in losing your baby teeth, your jaw will move forward or to the side to compensate for these changes, which may cause a crossbite.