Human teeth are held in the sockets of the jaw by the ligament. The ligament attaches the root of the tooth to the adjacent alveolar bone. The fibre groups of the ligament suspend the tooth and help in chewing, proprioception (ability to sense chewing forces and hard objects on biting) and holding the tooth in position. A disease like gingivitis that progresses to periodontitis affects the bone. The infection due to the disease process dissolves the supporting alveolar bone. This causes loss of attachment of the ligament. The tooth loses support and becomes mobile.