Human teeth are held in the sockets of the jaw bone by the ‘periodontal ligament’. The ligament attaches the root of the tooth to the adjacent 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 gum disease like gingivitis that progresses to periodontitis ( Advanced gum disease ) infects the bone. The infection dissolves the supporting bone. This causes loss of attachment of the ligament. The tooth loses support and becomes mobile.