Periodontitis is an infection of the Periodontium, the apparatus which holds teeth in place. Mainly this is made up of the gums and the bone areal surrounding the root. The ailment begins with an infection of the gums, which in turn, can lead to an infection of the bone. This is caused by bacteria and the reaction of the body to infection. This infection can spread and affect the bone, resulting in erosion. The erosion takes place in spurts. Strong erosion of bone results in an increasing loosening of teeth and, ultimately, loss of teeth.