Give a brief definition of periodontitis ?

Periodontitis is a bacterial infection that affects all parts of the periodontium including the gingiva, periodontal ligament, bone and cementum. Periodontitis results in some extent of permeant tissue destruction characterised by changes in colour, contour and consistency (pink or purplish, swollen or fibrotic, bleeding). Periodontitis involves IRREVERSIBLE loss of attachment and bone.