Periodontal disease is an infection that affects the tissues and bone that support the teeth. As the tissue is damaged, the sulcus (the v-shaped crevice formed where the gum meets the tooth) develops into a pocket that is greater than three millimeters.
Generally, the more severe the disease, the deeper the pocket depth and the more bone loss or damage. The enlarged pockets allow the harmful bacteria to flourish because you physically cannot clean down to the depth of the pocket. Left untreated, periodontal disease may eventually lead to tooth loss.