Most periodontal disease arises from, or is aggravated by, accumulation of plaque, and periodontitis is associated particularly with anaerobes such as Porphyromonas gingivalis, Bacteroides forsythus, and Actinobacillus actinomycetemcomitans. Calculus (tartar) may form from calcification of plaque above or below the gum line, and the plaque that collects on calculus exacerbates the inflammation. The inflammatory reaction is associated with progressive loss of periodontal ligament and alveolar bone and, eventually, with mobility and loss of teeth.

Periodontal diseases are ecogenetic in the sense that, in subjects rendered susceptible by genetic or environmental factors (such as polymorphisms in the gene for interleukin 1, cigarette smoking, immune depression, and diabetes), the infection leads to more rapidly progressive disease. Osteoporosis also seems to have some effect on periodontal bone loss.

The possible effects of periodontal disease on systemic health, via pro-inflammatory cytokines, have been the focus of much attention. Studies to test the strength of associations with atherosclerosis, hypertension, coronary heart disease, cerebrovascular disease, and low birth weight, and any effects on diabetic control, are ongoing.