Even though periodontitis is a disease that manifests itself with pus and foul oral smell, not everyone feels the urge to consult a dentist. The reason is that periodontitis often doesn't cause much pain. But they may consider these symptoms part of their physical constitution, just like shortsightedness, or baldness, or pimples, and not as a disease that requires the attention of a physician. Periodontitis and gingivitis start with the plaque that forms mostly at the base of the visible part of the teeth. This plaque is caused by food debris and bacteria that grow on it.
Tooth brushing removes plaque and thereby constitutes a preventive measure against periodontitis.
However, some plaque is likely to remain in spite of brushing one's teeth. This plaque hardens and then is called calculus. Because of its hardness, calculus will often result in a mechanical irritation of the gums. Additionally, calculus provides an area on which more bacteria easily grow. Like coral reefs, plaque and calculus will, if not removed, continue to grow and form deep pockets at the base of the teeth that will sooner or later fill with pus.