People may notice a foul smell emerging from the mouth, caused by pus and other effects of the gum infection. 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. However, carrying along, for months and possibly for years, an infection that causes pus and permanently engages the immune system, is not conducive to optimal health, even before gingivitis develops into its more severe manifestation, periodontal disease. Gingivitis, and its progression to periodontitis, 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 gingivitis.
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.