http://www.oramd.com/gingivitis/4-curegingivitis.htm The harmful bacteria responsible for causing gum disease and gingivitis problems are anaerobic in nature-anaerobic meaning "in the absence of [...]

http://www.oramd.com/gingivitis/4-curegingivitis.htm The harmful bacteria responsible for causing gum disease and gingivitis problems are anaerobic in nature-anaerobic meaning "in the absence of oxygen". These microbes like to hide behind plaque which then may harden into that stuff the dentist needs to scrape off during a cleaning: tartar. Anaerobic bacteria hide behind tartar because neither oxygen nor good oral hygiene like brushing or flossing can affect them.