Preventive Dentistry » Gum Disease What is the cause of gum disease? All gum disease is caused by plaque. Plaque is a film of bacteria which forms on the surface of the teeth and gums every day. Many of the bacteria in plaque are completely harmless, but there are some that have been shown to be the main cause of gum disease. To prevent and treat gum disease, you need to make sure you remove all the plaque from your teeth every day. This is done by brushing and flossing. What happens if gum disease is not treated? Unfortunately, gum disease progresses painlessly on the whole so that you do notice the damage it is doing. However, the bacteria are sometimes more active and this makes your gums sore. This can lead to gum abscesses, and pus may ooze from around the teeth. Over a number of years, the bone supporting the teeth can be lost. If the disease is left untreated for a long time, treatment can become more difficult.