What is Gum Disease? Gum disease is an inflammation of the gums that can progress to affect the bone that surrounds and supports your teeth. It is caused by the bacteria in plaque, a sticky, colorless film that constantly forms on your teeth. If not removed through daily brushing and flossing, plaque can build up and the bacteria infect not only your gums and teeth, but eventually the gum tissue and bone that support the teeth. This can cause them to become loose, fall out or have to be removed by a dentist.