Gum disease is usually caused by plaque, a sticky film of bacteria that constantly forms on teeth. If plaque is not removed with thorough daily brushing and cleaning between teeth, gums become irritated and inflamed. The irritated gum tissue can separate from the teeth and form spaces called pockets. Bacteria move into the pockets where they continue to promote irritation. Left untreated, the process can continue until the bone and other tooth-supporting tissues are destroyed. The early stage of periodontal disease is called gingivitis. It often results in gums that are red and swollen and may bleed easily.