Have you ever brushed your teeth and noticed a pink tinge on your toothbrush? It may have made you wonder if you have gum disease. So, what is gum disease? Gum disease is an inflammation of the gums that can lead to the deterioration of the tissues and bone that surround and support your teeth. The infection is primarily caused by plaque, a sticky film of bacteria that irritates the gum line if you let it build up. Gingivitis is a mild form of gum disease that can be reversed.