Gum disease is an infection of the tissues that hold teeth in place. It's typically caused by poor brushing and flossing habits that allow plaque (a sticky film of bacteria) to build up on the teeth and harden. Symptoms of gum disease include bad breath, red or swollen gums, tender or bleeding gums, painful chewing, sensitive teeth. Causes of gum disease are diabetes, hormonal changes, medications that lessen the flow of saliva. Gum diseases are treated by dental surgeons or dentists.