Trench mouth, also called necrotizing ulcerative gingivitis, is a form of gum disease caused by poor dental hygiene that leads to mouth ulcers, infections and bleeding, according to Mayo Clinic. The condition was named for World War I soldiers who often contracted the disease while in the trenches during battle.
Trench mouth occurs when the body's immune system fails to control the naturally occurring bacteria, fungi and viruses in the mouth, according to Mayo Clinic. Out of control bacteria cause gum infections, which can destroy gum tissue. Trench mouth may also cause ulcers on the gums that are filled with food debris and bacteria and which lead to severe pain, bad breath and a bad taste in the mouth.