Abscess in severe gum disease. Close-up of the mouth of a person with complex periodontitis - an inflammatory disease that affects the tissues that surround and support the teeth (the periodontium). Gum disease is most often caused by inadequate dental hygiene, allowing bacteria to build up between the teeth and below the gumline. This leads to chronic inflammation and gradual recession of the gums (as here). In severe cases (as here) the underlying bone can be eroded leading to loosened teeth and ultimately tooth loss. Here, it has caused an abscess to form in the upper gum tissue.