A common cause of gum infection is a tooth abscess that arises from an infected tooth. The infection may originate from tooth decay that spreads into the dental pulp, progressing into the roots of the tooth. Tooth decay resulting from acid attack on the enamel creates a cavity. Bacteria get lodged in the cavity and produce more acid, penetrating through the enamel and dentine, into the dental pulp where the nerves and blood vessels are. The resulting inflammation of the dental pulp, and root canal infection, causes pain and pulp death. The dead pulp tissues become infected and swell up with pus. The pus may find its way out of the root canal through the bone and gum, presenting as a bulge on the gum surface.
See also: Root canal treatment