A dental abscess is caused by bacteria that are normally present in the mouth. The bacteria invade a tooth by entering through a cavity, and then spread to the bone. Bacteria can also invade the surrounding gum.

A dental abscess forms in the following manner:

• Infecting organisms invade the tissue.
• The organism starts to destroy the tissue.
• The body sends white blood cells to fight the infection.
• Cells in the tissue that surround the infection form a barrier around the infection, in order to keep it from spreading.