A fistula is a tunnel conducting pus from one infection to the site of another. A mouth fistula is called a gum boil. More generally a fistula is due to destruction of intervening tissue between the two sites and is a major component of a periapical abscess. Inflamed pus forms an abscess causing a pressure increase in the surrounding tooth area. If the pus that accumulates at the end of the tooth have no alternate pathways for drainage over time spontaneous drainage may occur through bone next to the root end. The pathway through which the pus has burrowed is called a fistula.
Fistulas usually form near the roof of the mouth or on the gum and are difficult to detect. A fistula can also be known as a Parulis as this is the term given to the point at which the fistula reaches the surface of the mouth presented as a small pimple. This pimple usually ruptures to form an opening.
Treating a fistula requires antibiotics and extraction of the tooth that led to the fistula via root canal surgery. Also draining the abscess that led to the fistula is a treatment method although this is usually followed by root canal surgery.