A dental fistula (also called a parulis or a gum boil) forms in response to an infection at the base of the tooth's root (called the apex). They can also form in reaction to an abscess, cyst or other inflammation within the mouth. Fistulae are essentially channels that form within the bone and/or soft tissue to give infection an avenue for drainage. They typically occur on the gums or the roof of the mouth, but not necessarily near the source of the infection. Often, fistulae take extremely indirect routes before they reach the skin's surface to drain. The parulis is the term given to the point at which the fistula reaches the suface, presenting itself as a small pimple on the gum or palate (or, less frequently, on the skin of the face or neck). The parulis will usually rupture to form an opening. This small wound may heal and recur from time to time.

Fistulae can be difficult to detect. They do not show up on an x-ray, and they do not always reach the surface to drain through a parulis or gum boil. Furthermore, they can be completely non-painful, or they may cause slight pain just prior to drainage. This can be a problem, because a persistent infection can occur if fistulous tracts go undetected for long periods of time.

* Treating long-standing fistulous tracts with surgery or cauterization to resolve any infection at the parulis.