A parulis is also called a gum boil. It is really a drainage point for a tooth abscess. This abscess is caused by the body's response to the toxins which drain out of the tip of a root of a tooth with a dead nerve. This image shows two parulii, one over the root tips of each of the central incisors. The teeth are both decayed and the decay reaches down to the nerve of the teeth. The nerve under these circumstances will die off. The dead nerve inside the teeth tends to seep out of the tooth at the tip of the root. Any dead tissue is poisonous, and the body reacts to the toxic material seeping out of the tips of the roots by sending white blood cells to eat the infection.
These white blood cells die off and accumulate as pus at the tip of the root, causing draining abscesses. Over time, without treatment, the abscess finally breaks through the bone and the pus drains out of the gums into the mouth. The point at which the pus escapes forms a small blister, and this blister is called a parulis.
Copyright 2006 Martin S. Spiller, D.M.D. courtesy of Dr. Ed Cataldo
The image above shows what can happen when a patient uses a hard toothbrush in a sawing motion over many years. The notches you can see in all the teeth (also visible on the upper teeth) were cut by a hard toothbrush. The notch in the molar goes all the way to the nerve of the tooth, which accounts for the dead nerve which lead to the parulis.