Some creatures have teeth that keep on growing. Rats have open-rooted incisors which continue to grow throughout their lifetime, and are kept to a manageable length with constant gnawing. You probably think that your own teeth grow to a predetermined length before stopping, and this is true. But when a tooth is suddenly free of obstructions that limit its growth, it might continue to develop in length. There's an easy explanation for this, along with an easy solution.
The continued growth of a tooth is called overeruption. In dentistry, tooth eruption is the process of the tooth emerging (erupting) from the gum line and then growing to a predetermined length. This length is dependent on your teeth meeting a natural obstruction, namely another tooth.
Your teeth have opposing counterparts. When you close your bite, your upper incisors meet your lower incisors, your upper molars meet your lower molars, and so on. Overeruption can occur when that opposing counterpart is absent.
When you've lost a tooth due to periodontal disease or an accident, its absence will affect your overall bite. Instead of having its biting surface come into contact with its counterpart, a tooth directly above or below an empty dental socket lacks the natural opposition that should exist, and can continue to develop in length into the empty space.
It's not as though your tooth will continue to grow to a significant length, and its overeruption can be measured in millimeters. This can be disruptive to the alignment of your teeth, with the overerupted teeth causing friction as they unexpectedly rub against the inward-facing edges of the teeth on either side of the gap. If untreated, overeruption can contribute to the deterioration of these teeth, as well as causing minor discomfort, and sometimes even contribute to an unpleasant condition known as temporomandibular joint dysfunction.
Dentists can easily correct a tooth affected by overeruption. A section of the tooth is removed, and while sectioning a tooth in this manner isn't ideal, it's then given an artificial cover in the form of a dental crown, which looks identical to a natural tooth, allowing the altered tooth to retain its structural integrity. The missing dental socket should also receive an artificial replacement, whether this is a dental implant, a dental bridge, or even partial dentures.
It's hardly a dental emergency, but overeruption can be a considerable inconvenience, and should be treated before it can cause major problems.