Wisdom teeth comprise the third and final set of molars on the upper and lower jaws. If wisdom teeth come into place without any complications, a person would then have a total of 12 molars, six molars on each side of the mouth, or three molars on each half of the upper and lower jaws.
Wisdom teeth start coming out after about age 16. These teeth are the last ones to come out, hence they are associated with coming into age or maturity (and, presumably, with having gained greater wisdom). Unfortunately for most people, and for some still largely undetermined reason/s (which some theorise as being due to the change in the diet of modern humans), there isn’t enough space in the mouths of most modern humans to accommodate the wisdom teeth; so most wisdom teeth come out impacted, that is, instead of erupting straight up and out just like the other teeth, wisdom teeth usually erupt in three possible but wrong directions, or generally upwards, but at a too shallow depth.
Impacted wisdom teeth can grow at an angle towards the second molar in front of it (mesial impaction), at an angle towards the back of the mouth (distal impaction), perpendicular to the long axes of the other teeth (horizontal impaction), or straight up but not enough to come out of either the gums or the jawbone (soft tissue vertical impaction and bony vertical impaction, respectively). Impacted wisdom teeth can also be deflected towards the tongue or towards the cheeks. If some part of a wisdom tooth breaks out through the gums, the tooth is considered partially impacted. If no part of the tooth is visible, it is considered fully impacted. The most common impacted growth direction is towards the front of the jaw arches (mesial impaction).
As they continue to erupt and exert pressure on adjacent teeth, bone, or gums, impacted wisdom teeth can cause severe and throbbing pain. This pain may radiate towards the ear or may diffuse throughout the whole skull, causing earaches and headaches, respectively. Bleeding and swelling of the gums can also occur.
If left on its own, the presence of an impacted wisdom tooth can lead to a number of dental or oral-maxillofacial conditions and complications such as malocclusion of the adjacent teeth it is pushing out against (via a domino-effect type of reaction), tooth decay of the adjacent teeth and/or the wisdom tooth itself, contact pressure on the mandibular nerve (which could lead to numbness of the cheeks, lower lip, and chin), formation of an infected cyst or non-malignant tumour on the gums, infection of the jawbone (which in turn could lead to a temporomandibular joint disorder or to an infection of the mandibular nerve), and gingivitis (which in turn could lead to full-blown periodontal disease). With the high probability or the actual occurrence of these and other serious complications, it is generally advisable to have the impacted tooth extracted.