Wisdom teeth, officially known as third molars, are the final set of teeth to emerge in the mouth. These teeth are located at the very back corners of the upper and lower jaws, with one positioned in each quadrant. They are typically the last to arrive, usually erupting sometime between the late teenage years and the early twenties. Most adults who develop them will have four wisdom teeth in total. They are unique among human teeth due to their inconsistent presence and frequent complications.
The Absence of Wisdom Teeth
Not everyone develops a full set of four wisdom teeth, and some individuals do not develop any at all. The congenital absence of one or more teeth is known as dental agenesis, which is relatively common for third molars. The prevalence of third molar agenesis varies significantly across different populations worldwide, highlighting the strong influence of genetics.
Studies reviewing global data report that the worldwide rate of missing at least one wisdom tooth is around 22.63%. This variation suggests that the evolutionary trend toward fewer teeth is actively occurring in the human population.
It is important to distinguish between agenesis (never developing a tooth) and having a tooth that forms but fails to emerge fully. When a wisdom tooth forms but becomes blocked by another tooth, bone, or gum tissue, it is referred to as an impacted tooth. Impacted wisdom teeth are present in the jaw but cannot erupt properly. This impaction occurs in a substantial portion of the population, with one review finding that 36.9% of subjects had at least one impacted third molar.
Evolutionary Role
Third molars point directly to the dietary habits and jaw structure of early human ancestors. These teeth were an asset when the typical diet consisted of coarse, tough foods like raw meat and plants. Early humans possessed larger jaws that easily accommodated these additional molars, which provided necessary grinding power. Having a final set of molars erupt in late adolescence was an advantage, essentially replacing older, worn-out teeth damaged by the rough diet.
Over millennia, as humans developed fire, cooking techniques, and tools, their diet became much softer and required less intensive chewing. This shift led to an evolutionary change in human anatomy, resulting in smaller jawbones. The continued presence of wisdom teeth in these smaller jaws, where they often no longer fit, is why they are considered vestigial structures. They represent a feature that served a clear purpose in our evolutionary past but is gradually becoming obsolete.
Common Reasons for Removal
When wisdom teeth develop, they often cause problems necessitating removal by a dental professional. The most frequent issue is impaction, which happens when the tooth lacks enough space to fully erupt and grows in sideways or at an angle. An impacted tooth can lead to jaw pain, swelling, and damage to the adjacent second molar.
Another common complication is pericoronitis, an infection that occurs when a wisdom tooth is only partially erupted. This creates a flap of gum tissue where food debris and bacteria become trapped, leading to inflammation and infection. Even when fully erupted, their position makes them difficult to clean, increasing the risk of tooth decay and gum disease. These health problems are the primary reasons dentists recommend extraction.