The final teeth to emerge in the human mouth are the third set of molars, commonly known as wisdom teeth. They are positioned at the very back of the jaws, with two located in the upper arch and two in the lower arch. While the general function of molars is to grind and crush food during chewing, the third molars often have a limited or absent function in modern diets.
What Defines Third Molars
Third molars are the most posterior teeth in the dental arch, completing the row of large, flat-surfaced molars on each side of the jaw. Eruption of these molars is highly variable among individuals but typically occurs between the late teenage years and the early twenties (17 to 21 years of age). The timing of their emergence is a biological process influenced by factors like genetics and nutrition.
Historically, these teeth served a purpose for early humans who consumed a rougher, uncooked diet requiring significant grinding. The late-erupting third molars were often needed to replace chewing surfaces worn down by constant use. Modern diets are softer and easier to process, reducing the functional need for these molars. This shift has coincided with changes in human jaw structure, often leading to less space for the third molars to erupt properly.
Factors Causing Their Absence
Not everyone develops wisdom teeth, as a significant portion of the population is missing one or more of these molars. This congenital absence, known as dental agenesis, makes third molars the most commonly missing teeth in the human mouth. The worldwide rate of third molar agenesis is estimated to be around 22.63%, though rates vary widely; for instance, 10–25% of Americans with European ancestry are missing at least one, while the rate can reach 40% among Asian Americans.
The development of wisdom teeth is strongly controlled by genetic factors, which are estimated to account for 60–80% of the variation seen in their absence. This conclusion is supported by twin studies showing a higher prevalence of agenesis in identical twins. The formation of the tooth bud is influenced by several genes involved in facial and tooth development.
The trend toward missing wisdom teeth is considered an ongoing evolutionary change linked to the reduction in human jaw size. As the jaw has become smaller over millennia, there is less space available for the third molars to develop or erupt successfully. This evolutionary pressure, combined with strong genetic control, explains the high variability in the presence of third molars today.
Problems Associated With Eruption
When third molars develop, they often encounter mechanical problems due to insufficient space in the jaw. The most common issue is impaction, where the tooth is partially or completely trapped against the bone or another tooth, preventing full emergence. Impaction is classified based on the tooth’s orientation, including vertical, mesial (angled forward), distal (angled backward), and horizontal (lying sideways). Horizontal and mesial impactions are often the most problematic, as they directly pressure the adjacent second molar.
An impacted tooth can lead to a range of painful and damaging consequences for oral health. When a wisdom tooth only partially emerges, the overlying gum tissue can become inflamed and infected, a condition known as pericoronitis. Impaction also makes the area difficult to clean, increasing the risk of tooth decay and gum disease in the third molar and the neighboring second molar. In severe cases, the constant pressure or chronic infection can lead to the formation of cysts or damage to the roots of the adjacent teeth.
Management of a developing wisdom tooth depends on its position and whether it is causing symptoms. If the tooth is asymptomatic and not causing damage, a dental professional may recommend monitoring its development with regular X-rays. However, if an impacted tooth is causing pain, recurrent infection, or is likely to damage other teeth, surgical removal, or extraction, is often recommended to alleviate symptoms and prevent future complications.