The third molars, commonly known as wisdom teeth, are the final set of teeth to develop in the human mouth. They typically appear in late adolescence or early adulthood, an age associated with maturity, which is how they earned their name. While most adults have four of these molars, the idea that everyone gets them is not accurate. Due to evolutionary and genetic shifts, a significant portion of the population will never develop all four wisdom teeth, and some people develop none at all.
The Biological Answer: Genetic Absence (Agenesis)
The congenital absence of one or more teeth is known as dental agenesis, and it most frequently affects the third molars. This occurs when the tooth bud fails to develop in the jawbone. Third molar agenesis is strongly influenced by genetic factors, with specific genes like PAX9 and MSX1 being implicated in the developmental process.
Globally, the congenital absence of at least one wisdom tooth occurs in approximately 20 to 30 percent of the population. This prevalence varies widely across different ethnic groups, ranging from practically zero in certain indigenous populations to over 40 percent in others, such as those of Korean descent. This biological trend is tied to the evolution of the human jaw, which has become smaller over millennia as the human diet shifted from tough, uncooked foods to softer, processed meals.
The decreased formation of these final molars suggests an ongoing evolutionary trend toward a reduced number of teeth. Therefore, the absence of wisdom teeth is a normal biological variation.
Typical Development and Eruption Timing
For individuals who develop wisdom teeth, the initial formation of the tooth buds begins deep within the jawbone during childhood or early adolescence. As these structures mature over several years, they slowly move into position at the back of the mouth. The process of eruption, where the tooth pushes through the gumline, typically occurs between the ages of 17 and 25.
The wisdom teeth are the last permanent teeth to emerge, often coinciding with the completion of jaw growth. The exact timing of eruption is influenced by individual genetics and the available space in the jaw. If a wisdom tooth has not appeared by the mid-twenties, it is generally not expected to erupt spontaneously.
Issues Caused by Improper Alignment (Impaction)
When a wisdom tooth is present but cannot fully emerge into the mouth due to a lack of space or an obstruction, it is classified as impacted. The tooth remains trapped beneath the gum tissue, the jawbone, or both, causing a range of potential issues.
Impaction is categorized by the angle at which the tooth is positioned:
- Mesial impaction, where the tooth is angled forward toward the molar in front of it.
- Horizontal impaction, where the tooth lies completely on its side, pressing directly into the adjacent second molar.
- Vertical impaction, where the tooth is upright but still trapped.
- Distal impaction, where the tooth is angled toward the back of the mouth.
Symptoms of an impacted wisdom tooth can include pain and swelling in the jaw, tender or bleeding gums, and difficulty opening the mouth fully. If a tooth is only partially erupted, it creates a flap of gum tissue where food particles and bacteria can become trapped, leading to infection and inflammation known as pericoronitis. An impacted tooth can also exert pressure on the neighboring molar, potentially causing damage or increasing the risk of decay for the adjacent tooth.