The standard count for wisdom teeth, technically known as third molars, is four. These are the last set of molars to develop in the back of the mouth, completing the full adult set of 32 teeth. While four is the typical number, the actual count varies widely among individuals, ranging from zero to more than the usual amount. This variation reflects ongoing human evolution and a mix of genetic and environmental factors.
The Standard Count of Third Molars
The expected number of wisdom teeth is four, with one located in each of the mouth’s four quadrants. They are positioned just behind the second molars, which typically erupt around age twelve. Historically, these molars served a purpose for our ancestors who consumed a tougher, more abrasive diet of raw plants and meats. The large, strong molars helped grind down these coarse foods for proper digestion. As human diets softened and cooking methods advanced, the need for this extra grinding surface diminished. This change is linked to evolutionary shifts that resulted in smaller jaw sizes in modern humans. The third molars are now often considered vestigial, meaning they no longer serve a significant function.
Typical Age of Eruption
The name “wisdom teeth” is based on the age at which they typically emerge, usually between 17 and 25 years old. This period is generally associated with maturity. This developmental timing is significantly later than the other permanent teeth, which generally finish erupting in early adolescence. The lengthy process of wisdom tooth development actually begins much earlier, with the tooth structure starting to form within the jawbone around age seven to ten.
Regular dental X-rays taken during the teenage years allow dentists to monitor the growth and position of these developing third molars. The late eruption makes the third molars vulnerable to problems because the jawbone and surrounding teeth have usually completed their development. If there is not enough space remaining in the jaw, the wisdom teeth may become impacted, meaning they are trapped beneath the gums or bone. This lack of space is a common reason why many people have their third molars removed.
Having Fewer Than Four Wisdom Teeth
It is common for individuals to have fewer than the standard four wisdom teeth, a condition known as third molar agenesis or hypodontia. Globally, the rate of people missing at least one third molar is estimated to be around 22.6%, but this frequency varies widely across different populations. Individuals may be missing one, two, three, or all four of their third molars.
This absence is strongly tied to genetic factors, which account for a significant portion of the variation. Specific genes involved in facial and tooth development, such as AXIN2, MSX1, and PAX9, are known to influence whether a person develops all four molars. The decreasing frequency of third molars is considered an example of ongoing human evolution toward a reduced number of teeth.
The evolutionary pressure for this change stems from the fact that a smaller, softer diet led to smaller jaws over thousands of years. As the jaw size decreased, the third molars became more problematic due to impaction, leading to positive selection for the genetic variation that suppresses their development. The absence of these teeth is often confirmed by dental X-rays taken during adolescence.
Having More Than Four Wisdom Teeth
While having fewer than four wisdom teeth is a common variation, having more than four is a much rarer occurrence. This condition is known as hyperdontia, and the extra teeth are called supernumerary teeth. When these develop near the third molar region, they are often referred to as fourth molars, or distomolars.
The prevalence of supernumerary teeth in the permanent dentition is estimated to be between 1.5% and 3.5% of the population. The extra molars can appear as a single additional tooth or sometimes as multiple extra teeth. In extremely rare cases, individuals have been documented with as many as twelve wisdom teeth.
These additional teeth can cause dental complications, including crowding, the displacement of neighboring teeth, or the development of cysts. The formation of supernumerary teeth is thought to result from the hyperactivity of the dental lamina, the tissue from which teeth develop. Diagnosis and monitoring of these extra molars are typically done through radiographic examination, and they are often recommended for extraction to prevent future issues.