The molars are broad, flat teeth positioned toward the back of the mouth. Adults typically have 12 molars in total, with three sets on each side of the upper and lower jaws. The common term “last molars” refers specifically to the third set, which are more widely known as the wisdom teeth. They are the final teeth to complete the adult dentition, and their emergence timing is highly variable.
Identifying the Three Sets of Adult Molars
The full adult dentition normally includes three distinct sets of molars, all of which share the function of grinding and crushing food. The first set to emerge are the first molars, often nicknamed the “six-year molars” because they typically erupt around that age. These are the teeth most people have the longest and are the most important for chewing function.
Following the first set, the second molars usually appear around age 12, earning them the nickname “twelve-year molars.” These two sets of molars erupt successfully in the vast majority of people and are fully functional parts of the chewing surface. The third set, the wisdom teeth, are the last in the sequence and are technically named the third molars.
The third molars are situated at the very back of the mouth, behind the second molars. While the first two sets of molars are generally well-accommodated in the jaw, the final set often develops when the jaw structure is already fully formed. This late development is the primary reason the third molars often cause problems.
The Typical Timeline for Third Molar Eruption
The process of the last molars coming in spans several years, beginning with the tooth’s formation within the jawbone. Initial mineralization often begins around age 8. The actual eruption, which is the movement of the tooth through the bone and gum tissue, usually occurs much later.
For most individuals, the third molars first appear between the ages of 17 and 21. This wide age range is why they are commonly referred to as “wisdom teeth,” as they arrive during young adulthood. However, the exact timing depends on genetics and developmental factors, meaning some people may see them earlier or later.
The eruption process itself is not instantaneous and can span months or even years as the tooth slowly moves into position. In some cases, the third molars never erupt, remaining embedded within the jawbone or failing to develop entirely. This complete absence is known as agenesis, which affects a significant portion of the population.
The development of the roots is the final stage, which typically completes around 22 years of age. A dental professional can monitor the status of the third molars through routine X-rays. This provides an accurate picture of their development and trajectory long before they are expected to emerge.
Common Issues Arising from Late Eruption
The late arrival of the third molars often coincides with insufficient space in the jaw, leading to impaction. An impacted tooth is blocked from fully erupting into a functional position, often trapped against the second molar or beneath the gum tissue. Impaction can be partial (a portion of the crown breaks through the gum) or full (the tooth remains completely enclosed within the bone).
Partial eruption creates an opening where bacteria can accumulate beneath the gum flap covering the tooth, leading to localized infection called pericoronitis. Symptoms include pain, swelling, and difficulty opening the mouth. This infection is one of the most frequent reasons for urgent removal.
A partially erupted or poorly positioned third molar is also difficult to clean effectively, which significantly increases the risk of tooth decay. This decay can affect the third molar itself or the distal surface of the adjacent, fully functional second molar. While the link is debated, some dental professionals believe pressure from an erupting third molar can contribute to the crowding or misalignment of the front teeth.
Due to these potential complications, dentists often monitor third molar development with X-rays during the teen years. Regular assessments allow for early detection of impaction or other issues. This informs the decision on whether monitoring or preventative removal is the most appropriate course of action.