The third molars, commonly known as wisdom teeth, are the final set of teeth to develop, typically appearing in the late teenage years or early twenties. Their absence is a frequent question for many people. When eruption fails, the reason is generally one of two possibilities: either the teeth never formed at all or they are present but physically unable to break through the gum line.
When Wisdom Teeth Never Formed (Agenesis)
The first explanation for why wisdom teeth have not come in is that they never developed within the jawbone, a condition known as congenital absence or agenesis. This occurs when the tooth bud, the initial cluster of cells necessary for tooth formation, fails to develop early on. Agenesis is considered a genetic trait and often runs in families.
It is one of the most common developmental anomalies in humans. If the tooth is truly absent due to agenesis, it is a benign condition that requires no active treatment, as there is simply no tooth to manage.
When Wisdom Teeth Are Present But Hidden (Impaction)
The more frequent reason a person believes their wisdom teeth are missing is that the teeth are actually present in the jaw but are impacted, meaning they are physically obstructed from erupting. Impaction occurs because the jaw does not have enough space to accommodate these final molars, which are the last to arrive. This lack of space causes the tooth to become stuck beneath the gum tissue or bone.
The physical barrier preventing eruption can be classified based on the tissue involved. A soft tissue impaction means the tooth is fully developed and has cleared the bone but is trapped beneath a layer of gum tissue. In contrast, a bony impaction occurs when the tooth is fully or partially encased by dense jawbone, which presents a much stronger mechanical obstruction.
Impacted teeth can also be classified by the angle at which they are trapped:
- Horizontal impaction: The tooth is lying completely sideways.
- Mesial impaction: The tooth is angled forward toward the neighboring second molar.
- Vertical impaction: The tooth is upright but blocked from emerging.
- Distal impaction: The tooth is angled backward toward the jaw joint.
Confirming the Status of Third Molars
Since a non-erupted tooth can be either completely absent or deeply impacted, a clinical examination alone is insufficient to determine its true status. The definitive answer requires diagnostic imaging to visualize the structures beneath the gum line. The standard tool for this is a panoramic X-ray, also known as an orthopantomogram (OPG).
This image provides a comprehensive view of the entire upper and lower jaw, confirming the presence or absence of the third molars. If the teeth are present, the X-ray reveals their exact position, angulation, and depth of impaction within the bone. The imaging also shows the relationship of the roots to important anatomical structures, such as the mandibular nerve canal. Analyzing these images allows the dental professional to determine if the issue is agenesis or impaction, guiding the future treatment plan.
Implications of Non-Eruption
Once the status of the third molars is confirmed through imaging, the resulting management plan depends entirely on the diagnosis. If the X-ray confirms agenesis, no further action is necessary, as there is no tooth to monitor or treat. However, if the teeth are confirmed to be impacted, a decision must be made regarding retention or removal.
For impacted teeth that are currently asymptomatic, meaning they are causing no pain or damage, the approach is often watchful waiting, involving regular monitoring with clinical exams and periodic X-rays. This conservative approach is based on the idea that the expense and risks of extraction may not be justified if the tooth is not causing problems.
Conversely, extraction is strongly indicated if the impacted tooth is causing pathology, such as recurrent infection (pericoronitis), decay in the wisdom tooth or the adjacent second molar, or the development of cysts. Furthermore, extraction may be recommended prophylactically if the tooth’s position poses a high risk of future damage to the second molar or if the patient is older, as the removal procedure becomes more complex with age due to longer, more entrenched roots.