Impacted wisdom teeth is a condition where the third molars (wisdom teeth) are prevented from erupting into the mouth. This can be caused by a physical barrier, such as other teeth, or when the tooth is angled away from a vertical position. Completely unerupted wisdom teeth usually result in no symptoms, although they can sometimes develop cysts or neoplasms. Partially erupted wisdom teeth or wisdom teeth that are not erupted but are exposed to oral bacteria through deep periodontal pocket, can develop cavities or pericoronitis. Removal of impacted wisdom teeth is advised for the future prevention of or in the current presence of certain pathologies, such as caries (dental decay), periodontal disease or cysts. Prophylactic (preventative) extraction of wisdom teeth is preferred to be done at a younger age (middle to late teenage years) to take advantage of incomplete root development, which is associated with an easier surgical procedure and less probability of complications. However, in recent decades the preventive removal of impacted wisdom teeth has come into question, and some health organizations have issued guidelines calling to only remove impacted wisdom teeth in the case of current issues.

Impacted wisdom teeth are classified by their direction of impaction, their depth compared to the biting surface of adjacent teeth and the amount of the tooth's crown that extends through gum tissue or bone. Impacted wisdom teeth can also be classified by the presence or absence of symptoms and disease. Screening for the presence of wisdom teeth often begins in late adolescence when a partially developed tooth may become impacted. Screening commonly includes a clinical examination as well as x-rays such as panoramic radiographs.

Infection resulting from impacted wisdom teeth can be initially treated with antibiotics, local debridement or surgical removal of the gum overlying the tooth. Over time, most of these treatments tend to fail and patients develop recurrent symptoms. The most common treatment for recurrent pericoronitis is wisdom tooth removal. The risks of wisdom tooth removal are roughly proportional to the difficulty of the extraction. Sometimes, when there is a high risk to the inferior alveolar nerve, only the crown of the tooth will be removed (intentionally leaving the roots) in a procedure called a coronectomy. The long-term risk of coronectomy is that chronic infection can persist from the tooth remnants. The prognosis for the second molar is good following the wisdom teeth removal with the likelihood of bone loss after surgery increased when the extractions are completed in people who are 25 years of age or older. A treatment controversy exists about the need for and timing of the removal of disease-free impacted wisdom teeth. Supporters of early removal cite the increasing risks for extraction over time and the costs of monitoring the wisdom teeth. Supporters for retaining wisdom teeth cite the risk and cost of unnecessary surgery.

The condition can be common, with up to 72% of the Swedish population affected. Wisdom teeth have been described in the ancient texts of Plato and Hippocrates, the works of Charles Darwin and in the earliest manuals of operative dentistry. It was the meeting of sterile technique, radiology, and anesthesia in the late 19th and early 20th centuries that allowed the more routine management of impacted wisdom teeth.

All teeth are classified as either developing, erupted (into the mouth), embedded (failure to erupt despite lack of blockage from another tooth), or impacted. Impacted teeth are ones that fail to erupt due to blockage from other teeth. Wisdom teeth, as the last teeth to erupt in the mouth are the most likely to become impacted. They develop between the ages of 14 and 25, with 50% of root formation completed by age 16, and 95% of all teeth erupted by the age of 25, however, some tooth movement can continue beyond the age of 25.

Impacted wisdom teeth are classified by the direction and depth of impaction, the amount of available space for tooth eruption, and the amount of soft tissue or bone (or both) that covers them. The classification structure helps clinicians estimate the risks for impaction, infections and complications associated with wisdom teeth removal. Wisdom teeth are also classified by the presence (or absence) of symptoms and disease.

Impacted wisdom teeth are often described by the direction of their impaction (forward tilting, or mesioangular being the most common), the depth of impaction and the age of the patient as well as other factors such as pre-existing infection or the presence of pathology (cysts, tumors or other disease). Each of these factors is used to predict the difficulty (and rate of complications) when removing an impacted tooth, with age being the most reliable predictor rather than the orientation of the impaction.

Another classification system often taught in U.S. dental schools is known as Pell and Gregory Classification. This system includes a horizontal and vertical component to classify the location of third molars (predominately applicable to lower third molars): the third molar's relationship to the level of the teeth already in the mouth, being the vertical or x-component and to the anterior border of the ramus being the horizontal or y-component.