Impacted wisdom teeth (or impacted third molars) are wisdom teeth which do not fully erupt into the mouth because of blockage from other teeth (impaction). If the wisdom teeth do not have an open connection to the mouth, pain can develop with the onset of inflammation or infection or damage to the adjacent teeth.

Wisdom teeth likely become impacted because of a mismatch between the size of the teeth and the size of the jaw. 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 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 soft tissue surgery of the gum tissue overlying the tooth. Over time, most of these treatments tend to fail and patients develop recurrent symptoms. The most common treatment 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 that are not causing problems. Supporters of early removal cite the increasing risks for extraction over time and the costs of monitoring the wisdom teeth that are not removed. Supporters for retaining wisdom teeth cite the risk and cost of unnecessary surgery.

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

Classification

All teeth are classified as either developing, erupted (into the mouth), embedded (failure to erupt despite lack of blockage from another tooth) or impacted. An impacted tooth is one that fails to erupt due to blockage from another tooth.

Wisdom teeth 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, 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 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.

One review found that 11% of teeth will have evidence of disease and are symptomatic, 0.6% will be symptomatic but have no disease, 51% will be asymptomatic but have disease present and 37% will be asymptomatic and have no 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. Of these predictors, age correlates best with extraction difficulty and complications during wisdom teeth removal rather than the orientation of the impaction.

Signs and symptoms

Impacted wisdom teeth without a communication to the mouth, that have no pathology associated with the tooth and have not caused tooth resorption on the blocking tooth rarely have symptoms. In fact, only 12% of impacted wisdom teeth are associated with pathology.

When wisdom teeth communicate with the mouth, the most common symptom is localized pain, swelling and bleeding of the tissue overlying the tooth. This tissue is called the operculum and the disorder called pericoronitis which means inflammation around the crown of the tooth. Low grade chronic periodontitis commonly occurs on either the wisdom tooth or the second molar, causing less obvious symptoms such as bad breath and bleeding from the gums. The teeth can also remain asymptomatic (pain free), even with disease. As the teeth near the mouth during normal development, people sometimes report mild pressure of other symptoms similar to teething.

The term asymptomatic means that the person has no symptoms. The term asymptomatic should not be equated with absence of disease. Most diseases have no symptoms early in the disease process. A pain free or asymptomatic tooth can still be infected for many years before pain symptoms develop.

Causes

Wisdom teeth become impacted when there is not enough room in the jaws to allow for all of the teeth to erupt into the mouth. Because the wisdom teeth are the last to erupt, due to insufficient room in the jaws to accommodate more teeth, the wisdom teeth become stuck in the jaws, i.e., impacted. There is a genetic predisposition to tooth impaction. Genetics plays an important, albeit unpredictable role in dictating jaw and tooth size and tooth eruption potential of the teeth. Some also believe that there is a devolutionary decrease in jaw size due to softer modern diets that are more refined and less coarse than our ancestors’.

 

Diagnosis

The diagnosis of impaction can be made clinically if enough of the wisdom tooth is visible to determine its angulation, depth, and if the patient is old enough that further eruption or up righting is unlikely. Wisdom teeth continue to move into adulthood (20–30 years old) due to eruption and then continue some later movement owing to periodontal disease.

If the tooth cannot be assessed with clinical exam alone, the diagnosis is made using either a panoramic radiograph or cone-beam CT. Where unerupted wisdom teeth still have eruption potential several predictors are used to determine the chance of the teeth becoming impacted. The ratio of space between the tooth crown length and the amount of space available, the angle of the teeth compared to the other teeth are the two most commonly used predictors, with the space ratio being the most accurate. Despite the capacity for movement into early adulthood, the likelihood that the tooth will become impacted can be predicted when the ratio of space available to the length of the crown of the tooth is under 1.

Prognosis

The prognosis for impacted wisdom teeth depends on the depth of the impaction. When they lack a communication to the mouth, the main risk is the chance of cyst or neoplasm formation which is relatively uncommon.

Once communicating with the mouth, the onset of disease or symptoms cannot be predicted but the chance of it does increase with age. Less than 2% of wisdom teeth are free of either periodontal disease or caries by age 65. Further, several studies have found that between 30% – 60% of people with previously asymptomatic impacted wisdom teeth will have them extracted due to symptoms or disease, 4–12 years after initial examination.

Extraction of the wisdom teeth removes the disease on the wisdom tooth itself and also appears to improve the periodontal status of the second molar, although this benefit diminishes beyond the age of 25.