Impacted wisdom teeth
Impacted wisdom teeth is a condition where the third molars 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, periodontal disease or cysts. Prophylactic extraction of wisdom teeth is preferred to be done at a younger age 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 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.
Classification
All teeth are classified as either developing, erupted, embedded, 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 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 of symptoms and disease.
Impacted wisdom teeth are often described by the direction of their impaction, 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. Each of these factors is used to predict the difficulty 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 : 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.
Signs and symptoms
Impacted wisdom teeth without 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. The chances of developing pathology on an impacted wisdom tooth that is not communicating with the mouth is approximately 12%. However, when impacted wisdom teeth communicate with the mouth, food and bacteria penetrate to the space around the tooth and cause symptoms such as localized pain, swelling and bleeding of the tissue overlying the tooth. The tissue overlying the tooth is called the operculum, and the disorder is 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, even with disease.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. Studies have shown that impacted teeth, and crowded teeth in general, arose in humans in the move from hunter-gatherers to farmers, and increased with the industrial revolution, as well it has been shown that young animals fed on uncooked vegetables as opposed to cooked ones have larger jaws. This suggests that it is industrialized soft and processed diets that cause impacted wisdom teeth.Pathophysiology
Impactions completely covered by bone and soft tissue, do not communicate with the mouth, and have a low rate of clinically significant infection. Since the tooth never erupts, the dental follicle that surrounds the tooth does not degenerate during eruption, and can develop cysts or uncommon tumors over time. Estimates of the incidence of cysts or other neoplasms around impacted teeth average at 3%, usually seen in people under the age of 40. This suggests that the chance of tumor formation decreases with age.For partially impacted teeth in those over 20 year of age, the most common pathology seen, and the most common reason for wisdom teeth removal, is pericoronitis or infection of the gum tissue over the impacted tooth. The bacteria associated with infections include Peptostreptococcus, Fusobacterium, and Bacteroides bacteria. The next most common pathology seen is cavities or tooth decay. Fifteen percent of people with retained wisdom teeth exposed to the mouth have cavities on the wisdom tooth or adjacent second molar due to a wisdom tooth. The rate of cavities on the back of the second molar has been reported anywhere from 1% to 19% with the wide variation attributed to increased age.
In five percent of cases, advanced periodontitis or gum inflammation between the second and third molars precipitates the removal of wisdom teeth. Among patients with retained, asymptomatic wisdom teeth, roughly 25% have gum infections. Teeth with periodontal pockets of greater than 5mm have tooth loss rates that start at 10 teeth lost per 1000 teeth per year at 5mm to a rate of 70 teeth lost per year per 1000 teeth at 11mm. The risk of periodontal disease and caries on third molars increases with age with a small minority of adults age 65 years or older maintaining the teeth without caries or periodontal disease and 13% maintaining unimpacted wisdom teeth without caries or periodontal disease. Periodontal probing depths increase over time to greater than 4 mm in a significant proportion of young adults with retained impacted wisdom teeth which is associated with increases in serum inflammatory markers such as interleukin-6, soluble intracellular adhesion molecule-1 and C-reactive protein.
Crowding of the front teeth is not believed to be caused by the eruption of wisdom teeth although this is a reason many dental clinicians use to justify wisdom teeth extraction.,
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 uprighting is unlikely. Wisdom teeth continue to move to the age of 25 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.