An impacted wisdom tooth is a third molar that is blocked from fully erupting into the mouth, often because the jaw lacks the necessary space. This blockage can be caused by bone, gum tissue, or the adjacent second molar, leaving the tooth partially or completely trapped. Leaving an impacted third molar in place can lead to a range of severe, progressive problems that affect not just the tooth itself but also the surrounding structures and overall health. These potential consequences can escalate from acute infections to permanent structural harm and the formation of destructive lesions.
Localized Infection and Severe Inflammation
The most immediate and common complication of a partially erupted wisdom tooth is pericoronitis, an inflammation of the gum tissue that surrounds the crown of the partially exposed tooth. When the third molar breaks through the gum, a flap of tissue, called an operculum, forms a pocket that traps food debris and oral bacteria.
The protected, warm, and moist environment beneath the operculum is difficult to clean with brushing or flossing, making it an ideal breeding ground for bacteria. This leads to a rapid bacterial overgrowth, resulting in symptoms like intense pain, localized swelling, and a persistent bad taste in the mouth. The inflammation can become so severe that it restricts the patient’s ability to fully open their mouth and makes swallowing difficult.
If the localized infection is left untreated, it can potentially spread deeper into the surrounding tissues of the face, throat, or neck, leading to an abscess. This can result in systemic infection and may require hospitalization and emergency surgical drainage. The recurrent nature of pericoronitis means that even after a flare-up subsides, the risk of another infection remains high as long as the impacted tooth is present.
Structural Harm to Neighboring Teeth and Bone
Retaining an impacted wisdom tooth often leads to two distinct forms of damage to the adjacent second molar. The tight, inaccessible space between the impacted tooth and the second molar’s root creates a plaque-retention area that is nearly impossible to keep clean. This chronic inability to remove plaque and bacteria results in a high risk of dental caries, or decay, on the back surface of the second molar.
Because the decay occurs in a hidden area, it is often not detected until it has progressed significantly, potentially requiring extensive restorative work like a root canal or even the extraction of the otherwise healthy second molar. Root resorption is a process where the physical pressure from the impacted third molar causes the root structure of the second molar to slowly dissolve or be absorbed by the body. The risk of this damage is particularly high when the wisdom tooth is angled forward, known as a mesioangular impaction, or when it is lying horizontally.
Root resorption is a progressive and irreversible condition that weakens the structural support of the second molar. In severe cases, the entire root of the adjacent tooth can be destroyed, which inevitably leads to the loss of the second molar. External root resorption on the second molar is a prevalent issue when an impacted third molar is in contact with it.
Risk of Pathological Lesions
A long-term, non-infectious risk associated with impacted wisdom teeth is the development of pathological lesions in the jawbone. Every unerupted tooth is surrounded by a soft tissue sac called the dental follicle, which contains the remnants of the tooth-forming tissue. This follicle can undergo abnormal changes and transform into a fluid-filled sac known as an odontogenic cyst.
The most frequent type of these growths is the dentigerous cyst, which forms around the crown of the impacted tooth. These cysts expand slowly by accumulating fluid and exert pressure that destroys the surrounding jawbone, potentially displacing nearby teeth and weakening the jaw structure. Although often asymptomatic in their early stages, their growth can eventually lead to jaw swelling and an increased risk of fracture if the bone becomes sufficiently compromised.
The tissue surrounding the impacted tooth can, in rare instances, give rise to benign tumors. These odontogenic tumors, such as an ameloblastoma, are growths that require complex surgical removal and may necessitate bone grafting to repair the resulting defect. The presence of an impacted tooth is a recognized risk factor for these lesions, and early removal is often considered a preventive measure.