The third molars, commonly known as wisdom teeth, are the last teeth to emerge, typically appearing between the ages of 17 and 25. These teeth are an evolutionary remnant, but modern human jaws are often too small to accommodate them. While some wisdom teeth erupt successfully and align perfectly, many do not due to insufficient space. When there is insufficient room, a wisdom tooth may get stuck beneath the gumline or jawbone. Allowing the tooth to grow in can then lead to significant complications for overall oral health.
The Anatomy of Impaction
Impaction is the term used when a tooth is prevented from fully erupting into its correct functional position due to a physical obstruction. This obstruction can be either the jawbone itself, the overlying gum tissue, or the adjacent second molar. The angle at which the tooth develops determines the specific type and potential severity of the problem.
The most common type is a mesial impaction, where the tooth is angled forward toward the second molar. Conversely, a distal impaction angles the tooth backward toward the jaw joint. Horizontal impaction occurs when the tooth lies completely sideways, pushing directly into the root of the second molar.
A vertical impaction means the tooth is positioned straight up, but still lacks the necessary space to break through the gumline. Impactions are classified as soft tissue impaction, where the gum is the only barrier, or bony impaction, where the tooth is fully or partially encased in bone.
Immediate Dental Damage
A common problem with partially erupted wisdom teeth is pericoronitis, an infection and inflammation of the gum tissue surrounding the tooth crown. A flap of gum, called an operculum, often forms over a partially emerged tooth, trapping food particles and bacteria beneath it. This leads to symptoms such as localized pain, swelling, and difficulty opening the jaw.
The position of an impacted wisdom tooth makes it difficult to clean effectively, leading to a high risk of decay (caries). Bacteria thrive in the tight space between the wisdom tooth and the adjacent second molar. This often causes decay on the wisdom tooth and, more concerningly, on the back surface of the healthy second molar. Decay on the second molar can be extensive and difficult to restore without removing the wisdom tooth.
An erupting wisdom tooth can exert chronic pressure, contributing to localized shifting or misalignment of adjacent teeth. This pressure may potentially undo years of orthodontic work. An angled or horizontally positioned tooth can also create difficult-to-clean areas, which increases the risk of gum disease and decay across the dental arch.
Risks to Bone and Soft Tissue
Allowing a problematic wisdom tooth to remain can lead to serious pathology involving the jawbone and surrounding tissues. One risk is the development of a dentigerous cyst, which forms when the tissue sac surrounding an unerupted tooth fills with fluid. As these cysts grow, they exert pressure that destroys the adjacent jawbone and the roots of neighboring teeth.
The cells lining this follicular sac can sometimes transform into a benign tumor, such as an ameloblastoma, which requires aggressive surgical removal and reconstruction of the jaw. Chronic pressure from a horizontally impacted tooth can physically erode or cause root resorption of the second molar. This process is a gradual destruction of the second molar’s root structure, which compromises its long-term stability and function.
An infection starting as pericoronitis can spread into the deeper fascial spaces of the head and neck, potentially leading to cellulitis or an abscess. These deep-space infections cause significant swelling that may compromise the airway. This turns a localized dental issue into a life-threatening medical emergency requiring immediate hospitalization and surgical drainage.
Criteria for Retention
Not all wisdom teeth require removal; some can be safely retained under professional surveillance. A wisdom tooth is acceptable to keep if it is fully erupted, properly aligned, and completely functional in the biting and chewing process. Crucially, the tooth must be fully accessible for routine oral hygiene, allowing the patient to brush and floss all its surfaces and the adjacent second molar effectively. A dentist will only recommend retention if the tooth is asymptomatic and radiographic imaging shows no signs of associated disease.
Associated disease includes a lack of decay on the adjacent molar, no evidence of bone loss, and no cyst formation around the crown. If these criteria are met, the retained wisdom tooth still requires regular monitoring through routine dental examinations and periodic X-rays. This ensures that any early signs of pathology are detected before they cause irreversible damage.