Impacted Teeth

An impacted tooth is one that fails to erupt fully into its normal functional position, usually because it is blocked by an adjacent tooth, by bone, or by soft tissue, or because it is malpositioned. Mandibular and maxillary third molars (wisdom teeth) and maxillary canines are the most commonly impacted teeth, and their assessment and surgical removal are a central part of dentoalveolar surgery.

Definition

An impacted tooth is a tooth that has failed to erupt, or is prevented from erupting, into its expected position in the dental arch within the expected time, remaining partly or wholly embedded in bone or soft tissue.

Scope

This entry describes what tooth impaction is, how impactions are classified by angulation and depth, why they may or may not cause problems, and the main considerations and risks surrounding their surgical management. It is a reference description and does not provide operative instructions or individualized treatment advice.

Core questions

• Why do some teeth become impacted while others erupt normally?
• How are impactions classified, and how does classification relate to surgical difficulty?
• When does an impacted tooth cause disease, and when is it asymptomatic?
• What are the principal risks of removing an impacted tooth, and how is removal weighed against retention?

Key concepts

• Impaction (failure of eruption)
• Third molar (wisdom tooth)
• Angulation classification: mesioangular, distoangular, horizontal, vertical
• Depth and ramus relationship classification
• Pericoronitis
• Inferior alveolar and lingual nerve proximity
• Prophylactic versus therapeutic removal

Mechanisms

Impaction arises when a tooth's eruption path is obstructed—by an adjacent tooth, dense overlying bone, fibrous soft tissue, or arch-length deficiency—or when the tooth is malpositioned or develops in an abnormal site. Retained impacted teeth can give rise to local disease such as pericoronitis (inflammation around a partly erupted crown), caries and resorption of adjacent teeth, and, less commonly, cysts or other pathology. Surgical removal exposes the tooth, removes obstructing bone, and often sections the crown and roots; because mandibular third molar roots may lie close to the inferior alveolar and lingual nerves, this proximity is a recognised source of surgical risk (Jerjes, 2010; Hupp, 2019).

Clinical relevance

Impacted teeth are a frequent reason for referral and surgery in dentistry, and the decision to remove or retain them is informed by symptoms, associated disease, position, and the risks of intervention. This entry describes the topic for orientation and is not a basis for deciding on, or carrying out, treatment in any individual.

Epidemiology

Third molars are the most commonly impacted teeth, and their management is among the most common indications for minor oral surgery in young adults. The evidence on removing asymptomatic, disease-free impacted wisdom teeth is limited, and systematic review has found insufficient high-quality data to support either routine removal or routine retention as universally superior (Ghaeminia, 2016).

History

Classification of impactions developed in the twentieth century as oral surgery formalised, with widely taught schemes describing third-molar angulation and the relationship of the tooth to the ramus and the occlusal plane. Debate over prophylactic removal of asymptomatic wisdom teeth intensified as evidence-based dentistry questioned routine intervention.

Debates

Should asymptomatic, disease-free impacted wisdom teeth be removed prophylactically?

Whether to remove impacted third molars that cause no current symptoms or disease is contested; systematic review finds insufficient evidence that prophylactic removal improves outcomes, so the balance of future risk against surgical morbidity is judged case by case.

Seminal works

• ghaeminia-2016
• jerjes-2010
• hupp-2019

Frequently asked questions

What does it mean for a tooth to be impacted?

An impacted tooth has failed to erupt fully into its normal position, typically because it is blocked by another tooth, bone, or soft tissue, or because it is malpositioned; wisdom teeth and upper canines are the most commonly affected.

Why is removing a lower wisdom tooth sometimes considered risky?

The roots of lower (mandibular) third molars can lie close to the inferior alveolar and lingual nerves, so their surgical removal carries a recognised, though usually low, risk of temporary or, rarely, lasting nerve disturbance.