Patient-friendly definition from the DentistsDirectory.org dental glossary.
An impacted tooth is one that is unable to erupt fully into its normal position in the dental arch because its path is physically blocked by bone, an adjacent tooth, or overlying gum tissue. The tooth may be completely encased in bone (full bony impaction), partly emerged through the gum with some bone still covering part of it (partial bony impaction), or blocked only by soft tissue (soft tissue impaction). Third molars (wisdom teeth) are the teeth most commonly impacted, followed by upper canines.
The most common reason for wisdom tooth impaction is insufficient space in the jaw — the modern human jaw is often too small to accommodate the four additional molars. For upper canines, impaction typically results from developmental abnormalities in the eruption path, crowding, or the persistence of a baby canine tooth beyond its expected loss date. Impaction is diagnosed through dental X-rays, and panoramic radiographs are particularly useful for surveying all teeth at once.
Not all impacted teeth need to be removed. Fully impacted wisdom teeth that are symptom-free, not showing signs of infection or cyst development, and not damaging neighbouring teeth are sometimes monitored rather than extracted — especially in older patients where the risks of surgery increase. However, partially erupted wisdom teeth are prone to pericoronitis (infection of the surrounding gum flap) and are difficult to clean, making extraction commonly recommended. Impacted canines are typically exposed surgically and guided into place orthodontically rather than extracted, preserving important teeth for the bite and smile.