An impacted tooth fails to fully break through the gum line and settle into its correct position within the dental arch. This occurs because the tooth is trapped, either by surrounding bone, dense soft tissue, or another tooth blocking its path. What an impacted tooth truly “looks like” is rarely visible to the naked eye, as the problem lies beneath the surface of the gums. Professional imaging is necessary to assess the tooth’s exact position and the potential risk it poses to the surrounding structures. The external signs a person might notice are generally the complications resulting from the impaction, rather than the tooth itself.
Understanding Impaction and Common Locations
Impaction typically arises from a simple lack of adequate space in the jaw for the tooth to erupt properly. The most frequently impacted teeth are the third molars, commonly known as wisdom teeth. The second most common teeth to become impacted are the maxillary canines, sometimes called eye teeth. Impaction can be categorized based on the tissue covering the tooth.
A soft tissue impaction means the tooth is covered only by gum tissue, while a partial bony impaction indicates the tooth has broken through some bone but is still partly encased in the jaw. The most complex scenario is a complete bony impaction, where the tooth remains entirely encased within the jawbone, with no part of it visible through the gum. These types of obstructions determine the difficulty of removal and influence the potential for complications like infection. The lack of space may also force the tooth to grow at an abnormal angle, further preventing its emergence.
Observable Signs and Symptoms
While a fully bone-impacted tooth may cause no obvious signs, a partially erupted tooth can lead to highly visible symptoms, primarily due to localized infection. The most common manifestation is pericoronitis, the inflammation and infection of the gum flap (operculum) that partially covers the tooth. Visually, this appears as a localized area of redness and significant swelling directly behind the last molar.
The site of infection can also produce a foul taste or persistent bad breath because food particles and bacteria become trapped beneath the gum flap. In more severe cases, pressure and inflammation in the area can cause referred pain, which radiates away from the tooth. This discomfort is often felt as a persistent jaw ache, or a tension-style headache that concentrates around the temples or forehead.
Another noticeable sign is trismus, or difficulty opening the mouth. This occurs because the severe swelling from the infection or the constant pressure from the tooth causes the nearby chewing muscles to tighten and spasm. The inflammation and nerve irritation can also sometimes be felt as an earache, as the jaw and ear nerves share close anatomical connections.
How Dentists Visualize Impaction on Imaging
Since the impacted tooth is hidden, dental imaging is the decisive diagnostic tool. The primary image used is the panoramic X-ray, which provides a single, comprehensive view of the tooth’s position relative to all other structures. For complex cases, a Cone-Beam Computed Tomography (CBCT) scan is employed to create a detailed three-dimensional view, which eliminates the overlap seen on standard two-dimensional images.
On these images, the tooth’s angulation is the most descriptive visual feature, classifying the impaction in one of four primary ways. The mesioangular impaction is the most common, where the impacted tooth is tilted forward, angled towards the second molar in front of it. This angle makes it appear as if the tooth is trying to push its way into the neighboring tooth’s root.
A horizontal impaction is visually striking because the tooth lies completely sideways, at a 90-degree angle to the rest of the teeth. On a panoramic film, this appears as a tooth lying flat against the roots of the adjacent molar, which is a position strongly associated with complications.
Conversely, a vertical impaction shows the tooth oriented upright, positioned normally along the same axis as the other teeth, but still trapped beneath the bone or gum line. The fourth type is a distal impaction, which is the rarest, where the tooth is angled backward, pointing away from the tooth in front of it and toward the back of the jaw. Analyzing these angles, along with the depth of the tooth within the bone, allows the dentist to determine the exact relationship of the impacted tooth to the adjacent teeth and surrounding nerves.
Associated Damage and Long-Term Consequences
The physical presence of an impacted tooth can lead to secondary damage visible on dental imaging. One frequent consequence is external root resorption, where the pressure from the impacted tooth causes the body to break down the root structure of the neighboring, fully erupted tooth. On an X-ray, the adjacent tooth’s root appears to have a portion shaved off, or a scoop-like defect, often in the middle or lower third of the root.
Another serious long-term effect is the development of a dentigerous cyst, which is a fluid-filled sac that forms around the crown of the unerupted tooth. On an X-ray, this cyst appears as a dark, well-defined bubble or semicircle that balloons out from the neck of the impacted tooth. As this cyst grows, it can displace the impacted tooth and other surrounding teeth, and in rare cases, it may visibly expand the jawbone itself.
Furthermore, a partially erupted tooth creates a chronic trap for bacteria, leading to decay (caries) on both the impacted tooth and the distal surface of the adjacent molar. This decay is visible on the X-ray as a dark shadow or radiolucency on the side of the erupted tooth that is in contact with the impaction.