Tooth resorption is a condition where your body breaks down and absorbs the hard tissue of a tooth, gradually destroying it from either the inside or outside. Specialized cells called odontoclasts dissolve the mineral and protein structures of the tooth in much the same way that other cells naturally remodel bone throughout your life. When this process targets a permanent tooth, it’s considered pathological and can lead to significant damage or tooth loss if left untreated.
Resorption in baby teeth is completely normal. It’s the biological process that loosens primary teeth so they can fall out and make room for permanent ones. In those cases, the pulp inside the tooth stays healthy and no bacteria are involved. Pathological resorption in permanent teeth is a different story: it’s driven by injury, infection, or inflammation, and it doesn’t stop on its own.
How Resorption Breaks Down a Tooth
Odontoclasts, the cells responsible for resorption, work almost identically to osteoclasts, the cells that break down bone. The process happens in two stages. First, the cells dissolve the mineral component of the tooth using enzymes and acid. They pump hydrogen ions against the tooth surface, essentially bathing it in acid that eats away the hard crystalline structure. Second, once the minerals are cleared, other enzymes break apart the organic matrix, the collagen and protein framework that gives the tooth its shape and flexibility.
The debris from both stages is absorbed into the odontoclasts and transported out the other side of the cell, a process called transcytosis. Over time, this creates visible cavities or defects in the tooth structure. The resorption can progress slowly over months or years, or it can advance rapidly when driven by active infection.
Internal vs. External Resorption
Tooth resorption is classified by where it starts. Internal resorption begins inside the tooth, originating from the pulp chamber. External resorption starts on the outer root surface and works inward. External resorption is considerably more common.
Internal Resorption
Internal resorption is relatively rare. It starts when cells within the pulp begin dissolving the canal walls from the inside out, gradually enlarging the hollow interior of the tooth. For the process to continue, at least part of the pulp must remain alive, typically in the root’s tip. Trauma and deep decay that allows bacteria into the pulp are the most common triggers.
One distinctive sign is what’s known as a “pink spot,” first described by Mummery in 1920. As resorption hollows out the tooth from within, the highly vascular tissue behind the thinning enamel shows through, giving the crown a pinkish discoloration. On an X-ray, internal resorption appears as a well-defined, round or oval enlargement of the root canal with smooth, clear borders.
External Resorption
External resorption originates in the periodontal ligament, the thin tissue layer that connects the tooth root to the surrounding bone. The most common form is external inflammatory resorption, which typically follows dental trauma. After an injury, if the protective layer of cementum covering the root is damaged and the pulp becomes infected, bacterial toxins seep through the tiny tubules in the dentin and reach the root surface. This creates a powerful stimulus for the resorbing cells, which can eat deep, bowl-shaped craters into the root and surrounding cementum.
External cervical resorption is a specific subtype that occurs near the gum line. Studies using 3D imaging have found it affects roughly 1.3% of teeth examined, with prevalence estimates across different populations ranging from about 0.08% to 2.3%. On a standard X-ray, external resorption looks like an irregular, moth-eaten area on the root surface, and the outline of the root canal can usually still be seen running through or behind the defect.
Common Causes and Triggers
Dental trauma is the most frequently cited trigger, particularly injuries that push a tooth into its socket (luxation injuries). These injuries can damage both the root surface and the pulp simultaneously, setting up the conditions for inflammatory resorption. But trauma isn’t the only cause. Resorption can also be triggered by:
- Orthodontic treatment: The sustained pressure used to move teeth can cause apical root resorption, where the root tips gradually shorten. This is one of the recognized complications of braces, especially when forces are heavy or treatment is prolonged.
- Chronic infection or periodontal disease: Inflammatory molecules released during gum disease activate the same cellular pathways that drive bone loss around teeth, and they can trigger resorption of the root itself.
- Impacted teeth, cysts, or tumors: Pressure from a neighboring impacted tooth or a growing lesion can stimulate resorption of an adjacent root.
- Chemical exposure: Caustic compounds like hydrogen peroxide, sometimes used for internal bleaching of discolored teeth, can provoke resorption if they contact the root surface.
- Surgical procedures: Certain dental surgeries near the root can damage the protective cementum layer and initiate the process.
In some cases, no clear cause is identified. The resorption is discovered incidentally on a routine X-ray.
Symptoms and Warning Signs
Tooth resorption is often silent in its early stages. Many people have no pain or visible changes, which is why it’s frequently caught on dental X-rays taken for other reasons. As it progresses, symptoms depend on the type and location.
Internal resorption may produce a pink spot on the crown, though this only occurs when the resorption is close enough to the surface for the underlying tissue to show through. External resorption near the gum line can sometimes cause localized swelling or tenderness. In advanced cases of either type, the tooth may become loose, sensitive to temperature or pressure, or develop a dull ache. If the resorption perforates the root wall, you may notice signs of infection like swelling or a draining sore on the gum.
How Resorption Is Diagnosed
Standard dental X-rays can detect resorption, but they have limitations. Because a traditional X-ray compresses a three-dimensional structure into a flat image, it can be difficult to tell whether a lesion is internal or external, or to gauge its true size. Internal resorption stays in the same position on the X-ray no matter what angle is used, while external lesions appear to shift. Dentists use this “shift test” with angled X-rays as a diagnostic tool.
Cone beam computed tomography (CBCT), a type of 3D dental scan, has become the gold standard for evaluating resorption. It eliminates the overlapping of structures that makes traditional X-rays ambiguous and can detect lesions smaller than 1 millimeter. CBCT provides precise information about the location, size, and extent of the damage, which directly guides treatment decisions. It uses a lower radiation dose than medical CT scans while producing images with minimal distortion.
Treatment Options
Treatment depends on the type of resorption, how far it has progressed, and whether the tooth can realistically be saved. The goal is always to stop the resorption process and preserve as much tooth structure as possible.
For internal resorption, root canal treatment is the primary approach. Removing the pulp eliminates the vital tissue that the resorbing cells need to stay active, which halts the process. The challenge is filling the irregular, enlarged spaces left behind. A biocompatible cement called mineral trioxide aggregate (MTA) has become a preferred material for these cases because it seals well, is strong enough to reinforce weakened root walls, can set even in the presence of blood, and promotes healing of the surrounding tissues. Starting treatment promptly matters, because the longer resorption continues, the thinner and more fragile the remaining root walls become, increasing the risk of fracture.
For external resorption, the approach varies. If infection is driving the process, root canal treatment addresses the bacterial source. External cervical resorption may require surgical access to remove the damaged tissue and fill the defect. In cases caused by orthodontic forces, reducing or pausing treatment allows the body’s natural repair mechanisms to stabilize the root.
The prognosis for teeth treated conservatively is generally good, even when the resorption has perforated the root wall. However, teeth with extensive destruction, where the structural integrity is too compromised, may ultimately need extraction and replacement with an implant or bridge.
Resorption During Orthodontic Treatment
Some degree of root shortening is common during orthodontic treatment, particularly affecting the upper front teeth. In most cases, the amount of shortening is minor and clinically insignificant. Heavy forces, prolonged treatment times, and certain tooth shapes increase the risk. Your orthodontist typically monitors for this with periodic X-rays during treatment. If significant shortening is detected, the treatment plan can be adjusted to reduce forces or shorten the remaining treatment duration, which helps limit further damage.