Resorption is one of the few conditions where the body's own cells begin to destroy tooth structure — sometimes from the inside, sometimes from the outside. It is usually painless until late, often invisible on standard X-rays, and almost always requires a specialist's eye and 3D imaging to diagnose accurately.
Medically reviewed by Dr. Jason Kung, DDS, MS · Specialist Endodontist · UCLA DDS · OHSU MS ·
A short video from the American Association of Endodontists explaining the different types of internal and external tooth resorption.
What internal and external resorption are, how they progress, and what treatment options exist.Video courtesy of the American Association of Endodontists.Watch on its own page
How resorption usually announces itself
Most cases come to attention in one of three ways:
Found on a routine X-ray
Your general dentist notices an unusual oval shape inside or alongside the root and refers you for evaluation.
Pink spot on the tooth
A faint pink area shows through the enamel — the body's tissue replacing tooth structure becomes visible from outside.
After dental trauma
Following a significant injury, especially a knocked-out or severely loosened tooth, resorption can develop in the months that follow.
The five types of resorption
Type matters, because each has its own cause, behavior, and treatment outlook. The first job of an endodontic evaluation is to identify which type you have.
Internal Resorption
Inside the tooth
Generally favorable
Cells inside the root canal — usually after long-standing pulp inflammation — begin to dissolve the inner wall of the tooth from within. Often discovered as an unexplained pink spot showing through the crown of the tooth, or as an oval enlargement of the canal on a routine X-ray.
Typical cause
Chronic pulp inflammation, often from previous trauma or untreated decay. Usually painless until very advanced.
Prognosis
Generally treatable with timely root canal treatment that removes the resorbing cells. The earlier it is caught, the better the outlook.
External Cervical Resorption
Just below the gumline
Guarded — depends on stage
Cells from the periodontal ligament invade the root surface near the gumline and aggressively dissolve tooth structure from the outside in. Frequently linked to internal bleaching, orthodontic treatment, or trauma. Often only detected on CBCT 3D imaging — standard X-rays miss the true extent in most cases.
Typical cause
History of orthodontics, internal bleaching of a non-vital tooth, dental trauma, or sometimes idiopathic with no obvious trigger.
Prognosis
Depends entirely on how far the lesion has progressed. Small early lesions can sometimes be repaired surgically with biocompatible filling materials. Lesions that have invaded the root canal or undermined the crown often cannot be saved. Long-term outcome data support this staging: in a 2022 cohort followed for up to 10 years, early lesions (Heithersay Class 1–2) and teeth treated with root canal therapy had lower failure rates than advanced (Class 3–4) cases.
External Apical Resorption
Tip of the root
Generally favorable
Shortening of the root tip from the outside. Often a side effect of orthodontic forces, especially over long treatment courses. Usually painless and discovered on follow-up X-rays.
Typical cause
Orthodontic tooth movement is the most common cause. Chronic apical inflammation from an infected tooth can also drive it.
Prognosis
Usually self-limiting once the cause is removed. The shortened tooth typically remains functional. Only rarely requires endodontic intervention.
External Inflammatory Resorption
After trauma
Guarded — depends on stage
Following a significant injury — particularly tooth avulsion or severe luxation — the periodontal ligament cells can become activated and aggressively resorb the root from the outside. Progresses quickly if untreated and can destroy a root in months.
Typical cause
Dental trauma. The risk is highest after a knocked-out tooth that was out of the mouth for an extended period before being put back.
Prognosis
Time-critical. Prompt root canal treatment with calcium hydroxide medication can halt the process in many cases. Delay dramatically worsens the outlook.
Replacement Resorption (Ankylosis)
Tooth fusing to bone
Poor
After severe trauma kills the periodontal ligament, the body treats the tooth root as bone and begins to slowly replace it with new bone. The tooth fuses to the surrounding jawbone and, in growing children, will fail to erupt with the rest of the dentition.
Typical cause
Almost always traumatic — most often a knocked-out tooth that was stored dry or out of the mouth for a long time before reimplantation.
Prognosis
Cannot be reversed once established. Treatment focuses on managing the long-term consequences — including planning for eventual loss of the tooth and replacement with an implant or other restoration. In growing patients, careful coordination with an orthodontist is critical.
Why CBCT 3D imaging is non-negotiable
Standard 2D dental X-rays compress the entire tooth into a single image and routinely understate the size of a resorption lesion. CBCT (cone-beam computed tomography) shows the lesion in three dimensions — front-back, side-to-side, and top-to-bottom — which is the only reliable way to know whether a tooth can actually be saved or whether attempting to treat it would do more harm than good. Our Sunnyvale office uses the J. Morita Veraview X800 — widely regarded as the best dental CBCT for endodontics — in its high-resolution Endo Mode (80 µm voxel, 40 × 40 mm limited field of view) for every resorption workup. This is the small-volume, high-resolution protocol the AAE/AAOMR Joint Position Statement on the Use of CBCT in Endodontics (2015) and the AAE position statement on resorption both recommend.
References for further reading: Heithersay's classification of external cervical resorption (1999); Patel et al., External Cervical Resorption: A Review (J Endod, 2009); the resorption chapter in Endodontics Review: A Study Guide (Blicher, Lucier Pryles & Lin, Quintessence, 2016); and the AAE position statement on diagnosis and management of resorption.
Frequently asked questions about tooth resorption
What is tooth resorption?
Tooth resorption is a process where the body's own cells dissolve part of a tooth — either from inside the canal (internal resorption) or from the outer surface of the root (external resorption). It is one of the few conditions where your body actively destroys tooth structure. It is usually painless in early stages, which is why it is often discovered on a routine X-ray. Specialized 3D imaging called CBCT is often needed to see the true extent of the lesion.
What causes tooth resorption?
The cause depends on the type. Internal resorption is usually triggered by long-standing inflammation of the pulp, often from old trauma or untreated decay. External cervical resorption is linked to orthodontics, internal bleaching of a non-vital tooth, or dental trauma. External inflammatory resorption and replacement resorption almost always follow significant tooth trauma — particularly avulsion (a knocked-out tooth). Sometimes there is no identifiable cause.
Can a resorbing tooth be saved?
It depends on the type and how far it has progressed. Internal resorption that is caught early is often successfully treated with a root canal. Small external cervical lesions can sometimes be repaired surgically. Inflammatory resorption following trauma is time-critical — prompt root canal treatment with medicated fillings can halt the process in many cases. Replacement resorption (where the tooth is fusing to bone) cannot be reversed and the tooth will eventually be lost. The earlier we catch it, the more options we have.
Why do I need a CBCT scan to diagnose resorption?
Standard 2D dental X-rays show resorption lesions, but they often dramatically underestimate the true size and shape — particularly for external cervical resorption, where lesions can wrap around the root in three dimensions. CBCT (cone-beam computed tomography) gives us a true 3D view and is now considered the standard of care for evaluating resorption. We use J. Morita CBCT in our Sunnyvale office.
Does tooth resorption hurt?
Usually no, especially in the early stages. That is exactly what makes it dangerous — the destruction is happening silently and is often only discovered on a routine X-ray, or when a 'pink spot' appears showing through the crown of the tooth. By the time pain develops, the lesion is often advanced. If your dentist mentions seeing something suspicious on an X-ray, do not wait.
Can a tooth with external cervical resorption be saved?
Often, yes — but it depends on how early the lesion is found and how it is treated. In a 2022 University of British Columbia study that followed teeth with external cervical resorption for up to 10 years, early-stage lesions (Heithersay Class 1–2) had markedly better outcomes than advanced lesions (Class 3–4), and teeth that received root canal treatment — on its own or combined with repair of the defect — failed less often. Small, accessible lesions can frequently be repaired and the tooth kept for years; lesions that have spread deep into the root or undermined the crown may not be restorable. The single biggest factor in your favor is catching it early.
What is the success rate of treating tooth resorption?
There is no single number, because the outcome depends on the type of resorption, how advanced it is, and how it is treated. The best available long-term data show that stage matters most: in a 2022 cohort followed for up to 10 years, external cervical resorption caught early (Heithersay Class 1–2) did significantly better than advanced cases, and root canal treatment lowered the risk of failure. The same study found that back (posterior) teeth failed more often than front teeth. Rather than quote a generic success rate, we give you an honest, individualized prognosis after CBCT imaging shows the true extent of the lesion.
Does where the tooth is located affect whether it can be saved?
Yes. In the 2022 University of British Columbia cohort, posterior (back) teeth with external cervical resorption failed more often than anterior (front) teeth. Back teeth are harder to access, have more complex root anatomy, and their lesions are often discovered later. This does not mean a back tooth cannot be saved — many are — but it is one reason a specialist evaluates each tooth individually with 3D imaging before recommending treatment.
Has your dentist mentioned a "shadow" on a tooth?
Don't wait. Resorption is a time-sensitive diagnosis — small lesions are often treatable, but the same lesion six months later may be unsavable. A focused evaluation with CBCT imaging takes about an hour and gives you a definitive answer about what is happening and what your real options are.
How we diagnose and stage resorption follows the published classification literature and the AAE's prognosis framework — not a preference for extraction-and-implant over saving the tooth:
External cervical resorption is strongly associated with prior orthodontic treatment, dental trauma, and intracoronal bleaching — the predisposing factors Heithersay identified in his landmark series of treated cases.[1]
CBCT is essential to stage a lesion accurately: Patel's 3D classification grades external cervical resorption by height, circumferential spread, and proximity to the root canal, which is what determines whether a tooth is restorable.[2]
Whether a resorbing tooth is treatable or should be removed is matched to the lesion's location and extent using the AAE's favorable / questionable / unfavorable framework.[3]
Long-term outcomes depend on stage and treatment — not on a bias toward extraction over saving the tooth: in a 2022 University of British Columbia cohort that followed external cervical resorption for up to 10 years, early lesions (Heithersay Class 1–2) and teeth that received root canal treatment had significantly lower failure rates than advanced (Class 3–4) cases, while posterior teeth fared worse than anterior teeth.[4]
Tooth resorption treatment — serving 30+ Bay Area cities
Dr. Jason Kung provides tooth resorption treatment to patients across Silicon Valley from our Sunnyvale office. Evening and weekend hours, same-day emergencies, free on-site parking.
