Internal Root Resorption: The One That Catches You Looking the Wrong Way

4 days ago

3 min read

Internal resorption is the diagnosis that punishes complacency. You're looking at a symptomless tooth, maybe a slightly odd radiolucency on a routine bitewing, and the temptation is to file it under "watch and review." That's exactly how it gets missed until the crown's gone translucent-pink and you're explaining to the patient why their tooth is suddenly a different colour.

What's actually happening

Internal resorption starts inside the pulp chamber or canal, not on the root surface. Chronic pulpal inflammation — usually from trauma, a deep restoration, or a low-grade pulpitis that never fully declared itself — activates clastic cells inside the canal wall. They eat away dentine from the inside out, and if the process breaks through to the periodontal ligament before you catch it, you've lost the tooth's structural integrity from a direction you can't easily reach or predict.

Why it's easy to miss

The tooth is often asymptomatic for a long time. There's frequently a history of trauma years earlier that the patient has forgotten to mention because they don't connect it to a tooth that currently feels fine. And on a single periapical, internal resorption can look deceptively like external resorption or even a normal canal outline, depending on the angle.

The tell on the radiograph

This is the bit worth drilling into your own habits: take a second periapical at a different horizontal angle before you commit to a diagnosis. Internal resorption stays centred on the canal and appears to travel with the root outline as you shift the angle, because it's genuinely inside it. External resorption, by contrast, appears to shift position relative to the canal as the angle changes, because it's sitting on the surface, off-axis. That parallax difference is the single most reliable chairside distinguishing feature, and it costs you one extra film.

CBCT earns its place here more than almost anywhere else in endo. If you've got any doubt after two angled periapicals, or if the lesion looks large enough that perforation is a real possibility, get a small-volume CBCT before you commit to a treatment plan. It tells you whether the lesion is contained within the canal wall or has already perforated — which changes everything about prognosis and whether root canal treatment alone will resolve it.

Treatment reality

If it's caught early and hasn't perforated, conventional RCT with warm vertical obturation to fully obturate the irregular internal defect gives a genuinely good prognosis — the resorptive process stops once the pulp is removed and the space is sealed. If it's perforated, you're into MTA or bioceramic repair territory, sometimes combined with surgical access depending on the perforation site, and the prognosis drops accordingly. This is the point where "have a low threshold to refer" isn't a throwaway line — a perforated internal resorption managed well early is a saveable tooth; managed late, it often isn't.

The practical takeaway

Any symptomless pink-tinged crown, any radiolucency that doesn't quite make sense on a single film, any tooth with an old trauma history you'd otherwise dismiss — take the second angled periapical before you write it off. It's the cheapest diagnostic step in dentistry and it's the one that catches this before the patient notices their tooth changing colour in the mirror.