Why root canals fail — and why that's usually fixable
Most root canals that fail do so for a reason that can be corrected. The single most common is a canal that was never found and cleaned the first time — frequently the MB2 canal in an upper molar, which is present in about 90% of patients and is easy to miss without a microscope. Other causes include a new cavity that lets bacteria back in, a cracked or delayed crown, or complex anatomy that wasn't fully treated.
Option 1: nonsurgical retreatment
This is the first choice in most cases. The endodontist reopens the tooth through the crown, carefully removes the previous gutta-percha filling material (and any posts), re-cleans and disinfects every canal — including any that were missed — and re-seals the tooth. Under a microscope, with CBCT to map the anatomy, the success rate is high.
Option 2: apicoectomy (endodontic microsurgery)
When retreatment from the top isn't possible or hasn't worked — for example, when there's a post and crown that can't be safely removed, or infection persists at the root tip — a small surgery seals the root from the outside. The endodontist makes a tiny incision in the gum, removes the very tip of the root and the infected tissue, and places a root-end filling. It's a precise, microscope-guided procedure with a good track record. See apicoectomy and when an apicoectomy is needed.
How a specialist decides which one
| Situation | Usual first choice |
|---|---|
| A canal was likely missed; tooth is accessible | Nonsurgical retreatment |
| Post and crown that can't be safely removed | Apicoectomy |
| Retreatment already done but infection persists | Apicoectomy |
| Vertical root fracture or non-restorable tooth | Extraction (the genuine exception) |
A CBCT scan is often the deciding tool — it shows missed canals, the extent of infection, and whether the root is fractured.
When the tooth genuinely can't be saved
Honesty matters here: if the root is vertically fractured, or there isn't enough sound tooth left to restore, retreatment won't help and extraction is the right call. A specialist should tell you that directly rather than attempt a treatment destined to fail. Compare paths on retreatment vs extraction vs apicoectomy.
If you have a root canal that still hurts, has flared up again, or your dentist says is failing, get a specialist evaluation before agreeing to extraction. Call (669) 234-2354 — we see retreatment and surgical second opinions seven days a week. See failed root canal help in the Bay Area.
Related questions
Is redoing a root canal worth it?+
Usually yes — saving your natural tooth is generally preferable to extraction and replacement, and retreatment has a high success rate, especially when a missed canal is found and treated. Your specialist will use CBCT to confirm the tooth is genuinely savable before recommending it.
How successful is root canal retreatment?+
Retreatment is highly successful, particularly when the original failure was due to a missed canal that can now be found and cleaned under a microscope. Success is lower when the cause is a vertical root fracture — which is why a specialist evaluates the real cause first with CBCT.
Is retreatment more painful than the first root canal?+
No — it's done with the same profound local anesthesia and is typically no more uncomfortable than the original treatment. Retreatment takes a bit longer because the old filling material must be removed, but your comfort during the procedure is the same.
What if retreatment doesn't work either?+
There's still a path: an apicoectomy can seal the root tip from the outside when retreatment can't resolve the infection. Extraction is only the last resort, reserved for teeth that are fractured or no longer restorable.
Can any dentist redo a root canal?+
Retreatment is more complex than a first-time root canal and is best done by a specialist endodontist with a microscope and CBCT. Removing prior filling material, finding missed canals, and managing posts demand specialist tools and experience for the best chance of saving the tooth.
Still have questions? Talk to a specialist.
Dr. Kung is happy to answer your question by phone before you book — no pressure, no charge for the conversation.