“I already had a root canal on this tooth. Why does it still hurt?”
I hear some version of this almost every week at our Torrance office. A patient comes in frustrated. Sometimes confused. Sometimes angry. They did everything they were supposed to — went to the dentist, sat through a root canal, got the crown — and now, months or years later, the tooth is acting up again.
It’s a terrible feeling. And I get it.
The good news? A failed root canal doesn’t automatically mean you lose the tooth. In many cases, we can redo the treatment and give the tooth a second chance. That’s called retreatment, and it’s a big part of what I do as an endodontist.
Let me walk you through what’s really going on.
Why Do Root Canals Fail?
Root canals have a really high success rate — somewhere around 90 to 97%. But that means a small percentage don’t work out. When I see a failed root canal, the cause almost always falls into one of these categories.
Missed Canals
This is the number one reason I see. Teeth have complex anatomy. Molars especially. There’s a canal called the MB2 — that’s the second canal in the mesial buccal root of an upper molar. It’s tiny. It’s hidden. And it gets missed more often than you’d think.
If a canal is missed during the first root canal, bacteria stay inside the tooth. The infection never fully clears. The tooth feels fine for a while, but eventually the bacteria multiply and the problem comes back.
About that MB2 canal: Studies show the MB2 canal is present in up to 90% of upper first molars, but it’s found and treated in far fewer cases — especially without a microscope. This single missed canal is responsible for a huge number of failed root canals on upper molars.
Incomplete Cleaning
Even if all the canals were found, they may not have been cleaned thoroughly. Root canals aren’t simple tubes. They have branches, curves, and tiny offshoots called lateral canals. If bacteria linger in any of these spaces, infection can return.
New Decay Under the Crown
A root canal treats the inside of the tooth. But the outside is still vulnerable. If new decay develops around the crown margin and bacteria leak back into the root canal system, the treatment can fail — even if the original root canal was perfect.
A Cracked Root
Sometimes a tooth develops a crack after treatment. This can happen from grinding, clenching, or just normal wear over time. A crack in the root lets bacteria in, and no amount of retreatment can fix a vertical root fracture.
Delayed Crown Placement
After a root canal, the tooth needs a crown to protect it. If the crown is delayed too long — weeks or months — the temporary filling can leak. Bacteria get back inside. The whole thing is recontaminated, and the root canal fails before the tooth even gets its final restoration.
Signs Your Root Canal Has Failed
Not every ache or twinge after a root canal means failure. Some discomfort in the first week or two is normal. But if you notice any of these things — especially months or years after treatment — something may be wrong.
Pain That Comes Back
The tooth starts hurting again. Maybe it’s a dull ache. Maybe it’s sharp pain when you bite down. Either way, pain that returns long after a root canal should be evaluated.
Swelling
Swelling near the treated tooth — in the gums, the jaw, or even the face — is a sign that infection has returned or never fully resolved.
A Pimple on Your Gum
Dentists call this a sinus tract. It looks like a small pimple or bump on the gum near the tooth. It’s actually a drainage channel for pus from the infection at the root tip. If you see one of these, the tooth needs attention.
Darkening of the Tooth
A tooth that gradually turns gray or dark after a root canal may have lingering infection or breakdown happening inside.
Don’t ignore these signs. A failed root canal won’t fix itself. The infection will continue to damage the bone around the tooth. The longer you wait, the harder it becomes to save. If you’re noticing any of these symptoms, get it checked.
Retreatment vs. Extraction: An Honest Comparison
This is the question every patient with a failed root canal asks: “Should I just have it pulled this time?”
I’ll be straight with you. Sometimes extraction is the right answer. But more often than not, retreatment is worth trying first.
When Retreatment Makes Sense
- The tooth has good structure and can support a new crown
- There’s a clear reason the first root canal failed (missed canal, incomplete cleaning)
- The root isn’t cracked
- There’s enough bone support around the tooth
If these things check out, retreatment has a strong chance of saving the tooth. And your natural tooth — even a retreated one — functions better than any implant.
When Extraction Makes More Sense
- The root has a vertical fracture
- The tooth is too broken down to restore
- There’s been severe bone loss from long-standing infection
- Previous retreatment or surgery has already been attempted without success
I won’t push retreatment if the prognosis is poor. If I look at your tooth under the microscope and on the CBCT scan and I don’t think we can save it, I’ll tell you that directly.
Here’s the thing: Retreatment keeps your options open. If you try retreatment and it doesn’t work, you can still extract and place an implant later. But once you pull the tooth, there’s no going back. You can’t un-extract a tooth.
What Retreatment Actually Involves
Retreatment is more involved than the original root canal. We’re not starting from scratch — we’re undoing what was done before and doing it better. Here’s what the process looks like.
Step 1: Get the Full Picture
Before I touch the tooth, I take a CBCT 3D scan. This gives me a detailed view of the roots, the old filling material, any missed canals, and the infection around the root tips. A regular X-ray shows a flat, 2D image. The CBCT shows everything — angles, hidden anatomy, the extent of bone loss. It changes the game.
Step 2: Remove the Old Crown and Filling Material
I access the inside of the tooth and carefully remove the old root canal filling material — usually gutta percha and sealer. I use ultrasonic instruments and the microscope to do this precisely without damaging the root walls.
Step 3: Find What Was Missed
This is where the microscope really matters. Under 20x magnification, I can find canals and anatomy that were invisible during the first treatment. That MB2 canal I mentioned earlier? It shows up under the microscope almost every time.
Step 4: Clean and Disinfect
Once every canal is located and the old material is out, I re-clean and disinfect the entire canal system. At our office, we use GentleWave technology for this step. It uses acoustic energy and advanced fluid dynamics to clean areas that traditional instruments can’t reach — the lateral canals, the branches, the microscopic spaces where bacteria hide.
Step 5: Refill and Seal
After thorough disinfection, I fill and seal the canals with new material. The tooth is then ready for a new crown from your general dentist.
The Technology Behind Successful Retreatment
Retreatment done well requires tools that most general dental offices don’t have. Here’s what makes a difference.
- Surgical microscope — 20x magnification. I can see anatomy and details that are invisible to the naked eye. This is how missed canals get found.
- CBCT 3D imaging — Shows the full anatomy of the tooth and surrounding bone in three dimensions. Identifies fractures, extra canals, and the extent of infection.
- Ultrasonic instruments — Precisely remove old filling material and calcifications without removing excess tooth structure.
- GentleWave cleaning system — Reaches areas of the root canal system that files and syringes can’t. Particularly valuable in retreatment cases where thorough disinfection is the whole point.
These aren’t optional extras. For retreatment cases, they make the difference between success and another failure.
What Are the Success Rates?
Retreatment has a success rate of about 75 to 85%. That’s lower than a first-time root canal (90–97%), and I want to be upfront about that. Retreatment is harder. The anatomy has been altered by the first procedure. Scar tissue, ledges, and separated instruments can complicate things.
But 75–85% is still a really good number. For most patients, those odds are well worth it — especially when the alternative is losing the tooth and spending $4,000 to $6,000 or more on an implant.
Patients Come to Us From Across the South Bay
We see retreatment patients at our Torrance office from all over — Redondo Beach, Hermosa Beach, Palos Verdes, Lomita, Carson, Gardena, and beyond. Many are referred by their general dentist specifically because the case is complex and needs a specialist with the right equipment.
Some patients find us on their own, looking for a second opinion after being told their tooth can’t be saved. I’m glad when they do, because in many of those cases, the tooth actually can be saved. The right tools and the right training make a real difference.
A Failed Root Canal Doesn’t Mean a Lost Tooth
If your root canal didn’t work, you have options. Retreatment gives your tooth a real second chance — and it’s almost always worth exploring before you go the extraction route.
The key is having it done by a specialist with the right technology to figure out why the first treatment failed and to fix the problem at its source.
If you’re dealing with a failed root canal, don’t wait for the infection to get worse. The sooner we evaluate the tooth, the better the chances of saving it. We’ll take a 3D scan, look at the tooth under the microscope, and give you a straight answer about your options.
Ready to get answers? Call Phan Endodontic Partners at (310) 378-8342 to schedule a consultation at our Torrance office. We’ll tell you exactly what’s going on and whether retreatment can save your tooth.