You had the root canal. The pain went away. Then, months or years later, it came back — a dull ache when you bite, a bump on the gum that drains and refills, a tooth that feels wrong in a way you cannot quite describe. Your general dentist looked at the radiograph, saw a dark shadow at the root tip, and used the word that patients dread: extraction.
Before you accept that, understand what a failed root canal actually is. A failed root canal is almost never a failure of the tooth. It is a persistent infection inside a space that was cleaned incompletely, sealed imperfectly, or recontaminated afterward. Infections in a sealed space are a specialist’s problem, and specialists solve them regularly. The tooth itself is often perfectly sound.
Why Root Canals Fail
Root canal treatment succeeds roughly 90% of the time, which means a meaningful number of teeth end up in the other category. The reasons cluster into a handful of patterns, and most of them are anatomical rather than clinical error.
The most common is a missed canal. Upper first molars frequently carry a second canal in the mesiobuccal root — the MB2 — that is narrow, curved, and hidden under a shelf of dentin. Studies using magnification find it in the large majority of these teeth, yet it is routinely missed without a microscope. If bacteria remain in that untreated canal, the infection continues no matter how well the other three were sealed.
Other causes include: canals that were calcified and could not be negotiated to their full length, complex anatomy such as fins, isthmuses, and accessory canals that harbor bacteria beyond the reach of a file, a permanent crown placed months after the root canal rather than promptly, allowing saliva and bacteria to leak back down the canal, new decay undermining the restoration, and a crack in the root that developed after treatment. Each of these has a different answer, which is why the diagnosis matters more than the label.
Recognizing the Problem
Signs Your Root Canal May Have Failed
Failure does not always announce itself with severe pain. Some teeth ache constantly; others feel fine and are caught only on a routine radiograph. The signals worth acting on include tenderness when you bite or press on the tooth, a persistent dull ache that never fully resolved after treatment, swelling in the gum or face, a small pimple-like bump on the gum near the root, a bad taste that returns when the bump drains, and a lesion at the root tip that appears or enlarges on an x-ray.
A gum bump that drains and disappears is not the infection resolving. It is a sinus tract — a channel the body built to release pressure from an ongoing infection. When it closes, pressure builds again. Painless does not mean healed.
Finding Out What Actually Went Wrong
A conventional dental x-ray is a two-dimensional shadow of a three-dimensional object. Roots overlap, bone density obscures early lesions, and a missed canal hiding directly behind a filled one is often invisible. This is the single biggest reason failing teeth get extracted unnecessarily: the film does not show the cause, so the tooth is blamed.
We use CBCT cone beam imaging to look at the tooth in three dimensions, slice by slice. A CBCT scan shows untreated canals, the true extent of a lesion, perforations, resorption, and separated instruments — findings that change the treatment plan in a substantial share of retreatment cases. Combined with the dental operating microscope at up to 25× magnification, it lets us identify the specific reason your tooth failed rather than guessing at it.
That distinction matters because the cause determines whether the tooth is savable and how. An untreated MB2 canal is a highly fixable problem. A vertical root fracture running the length of the root is not. Only imaging and direct visualization can tell you which one you have.
Option One
Root Canal Retreatment
For most failing teeth, retreatment is the first and best option. We reopen the tooth, carefully remove the crown or filling material and the previous root filling, and gain access to the canal system as it truly exists rather than as it was originally mapped.
With the canals reopened, we search for what was missed — under magnification, an untreated canal orifice is usually visible as a subtle line or a color change in the dentin floor. Canals are then cleaned along their full length with ultrasonic instrumentation and irrigants, disinfected, and resealed. Our WaterLase laser with a radial firing tip is used as an adjunct here, carrying disinfection into the lateral anatomy that files cannot physically touch.
Retreatment is done under local anesthetic, usually in one or two visits, and it feels much like the original procedure. The bone lesion at the root tip then heals on its own over the following months once the source of the infection is gone, which we confirm at follow-up.
Option Two
Apicoectomy — Treating the Tooth From Outside
Sometimes going back through the top of the tooth is not the right route. A well-fitting post and crown that would be destroyed on removal, a canal blocked by a separated instrument, or an infection confined to the last few millimeters of root all point toward apicoectomy, also called endodontic microsurgery.
In this procedure we access the root tip through the gum, remove the infected tissue and the terminal few millimeters of the root, and place a small biocompatible seal at the cut end. Modern microsurgery bears little resemblance to the apicoectomies of thirty years ago: performed under the microscope with ultrasonic tips and modern sealing materials, reported success rates now approach those of retreatment. The appointment takes about an hour, and most patients describe recovery as comparable to a routine extraction site — sore for a few days, managed with over-the-counter medication.
Choosing between the two approaches is a clinical judgment, and we walk through it in detail in retreatment versus apicoectomy.
When a Tooth Genuinely Cannot Be Saved
We will tell you honestly when the answer is no. A vertical root fracture extending below the bone level cannot be sealed, and no amount of disinfection changes that. A tooth with too little remaining structure to support a restoration will not hold a crown regardless of how well the canals are treated. Severe periodontal bone loss around the root, or a perforation in a location that cannot be repaired, can also make the prognosis poor enough that treatment is not the right investment.
In those cases we say so, explain what we saw and why, and help you plan what comes next. Recommending treatment that is unlikely to work serves nobody. If you are weighing that decision, root canal versus extraction lays out the trade-offs.
Get a Second Opinion Before You Agree to an Extraction
An extraction is permanent. Retreatment is not, and neither is a consultation. If a general dentist has told you a previously treated tooth needs to come out, that recommendation is worth confirming with a specialist who has three-dimensional imaging and a microscope, because the equipment used to make the call changes the call.
Our second opinion consultations exist for exactly this situation. We image the tooth, examine it under magnification, tell you what we find, and give you a straight answer about whether it can be saved — including when it cannot. Nothing is decided in that visit but the facts.
Don’t Extract a Tooth That Can Still Be Saved
Our specialists in Union Square and Laurel Heights evaluate failing root canals with CBCT imaging and microscopic examination, then tell you honestly what your tooth needs.