When Is a Tooth Too Far Gone for a Root Canal?
Not Enough Tooth Left Above the Gum
A root canal cleans the inside of a tooth. It does nothing for the outside walls, and those walls are what a crown has to hold onto. So what Pure Dentistry dentists measure at the consult is how much solid tooth still stands above the gum, right around the circumference. Dentists call that band the ferrule, and a review in the Journal of Endodontics puts the useful amount at roughly 1.5 to 2 mm.
The Australian Dental Association lists the amount of natural tooth still present as one of the things your dentist weighs before deciding how to rebuild a root-treated tooth, alongside where the tooth sits and how much force goes through it. Which means the question we’re really asking isn’t whether the tooth can have a root canal. Nearly any tooth can. The question is whether anything will still be holding a crown in five years. Even a perfect root canal doesn’t change that. The tooth is cleaned and sealed beautifully, then snaps off at the gum a year or two later, and it comes out anyway.
Decay That Has Spread Below the Gum and Into the Bone
Decay doesn’t always stay above the gum. It can keep spreading down the root, and once that happens, we’re dealing with a different problem. To repair a tooth, we need a clean, dry rim of healthy tooth for the filling or crown to seal against, and in our experience, that’s very hard to get under the gum. Moisture gets in, the seal doesn’t hold, and the decay keeps going underneath, where you can’t see it or clean it. There’s a second reason as well. Just above the bone, your gum is attached to the tooth by a thin band of tissue.
Published research shows that when the edge of a filling or crown is placed down into that band, the gum stays inflamed, the pocket around the tooth deepens, and bone is lost more quickly. So even a root canal done well would be sitting on something that keeps breaking down. We check carefully before we say a tooth can’t be kept. We measure right around it, clean under the gum so we can see the edge properly, and take a 3D scan when an ordinary X-ray doesn’t tell us enough. Sometimes we can reach healthy tooth again by reshaping the gum and bone, or by gently moving the root up with orthodontic treatment. When the decay has already reached the bone, and neither of those will get us there, the tooth needs to come out.
A Crack That Runs Down Into the Root
A crack that stays in the top of the tooth can often be repaired. A crack that keeps running down into the root usually can’t. A root canal cleans and seals the inside of a tooth, but it can’t join the split back together, so the two halves keep moving apart slightly every time you bite. Bacteria travel down the line of the crack, and the pain comes back. The Australian Dental Association explains that cracks running from the top of the tooth down towards the gum are harder to fix, and that if the crack reaches the nerve in the middle of the tooth, your dentist or specialist may say a root canal is no longer possible and removing the tooth is the better option.
Cracks are also hard to find. One patient came to us after biting something hard, with a sharp pain deep in one side that they couldn’t point to. Every tooth tested normally, and the X-ray looked clear. Instead of starting a root canal on our best guess, we arranged a specialist opinion, because we didn’t want to treat a tooth that wasn’t the cause. Often, the picture only becomes clear once we take the old filling out and look at the tooth under a microscope. If the crack stops in the top part, we can usually protect it with a crown. If it has already travelled into the root, we’ll tell you plainly that the tooth needs to come out.
Roots We Cannot Clean or Seal Properly
A root canal only works if we can reach the full length of every canal, clean it, and seal it. Some roots won’t let us. Canals can be very curved, or they can narrow and close over the years until there’s no clear path to follow. Sometimes a fine instrument snaps off inside a canal and blocks the way. Sometimes a hole has been made through the side of the root during earlier treatment. Any of those leaves part of the canal out of our reach, bacteria stay in there, and the tooth keeps flaring up. How far the filling reaches, how well it seals, and whether the root wall has been perforated turn out to be among the strongest influences on whether the infection settles, according to a 2023 review in the International Endodontic Journal.
We don’t give up quickly on this. We’ve had a back tooth where an instrument broke off inside a canal, and rather than remove it, a specialist reopened the tooth, found an extra canal that had been missed, and worked past the blockage. That tooth was kept. But when the blockage can’t be passed, or the hole in the root can’t be sealed, no amount of further treatment will settle it, and removing the tooth is the honest answer.
Holes, Damage and Problems From Earlier Dental Work
Old dental work matters more than most people expect. A root canal needs two things to hold: a well-sealed root and a well-sealed cover over the top of it. A 2011 systematic review in the Journal of Endodontics put those two on almost equal footing, with the odds of healing rising when both are sound. So when we lift off an old crown or filling and find the tooth underneath has been leaking for years, we’re often looking at a root that has been reinfected the whole time. That’s a different situation from a root canal that was never completed, which we cover separately.
There are other things we find. A small hole can be worn or made through the side of a root, letting bacteria in from the outside where no filling can reach. A tooth carrying the weight of a bridge takes far more force than it was built for. A root already hollowed out for a post has thin walls left. Any one of these can be worked around. Several together usually can’t, and at that point, another root canal is just delaying the same outcome. That outcome is losing the tooth, so we’d rather take it out now than have you go through another treatment first.
When the Root Is Dissolving Away
Sometimes the body starts dissolving the tooth itself. It’s called resorption, it usually causes no pain, and most people only find out because it turns up on an X-ray taken for something else. Where it begins matters. When it starts inside the canal, a root canal can sometimes stop it, because the cells causing the damage sit inside the tooth and cleaning the canal clears them out. When it starts on the outside of the root near the gumline, a root canal alone does nothing for it. The damage is coming from the outside in, so the only way to halt it is to reach the affected area and repair it there.
Guidance on managing this in the International Endodontic Journal makes the point that a 3D scan is needed first, because an ordinary X-ray understates how deep and how far around the root the damage has spread. That measurement is what decides it for us. If we can reach the edges of the damage and enough solid root remains, we’ll repair it and keep the tooth under review. If it has wrapped around the root or spread into the middle of it, there is nothing solid left to repair against, and further root canal treatment won’t stop it. At that point, the tooth needs to come out.
When the Gum and Bone Can No Longer Hold the Tooth in Place
As explained earlier, a root canal deals with infection inside the tooth. It does nothing for the bone outside it. Your teeth are held in the jaw by bone and by a layer of fibres attaching the root to that bone, and gum disease slowly destroys both. Around 70% of adult tooth loss comes down to this, according to the European Federation of Periodontology’s estimate. What makes it confusing is that the tooth itself can look fine. The nerve may be perfectly healthy, there may be no decay at all, and the tooth still wobbles because there isn’t enough bone left holding the root.
A deep pocket can also ache in a way that feels exactly like a nerve problem, which is why we measure the pockets around every tooth and check the bone level on an X-ray before recommending anything. Where enough support remains, treating the gum disease can settle things down, and the tooth stays. Where most of the bone has already gone, and the tooth moves when you bite, a root canal cannot bring that bone back. Nothing can. Keeping a tooth in that state usually means repeated flare-ups and losing more bone from the teeth on either side of it, so removing it is the better decision.
Can I Be Asleep for a Root Canal or Extraction?
For some people, the hardest part isn’t the decision. It’s sitting in the chair at all. If fear has kept you away for years, that’s worth telling us before anything else, because it changes how we plan the appointment. Whichever way the decision goes, a root canal or a tooth extraction, we can carry it out with a sedation option that suits your situation.
Laughing gas suits people who are nervous but can manage the chair, and it wears off within minutes of the mask coming off. IV sedation suits stronger anxiety, a sensitive gag reflex, or longer appointments, and most people remember little of it afterwards. Sleep dentistry in Brisbane under general anaesthesia is there for severe dental phobia or when several things need doing at once, with a specialist anaesthetist looking after you throughout. We’ll talk through which one fits during the consultation session.
Brisbane Dental Sleep Clinic claims that options like Sleep Dentistry Brisbane may be an ideal option for patients who find the idea of complex procedures overwhelming.
