Getting to the root of the issue

Media item: article

Date published: 26 October 2013

Subject: root canal treatment (endodontics)

This page records the media item. The original article is the property of its publisher and is not reproduced here.

What root canal treatment actually is

Every tooth contains a pulp — a soft tissue core of nerves, blood vessels and connective tissue running from the crown down through the root canals to the tip of each root.

When bacteria reach the pulp — through deep decay, a crack, a failed restoration, or trauma — the pulp becomes inflamed and then dies. Because the pulp is enclosed in rigid dentine, it cannot swell, so pressure rises and the pain can be severe. Once the pulp dies, the infection continues out through the root tip into the surrounding bone, producing an apical abscess.

Root canal treatment removes the infected pulp, cleans and shapes the canal system, and fills it with an inert material (usually gutta-percha and a sealer) to prevent reinfection. The full sequence is set out separately.

That is the whole procedure. It treats an infection inside a tooth that cannot be reached any other way.

The alternative is extraction. There is no third option, and antibiotics alone are not a treatment — they may settle an acute swelling, but antibiotics cannot reach a dead pulp with no blood supply, and the infection returns. Prescribing antibiotics instead of treating the tooth simply delays the same decision.

The myths, dealt with directly

"Root canals are agonising." Root canal treatment is done under local anaesthetic, and for most people it feels much like having a filling — long, but not painful. The pain people associate with root canals is the pain of the abscess or the pulpitis that brought them in. The treatment is what relieves it. There can be tenderness for a few days afterwards as the surrounding tissues settle. If anxiety is the barrier, say so before the appointment.

"Root canals cause disease elsewhere in the body." This claim traces to the "focal infection theory", promoted in the early twentieth century and abandoned decades ago because the research behind it was methodologically unsound and was not reproduced. It has been repeatedly revived online, often alongside advice to have healthy root-filled teeth extracted. There is no credible evidence for it, and the major dental and endodontic bodies internationally have addressed it directly. Extracting a functioning root-filled tooth on this basis is irreversible harm for no benefit. Other myths in the same family are dealt with elsewhere.

"The tooth is dead so it doesn't matter." The pulp is removed; the tooth remains held in bone by a living periodontal ligament, and it still functions, still bears load, still holds space, and still preserves the bone that would otherwise resorb after extraction.

"It's cheaper to just pull it out." Extraction is cheaper on the day. Replacing a missing tooth is not. An implant or bridge generally costs several times a root canal and crown, and the alternative — leaving the gap — has its own consequences: adjacent teeth drift, the opposing tooth over-erupts, chewing load redistributes, and bone in the site resorbs over time. That is a legitimate choice for some people and some teeth, but it should be made knowing the sequence, not as a way of avoiding a one-day cost.

What actually determines whether it works

Root canal treatment has good success rates — studies commonly report survival in the high 80s to mid 90s per cent over several years, depending heavily on which tooth, the starting diagnosis, and what happens afterwards.

The things that genuinely move that number:

Whether the tooth is restored properly afterwards, and how quickly. This is the single most under-appreciated factor. A root-filled tooth has lost structure to decay, to the access cavity, and often to a previous large filling, and root-filled teeth are more prone to fracture. Back teeth in particular usually need cuspal coverage — a crown or onlay — and the evidence that this improves survival is strong. A root canal left under a temporary filling for months is a treatment likely to fail, because saliva and bacteria leak back down the canal.

The complexity of the canal anatomy. Molars have multiple canals — often three or four, sometimes more — that curve, branch and occasionally join. Missing one canal is a common reason for failure. This is why cone beam CT is sometimes justified in endodontics, and why complex cases are referred. Broken instruments are a separate, uncommon complication with its own literature.

Whether there was already an apical lesion. Teeth with established periapical infection have somewhat lower success rates than teeth treated before the infection established — and an abscess can have general health consequences of its own.

Isolation. Treatment done under rubber dam — which is the standard of care — keeps saliva and its bacteria out of the canal during treatment.

Who does it

Root canal treatment is within the scope of a general dentist, and most straightforward cases are done in general practice.

Endodontics is one of the recognised dental specialties in Australia. An endodontist is a dentist who has completed an approved postgraduate qualification and holds specialist registration with the Dental Board of Australia. Referral is common for molars with difficult anatomy, retreatment of a previous root filling, calcified canals, or where a previous attempt has failed.

Specialist titles are protected by law. Only a practitioner with specialist registration in endodontics may be called an endodontist, and any patient can verify that free on the AHPRA public register at ahpra.gov.au — the register shows the division of registration and any specialist entry.

When it does not work

Sometimes it fails, and the honest options are:

• Retreatment — removing the existing root filling, re-cleaning and refilling. Often successful, particularly where a canal was missed.
• Apical surgery (apicectomy) — surgically removing the root tip and sealing it from the end, where retreatment is not feasible.
• Extraction, and then a decision about replacement.

A vertical root fracture is generally not restorable and usually means extraction. It is one of the main reasons a root-filled tooth is eventually lost, and it is the reason cuspal coverage matters so much.

What to ask before agreeing to one

• "What is the diagnosis?" Reversible pulpitis, irreversible pulpitis, necrotic pulp with apical periodontitis — these are different, and only some need root canal treatment. Not every sensitive tooth needs one.
• "What is the prognosis for this specific tooth?" A cracked tooth with deep bone loss has a very different outlook from an otherwise sound tooth with deep decay.
• "What is the plan for restoring it, when, and what does that cost?" Get the whole cost — treatment plus crown — before starting, with item numbers. A root canal quoted without the crown is half a quote.
• "Should this be referred to an endodontist?"
• "What are the consequences if I have it extracted instead?" A second opinion is reasonable before an extraction you cannot undo.

Common questions

What are the actual numbers — how long do root-filled teeth last?

A review of the survival literature reports studies finding 82% to 95% of root-filled teeth surviving over 2 to 10 years. Beyond that the data thin out sharply, and the figures drop: in two Swedish studies with longer observation, tooth survival was 65% and 71% over 20 years.

There is a second number that complicates the picture, and it deserves stating rather than hiding. Cross-sectional studies find that “about 40 per cent of root filled teeth have AP” — apical periodontitis, meaning persisting inflammation at the root tip — when a population is examined at a given moment. The same review notes that European Society of Endodontology guidelines say that where normal periapical conditions are not achieved after a period, “the case should be considered as a failure and the infection/inflammation should be treated”.

So a large share of root-filled teeth in the population are being retained rather than healed, which the literature calls functional retention. The review is candid that “the potential impact on the individuals' health of accepting the concept of functional retention is still mainly unknown.”

Practically, that means a root canal is not a set-and-forget treatment. Ask to have the tooth reviewed radiographically after treatment, and ask what the film shows.

Why is my dentist so insistent about the crown, and about doing it soon?

Because the delay is measurable. In a retrospective study, posterior root-filled teeth that received a crown four months after treatment were extracted at three times the rate of those crowned within four months. That is the strongest single argument for not leaving a back tooth under a temporary filling while you save up.

How much tooth is left matters just as much. A study of root-canal-retreated posterior teeth found that where less than 29.5% of tooth structure remained, the percentage of extractions was three times higher than in teeth with more than 29.5% remaining.

And there is a specific measurement your dentist is looking for, called a ferrule — an encircling band of remaining tooth for the crown to grip. A literature review concluded that a 1.5–2 mm ferrule has a positive effect on the fracture resistance of root-filled teeth, and that “an incomplete ferrule is considered better than a complete lack of ferrule”. Where there is no ferrule at all, the honest question becomes whether the tooth is restorable.

A reasonable thing to ask: “how much sound tooth is left above the gum, and is there enough for a crown to hold?” Types of dental crown covers the options.

Does it matter how long I have left it?

Yes, and the effect has been quantified. The absence of a periapical lesion is a positive prognostic factor; its presence has “a significant negative effect on healing outcome”, and the larger the lesion the worse the outlook, because “the larger the lesion, the more complex the infection”.

In one prospective study, the authors concluded that “the odds of success of treatment were found to decrease by 14% for every 1 mm increase in diameter of the preoperative lesion”.

That is the arithmetic behind ‘don't wait’ — not urgency for its own sake, but a prognosis that erodes measurably while the lesion grows. It is also why a tooth treated before infection establishes does better than the same tooth treated after.

Why do root-filled teeth actually get pulled out in the end?

Usually not because the root filling failed. The survival literature is clear on this and it reframes the whole decision: extractions of root-filled teeth “may be due to failure of the endodontic treatment; however, the main reasons have been reported to be caries, cracks and fractures, leading to a non-restorable condition.”

Two structural factors compound it. Loss of the marginal ridges weakens the tooth significantly, and “terminal or lone-standing teeth show poorer survival, being at a greater risk of fracture due to increased occlusal forces” — so the last tooth in the arch, with nothing behind it, is carrying more load than its neighbours ever did.

Which means the things that protect a root-filled tooth are mostly the ordinary things: keeping it free of new decay, getting proper cuspal coverage, and — if you grind — protecting it at night.

If the root canal fails, is surgery as good as starting again?

The survival figures are lower, and it is fair to know that before choosing. Studies of endodontic surgery report survival of 48% to 88% of teeth over 3 to 10 years, against 82% to 95% over 2 to 10 years for root canal treatment — and the review notes it has not been possible to find any studies with extended follow-up after endodontic surgery at all.

Those are different populations, not a head-to-head trial: surgery is done on teeth where retreatment has already failed or is not feasible, so the cases are harder by selection. The gap is not purely a verdict on the technique.

What it does support is the usual sequence — retreatment first where it is feasible, surgery where it is not — and it is a reasonable question to ask which category your tooth falls into, and why.

Related reading

• Root Canal Therapy and Specialist Endodontists
• Root canal treatment: who and what is involved?
• Why are dental abscesses so painful?
• Fighting decay and Emergency Dentistry
• More coverage in Our Media

Practical details

Smile Solutions, Level 1, 220 Collins Street, Manchester Unity Building, Melbourne VIC 3000. Phone 13 13 96, or theteam@smilesolutions.com.au. Monday–Friday 8.00am–6.00pm, Saturday 8.30am–1.30pm, Sunday by appointment.

Every practitioner's registration and any specialist entry can be verified free on the AHPRA public register at ahpra.gov.au.

This page records a published article and its date, with general information. It is not a diagnosis, a treatment plan or a promise of any particular outcome; success rates vary by tooth and by individual circumstances. Third-party published content is not reproduced.

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