Why do crowns fail, and how long do they last?

Why do crowns fail? If you have a crown that has come loose, started to ache or been flagged at a check-up, it is natural to wonder why it failed and how long crowns are meant to last. The reassuring news first: most crowns last well. When a crown does fail, it is usually not the crown material but the tooth underneath. Here Dr Andrew explains what the research shows, the signs worth mentioning to us, and what your options are if a crown has failed.

How long do crowns last?

Studies have measured that most crowns last well. Large reviews of studies found that, depending on the type, roughly 94 to 98% of single crowns were still in place and working after five years. The same research found that most modern all-ceramic crowns did about as well as traditional metal-ceramic crowns, so the material is rarely the main story.

What about ten years or more? There is no reliable pooled figure from reviews beyond five years, so we do not quote one. Individual long-term studies do exist. For example, one Australian specialist practice that followed its own crowns over many years measured about 97% still in place at 10 years and about 85% at 25 years. That is one practice's experience rather than a general promise, but it shows that a crown can serve a tooth for a long time.

How long do crowns last on molars? The studies we have cited report single crowns overall rather than back teeth separately, so we cannot honestly give you a molar-specific number. On a back tooth, how long a crown lasts depends on the tooth underneath, the forces of your bite (including clenching or grinding) and your home care. As our patient guide puts it: you do your bit with home care, regular hygiene and check-ups; we do our bit by monitoring the tooth, checking the bite and acting early if something changes.

Why crowns fail: usually the tooth underneath

Why did my crown fail? When researchers look at the crowns that do fail, the reasons are mostly biological, meaning they come from the living tooth and gums rather than the crown itself. In the Australian practice mentioned above, the large majority of the failures they recorded had a biological cause. In patient language, the three most common are:

• Decay at the edge of the crown. A crown covers the tooth, but the tooth underneath is still a tooth. Crowned teeth can still be damaged by tooth decay, including at the edge where the crown meets the tooth.
• Problems with the nerve. The nerve (pulp) inside a crowned tooth can become inflamed or infected, sometimes years later. We explain this further below.
• The remaining tooth breaking. In one study of crowns that needed redoing, the tooth itself breaking was the reason more than half the time. If the tooth under a crown has cracked, our guide on whether a cracked tooth can be fixed without a crown explains how cracks behave.

A widely cited review of crown complications found the most common problems with single crowns were the tooth needing root canal treatment, the porcelain chipping or fracturing, and the crown coming loose. None of these is common, but they are the ones worth knowing about.

It is also worth saying plainly: crowns fail for many reasons, most of them biological and nobody's fault. A crown that has needed attention after some years is not a sign that you, or the dentist who placed it, did something wrong. As ADA Australia puts it, a crown does not mean no treatment will ever be needed again.

Signs a crown may need attention

What are the signs a crown is failing? Healthdirect lists these as problems to watch for with a crown:

• the crown coming loose, breaking, chipping, cracking or falling off
• the tooth under the crown breaking
• tooth decay around or under the crown
• sore or swollen gums around the crown
• the crown not fitting properly, which can cause pain or trouble chewing

ADA Australia also notes that crowns can chip, fracture or no longer match the colour of your teeth and need to be replaced. Some of these problems cause no symptoms at first and are picked up at a routine check, which is one reason regular check-ups matter for crowned teeth too.

Why a tooth can hurt after a crown

Tooth hurts after a crown? There is more than one possible reason, and the right answer depends on the tooth. Common causes include the crown not fitting properly, which can cause pain or trouble chewing; sore or swollen gums around the crown; decay around or under the crown; or the tooth under the crown breaking. Less commonly, the nerve (pulp) inside the tooth becomes inflamed or infected after the tooth was prepared for the crown.

Because these causes need quite different treatment, we would rather see the tooth than guess. If a crowned tooth is sore, call us on (07) 3281 6666.

Root canal after a crown

Why would a tooth need root canal treatment after it has been crowned? Preparing a tooth for a crown, and whatever happened to the tooth before that, can affect the nerve. Nerve problems after crown preparation are uncommon but real. In one long-term study, around 15% of single crowns developed nerve (pulp) problems over about 14 years. Another study found nerve problems happened noticeably more often in teeth that had already been decayed or filled before the crown than in teeth that had been intact. A large review of studies reached a similar conclusion, that the risk is low overall and higher in previously decayed or filled teeth, while noting the overall quality of that evidence is low.

A crowned tooth can also need root canal treatment later for other reasons. New decay, or a loose, cracked or broken crown, can let bacteria reach the inside of the tooth.

Can a root canal be done through a crown? It may be possible, depending on the crown's condition, but sometimes the crown needs replacing. We will check the crown and the tooth and explain which applies to yours. You can read more about root canal treatment here.

What about a crown after root canal treatment? Root-filled teeth can carry more risk: in one study of 688 crowns, crowns on root-filled teeth failed more often than crowns on teeth with a living nerve. That is simply one more reason we assess each tooth carefully.

If your crown has come loose or fallen off

Crown fell off, or feels loose? Call us on (07) 3281 6666. A lost filling or crown is one of the situations we treat as a dental emergency, and we prioritise urgent care. When you come in, we will check the crown and the tooth underneath and explain what we find. Our emergency dental page has more on how we look after urgent visits.

Why we think carefully before shaping a tooth for a crown

Because crowns usually fail through the tooth underneath, we pay close attention to that tooth before recommending one. Every crown starts with removing tooth structure: studies have measured that preparing a tooth for a full crown removes roughly 63 to 72% of the tooth structure above the gum. Teeth that were already heavily filled also carry more risk, which our guide to a broken large filling explains.

So we start with the same question every time: "What is the least invasive treatment that will properly protect this tooth?" Conservative dentistry means doing no more than is needed, but also no less than is required to protect the tooth. For many teeth, the answer is a crown, and we use one when the tooth genuinely needs it. This is a way of thinking about your tooth, not a promise that any one option will outlast another. It is the approach behind our crown alternatives page.

If your crown has failed: your options

If your crown has failed, there are options, and the right one depends on what happened and how much sound tooth remains. Whether a crown can be repaired or needs replacing depends on the restoration and the way it failed.

• Repairing or replacing the crown. A small chip can sometimes be repaired. Where the crown or the tooth edge underneath needs more than that, a new crown may be the right choice. If a new crown is the right choice for your tooth, our crowns and bridges page explains what is involved. If you are wondering how the fee for a new crown is worked out and how to check your health fund rebate, see what you are actually paying for.
• Root canal treatment. If the nerve has become inflamed or infected, the tooth may need root canal treatment, and then protection with a new restoration afterwards.
• A more conservative rebuild. Sometimes, once the old crown and any decay are removed, enough sound tooth remains to rebuild it more conservatively, for example with a BioClear restoration or a biomimetic crown.

Where these sit among your options, in one sentence: a traditional filling repairs the space; a BioClear restoration rebuilds and supports more of the tooth; a biomimetic crown provides broader protection when the remaining foundation is not enough. For the full comparison, see our guide to crown or filling.

Want to understand what happened to your crown?

If a crown has failed, it is completely reasonable to want to understand why. A second opinion appointment helps you understand what happened and what makes sense now. At our Ipswich practice, we will look carefully at the tooth, show you what we see, and talk you through every suitable option, from least to most invasive, including when a new crown is genuinely the best way to protect it. If your crown has come loose or fallen off, call us first and we will see you as soon as we can.

Been told you need a crown? Call us on (07) 3281 6666 and ask for a second opinion appointment, or book an appointment online. You can also read more about our crown alternatives first.