How long do dental crowns last? / Why do they need to be replaced? -

Statistics about crown longevity. / Reasons for crown replacement (photos): breakage, perforation (hole formation), tooth decay, failed cosmetic appearance.

How long should a crown last?

  • It would be reasonable to expect that a dental crown could last between five and fifteen years (see statistics section below).
  • Many dental insurance plans stipulate that they'll only pay for replacement crowns after the previous one has provided at least 5 years of service.
  • Most likely one that has only lasted five years would be a disappointment to your dentist. It's probably their hope that any crown they make for you will last ten years or longer.
  • Depending on: 1) The amount of wear and tear the crown is exposed to (chewing and biting forces, accidental trauma, tooth grinding)  and  2) How well you keep its tooth free of dental plaque,  a crown can last somewhat indefinitely.

a) Statistics about crown longevity from research.

  • Pjetursson (2007) performed a literature review of published research and from it estimated a survival rate of 94% for crowns at 5 years and 90% at 10 years.
  • A study by Reitemeier (2013) determined that at the 8 year mark, the survival rate for porcelain-fused-to-metal (PFM) crowns lay on the order of 94% (138 teeth studied, private practice setting).
  • De Backer (2007) evaluated teeth that had been crowned by student clinicians at a dental school over a 16 to 20 year period. The 18-year survival rate calculated was 75%.
  • Walton (2013) reported on the long-term outcome for 2,340 crowns placed by an individual prosthodontist (a dental specialist). A survival rate of 97% was found at 10 years, 85% at 25 years.

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Our comments.

The vast majority of crowns evaluated in the studies above, especially the longer-term ones, were most likely PFM's, and then a fewer number of (less frequently placed) all-metal and (newer technology) all-ceramic ones. (If you need information, here's a link to our page about types of dental crowns.)

Due to their single-unit, all-metal construction, metal/gold crowns don't suffer from the problem of porcelain breakage, and therefore if evaluated as a separate group might be expected to have a comparatively higher success rate than stated above.

In a similar vein, all-ceramic crowns might be expected to experience fracture at a higher rate than their all or partially-metal counterparts (gold and PFM restorations), and therefore have lower longevity that reported above.

b) The relative longevity of different types of dental crowns.

Our comments above correlate well with the findings of Fernandes (2015). This paper evaluated dental literature published between 1974 and 2014 pertaining to the topic of dental restoration survival rates. It concluded that:

  • ... gold restorations are still the “gold standard” with a 96% over 10 years survival rate, followed by porcelain-fused-to-metal crowns (PFM) (90% over 10 years), and all ceramic crowns (75-80% over 10 years).
Our comments.

Due to advances in both materials and fabrication techniques, the strength characteristics of some types of all-ceramic crowns that are now available are substantially improved over others, and especially those of decades past.

And in fact, the Fernandes paper reported survival rates for some modern, high-strength all-ceramic crowns (a very limited select group) to be on the same order as PFM crowns (see below).

Survival of the fittest.

It should also be said that once past an initial period, the survival of more modern all-ceramic crowns may rival other types.

A study by Dhima (2014) evaluated 226 all-ceramics placed in both front and back-tooth applications. 6% failed (on average) 3.3 years after insertion. Of those that hadn't failed, at 5 years 95% were still in service, at 10 years 93%.


Why do dental crowns need to be replaced?

There can be a variety of reasons why a crown might need to be slated for replacement. We've listed some of them below, along with the type of restoration (porcelain/ceramic, porcelain-fused-to-metal/PFM, metal/gold) most frequently affected or involved.

  1. Damage - Cracked or broken crowns (ceramic, PFM).
  2. Excessive wear - Hole formation (metal), wear of opposing teeth (PFM).
  3. Complications with tooth decay - (All types are equally at risk.)
  4. Deteriorated cosmetic appearance - (Any front porcelain crown but especially PFM's.)

Reasons for dental crown failure -

A) The dental crown has broken or been damaged.

Dental crowns can break, or more precisely the porcelain component of one may fracture. With the exception of possibly one that's worn excessively, it's rare to see an all-metal (gold) crown break.

1) Broken porcelain crowns.

a) All-ceramic.

Some dental crowns have a construction where their full thickness is a glass-like ceramic (all-ceramic crowns, porcelain jackets).

If this type of restoration fractures, it's quite possible that the break is through its full thickness. If so, it will compromise both the crown's structural integrity and the seal it creates over its tooth. The only solution is to remake the restoration, no repair is possible.

Making the right initial choice.

This is a prime reason why the type of crown you have placed on a back tooth should have a proven history of being able to withstand the level of forces involved. All-metal and porcelain-fused-to-metal ones do. Many types of all-ceramics don't.

High-strength all-ceramics.

Currently there are two types of high-strength dental ceramics that are most talked about for use with back teeth. One is lithium disilicate (IPS e.max®) and the other is zirconia (BruxZir®).

In terms of strength, zirconia tests as the stronger of the two. But Fernandes (2015) cites sources that suggest that crowns made using the e.Max® product have a 10-year survival rate of 90% (similar to PFM crowns), whereas with zirconia it's only 88% at 5 years.

High-strength construction.

In applications where crown strength is a great concern (like with back teeth), monolithic crown construction probably makes the better choice.

The term "monolithic" means that the restoration has been ground out of a single block of ceramic (CAD/CAM technology). The other method of construction is one where layers of porcelain are fused together to create the crown.

Dhima (2014) determined that the most common reason for all-ceramic failure was fracture to the core of layered crowns. Monolithic restorations did not suffer from this problem as often and therefore were suggested for use on posterior teeth.

Repair solutions for all-ceramic restorations.
  • As stated above, with cracking or breakage that involves the full thickness of the ceramic, no repair is possible and replacement is required before the remainder of the restoration breaks free or decay has a chance to form underneath it.
  • With small chips (cases where the seal of the crown remains intact), just rounding off or smoothing the affected area with a dental drill may suffice.
  • It's possible that moderate sized porcelain defects can be patched, although the specific type of ceramic used to make the crown may play a role in their success.

    Generally speaking, these types of repairs are just patches and likely won't provide the same lasting service that crown replacement would. (See our PFM section below for more details about repairing dental ceramics.)

A broken porcelain-fused-to-metal dental crown.

A broken PFM dental crown.

b) Porcelain-fused-to-metal.

Background

A porcelain-fused-to-metal (PFM) crown has two components. One is a thimble of metal that covers over your tooth. The other is a layer of porcelain that's been fused over it so to create a tooth-like appearance.

In situations where a PFM has broken, it's typically the layer of porcelain that's fractured off (frequently revealing the metal stub that lies underneath). It's rare that the metal thimble itself has broken.

That means that after breaking, the seal of the crown over the tooth is still basically intact. But depending on the amount of porcelain that has come off, it's aesthetics or function may be seriously compromised.

Repair solutions for PFM crowns.
  • Minor damage might not be much of a concern, and possibly remedied by just smoothing off the area using a dental drill.
  • For moderate defects, placing a patch may be possible. The general difficulty is that the crown's porcelain surface was created in a high-heat furnace but its repair must be made in the patient's mouth.

    Tooth-colored dental restorative (dental composite) can be bonded to porcelain surfaces (via acid-etching, silane coupling) but careful case selection is needed. Overall, these types of fixes are unlikely to provide the same predictable, long-term service that placing a new crown can. However, repair may offer a cost-effective solution over the inteirm.

    Ozcam (2002) evaluated 289 repaired PFM restorations. If failure did occur, it usually took place within the first 3 months. At 3 years the survival rate for the patches was 89%. The most common reasons for repair loss were trauma, chewing failure and the fix having been performed under less than ideal conditions (the tooth couldn't be kept saliva-free during its procedure).

  • In cases where the look or function of the crown has been significantly compromised by its loss of porcelain, it will need to be replaced.
How frequently is this issue a problem?

a) A study by Behr (2014) investigated the subject of PFM crown veneer chipping. It evaluated 997 restorations that had been placed on both front and back teeth.

  • Porcelain loss was only experienced by 1.7% of all of the crowns over a 10-year period.
  • PFM crowns on posterior teeth (molars and premolars) fared the worst with a incidence rate of 2.7% chipping at 10 years.

Overall the findings of this study demonstrate that PFM crowns typically provide lasting service, even when placed on teeth that are regularly exposed to comparatively heavy chewing forces.

b) Reitemeier (2013) reported higher numbers. This paper determined that at 10 years the incident rate of ceramic defect lay on the order of 11%. However, it was specifically stated that the majority of events were either not treated or just smoothed and/or polished. Only 10% of the failures (and therefore only about 1% of all crowns studied) required repair or crown removal.

An access cavity made through a dental crown.

The access cavity for root canal treatment make through a dental crown.

2) Damage as a consequence of having root canal treatment.

The first step of performing root canal treatment is creating an "access cavity." This is the opening through which the dentist accesses the interior of the tooth and performs their work.

If the crown can't be removed first, the hole will need to be made right through it. And doing so compromises the restoration's seal over the tooth (even placing a filling in the opening can't predictably reestablish it).

Repair solutions.

Ideal treatment is to replace the crown after the root canal therapy has been completed. We discuss this topic, and explain possible alternatives and outcomes, on this page.

 

B) Excessive wear.

Background - The ideal crown.

Dental crowns aren't necessarily more wear resistant than your own natural teeth, nor is it in your best interest that one should be.

The ideal dental crown would be one made out of a material that has the same wear characteristics as tooth enamel. This way neither the crown nor your natural teeth would wear the other excessively. (FYI: Gold crowns and some types of all-ceramic ones come closest in this regard.)

A perforated gold dental crown.

This gold crown has a hole in it.

1) Perforations (crowns with holes).

Especially in instances where a person has a tooth clenching or grinding habit, a crown will sometimes develop a hole on its chewing surface, where it makes contact with an opposing tooth (a tooth that it bites against).

Repair solution - Since the hole compromises the seal of the crown, a new one should be made before that point in time when dental plaque has had a chance to seep under and start a cavity.

2) Worn opposing teeth.

In some cases, the problem is not that the crown has worn but instead that it has caused excessive wear of the teeth it opposes.

Repair solution - Making a replacement crown out of a material (gold, dental ceramic) that is less abrasive to tooth enamel can slow the wear rate.

A cavity that's formed at the edge of a dental crown.

Tooth decay can extend underneath the crown.

C) Recurrent tooth decay.

While a dental crown can't be damaged by decay, the tooth on which it's cemented certainly can be. If dental plaque is allowed to accumulate on tooth surfaces that lie beyond the edges of its crown, a cavity can form.

Dentists use the term "recurrent decay" to refer to this scenario, meaning the formation of a new cavity on a tooth that has already had a restoration placed on it.

There are two main difficulties associated with decay forming in this location.

  • It's difficult for the dentist to know the full extent of the cavity. Decay that has spread underneath the crown (see illustration) is both hard to evaluate, access and know for certain that it's been totally removed.
  • A basic tenant of crown placement is that its edges lie on sound tooth structure (this creates the most predictable, lasting seal over the tooth). Placing a filling right at the edge of a crown breaks this rule.
Repair solutions.

That's not to say that dentists never solve this problem by just going ahead and placing a filling. But doing so is patchwork dentistry. The textbook solution is to remove the existing restoration, remove the decay and then make a new crown for the tooth.

How frequently is this issue a problem?

The study by Behr (2014) referenced above also investigated the decay rate of teeth that had received crowns.

  • At 5 years, 1.3% of the crowned teeth were found to have developed a cavity.
  • At 10 years, 2.8% had.

Overall this study suggests that the formation of recurrent decay is a present but relatively minor complication. The tooth's risk increases over time.

D) The cosmetic appearance of the crown has become objectionable.

1) The crown's edge has become visible and it has a grey appearance.

Background.

Over time, the gum line of a tooth may recede. This is especially likely in those cases where a person has been lax in their brushing and flossing habits.

If enough recession takes place, the edge of a crown (which was originally tucked out of sight just below the gum line) will become visible.

Gum recession reveals the dark edge of a PFM dental crown.

A hint of the metal edge of a PFM crown has started to show.

a) The problem with PFM's.

Inherent to porcelain-fused-to-metal crowns is the fact that their edge typically shows some darkness (a hint of the grey metal that lies underneath their porcelain). And if enough gum recession occurs, this dark edge will become visible, thus spoiling the appearance of the crown.

b) All-ceramic crowns.

Because there's no metal involved, all-porcelain dental restorations do not suffer from this same problem. However, gum recession can expose that portion of the tooth (usually the root) that lies beyond the edge of the crown. This part of the tooth usually appears darker, or at least different in comparison to the color of the crown itself, thus spoiling the overall appearance of the tooth.

Repair solutions.
  • A dentist may make an attempt to cover over the discoloration with dental bonding (a white filling). However, even if this gives an acceptable outcome initially (which is not always the case), it's never a long-term solution.
  • The only lasting repair is to replace the crown with a new one, making adjustments for the way the gum line has changed.
How often does the dark-line problem occur?

We don't have a precise estimate of how often the PFM/dark-edge issue is problematic enough that crown replacement is needed.

We did find a study (Walton 2013) that stated that out of 2211 PFM's evaluated over a 25-year period, 1% of them needed to be replaced due to "unacceptable esthetics," on average after 14 years of service.

When considering that number the following should be kept in mind: 1) The restorations evaluated were all placed by a prosthodontist (crown specialist), who would be expert at minimizing the potential for this complication. 2) Some of the failures reported would be related to other cosmetic deficiencies too, not just the visibility of a dark line. With both caveats considered, it seems likely that this is just an "issue" rather than an inevitable significant problem with PFM's.

2) The color of the dental crown no longer matches its neighboring teeth.

Background.
A dental crown that no longer matches the color of its neighboring teeth.

A dental crown whose color no longer matches well.

As years elapse, the color of a crown may no longer closely match the shade of its neighboring teeth. In these cases, it's not that the porcelain has changed but instead that the neighboring teeth have stained and darkened.

Repair solutions.

There can be two ways to remedy this situation.

  • One is to replace the offending crown with a new one that more closely matches the current color of the neighboring teeth.
  • Another is to use teeth-whitening treatments (as explained here) in an attempt to return the neighboring teeth back to the color they were when the dental crown was originally placed.

One last point to think about.

You've just learned that having a "permanent" crown placed doesn't mean that it's going to last forever. And that means to whatever extent is possible, one of your dental goals should be to avoid the need of having crowns placed on other teeth.

Toward achieving this goal, read through our page: Precautions to take that can help you to prevent having to get teeth capped.

 

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