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

Crown longevity. / Reasons for crown replacement (with photos) - Breakage, perforation (hole formation), tooth decay, failed cosmetic appearance.

1) How long should a crown last?

  • It would be reasonable to expect that a dental crown could last between five and fifteen years.
  • 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.

2) 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, with some possible exceptions.

Repair solutions.
  • 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 (the seal of the crown remains intact), just smoothing the affected area with a dental drill may suffice.
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.
  • Minor damage might not be much of a concern, and possibly remedied by just smoothing off the area using a dental drill.
  • In cases where the look or function of the crown has been significantly compromised, it will need to be replaced.
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) Tooth decay formation.

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.

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.

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.

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.
 

 

[Reference sources for this topic.]

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