All-ceramic dental crowns.

What are they? / Advantages and disadvantages. / Examples of applications where an all-ceramic might make a good choice.

An all-ceramic (porcelain) dental crown.

What are they?

Just as their name implies, all-ceramic dental crowns are restorations whose full thickness is made entirely of a glass-like substance, such as porcelain.

  • The original type of all-ceramic was the "porcelain jacket."
  • Nowadays, instead of porcelain it's much more likely that an "engineered" compound is used.

(To keep things simple, on this page we just use the word "porcelain" to refer to all types of dental ceramics.)

Some of the brand names associated with all-ceramic crowns are: Dicor, Cerapearl, Optec, Empress, BruxZir, IPS e.max, Vitadur, Hyceram, Cerestore, Procera, Inceram, Cerec, ProCad, Vitablocs and Paradigm.

Advantages of ceramic crowns.

a) Superior esthetics.

The single biggest advantage of placing an all-ceramic crown instead of other types has to do with appearance.

  • Their 100% ceramic construction allows them to altogether avoid some problems that must be managed when other types of crowns are used (see below).
  • Some of the fabrication techniques used to make these crowns can produce results that are amazingly lifelike and unmatched by any other type of restoration.
What you need to know about tooth-colored crowns.

In the world of dentistry there are two types of "porcelain" crown construction, all-ceramic and porcelain-fused-to-metal (PFM).

  • PFM's - These crowns are made up of two components. Crown fabrication starts with creating a metal shell (the "substructure") that fits over the trimmed tooth. Porcelain is them fused over this substructure so to give the crown its tooth-like shape and color. (See diagram below.)
  • All-ceramics - The entire thickness of the crown is 100% ceramic .
Why this difference matters.
Light handling characteristics.

The lustrous (shiny, glossy, luminous, sparkling, glistening) look of a natural tooth is generated by the way light penetrates into its enamel layer and then is reflected back out.

The goal of porcelain crown construction is to mimic this effect. And generally speaking, the thicker and more translucent the crown's porcelain, the closer it will match the light handling characteristics (and thus appearance) of a natural tooth.

All-ceramic crowns often have more translucency than PFM's.
The problem with PFM's.

Since the metal substructure of a PFM crown is dark, it must be masked over with a layer of very opaque (chalky-white) porcelain so its tint doesn't show through.

As a result, only a comparatively thinner layer of translucent porcelain can be placed (see diagram), thus reducing the crown's overall ability to truly mimic the look of a natural tooth.

The advantage of all-ceramics.

Since all-ceramic crowns aren't burdened with the task of masking a dark metal substructure, a greater portion of their thickness can be composed of comparatively more translucent porcelain. And due to this fact, they tend to create a more lifelike look.

Another esthetic advantage of ceramics over PFM's.

Beyond the obstacle just described, the metal substructure of a PFM crown also creates a second difficulty. Its edge may possibly start to show if the patient's gums recede, thus spoiling the overall appearance of the tooth. (Use this link for a more thorough explanation of this problem.)

While dentists do have techniques that can help to address this issue, a giant advantage of placing an all-ceramic crown is that this problem simply doesn't exist with them.

How the method of crown fabrication can affect appearance.

When it comes to esthetics, it's important to know that (literally) not all full-ceramic crowns are created equally.

An all-ceramic dental crown.

A ceramic dental crown with a high level of characterization.

Notice the amount of characterization, both in terms of porcelain shade (dark to light) and translucency (white to grey).

  • The type of all-ceramics that are best able to mimic the lustrous, characterized look of natural teeth are those where their construction allows for placing different types of porcelains (each having a slightly different shade or translucency) in different regions of the crown.
  • In comparison, some all-ceramics are milled out of a single homogeneous block of material (CAD/CAM technology), resulting in a crown that just has one uniform shade and translucency.

Of course, teeth typically aren't uniform in appearance. Their color will tend to vary in different regions, as will their degree of translucency.

And for that reason, in cases where just one or a few milled all-ceramic crowns are placed, their ability to accurately match the characterization of their neighboring teeth may be limited. Or in cases where a set of crowns is called for, they may be too uniform looking to appear natural.

c) Biocompatibility.

Placing an all-ceramic crown may offer some advantages in regard to biocompatibility.

  • The types of ceramics used to make them are typically no more abrasive than dental enamel itself (gold crowns have this advantage too.).

    In comparison, the type of porcelain used to make PFM crowns can be very abrasive to opposing teeth and dental restorations and cause significant wear of them (especially in cases where it hasn't been polished or glazed appropriately).

  • While relatively rare, some people are allergic to some of the component metals found in the various types of alloys that can be used to make PFM crowns.

d) With all-ceramics, single-visit placement may be possible.

Some dentists have milling (CAD/CAM) units in their office that can be programmed to grind crowns out of ceramic blocks. Some of the brand names associated with this technology are: Cerec®, ProCad®, Vitablocs® and Paradigm®.

Just one appointment.

That means after preparing the patient's tooth, its crown can be milled immediately (it takes about 20 to 30 minutes) and then cemented into place. (All of the patient's work is completed in a single office sitting.)

This is in contrast to the two-visit process used with traditional crowning technique where the restoration is made by a dental technician who typically requires a turn-around time of about two weeks.

Other advantages.
  • You won't have to wear a temporary crown (which might dislodge or not look very good).
  • Since your tooth only has to be numbed up for one appointment, overall there are fewer dental shots involved.

Disadvantages of all-ceramic crowns.

a) Longevity issues.

Here are some things you should know:

  • In terms of durability and longevity, no type of crown compares to an all-metal one.
  • In those applications where the appearance of an all-metal would not be acceptable, porcelain-fused-to-metal crowns are next in line for having an established track record of being able to deliver lasting service.
Ceramic crowns are comparatively less predictable.

All-ceramic's certainly don't have the same long-term track record for longevity and durability as all-metal and PFM crowns do. And in fact, some types of ceramics have substantially inferior physical characteristics in terms of strength, hardness, brittleness and resistance to fracture.

That doesn't necessarily mean that an all-ceramic can't make a good choice, even for a back tooth (see below). But in cases where durability and longevity are vital, these issues should be thoroughly discussed with your dentist before you choose to have one placed.

All-ceramic crown repair.

If the full thickness of an all-ceramic has cracked, no repair is possible. The restoration will need to be replaced and preferably before the bacteria that can now penetrate underneath it create problems (tooth decay, recontamination of the tooth's root canal treatment).

Just minor chips can be smoothed over using a dental drill. Larger defects might be repaired by bonding dental composite onto the area, although the longevity of such repairs can be problematic.

Ultra-strong ceramics.

The recent history of dentistry is littered with the perpetual introduction of "new, next generation" dental ceramics whose claim is to offer durability characteristics somewhat on par with PFM or metal crowns.

These claims are usually founded on short-term study results that are then inappropriately extrapolated into long-term claims. So, buyer beware.

Zirconia

Zirconia is a relatively new dental ceramic that does factually seem to possess superior strength characteristics. And especially in cases where the entire crown is carved (via CAD/CAM technology) from a single block of it (this is termed "monolithic" construction) the number of dentists who choose them for placement on back teeth as an alternative to PFM's seems to be growing substantially each year.

Only time will tell if zirconia restorations ultimately become the dominant crown of the future.

b) The appearance of milled ceramic crowns may be mediocre.

We discussed this issue above but it does bear repeating. In the case of milled (CAD/CAM) crowns, since the crown is cut out of a uniform block of ceramic, it can't possess the same degree of color and translucency characterization as one handcrafted by a dental technician. As a result, it's likely to look less natural or lifelike than other types of all-ceramics.

When this matters.

This issue may not be much of a concern for teeth that don't show prominently, like molars and possibly even premolars. But for upper front teeth (incisors and canines), this issue may be of paramount importance.

Note: Milled crowns can be characterized by "staining and glazing" them. But this is just a surface treatment and doesn't generate the same enamel-like luster as explained above.


 

When might choosing an all-ceramic crown make a good choice?

In those situations where the cosmetic appearance of a tooth is of at least some concern, then placing an all-ceramic crown may make sense.

Applications.

Front teeth (incisors and canines) -

a) Teeth that show prominently.
  • In cases where the esthetics of the crown are critically important, a ceramic one might make the best choice above all other types. They're known for their ability to mimic the lustrous nature of natural teeth due to the level of characterization and translucency that can be built into them.
  • Milled all-ceramic crowns are a different matter. Since they're carved out of a single uniform block of ceramic, they tend to have a very uniform look.

    That means making a milled ceramic that matches its neighboring teeth exactly can be a difficult task. These crowns can be "stained and glazed," meaning colored porcelains are fused to their surface so to add characterization. But this approach is second-tier as compared to the results possible with other types of all-ceramics.

    In the case where all of a person's front teeth will be crowned (6 or more), the lack of characterization associated with milled ceramics may not be as noticeable and therefore possibly produce an acceptable result.

b) Front teeth that are less visible.
  • Some people have low lip lines and as a result their teeth really don't show all that much. If so, the less characterized look of a milled ceramic crown might be good enough.
c) Situations where crown strength is important.
  • Some of the types of "porcelains" that can be used to make milled ceramic crowns have superior strength characteristics. Two examples are zirconia and then less so lithium disilicate.

    In cases where crown strength is important (like with people who grind their teeth), choosing one of these comparatively less esthetic yet stronger types of milled crowns might make sense.

Premolars -

A person's premolars are those teeth positioned directly behind their eyeteeth. And even though these are technically "back" teeth, they usually hold a prominent position in a person's smile.

  • If an all-ceramic crown is placed, one made using zirconia or lithium disilicate would probably make the better choice due to the greater strength characteristics that these materials offer.
  • The alternative to an all-ceramic would be a PFM crown, which has a longer track record of providing lasting, durable service.

    The advantage of choosing an all-ceramic over a PFM would be the fact that it will never suffer from the "dark line" issue mentioned above.

Molars -

a) Those that don't show.
  • If the molar being crowned is not or is just minimally visible there's little reason to consider an all-ceramic crown. All-metal and PFM crowns make the better choice due to their well established history of being able to provide lasting service for teeth regularly exposed to substantial chewing forces.
b) Molars that are visible.
  • If an all-ceramic crown is placed, one made using zirconia would likely make the best choice due to the greater strength characteristics that this material offers.
  • The alternative to an all-ceramic would be a PFM crown, which has a long established track record of providing lasting service for molars.

    The placement of zirconia crowns instead of PFM's is growing. Only time will tell if this proves to be a prudent trend.

c) Situations where crown strength is important.
  • There can be applications where the strength of the crown needs to be relied upon. This might include cases where the patient clenches or grinds their teeth, the patient generates exceptionally heavy chewing forces, teeth that have obvious fracture lines in them, or cases where crown failure might compromise other completed work, such as root canal treatment.

    If so, an all-metal or PFM crown would likely make the better, or at least more predictable, choice over an all-ceramic.

 
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