Types of dental crowns. -
a) Porcelain (all-ceramic), b) All-metal (gold), c) Porcelain-fused-to-metal (PFM). / Advantages, disadvantages and applications (best practices) for each type.
What are the different types of crowns?
Figure out what kind of crown makes the best choice for you by answering questions.
The three basic kinds of dental crowns ("caps") are:
- All-metal - These restorations are made using gold or "white" (silver-colored) dental alloy. They're known for their great strength and exceptional durability.
- All-ceramic - These crowns are fabricated using porcelain or "engineered" dental ceramic. Some of these materials are known for their superior aesthetics, others for their strength (unfortunately none for both).
- Porcelain-fused-to-metal ("PFM") - A hybrid construction type where a porcelain covering encases a metal substructure. These crowns can provide both good aesthetics and strength.
Which kind makes the right choice for your tooth?
As this page outlines, each type of crown has its own unique set of advantages and disadvantages, which must be weighed and evaluated in light of the patient's specific situation.
No one kind universally makes the best choice for all circumstances.
It is true that some types are better suited for some kinds of teeth than others. We give general rules covering this issue at the bottom of this page.
[If the restoration you're having made is a replacement for an existing all-metal or PFM crown, don't overlook asking for your old one and then selling it for it's precious metal content.]
Overview - Types of dental crowns.
Details about all-metal (gold) dental crowns.
A) All-metal dental crowns. / "Gold" dental crowns.
(Metal crown advantages & disadvantages.)
Some crowns are made entirely out of metal. The classic metallic crown is one made out of gold, or more precisely, a gold alloy.
Actually, there are a number of different types of dental alloys that can be used for crown fabrication. Some of these metals are silver ("white") in color, rather than yellow like gold.
Dentists have been placing all-metal crowns for over 100 years, the longest of any type by far.
1) Advantages of gold crowns.
All-metal crowns made using dental alloy that has a high gold content have many advantages. They include:
They're long lasting.
Gold crowns (and metal ones in general) are very strong and can be expected to withstand even the heaviest biting and chewing forces well.
They will not chip. It would be uncharacteristic for one to break. And of all of the different types of crowns, all-metal ones generally have the greatest potential for lasting the longest.
They're kind to neighboring teeth.
The precious alloys that are used to make gold dental crowns have a wear rate that's similar to tooth enamel. That means the crown won't create excessive wear on the teeth that oppose it (the teeth that it bites against).
Gold crowns are easy for a dentist to work with.
Dental alloys that have a high gold content are typically very workable metals. This factor makes it possible for the dentist to achieve a very precise crown-to-tooth fit.
The only disadvantage of gold crowns is they're not white.
2) Disadvantages of all-metal crowns.
They're not white like teeth.
About the only disadvantage of metal dental crowns is their appearance. And for this reason, they're not usually placed on teeth that show prominently when the person smiles. They can, however, make a great choice for some molars.
Get your significant other's OK. - If you're considering some type of metal crown, take our advice on this point. Before giving your dentist the go ahead to make it, check with your spouse first. They're the one who will be looking at your smile, and your shiny new crown, the most.
3) Popularity / Use of all-metal crowns.
We ran across an editorial in the Journal of the American Dental Association (Christiansen, 2011) [page references] that made reference to information reported by a prominent dental lab (Glidewell Laboratories, Newport Beach, CA) in regard to the relative percentage of different types of crowns dentists had ordered in 1997 vs. 2010. (Their manufacturing volume is on the order of 1 million crowns per year).
What they reported.
- In 1997, 12% of all crowns made were metal but by 2010 this number had fallen to just 6%. (The remainder of Glidewell's volume would have been either all-ceramic or porcelain-fused-to-metal crowns.)
- In support of our opinion that metal crowns often make the overlooked best choice, the author of the editorial stated that "most of my dentist patients want gold alloy restorations."
Interpreting this data.
We think it's important to mention that the data from this lab (which we also cite below) possibly has a bias toward ceramic crowns.
Glidewell is a national leader in promoting the use of all-ceramic crowns. And as such has equipped their laboratory to be able to fabricate them. In comparison, the "average", often local, dental lab frequently doesn't have this capability.
That means it's possible that a comparatively greater percentage of Glidewell's work is creating types of crowns that other labs can't. For more routine needs (all-metal and porcelain-fused-to-metal crowns), dentists may be using a different (often local) source. (A choice often based on cost, convenience or personal reasons).
Details about veneered metal dental crowns.
4) If appearance is an issue, consider a porcelain "window."
Giving a white look to all-metal crowns.
- There can be times when a patient wants or needs the strength, durability and predictability that an all-metal crown can offer.
- But the way placing one would look would be simply too objectionable.
As a solution for this dilemma, it's possible for metal crowns to be surfaced with porcelain on their side that shows. Dentists refer to this type of option as a "veneer" or "window."
Some metal will still show.
The downside is that others will still be able to see a hint of the metal that surrounds the porcelain. And they'll also be able to see the metal chewing surface of the crown. But this option may make the look of having a metal crown passable where otherwise it would not.
Details about all-ceramic dental crowns.
B) All-porcelain (ceramic) dental crowns.
(All-ceramic crown advantages & disadvantages.)
All-ceramic crowns are just that. Restorations that have a construction where their entire thickness is made up of dental ceramic (a white glass-like material that resembles the look of tooth enamel).
Originally the ceramic used was porcelain. This type of crown was called a "porcelain jacket," and it was first introduced in the early 1900's.
Nowadays, all-ceramics are typically fabricated out of some type of synthetic or engineered compound, using construction techniques developed in the 1990's or after.
1) Advantages of all-ceramic crowns.
There's no more natural-looking type of crown.
Due to the life-like translucency of the materials from which they're made, all-ceramics can be the most aesthetically pleasing of all of the different types of dental crowns. And for this reason, they often make an excellent choice for restoring front teeth.
!! Not all all-ceramics can make this claim.
It's important to know that some types of all-ceramic crowns are much better than others in their ability to closely mimic the look and luster of natural teeth. This is due to both the type of ceramic and fabrication method used in their construction.
- At one end of the spectrum lies those crowns whose full thickness has been crafted by hand by combining multiple layers of porcelain.
Since each one can be different in terms of shade or level of translucency, the restoration can be given a very life-like appearance. (Unfortunately, due to both the technique involved and the materials used, these types of crowns are comparatively brittle.)
- At the other end of the range lies those crowns milled from a single homogeneous cube of ceramic. In this case, the result is one where the restoration just has one uniform color. And that means it really can't mimic the normal shade and translucency variations found in natural teeth.
As a compromise, nowadays all-ceramics for front teeth are typically constructed in a fashion where those portions of the crown that aren't readily visible are premade (milled, pressed or cast), using ceramics that are generally less natural-looking but have better physical properties. The front surface of the restoration is then crafted by hand, by adding on individual layers of porcelain.
Doing things this way provides a way where the crown can be given great characterization, and also better mechanical properties (such as greater strength). But you can't just assume that this is the way the crown for your front tooth will be constructed. You absolutely have to ask.
2) Disadvantages of all-ceramic crowns.
Concerns about strength and longevity.
Generally speaking, porcelain-fused-to-metal and especially all-metal crowns can be considered to be stronger types of restorations.
That means in the back of the mouth where substantial chewing forces are routinely generated, placing an all-ceramic might not make the best choice. (Your dentist's judgment will be required on this point.)
In the front of the mouth, crown strength is less of an issue and easily out weighed by the superior aesthetics that an all-ceramic restoration can typically provide.
3) High-strength dental ceramics.
In response to durability issues, synthetic or "engineered" porcelains having enhanced strength characteristics have been developed. The leading compounds in this field are lithium disilicate (IPS e.max®) and zirconia (BruxZir®).
The strongest, most durable construction type for crowns made out of these materials is the "full" or "monolithic" form, meaning the entire thickness of the restoration is made out of a solid, uniform piece of the ceramic (as opposed to a construction where individual layers are fused together).
As evidence, a study by Dhima (2014) evaluated 226 all-ceramic crowns (on average) 6 years after placement. The most common type of failure was fracture to the core of layered (non-monolithic) crowns (this means the full thickness of the crown had cracked). Based on this finding, the paper advised the use of monolithic crowns on back teeth.
As a comparison of the two compounds above, in its monolithic form lithium disilicate has a rating of 360 to 400 MPa (a measure of how much stress the material can withstand without breaking). Solid (full) zirconia has a strength rating in the neighborhood of 1000 MPa, making it the stronger of the two. However, survival-rate studies suggest that possibly the e.Max product still makes the better choice.
One primary disadvantage of monolithic high-strength ceramic restorations is that their appearance generally isn't as translucent and life-like as others types of porcelain crowns can be. However, for back teeth where great strength is needed the most, this likely isn't much of an issue.
For front teeth, appearance is of course of utmost importance. And between the two dominant materials in this field, lithium disilicate is generally considered to have better aesthetic characteristics than zirconia. And for that reason, if a high-strength ceramic crown is needed for an anterior tooth, that is the type typically placed.
3) Popularity / Use of all-ceramic crowns.
The editorial we cited above (Christiansen 2011) provided information about ceramic crowns too.
The numbers reported.
- In 1997, 16% of crowns made by Glidewell Laboratories were all-ceramic whereas in 2010 this number grew to 50%.
- As we mentioned above, this lab involved is a national leader in promoting and fabricating this type of crown, so their numbers are likely skewed toward them.
- The greatest amount of production growth involved the manufacture of high-strength all-ceramic crowns. (The type considered most appropriate for placement on back teeth.)
Details about porcelain-fused-to-metal dental crowns.
(PFM crown advantages & disadvantages.)
Dentists have been placing porcelain-fused-to-metal crowns for patients since the late 1950's. And over the decades that followed, they became the "gold standard" for restoring front teeth, and back teeth where a tooth-colored restoration was required.
In more recent decades, the popularity of PFM's have lost ground to more modern techniques (i.e., all-ceramic crowns constructed using engineered/synthetic porcelain). But unlike newer methodologies, porcelain-metal crowns have a long, well-established track record of providing predictable, lasting service.
How they're made.
Porcelain-fused-to-metal restorations are somewhat of a hybrid between all-metal and all-ceramic crowns.
When they're constructed, the dental technician first makes a thin thimble of metal that fits over the tooth. A veneering of porcelain is then fused over it in a high-heat oven, giving the crown both it's tooth-like shape and color.
Related Page: Types of dental alloys used to make PFM crowns (precious, semiprecious, nonprecious)
1) Advantages of porcelain-fused-to-metal crowns.
Due to their great strength, PFM dental crowns can make a good choice for either front or back teeth.
As a class, this type of crown would only place second to all-metal ones in terms of strength and durability. And as mentioned above, PFM's have a very long, well documented history of providing lasting service.
They're natural looking.
For some people, and some applications, the big advantage of a PFM crown over an all-metal one is simply the fact that it's tooth colored.
A hint of the metal edge of a PFM crown has started to show.
2) Disadvantages of PFM's.
There are some disadvantages associated with porcelain-fused-to-metal crowns. They include:
The "dark line" phenomenon.
The metal that lies underneath the crown's porcelain surface can sometimes be seen as a dark line right at the crown's edge.
A dentist will usually try to position the edge of a PFM crown just underneath the tooth's gum line. But, if a person's gums happen to recede, this dark line can show, thus spoiling the crown's appearance.
Achieving superior aesthetics can be a challenge.
While the appearance of a PFM crown can be excellent, it's often difficult to create one that's as natural-looking as the best all-ceramic ones.
For the most part, this difficulty stems from the crown's metal substructure and how it must be masked by covering it with relatively opaque (less translucent and therefore less natural-looking) porcelain. And while this doesn't create a problem in all cases, it frequently involves challenges or compromises.
It's possible for the porcelain surface of a PFM crown to chip or break off. (It would generally be expected that a PFM would pose less risk of catastrophically cracking or breaking than most types of all-ceramics. Of course, all-metal crowns avoid this complication all together.)
If porcelain breakage does occur, it's very difficult to make a lasting repair. The most predictable solution typically involves making a new crown. As a compromise, some minor chipping may just be smoothed over or polished.
PFM crowns may wear opposing teeth.
The porcelain surface of a porcelain-fused-to-metal crown can create (possibly significant) wear on those teeth that it bites on or rubs against. (Many types of all-metal or all-ceramic crowns are more bio-compatible in this regard.) This issue might be especially important for people who brux (clench and grind) their teeth.
This potential is greatest in cases where during placement the crown's biting surface needed to be trimmed and it was not subsequently re-glazed (given a glass-like finish in a high-heat oven), or at least thoroughly smoothed and polished.
3) Popularity / Use of porcelain-fused-to-metal crowns.
The editorial we cite above (Christiansen 2011) provided information about PFM crowns.
The numbers reported.
Which type of dental crown makes the best choice for you?
Answer the questions below to drill down to the kind of crown whose characteristics best match up with your needs. You can find an extended summary of this same information just below.
Will your crown be placed on a front tooth or back one? -
Front teeth = Incisors, Canines (cuspids, eyeteeth).
Back teeth = Molars, Premolars (bicuspids).
Summary: What type of crown makes the best choice for your tooth?
The following information comes from an article written by Dr. Gordon Christensen (a well respected dental researcher and clinician) in 2014. In it, he listed the kind of crown that he felt typically made the best choice for each type of tooth.
The preferred material is listed first, and then others in decreasing order of preference. We've added notes to this list so to help you understand what we expect was the rationale associated with these choices.
- Upper or lower second molars - all-metal (gold alloy), PFM (porcelain-fused-to-metal), full zirconia, lithium disilicate
Notes: This order of crown types suggest that for back teeth where heavy chewing forces are involved, the strongest type of restoration makes the best choice. Gold is listed as the preferred construction material because most people's second molars don't show prominently and therefore its metallic look is not typically an issue.
- Lower first molars - all-metal (gold alloy), PFM, full zirconia, lithium disilicate
Notes: Once again, for teeth that don't show prominently when the person smiles, choosing the type of restoration that has the greatest strength makes the best choice.
- Upper first molars - PFM, lithium disilicate, full zirconia
Notes: Upper first molars typically are visible to others, so for that reason only porcelain crowns are included in this list. PFM is shown as the first choice, no doubt due to the great strength and longevity this type of construction usually provides.
Since lithium disilicate doesn't create as strong a restoration, we were surprised to see it listed ahead of full zirconia. The text of the article stated that the preference for it was based on it's more favorable aesthetic characteristics.
- Upper or lower premolars (bicuspids) - lithium disilicate, PFM, full zirconia
Notes: For premolars, lithium disilicate is listed ahead of PFM. This would imply that for these teeth the superior strength of a porcelain-fused-to-metal crown is not necessarily needed. It also suggests that the aesthetic disadvantages of PFM's (primarily the "dark line," see above) make the all-ceramic construction of lithium disilicate crowns the better choice.
- An individual upper or lower front tooth - all-ceramic, lithium disilicate
Notes: Here the first recommendation is for some type of all-ceramic crown but not one made using a high-strength synthetic porcelain.
That's because creating an individual crown that precisely matches the color and translucency of neighboring teeth is very challenging. And using a high-strength porcelain would only make this task even more difficult (see above).
- All 6 upper or lower anterior (front) teeth - lithium disilicate
Notes: When placing an entire set of crowns, the issue of color matching is much less of an issue. As long as all of the crowns match each other, the case will usually look acceptable (and hopefully much better than just that).
That means choosing lithium disilicate makes the better choice. It has reasonably good aesthetic characteristics and also has greater strength that the typical dental ceramic.
What does the future hold?
It seems likely that with the advancement of dental materials there will be a time (possibly soon) when an engineered porcelain for use with all-ceramic crowns is developed that features both great strength and ideal aesthetic properties. But it's important to understand that that day has not yet come.
It's true that dental science won't advance unless new techniques are put to the test. But the question is, do you want your case to be a part of that experiment?
Despite their limitations, one thing all-metal and porcelain-fused-to-metal crowns do possess is a long track record of providing lasting service. In comparison, all-ceramics don't. And until that point when they definitively do, dentists should decide to place them and patients choose to accept them judiciously.
[page reference sources]
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