Types of dental crowns -
Once you've been informed that your tooth requires a dental crown, a decision must be made about what kind should be placed.
What issues should be considered?
There are a number of factors that need to be evaluated when making this determination, including the comparative strength, durability and appearance of each kind of crown.
The goal of this page is to outline these issues for you, so you're able to speak intelligently with your dentist as the two of you figure out which type seems to make the best choice for your specific situation.
What are the different types of crowns?
There are three kinds of dental crowns, each based on its type of construction:
The next few paragraphs provide a brief description of each type. If you need more detailed information about a certain one, then use its associated link.
(If perchance you don't really know what a dental crown is, use this link for a brief overview.)
a) All-metal crowns
An all-metal "gold" dental crown.
As their name implies, all-metal dental crowns are fabricated entirely out of metal.
While the classic all-metal crown is a "gold" one, a number of other types of dental alloys can be used during the fabrication process. Some of these metals have a silver ("white gold") coloration.
Metal crowns are typically placed in situations where great strength is required (they're the strongest, most durable type) and cosmetic appearance is of little concern. For example, they are frequently placed on molars.
b) All-ceramic crowns
An all-ceramic dental crown.
This type of crown is made entirely out of some type of dental ceramic, such as porcelain. When they're made, they can either be:
- Handcrafted by a dental technician.
- Carved out of a single block of ceramic by a computerized milling machine (CAD/CAM unit).
Both methods offer their own unique advantages and disadvantages.
Some types of all-ceramics are known for their outstanding ability to mimic the look of natural teeth. Other kinds are tooth-colored, but aren't able to generate a truly lifelike appearance.
All-ceramics are typically placed in those situations where the tooth's appearance is a major consideration. (Some, but not all, kinds of ceramics are the most natural-looking type of crown a dentist can place.)
That means they are most frequently placed on front teeth (incisors and canines), although they can be placed on premolars and molars too.
A primary disadvantage is that all-ceramics generally aren't as strong as other types of crowns. Although this factor varies according to the specific type of ceramic that's been used.
A porcelain-fused-to-metal dental crown.
c) Porcelain-fused-to-metal crowns
Porcelain-fused-to-metal dental crowns (PFM's) can be thought of as a hybrid between their all-metal and all-ceramic counterparts.
When they're made:
- A thin metal thimble is fabricated that fits over the tooth (the substructure).
- Porcelain is then fused over this metal shell in a high-heat furnace.
Even though a substantial portion of the crown may be metal, the side that people see is covered over with porcelain so it looks white like its neighboring teeth.
As a disadvantage however, insuring that the underlying metal remains fully masked by porcelain over the full lifespan of the crown can be difficult to manage in some cases. (See PFM link below.)
PFM crowns offer good strength characteristics. And that means they make a good choice for situations where strength and durability are required (like on molars and premolars). Generally speaking, they can be considered to be stronger than all-ceramic crowns, but not as durable as metal ones.
The fact that their front surface is porcelain-covered means that they make a suitable choice for front teeth (incisors and canines), especially in applications where strength considerations are important. But in cases where perfect tooth esthetics are paramount, an all-ceramic crown may make the better esthetic choice.
Which type of dental crown makes the best choice?
It's important to understand that there's no single type of crown that always makes the best choice in every application. The right selection always varies depending on the needs of the patient's specific circumstances.
The following examples can give you an idea of which types of crowns frequently make the best choice in certain situations.
- In the discussion below we use the term "milled all-ceramic" (referring to a type of crown construction that typically results in mediocre esthetics but possibly provides for substantial strength characteristics) in contrast with "all-ceramic" (meaning a construction technique that frequently creates superior esthetics but doesn't provide for great crown strength).
- Remember, the letters PFM stand for porcelain-fused-to-metal.
- For more information about any of the types of crowns listed below, use the respective links above.
1) Front teeth -
A smile with a very high lip line.
a) Patients with high lip or smile lines.
If a person's lip line is very high, most, if not 100%, of their front teeth will constantly be on display to others. If so, it will be paramount that the crown that's placed looks as life-like as possible.
- Placing an all-ceramic crown might be a first choice for this scenario because of the superior esthetics that this type of restoration can provide.
- Placing a milled all-ceramic or PFM might give perfectly acceptable results too. But both have their own difficulties in being able to truly mimic a natural look.
b) Patients with low lip or smile lines.
If only a portion of the person's teeth show, the esthetic demands placed on the crown will be reduced. Possibly even to the point where other characteristics (such as strength and durability) can be given more weight in the selection process.
- An all-ceramic, milled all-ceramic or PFM might each be considered for this type of application. The latter two more so in cases where the patient's situation would benefit from greater crown strength.
2) Back teeth -
Some people's molars show very little when they open their mouth. And when this is the case, the strength and durability characteristics of the type of crown selected for placement should be given primary emphasis.
The look of these gold crowns may be too much for some people.
- For molars that don't show at all, no kind of crown makes a better choice than an all-metal ("gold") one.
- In cases where the appearance of a molar is a factor (like with 1st upper molars), PFM crowns have a long history of being able to provide excellent service, yet are more esthetically pleasing than all-metal ones.
- Milled all-ceramic crowns (especially those fabricated using the ceramic zirconia) may make a reasonable choice for molars too.
b) Premolars (bicuspids)
Even though premolars usually hold a prominent position in a person's smile, by definition they are "back" teeth. And as such, it can be expected that they may be exposed to heavy chewing forces.
- PFM crowns are both pleasing in appearance and have a long track record of being strong, durable restorations.
- Milled all-ceramic crowns carved out of blocks of modern ceramics (especially zirconia) are gaining a reputation for being strong, reasonably esthetic restorations.
Dental crown basics -
Just in case you're not sure what a crown is, here are a few things you should know about them.
A) What are they?
Crowns are a type of dental restoration that fit over that part of a tooth that lies above the gum line. For all practical purposes, once one has been cemented in place, it becomes the new outer surface for its tooth.
B) How are they placed?
Making a crown for a patient involves the following steps:
1) Tooth preparation and impression taking.
The first step involves trimming the patient's tooth. Dental crowns generally need to be on the order of 2 to 3 mm thick (so they have good cosmetic and strength characteristics). That means that a tooth receiving one needs to be trimmed down by this same amount.
Once it's been properly shaped, the dentist will need to make a copy of the tooth that can be used to make its crown. In most cases, the dentist will do this using impress paste (a putty-like material that's squished over the tooth which then sets). As an alternative, the dentist may take an optical impression (a picture of the tooth that's then fed into a computer).
2) Crown cementation.
Once the crown has been fabricated, the dentist will check its fit, both on the tooth and the way it touches neighboring and opposing teeth. After making any needed adjustments, the crown is then permanently cemented onto its tooth.
3) How many visits does this process take?
Typically the steps outlined above are performed during two separate appointments. Usually these visits are scheduled about two weeks a part. During the time in between, the patient wears a temporary dental crown.
In the case where an optical impression is taken, a dental milling machine may be used that can grind the crown out of a block of ceramic in about 20 minutes. If so, the tooth can be prepared, and its crown cemented, in just one dental visit. (This technique variation is only available with all-ceramic crowns.)
D) Why do teeth require crowns?
Dental crowns are typically placed for the following reasons. Any one tooth may be in need of one or more of these benefits.
1) Restoring teeth to their original shape and function.
Crown placement is one way a dentist can rebuild broken teeth. Crowns, above all other types of dental restoration, create a very lasting repair.
2) Strengthening teeth.
Some teeth, especially back ones, may require crown placement because it is the type of dental restoration that can best withstand heavy chewing forces. Additionally, any fragile tooth, including those that have had root canal treatment, may benefit from a crown's strengthening effect.
3) Improving the appearance of teeth.
Since a dental crown becomes the new outer surface of a tooth, its cosmetic appearance can be vastly improved when one is placed. This includes tooth color, shape and even apparent alignment.