A crown (slang term “cap”) is a complete covering over a tooth. A crown is usually done to protect a tooth from breaking or cracking. When a tooth has a large filling that develops decay around the large filling, a crown is frequently recommended instead of an even larger filling, because the larger the filling in a tooth, the more the filling weakens the tooth. Front teeth are frequently crowned because the teeth have had multiple plastic (composite) fillings done over the years and crowns protect the teeth better and look much better than large plastic fillings that stain easily. For more information about crowns or to schedule an appointment, please call our Augusta office at 706-738-8070.
How Is A Crown Made?
The process to make a crown takes two appointments:
First Appointment - If the tooth has an old filling, and most do, the old filling will be removed and any decay under the filling will be removed. A new filling will be done on the tooth that gets the tooth back to its original size and shape. This filling is called a “build-up”. The tooth and build-up are then shaped by removing the approximate thickness of a dime or less from the top and sides of the tooth. Most of the tooth still remains. The crown will be made in the laboratory and will slide over the prepared tooth and be cemented in place. The reason the tooth must be prepared is that the crown needs to be the same size as the original tooth, so some tooth structure must be removed. An impression is made of the prepared tooth. An impression is also made of the teeth in the opposing jaw (so we know what the “bite” is like). We do not want to send the patient out of the office with a prepared tooth, so a temporary crown is made at chairside for the tooth or teeth being crowned. We have our own laboratory technicians at West Augusta Dental Associates and one of our technicians may come into the operatory with a shade or color guide to help select the shade for the crown. There are very few dental practices that have their own laboratory in the office and extremely few that have crown and bridge technicians and a removable technician.
Second Appointment - The second visit is about 2 weeks after the first visit and on the second visit the temporary crown or crowns are removed and the permanent crown or crowns are cemented in place.
What Are “Same Day” Crowns?
There is a technology where crowns can be made in one day. The technology involves using a device to “scan” the tooth rather than take an impression of the tooth. A computer based system can be used to cut a crown out of a piece of ceramic. We have studied this system and there are several aspects of the system we are not comfortable with:
Many dentists involved with research in this field report that the scanning process is not as reliable as an impression to replicate a tooth on a model. It is very difficult to scan many areas of teeth due to technical reasons.
If a crown is done with the standard “two appointment” technique, the second appointment is a short appointment and local anesthesia is not usually necessary. Patients usually do very well with the temporary crown because we make good temporary crowns. In the case of the “one day” crown, the patient has to be involved with the procedure all day because a temporary crown is not placed over the crown from the time the tooth is prepared and scanned until the crown is placed, which will take several hours. If a prepared tooth is exposed to the saliva in the mouth for several hours, then the tooth can become sensitive because saliva and bacteria soak into the tooth.
Certainly not all, but many dental offices that have incorporated the “one day” crown into their practices have done so to make their practices look “high tech” in order to attract patients. Scanning technology is “high tech” but it is not necessarily better. Also, many dentists that use this technology use the technology to do white ceramic inlays. An inlay is a filling made outside the mouth and then cemented in place. There is nothing wrong with ceramic inlays, except that an inlay does not protect a tooth from splitting or fracturing like a crown does, but ceramic inlays usually cost about as much as a crown. A disturbing trend now is that there are “institutes” that dentists go to, mostly in resort locations in western states that teach dentists to pressure patients into having all their fillings removed and replaced with ceramic inlays or crowns. The ceramic inlays or crowns themselves are not the problem, the problem is the treatment planning philosophy. We continue to evaluate scanning technology but we are convinced that we can deliver a more consistent quality control by using impression based systems. Most dental school faculty in this country still use and teach impression based crowns. If the scanning technology improves and develops a longer history, we may incorporate it into our practice. Most dentists that use this technology are good ethical dentists, but some are over-promoting the technology.
What Material Are Crowns Made From?
The three basic types of crowns done are porcelain fused- to-metal, all ceramic, or all metal.
An example of two porcelain fused-to-metal crowns, along with a porcelain fused-to-metal bridge are illustrated in the case below that Dr. Clepper did on a patient in her early 70s:
“PFM bridge and crowns pre-op”
Pre-op photo showing one front tooth replaced by an artificial tooth bonded to adjacent teeth. The other natural front teeth are tetracycline stained with some stained fillings.
“PFM bridge and crowns butt margins”
The two restorations on the left are porcelain fused-to-metal crowns. The bridge is on the
right. The bridge is an artificial tooth supported by two crowns.
“PFM on blue paper”
This front view shows the bridge on the left and the two individual crowns on the right.
“PFM bridge and crowns, post-op”
Dr. Clepper had previously done some other crowns on the right side of this photo. This is the photo after the bridge and two crowns were placed. It is common for a patient to get one section of their mouth done at a time with crowns.
Porcelain fused-to-metal crowns are the most common crowns done in this country. These crowns offer strength and are attractive. The metal is under the porcelain for strength.
All porcelain crowns (also called all ceramic or just ceramic crowns) do not have metal under the porcelain. These crowns are not quite as strong as porcelain fused-to-metal crowns, but are usually strong enough for most cases, especially for front teeth. It is even possible to make a bridge replacing one tooth out of all ceramic, but this technology is very new and has not come into widespread use by the dental profession because of the concern for strength. All porcelain crowns look better in some mouths than porcelain-to- metal. All porcelain crowns are essentially the same restoration as a porcelain veneer. The difference between an all porcelain crown and a veneer is how much of the tooth is being covered by the porcelain. If the entire tooth is being covered, we call it an all porcelain crown. If only the front and biting edge of the tooth is covered, we call it a veneer.
Some practices emphasize that the tooth preparation to do a veneer is very conservative and some practices claim they can do a veneer with no preparation. Veneers can almost never be done well without tooth preparation. If no tooth structure is removed before the veneers are done, these teeth will look like white marbles because they will be too bulky. The dental practices that make claims that very little or no tooth structure needs to be removed to do veneers properly are doing so to overcome a patient's fear of having their teeth "prepared". A veneer preparation is a tooth preparation and it is practically always done under local anesthesia.
Having said that, an all porcelain crown and a porcelain veneer are basically the same type restoration. They both give absolutely beautiful results because they allow the light to penetrate through the tooth and there is no chance of getting any gray shadows at the gumline. Occasionally, porcelain fused-to-metal crowns will show just a little gray shadow at the gumlines. There are ways to prevent this, but so many times this depends on the patient's gum type.
The third type of crowns are all metal crowns. All metal crowns are usually made from gold, and gold is yellow color unless platinum is alloyed with it, then they are silver colored. Gold crowns represent the absolute highest in strength, but they are either gold or silver colored. Gold metal crowns look like dentistry and at West Augusta Dental Associates we want our dentistry to look like teeth. However, even porcelain-to-metal crowns are not as durable as gold because the porcelain on porcelain-to-metal crowns can chip off in heavy function.
Where Would A Gold Crown Be Recommended?
We sometimes recommend gold crowns on the very back teeth. We call these teeth second molars (most patients do not have 3rd molars or wisdom teeth in function). The jaw works like a nutcracker and the closer you get to the hinge of a nutcracker the more force is exerted. Therefore, the second molars are subjected to the greatest forces in the mouth during chewing and are the most likely to have porcelain broken if they are crowned.
We rarely recommend gold crowns for any teeth other than second molars and if the patient does not want any metal crowns in his or her mouth, we would do a porcelain-to-metal crown on the second molar. Another option we sometimes offer is a silver color (white gold) crown because some patients do not object to a silver color but do not want yellow gold anywhere in their mouth.
At West Augusta Dental Associates, we recommend the crowns that are the most appropriate for the teeth that need to be crowned.