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Dental Crowns

Crowns are like little hats for your teeth.
Crowns are like little hats for your teeth.
iStockphoto/Thinkstock

Some of us have the good genes, excellent dental habits, regular visits to the dentist and sheer luck that add up to beautiful, healthy teeth. Others need what dentists call "restoration." Fillings are par for the course, but hearing that you need a crown can conjure up a special feeling of dread. Or it may sound kind of nice, like a sort of royal treatment for your tooth. However, the process can be painful -- both for your mouth and your bank account.

Crowns are caps that are placed over teeth to both improve their appearance and their functionality. Dentists install them when you have a weak, damaged, broken or discolored tooth. Teeth that have gotten a root canal (removal of infected pulp inside the tooth's root, rendering it "dead") may be capped because the tooth itself can become fragile and brittle. Sometimes dentists suggest capping a tooth rather than filling it because the filling would take up most of the tooth or go below the gumline, threatening its structural integrity.

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If you need a tooth to be pulled entirely and replaced with an implant, a crown would go over the actual metal post that gets implanted. Crowns may also be used to attach a bridge -- a partial denture. There are also 3/4 and 7/8 crowns -- sort of a cross between a crown and an inlay that preserves more of the original tooth, with more of a "seam" between the tooth and crown.

If the tooth is healthy and structurally sound, a crown is probably not something that you'd want to do -- not only for the reasons above, but because it's a permanent procedure that forever alters the existing tooth. A tooth that is discolored on the surface or has minor damage may need a veneer instead -- a thin layer of material that is usually placed on a front tooth.

You may think of dental restoration as a modern invention, but believe it or not, crowns have been around since ancient times. Next, find out how crowns have evolved over the years.

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Of course, ancient dentistry was nothing like today -- most of the time, you went around with a tooth that bothered you until it either rotted and fell out, or you had it pulled out (by a person with many other tasks in his job description and without the benefit of modern pain medications). However, there were some restorative techniques, including crowns, even in ancient times.

The first known crowns were made of gold and used by the Etruscans, people who occupied most of what is today the Tuscan region of Italy from 700 B.C. to the first century B.C. Making and using crowns seems to have fallen out of favor during the Middle Ages, however. In 1530, the first book of dentistry, the Artney Buchlein, or "The Little Medicinal Book for All Kinds of Diseases and Infirmities of the Teeth," was published in Germany. It set the stage for treating dentistry as a profession and a science (rather than a side practice for barbers and blacksmiths, based on superstition) and included information about all types of restorations, including crowns. In the 1700s, crowns crudely made from animal or human teeth were installed using metal or wooden posts. By the mid-1800s, porcelain began to be used in crown making.

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Crowns that truly fit your mouth, however, didn't come about until the early 1900s. The investment, or lost-wax casting method, was first applied to making them around this time. This method uses wax to create a mold, into which a material is poured and cooled to form the final product. In 1907, Dr. William Taggert not only built a machine used to cast the crowns, but also refined the technique, which allowed dentists to make precise, detailed crowns. Until the 1960s, when the porcelain-fused-to-metal crowns became available, most crowns were either porcelain or gold.

Now that you know how far crowns have come, read on to learn more about the types of crowns available today.

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Gold crowns definitely make a statement!
Gold crowns definitely make a statement!
Charles Gullung/The Image Bank/Getty Images

Have you ever seen a person with a gold tooth and admired the look? Then a gold crown might be for you. Crowns are also available in all porcelain or ceramic as well as porcelain-fused-to-metal (PFM) or porcelain-fused-to-gold (PFG). Different materials not only have different price points but also different life spans. Which type of crown you get depends on what you want and what you can afford.

As you might imagine, full gold crowns are the most expensive option, and they do make quite a statement. They're formed from a single piece of metal alloy (mostly gold, but also platinum, copper, tin and other metals). Gold casts easily, and it expands and contracts with cold or heat at the same rate that teeth do, which means a better-fitting crown. Gold crowns also take the prize as the most resilient and longest-lasting crowns, and they're the best option for molar crowns or if you grind your teeth. However, they can also conduct heat and cold well, which can make the tooth underneath more sensitive if you haven't gotten a root canal.

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At the other end of the spectrum are porcelain or ceramic crowns. They look just like real teeth, because they can be colored to perfectly match the rest of your teeth, and they have just the right amount of translucency. They are also the least expensive option, and are more prone to chipping or cracking. Most dentists don't recommend all-porcelain or all-ceramic crowns on molars because the grinding action can quickly wear them down.

The PFM or PFG options provide the best of both worlds, so to speak. These crowns consist of a thin shell of porcelain fused to a metal post. The metal post provides durability, while the porcelain shell gives a more natural look (although not as natural as a purely porcelain crown because of the metal underlay). Depending on where the crown is placed, the porcelain may just be applied to the front of the tooth where it will be visible. One negative with PFM crowns is that if your gumline recedes at all, a thin gray line may become visible.

Making crowns is a kind of art. Read on to learn how laboratories make each one unique.

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Dental technicians make crowns in a lab in Algodones, Mexico.
Dental technicians make crowns in a lab in Algodones, Mexico.
Radhika Chalasani/Getty Images News/Getty Images

Traditionally metal crowns have been made using the investment casting, or lost-wax, technique. This means sending an impression (taken in a rubber mold) of the tooth to be replaced, as well as the teeth next to it and the ones opposing it, off to a laboratory. The laboratory makes a model of the tooth and its adjacent teeth out of special type of plaster called dental stone or die stone.

The tooth to be crowned and its adjacent teeth are separated into two or more dies, as the models are called. These dies look just like the original teeth sitting in the jaw, just made out of stone. Next, a technician covers the die with paint to create a die spacer -- room between the crown and the existing tooth to allow for cementing the crown. Then, the technician uses wax to build up the die so that it the shape is correct and the fit works with the dies of the adjacent and opposing teeth. This buildup of wax is called a wax pattern and functions as a mold for the crown.

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The wax pattern is attached to a stick known as a sprue, which ultimately allows the finished material to flow into the mold. The wax pattern and sprue together are dipped in plaster. This is the investment. After being attached to an investment ring and placed in a furnace, the wax melts. Melted metal, such as gold alloy, is injected into the ring as it spins in a centrifuge. A hollow metal shell of gold forms inside the plaster. After immersion in cold water, the plaster layer shatters, the sprue is removed, and the crown is polished. If the crown is a porcelain-fused-to-metal (PFM), a porcelain veneer is either milled (ground down from a larger piece of porcelain) or pressed and baked, then heat-fused to the metal crown.

Milling or pressing and baking have been the only methods used to create ceramic or porcelain crowns until recently. CAD/CAM (computer-aided design and computer-aided manufacturing) dentistry has made it possible to get one of these types of crowns much sooner. Instead of taking an impression, a dentist takes a picture of the prepared tooth to be crowned and in-office software creates a virtual crown in three dimensions. Then a computer uses this data to mill the crown, after which it is heat-treated for strength and colored to match the existing teeth. The whole process takes an hour or two, eliminating the need for getting a temporary crown and waiting weeks for the permanent one.

Even if you're getting a crown via the CAD/CAM method, it can still take some time. In the next section, learn about preparing for a crown.

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Before a crown is placed, the remaining tooth must be ground down to accomodate it.
Before a crown is placed, the remaining tooth must be ground down to accomodate it.
iStockphoto/Thinkstock

Once you and your dentist have decided that you need a crown, the process may involve several more steps if you need a root canal or are getting an implant (which is a surgical procedure and requires recovery time before a crown can be placed). For implants, you'll probably get a temporary crown, made quickly in the dentist's office out of a white composite material (usually synthetic resins) and attached with a weak cement to allow for easy removal when the real crown is placed over the implant.

If you still have your tooth, however, it has to be prepared for a crown. Usually this means grinding it down (after your dentist has taken an impression if necessary). Some of the healthy tooth will probably be ground away to allow the crown to fit properly. This is why crowning is a permanent solution -- if ultimately a crown doesn't work for you, the remaining tooth will have to be pulled and you'll need an implant or another dental appliance like a bridge. How much of the tooth is removed depends on the type of crown you get; a gold crown requires the least amount of grinding because it can be as thin as half a millimeter. Porcelain crowns can be twice as thick.

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On the other hand, your tooth may be so damaged that the dentist has to strengthen it to prepare it for a crown. He may build it up with a composite material, or if you've had a root canal, perform a post and core. This means inserting metal posts into the empty root canal area and filling around it with a material like latex. Post-and-cores are different from implants because you still have the root system and some existing tooth left.

When the crown is ready, you and your dentist need to agree that it matches the color of your other teeth (unless you got a gold crown, of course) and fits properly before cementing it. A poorly fitting crown can invite bacteria to grow underneath, cause problems eating, wear down other teeth or just plain hurt. Crowns should be treated like the rest of your teeth -- avoiding acidic foods and biting on things like ice will help keep them in good shape. Most are meant to last at least a decade but usually last longer.

While the whole story of dental crowns may be fascinating, getting one isn't high on most people's wish lists. Take good care of your teeth and reading this article may be closest you come to a crown!

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Sources

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