Crowns

A dental crown is a tooth-shaped “cap” that is placed over a tooth to cover the tooth in order to restore its shape, size, strength, and improve its appearance.

The crown, when cemented into place, fully covers the visible portion of a tooth that lies at and above the gum line.

Why Is a Dental Crown Needed?

A dental crown may be needed in the following situations:

1. To protect a weak tooth (for instance, from decay) from breaking or to hold together parts of a cracked tooth
2. To restore an already broken tooth or a tooth that has been severely worn down
3. To cover and support a tooth with a large filling when there isn’t a lot of natural tooth left
4. To cover a tooth that has had root canal therapy
5. To hold a dental bridge in place
6. To cover misshaped or severely discolored teeth
7. To cover a dental implant
8. To make a cosmetic modification

What Types of Crowns Are Available?

The material choice for a crown is dictated by a number of factors including the tooth’s location and function, the amount of discoloration of the underlying tooth structure, the position of the gums, the patient’s smile, and the patient’s preference. Dr. Goring will discuss the pros and cons of each crown type and what will be best for each patient. Below is a summary of the different crown materials:

• Gold/metal alloys: All gold crowns are really an alloy, meaning they are not pure gold but contain some other metals such as platinum, palladium, and others. To truly be considered a gold crown it must be at least 60% gold. Gold has been used for a long time in dentistry and for good reason. Gold is extremely durable and is one of the least reactive of all the metals in the mouth. It is also more gentle to the opposing teeth making it well-suited for molars in patients who clench or grind. Due to gold’s strength it remains durable when thin, allowing for less reduction of the tooth and preservation of more healthy tooth structure. While gold is still one of the best crown materials, there are some drawbacks that are causing it to be used less and less. Gold is a very obvious crown and many patients don’t like the aesthetics of it. They would prefer for their teeth to look like they haven’t had a crown. Gold is also very costly these days, making it more cost prohibitive. It also conducts cold and heat more than other types of crown materials. Lastly, over time the gold can wear thin all the way to the underlying tooth structure.
• Porcelain-fused-to-metal: Porcelain-fused-to-metal or PFM crowns have been around for a long time and helped to solve the aesthetic challenges of the gold crown. Like gold crowns, they have a gold alloy substructure providing strength and durability, but porcelain is fused to it creating a more normal tooth appearance. The PFM crown is stronger than most porcelain crowns but as newer porcelains continue to be developed the gap is closing. Because of the metal substructure, light does not transmit through it as naturally as a full porcelain crown. Also, while the crown is strong, porcelain chipping or fracture can be common over the life of the crown, but the metal substructure is usually left intact making the crown still functional. The porcelain on the crown is harder and more abrasive than natural tooth structure and can cause wear of the opposing teeth. Also, the underlying metal can sometimes show at the gum line if any recession occurs around the tooth. Finally, because the crown is a combination of metal and porcelain, it requires more tooth reduction for adequate space for the crown materials. The PFM crown is still a good choice when being used as a bridge material for added strength and also when being used in conjunction with a partial denture. 
• All-ceramic or all-porcelain: Porcelain crowns are newer than gold and PFM crowns and are more aesthetic due to how they let light transmit more naturally through them. They are the most natural looking of all crown materials. Initially they were weak making them only suitable for the front teeth, but advancements in materials have made them suitable for most patients. Porcelain crowns can also be bonded to the tooth instead of cementing, making them stronger than they would be if cemented. Porcelain crowns are less thermally conductive, making the underlying tooth less sensitive to hot and cold. Porcelain crowns are harder than natural tooth structure and more brittle. Due to this, the crown material needs to be thicker for strength, requiring more tooth reduction. Also, while newer porcelain crowns are strong, in patients that have clenching or grinding habits they may still fracture.
• Zirconia and Porcelain-Fused-to-Zirconia: One of the newest crown materials is zirconia. Most people are familiar with cubic zirconia – sometimes used as a fake diamond in jewelry. In it’s other crystalline forms it takes on a stronger, whiter appearance that can be used for dental crowns. Zirconia is unique in that it has properties of both metal and ceramic. This allows it to be used by itself as a crown material or with porcelain fused to it as well. By itself, zirconia is very strong and resistant to chipping and fracture. Its strength allows it to be used thin like gold requiring less tooth reduction. Newer formulations are more aesthetic but still do not transmit light as well as porcelain or porcelain-fused-to-metal crowns. This makes them better suited for molars where aesthetics are not quite as crucial. Also, zirconia crowns while being very strong and hard, are not as abrasive to opposing teeth. This makes them a great option for molars in patients that clench or grind their teeth. When aesthetics are more of a concern, as in the front teeth, porcelain can be fused to a zirconia base making it closer in aesthetics to an all porcelain crown. Porcelain-fused-to-zirconia crowns require the same amount of tooth reduction as porcelain and PFM crowns.

What Steps Are Involved in Preparing a Tooth for a Crown?

Preparing a tooth for a crown usually requires two visits. The first step involves examining and preparing the tooth, the second visit involves placement of the permanent crown.

First visit: Examining and preparing the tooth

At the first visit in preparation for a crown, Dr. Goring may take a few X-rays to check the roots of the tooth receiving the crown and the surrounding bone. If the tooth has extensive decay or if there is a risk of infection or injury to the tooth’s nerve, root canal therapy may be recommended before proceeding with a crown.

Before the process of making a crown begins, Dr. Goring will anesthetize (numb) the tooth and the gum tissue around the tooth. Next, the tooth receiving the crown is filed down along the chewing surface and sides to make room for the crown. The amount removed depends on the type of crown used. If, on the other hand, a large area of the tooth is missing (due to decay or damage), your dentist will use filling material to “build up” the tooth to support the crown.

After reshaping the tooth, Dr. Goring will make an impression of the prepared tooth. Impressions will also be made of the teeth above and below the tooth to receive the dental crown to make sure that the crown will work in harmony with your bite.

The impressions are sent to a dental lab where the crown will be manufactured. The crown is usually returned in two to three weeks. If the crown is tooth-colored, Dr. Goring will work with the patient to select the shade that most closely matches the color of the neighboring teeth. During this first office visit Dr. Goring will make a temporary crown to cover and protect the prepared tooth while the crown is being made. Temporary crowns are usually made of tooth-colored acrylic or composite and are held in place using a temporary cement.

Second visit: Receiving the permanent dental crown

At the second visit, Dr. Goring will remove the temporary crown and check the fit and color of the permanent crown. If everything is acceptable, the new crown is permanently cemented in place. Often minor adjustments to the bite will be needed.

How Should I Care for My Temporary Dental Crown?

Because temporary dental crowns are just that – a temporary fix until a permanent crown is ready – Dr. Goring recommends a few precautions. These include:

• Avoiding sticky, chewy foods (for example, chewing gum, caramel), which have the potential of grabbing and pulling off the crown.
• Minimizing the use of the side of your mouth with the temporary crown. Shift the bulk of your chewing to the other side of the mouth.
• Avoid chewing hard foods (such as raw vegetables), which could dislodge or break the crown.
• Slide rather than lift out dental floss when cleaning between your teeth to avoid pulling off the temporary crown. 

How Long Do Dental Crowns Last?

On average, dental crowns last between 5-15 years. The lifespan of a crown depends on many factors including the amount of “wear and tear” the crown is exposed to, how well you follow good oral hygiene practices, and your personal mouth-related habits (grinding or clenching your teeth, chewing ice, biting fingernails, and using your teeth to open packaging).

How Do I Care for a Dental Crown?

While a crowned tooth does not require any special care, remember that simply because a tooth is crowned does not mean the tooth is protected from decay or gum disease. The most important way to care for a dental crown is to maintain excellent oral hygiene. For most people this would include brushing twice a day – in the morning after breakfast and at night before bed. Regular flossing between the teeth once a day is also important. Certain patients that are at higher risk for cavities may require a more rigorous oral hygiene program that Dr. Goring would outline specific to that patient. In patients that have grinding or clenching habits, it may be recommended to have a night guard made to help protect the teeth and dental bridge.