Dental Crowns: Types, Purpose, and Cost

A dental crown is a tooth-shaped "cap" that is placed over a tooth.

• The anatomy of a tooth can be divided into two basic parts -- the root and the crown.
• In a person with healthy gums and bone, the root of the tooth is covered by the gums and bone.
• The crown is the part of the tooth visible in the mouth, above the gum line on lower teeth and below the gum line on upper teeth.
• A cemented restoration that partially or completely covers the outside of the tooth is referred to as a dental crown or cap.

In this case, veneers and crowns have been used to correct multiple problems including chipped teeth, an uneven gum line, and tooth discoloration.

The cost of getting a crown can vary widely depending on the materials used and the expertise of the dentist and lab technician. Insurance will typically cover part of the expense, but the amount varies with each carrier and plan. A person should expect to pay anywhere between $600 and $2,000 for a crown or veneer.

Crown preparation: This is the design of the tooth after it has been shaved down to allow room for a crown. The preparation design depends on the material that the crown will be made from, previous fillings, fractures, and root canal therapy. There must be enough tooth structure for the crown to adhere onto.

Margin: This is the edge of the crown that meets the prepared surface of the tooth. This needs to be smooth with no gaps or ledges.

Cusps: These are the raised or pointy parts of a toothn that are the primary tools for tearing and chewing food. When a cusp has been damaged from a cavity or fracture, the tooth needs a crown to prevent further damage.

Partial crown/onlay: This is a restoration that only covers some of the cusps of the tooth, but not all of them. This restoration is chosen as a conservative measure to preserve as much tooth structure as possible. When conditions allow, this is the preferred type of crown restoration.

Dental veneer: Porcelain veneers are partial crowns that cover only the front and biting edge of teeth. These all-ceramic restorations are usually placed on front teeth to change the color or shape of teeth or add symmetry and balance to a smile. Since they are sometimes placed on crooked teeth, treatment with veneers has sometimes been referred to as "instant orthodontics."

Temporary/provisional: This is a temporary crown that is placed on the tooth while waiting for the final crown to be made by the dental lab. Temporary crowns shouldn't be left on a tooth for very long because they are made of weak materials and cemented with weak cement that doesn't seal the tooth for very long. Occasionally, a temporary crown will purposely be left on for a prolonged period of time by the dentist to make sure it becomes free of pain or other symptoms.

There are a variety of situations that require a tooth to be restored with a dental crown. The following are the most common:

Large filling: When a tooth has a cavity or fracture that involves half the width of the tooth or more, it needs to be covered with a crown. This is because the remaining tooth around the large filling is so weak that it is prone to fracture. Sometimes a large filling that has been in the mouth for a while will need to be replaced with a crown because the tooth shows signs of stress and cracks around the filling.

Root canal: Root canal treatment leaves the tooth hollowed out and predisposes the remaining tooth to cracking. So, a tooth that has had a root canal almost always needs to be restored with a crown immediately to prevent it from fracturing.

Cracked tooth syndrome: This is a condition whereby a patient has fractures inside a tooth that cause pain when it is chewed on a certain way. Chewing produces stress on fracture lines that make it feel like it is splitting apart. A crown will hold the tooth together and redistribute the stress evenly throughout the tooth, eliminating the pain in most instances. In these situations, it is best to leave a temporary crown on for a while to make sure the pain goes away and the tooth doesn't require a root canal.

Broken cusps: Cusps frequently break off of teeth due to trauma or large existing fillings. Since the cusps are the part of the tooth that take the most stress during chewing, they need to be completely covered or the tooth or filling will keep fracturing. Sometimes the tooth breaks all the way to the bone, and a crown-lengthening procedure is necessary. This means the bone and gums need to be trimmed down below the edge of the fractured part of the tooth so the margin of the crown can be placed on healthy, strong tooth structure.

Excessive wear of teeth: If a person has a habit of grinding their teeth, the teeth will become shorter over time. The teeth can also wear away due to acid erosion caused by gastrointestinal acid reflux (GERD), bulimia, or an acidic diet. Sometimes, the enamel will wear away completely, leaving small, soft teeth. Over time, the bite can collapse and the only way of restoring the teeth to normal size is by covering the teeth with crowns.

Undesirable appearance of teeth: Teeth that have an unacceptable appearance due to color, shape, or spaces between teeth can be made to look very natural and beautiful with crowns. Dental veneers are a very effective and conservative way of enhancing the look of the front teeth. They can be made to look very natural, and sometimes they don't even require preparing or shaving the existing teeth.

Other: Crowns are placed on dental implants to restore spaces left from missing teeth. Another way of filling these spaces is with dental bridges, which are made from crowns on the teeth next to the spaces attached to fake teeth in the middle. If teeth are loose, crowns can be placed on multiple teeth and splinted together to provide more stability.

Crowns can be made out of a gold alloy, some other metal alloy, stainless steel, all-porcelain/all-ceramic, composite resin, zirconia, or porcelain on the outside fused to metal or zirconia on the inside.

In some cases, ceramic crowns can be made with CAD/CAM technology by milling the crowns out of blocks of porcelain in the dental office, without the need for temporaries or a dental laboratory. There are advantages and disadvantages to all of the types of dental crowns.

• Stainless steel crowns are preformed crowns used to cover baby teeth for children.
• Gold dental crowns have traditionally been the most durable and require less of the tooth to be removed or shaved down.
• The primary advantage of porcelain crowns is their esthetics, while newer types of ceramic crowns have become increasingly more durable.

The dental crown procedure first involves numbing the tooth with local anesthesia. If the tooth has been fractured or had a root canal treatment, it will first need to have a buildup -- a filling that restores enough of the tooth for the crown to hold onto. Then the tooth is shaved down to make room for the crown, and an impression is made of the prepared tooth with a putty-like substance or a digital scanner. The dentist will then determine the shade of the patient's teeth using a shade guide or take pictures of the teeth to help the lab technician make crowns that will match the rest of the patient's teeth. A temporary crown is made from a resin or acrylic material using a molding or stent of the original tooth. This temporary crown is cemented with temporary cement so that it can come off easily once the permanent crown is ready.

Usually a few weeks after a temporary crown, the patient returns for a second visit. During this visit, the tooth may or may not need to be numbed again and the temporary crown is removed. The permanent crown is placed on the tooth and inspected for acceptable fit, bite, and smooth margins. After any necessary adjustments have been performed, the crown is cemented with a permanent cement or dental glue.

The tooth being restored is numbed so that it isn't painful during the crown preparation. This requires a shot in the gums of lidocaine or another local anesthetic. After the procedure is over and the anesthesia has worn off, the patient may feel some sensitivity with the temporary crown or some soreness in the gums around the tooth. The pain is very minimal though and shouldn't last long.

If it is possible, it is best to wait until after pregnancy for elective dental procedures to minimize stress on both the mother and baby. Getting crowns is often the result of a sudden fracture or other unavoidable situation though, and treatment may need to be immediate. The materials used for crowns are all safe during pregnancy, so when necessary, it is possible to get a dental crown during pregnancy.

Crown preparation sometimes places a lot of stress on a tooth, causing the nerve to become irreversibly inflamed. If this happens, the tooth may need root canal treatment.

Dental crowns should last on average from 10 to 20 years. Crowns are still subject to fracture and cavities, so it is important to take extra care in brushing and flossing around crowned teeth to prevent them from needing replacement too often. When all-ceramic crowns or veneers are present, it is often advisable to wear a mouth guard to protect the porcelain from fracturing and prolong the life of the crowns.