Crown Replacements

There are a variety of reasons a patient might need a crown replacement ranging from sensitivity and decay to cracks or chips in the porcelain.

Many people think a crown lasts a lifetime but it often does not last that long. A few things can happen:

1. The cement used to put on the crown can wash out and dissolve over time. This results in marginal breakdown causing decay and sensitivity. The crown may also just come off when eating something sticky. This can be the case with a lot of older crowns. The crown material might outlast the cement holding it on.
2. The other big reason is people chew on crowns every day so they are going to wear out. This results in separation of the porcelain from the base material or in the case of solid porcelain crowns, the material may just fracture away, exposing the underlying tooth. The tooth will then require a new crown using with stronger cement, or redesigned for more clearance and a better fit.

PREVENTATIVE MAINTENANCE 

A patient should try to brush and floss regularly because the margin on the crown extends all the way around the gum line. It is important to keep crowns clean and have regular hygiene visits so the crown margins will stay free of debris.

Patients should not bite hard on crunchy things like ice, popcorn kernels, crusty bread, and hard candy.

Wearing some kind of bite guard protection at night to reduce the force of grinding on the crowns can reduce a lot of problems and reduce the need for replacement.

If patients take care of their crowns properly, they can last 10 to 15 years and sometimes even 20 or 30 years.

IMPLANTS AND VENEERS 

Dental implants are a replacement for an entire tooth.  An implant is placed in a spot where there is a tooth missing due to trauma or planned removal. An implant is placed beneath the gum line into the bone and a crown is attached to the top of the implant. So to summarize, the implant is the part that goes into the bone and the crown is the part that goes on top. While the implant may last a lifetime, the implant crown may wear out and have to be replaced just as in natural teeth. Implants are very predictable and now considered the standard of care for tooth replacement as opposed to a bridge.

Veneers are basically a partial crown and they are typically placed on natural teeth. A veneer would not go on an implant because an implant requires a full crown. A veneer just covers the front half of the tooth. It is more conservative and is used to provide support for cracking and chipping as well as color changes, shape changes and length changes. While veneers are also a long lasting treatment option similar to full crowns, they also may need to be replaced depending on the patient’s hygiene and bite habits.

CAN CROWNS BE REPAIRED?

Repairs are not considered a long term fix. A temporary repair can be bonded to the ceramic but it does not last very long. There are rare situations where a repair may ne needed where the crown margin meets the tooth and the spot can be sealed as a temporary measure. Once a piece of crown comes off, the area can be smoothed off however, if it is in the aesthetic area (like the front of the smile) then the crown has to be replaced.

In general, once a crown breaks or starts to fail, it needs to be replaced.

REPLACING METAL WITH PORCELAIN 

Originally, all crowns were all metal or metal-based. The only way to have an aesthetic crown was to bond porcelain over the top. The metal underneath was for strength and the porcelain over the top was for the overall look. However, once the crown was chipped, it would reveal the metal underneath. Also, the gum line showed a gray or dark line. That was the metal showing underneath and it was not very aesthetic.

Patients that come in now with all metal crowns, or porcelain fused to the metal crowns, can usually change those out to porcelain. There are different types of tooth-colored porcelain materials available such as high-impact ceramics and cubic zirconia. They have a similar strength to metal.  Gold is very expensive so most people do porcelain and zirconia crowns which are just as strong and look like teeth.

TREATMENT PLANS 

There are full coverage crowns which cover 360-degrees all the way around the tooth down to the gum line. This treatment plan requires cutting down the tooth all the way around and seating the crown with traditional cement.

Partial crowns like veneers, inlays, and onlays require a different treatment plan. They are all ceramic and do not require as much tooth to be removed so more tooth structure can be preserved and the material can be bonded to the tooth instead of cementing it. This type of restoration is popular because patients and doctors understand it is important to try to preserve as much tooth structure as possible.

Some teeth require a foundation underneath them like a house requires a foundation. Sometimes teeth require a foundation because there is missing tooth structure underneath either from decay or fracturing. The treatment plan might involve a buildup underneath to support the crown better. The buildup would be done on top of the actual tooth itself because there is missing tooth structure and the crown needs something to grip on to.

PREFERRED CROWNS 

The most durable crown is a yellow gold crown, but nobody really wants those anymore. The reason yellow gold works so well is that it is kind to the opposing tooth and does not wear on the tooth that it is up against. The disadvantage is the cost and the dentist is required to make a precise preparation on the tooth.

Most dentists are comfortable doing full-coverage crowns even though they have to grind more of the teeth away. What is normally preferred is porcelain or tooth-colored for a more natural look. Both metal and porcelain are reliable and durable but porcelain is more popular. These are typically going to be cemented more traditionally and not bonded. Patients want something that looks tooth-colored so dentists are most often using high-impact ceramics and zirconia for their full coverage crowns.

Porcelain also has the option of not taking as much tooth away because the porcelain can be bonded to the tooth. So we are starting to see more partial coverage bonded crowns. This cannot be done with metal so ceramics are used for this procedure. Once bonded they can be as strong as metal.

FINAL THOUGHTS

In dentistry, advances in digital CAD CAM technologies, adhesives and materials allow for more conservative approaches to crowns. In the past, they were typically all full coverage and metal-based. Now dentists can do more partial coverage and non-metal based to preserve the tooth structure.

However, a higher level of skill is required by doctors that use these newer systems and new materials. Doctors need to advance their skills to meet the demands of the market. There is an organization called AACD (American Academy of Cosmetic Dentistry) and patients can go online and look at the credentials of doctors. A doctor that is credentialed with AACD is more likely to be skilled and experienced with the newer partial coverage porcelain bonding systems and materials.

Written by Cosmetic Town Editorial Team- MA

Based on an exclusive interview with John Weston, DDS in San Diego, CA