A New Technology for Crowns and Other Dental Restorations
For those looking to leave the dentist's office with same-day dental restorations such as crowns, learn what you need to know about the Computer-Aided Design and Computer-Aided Manufacturing (CAD/CAM) technology.
My dentist says he can fabricate my dental crowns in one day. Is this possible?
Yes. Your dentist will use a CAD/CAM machine, which stands for Computer Aided Design and Computer Aided manufacturing. This technology can scan and send virtual data of a tooth to a milling chamber where the final restoration is carved out of a solid block of zirconia or porcelain. CAD/CAM machines allow a crown, bridge or veneers to be fabricated while the patient remains in the dental office.
There are some criticisms regarding the quality of devices created using the CAD/CAM machine, but many of the latest milling technologies are producing excellent results. However, these machines are very expensive and typically are not cost effective for many dental offices. Another disadvantage is the availability of limited blocks of porcelain shades. So if the color is not ideal, the dentist may add surface stains to the blocks and fire them in the oven. This stain can wear off over time, so for very aesthetic crowns, it is preferable for the ceramist to layer color within the crown for the most natural and long-lasting look.
I had a milled crown put in, and it looks very dull. Is this normal?
Some zirconia crowns are very monochromatic, or one colored. These are very strong crowns, but are not always the most cosmetic.
My dentist says they use all milled fillings in their office, but they are a lot more expensive than a regular filling. What is the advantage of a milled filling?
Fillings that are too big will not last as long as a milled-precision filling. These fillings are called inlays or onlays, and they can be made to match the contours of your teeth better than a larger, traditional filling. Traditional composite "white" fillings will last between five and seven years if they are not in high-stress areas like the edges of front teeth. A well-milled and cemented restoration can last 10 to 15 years or longer. That being said, there is no guarantee as to how long any restoration will last. This is because a lot depends upon how they are maintained.
When should I consider a milled filling?
When the width of the filling is 50 percent or greater of the remaining tooth, a milled or cast-gold restoration is the best choice.
Using CAD/CAM technologies can allow a dentist to use a scanner and have the image sent digitally to the lab. This will lower lab costs and may help reduce the fees associated with these types of crowns.
How do CAD/CAM machines know how to build teeth to the correct sizes and shapes?
When a dentist prepares a tooth, they take photos of the teeth to upload to a computer. From here, the dentist can use libraries of teeth and occlusions to create a virtual representation of the desired tooth. The CAD software will allow the dentist to design the biting surface in three dimensions, the shape of the contacts with the adjacent teeth and the size of the teeth. The restoration design is then sent to the milling station where it will replicate the 3D design on the computer. The restoration will then be stained, glazed and fired in a ceramic oven before it is finished and polished.
What is a zirconia crown?
This is a milled crown made out of a zirconium oxide material that is strong, durable and metal free.
How long have these restorations been available?
CEREC (Chairside Economical Restoration of Esthetic Ceramics) restorations have been around for 20 years. They are present in more than 28 dental schools and are used by more than 17,000 dentists.
How long do CAD/CAM crowns last?
In a study at the University of Michigan, it was found that at the three-year mark, these restorations demonstrated a 100 percent survival rate. In a study at the University of Washington-Seattle, after evaluating 10,999 Lava zirconia crowns, there was a 99.2 percent success rate at seven years of service.
Are zirconia crowns made out of one solid block?
For back teeth where aesthetics are not as important, a solid zirconia crown may be used. These are called monolithic crowns, as they are made out of one material. They are indicated for people with limited room in the back of their mouths, people that grind their teeth at night and dark teeth that need to be covered so the underlying tooth structure can be blocked out.
The advantage of solid zirconia CAD/CAM crowns is that they have a high resistance to fractures and wear. They also have an excellent fit and require less tooth reduction than a traditional porcelain-fused-to-gold crown. There is less labor involved in making them, so they may be a more cost effective crown option.
