Crowns
There are two main types of dental crowns: temporary and permanent. Permanent crowns are what most people know as dental crowns or caps.
As the name suggests, temporary crowns are intended for short-term use only. Temporary crowns are made from plastic resin during the appointment, are bonded to the tooth with temporary cement (so they can be removed at a later date), and are used in all sorts of dental treatments. Many treatments require that the patient leave the dental office with a drilled tooth while the dental laboratory makes the final dental appliance. Since the patient cannot leave the clinic with drilled teeth, temporary crowns are made that fit over the tooth to provide normal appearance and function for the patient. Once the final prosthesis is fabricated, the temporary crown is removed and the final product is inserted.
Permanent crowns are similar to the temporary crown, but made of different material and with more care. Instead of plastic resin, permanent crowns are made from metal and/or porcelain to provide a more natural appearance and last for decades. Unlike temporary crowns, the permanent variety are fabricated at a dental laboratory (not beside the dental chair) and placed in the mouth at the next appointment.
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Permanent crowns are made from one of three types of material: all metallic, all porcelain, or porcelain-fused-to-metal. Each has its advantages and disadvantages that you need to be aware of prior to making your decision.
All metallic crowns are made from gold or other metal alloys, such as palladium or nickel-chromium. Metallic crowns have many advantages over other crown types; they wear down opposing teeth less, withstand biting and chewing forces best, rarely chip or break and less tooth structure needs to be removed for them to fit the tooth. Unfortunately, they are metallic in color but are a great choice for back teeth such as molars that are rarely seen when you smile or speak.
All-ceramic or all-porcelain dental crowns provide the best natural color match than any other crown type and may be more suitable for people with metal allergies. However, they are not as strong as porcelain-fused-to-metal crowns and they wear down opposing teeth a little more than metal or resin crowns. All-ceramic crowns are a good choice for front teeth, but no matter what your dentist tells you, modern all-porcelain crowns cannot withstand the demands of being placed on molar teeth.
The most popular choice for dental crowns is the middle-road option of porcelain-fused-to-metal crowns. They can be color matched to look like natural teeth (unlike all metallic crowns), however they do not wear down opposing teeth, chip or break like all-ceramic crowns. However, sometimes the metal underlying the crown’s porcelain can show through as a dark line, especially at the gum line and even more so if your gums recede. These crowns can be a good choice for front or back teeth.
Dental crown procedure
The entire dental crown procedure usually runs along two dental appointments spaced a week or two apart. During the first appointment you are clinically assessed and the tooth is prepared. After the dental laboratory has fabricated your crown, it will be fitted and inserted in the second appointment.
At the first visit, (1) your dentist will use x-rays and other methods to assess the roots of the tooth receiving the crown. This is to ensure that the roots are healthy – there is little point in placing an expensive crown on a tooth that fails a few months or years later because the roots were too weak to support it. A root canal treatment may be performed first if your tooth is decayed and there is a risk of infection to the tooth’s pulp.
Next, your dentist will provide local anesthetic to numb any sensation to the tooth and nearby gum tissue. The tooth is then wedged to separate it from nearby teeth, and (2) its surface is systematically reduced using various drilling burs. This reduction in enamel is to ensure that there is room for the future dental crown. The amount removed depends on the type of crown used – all metallic crowns require the least and all ceramic require the greatest reduction. If 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, (3) your dentist will use impression paste or putty to make an impression of the tooth to receive the crown. The impression is sent to a dental laboratory where your crown will be manufactured to exactly fit. If you have chosen to have porcelain on your crown, you and your dentist will choose the best shade and color at this point.
During this first office visit, your dentist will make a temporary crown to cover and protect the prepared tooth while the crown is being made. Temporary crowns usually are made of acrylic and are held in place using a temporary cement.
For the second dental visit, one or two weeks later, your temporary crown will be removed, and the permanent crown will be placed. Your dentist will check its fit and color, and only after everything appears correct, will it be cemented permanently in place.
Color selection process
During your first dental visit, you will have to choose the color of the future crown. Most patients are quick to select the whitest shade possible, only to realize their blunder afterwards.
It is important that the chosen shade blend with your remaining teeth. Selecting a shade that is pure white, but which doesn’t fit your profile, only helps to identify the crown. The goal for everyone is to achieve his or her individual optimum whiteness while still looking natural.
When selecting shades, do so under natural light. Artificial room lighting often changes how a shade truly appears. Teeth are not monochromatic, so more than one color is used in making crowns. If needed, ask whether the dental laboratory offers custom staining – this helps to make them appear authentic, but for an added cost.
There is no one standard system in the dental field to measure and determine tooth color. The most often heard about, however, is the Vita shade guide. This guide divides tooth color into four basic shade ranges. The guide accommodates for the fact that the front teeth are typically the whitest, and the remaining teeth are more stained and darker as they advance backwards to the molars. Most dentists will show you a shade chart (like the above mentioned Vita Shade Guide) for you to pick from. Other considerations are your complexion, hair color, the color of your natural teeth and even your eye color.
Remember that teeth whitening does not change the color of dental crowns. If you plan on bleaching your teeth in the future, either choose a lighter shade for your crown, or more sensibly, have your crown placed after you have bleached your teeth.