A crown is a restoration that covers a tooth to restore it to its normal shape, size, and to improve the appearance of a tooth. Crowns are indicated when a tooth is broken down, cracked, or fillings that are too large.
To prepare the tooth for a crown, it is reduced with a diamond bur so that a crown can fit over it. An impression of the teeth and gums is made and sent to the lab for the crown fabrication. A temporary crown is fitted over the tooth until the permanent crown is ready. On the next visit, the dentist verifies the fit and contour of the crown and, if it is satisfactory, it will get cemented onto the tooth.
If properly fabricated, crowns can be as natural looking as a real tooth. To accomplish this, two criteria will need to be met. First criteria: the tooth preparation will need to be very precise, providing the technician with proper reduction and shape. Second criteria: having a technician who is excellent at fabricating a crown. Achieving even porcelain thickness, incorporating different colors into the porcelain layers, and giving it a proper shape is not an easy task. Technicians who are very talented to accomplish this are known as a master ceramist. Hiring such technicians will significantly increase the lab fees and depending on the crown fee that is typically dictated by a dental insurance company, it is not feasible to use a master ceramist.
The longevity of any type of restoration depends on many factors. Crowns are no different. Crowns can last anywhere from a couple of years if the oral hygiene is poor, to more than 10 years if oral hygiene is excellent. Material selection, how well the tooth was prepared, the skills of the technician, mastication forces, diet, oral hygiene, etc. However, statistically speaking crowns last 7 to 10 years.
To prevent fracturing the crown, avoid chewing hard foods and teeth grinding. Besides visiting your dentist and brushing twice a day, cleaning between your teeth is vital to your crown. Floss is an important tool to remove plaque from the crown as they have a tendency to accumulate more plaque at margins. Plaque in that area can cause dental decay and gum disease.
A crown covers every tooth cusp and an onlay covers some of the cusps. What is the benefit? A crown will require more of the tooth to be trimmed away. An onlay is more conservative and preserves as much of the natural tooth structure as possible.
Onlays are more technique sensitive to prepare and cement. The dentist would need to spend extra time and care to maximize the longevity of the restoration. Temporizing the tooth could be a challenge as well. Unfortunately, most insurance plans do not cover it. As a result, many patients choose crowns over onlays.
The cost of your crown depends on multiple factors. Not all crowns are created equal. It all starts with how much care the dentist takes to prepare the tooth for a crown. Just as with anything that depends on hand skills, a certain amount of time is needed to make sure the proper amount of tooth structure is removed, the proper shape and taper are created, and an accurate tooth impression is obtained. To accomplish this, the dentist needs a fair amount of time and the fee will reflect the time spent on the appointment. Typically, a lower crown fee will mean that your appointment will be shorter and a less expensive lab is utilized for fabrication. You should still get a well-fitted crown but the aesthetic and longevity may be average at best.
In addition, the selection of a lab technician is very crucial as far as the quality of the crown is concerned. A good technician charges a fair amount to make you a well fitted and pleasant appearing crown.
Many newer materials have been introduced over the last few decades. The type of material depends on each case. Sometimes your dentist has no choice but to select a specific material, and other times it depends on the circumstances and patient’s expectation. For example, if longevity is your main concern, a gold crown is your best bet. If aesthetic is on top of your list, a porcelain crown is a much better choice.
Pure gold is too soft to withstand biting forces; therefore, a mixture of other metals are added to make it stronger. The gold content can vary greatly. Typically the higher gold content will give you a better crown with a deep rich yellow color.
Gold crowns have the longest lifespan compared to other types because gold does not corrode and the margins can be exceptionally well adapted to the tooth. Gold crowns do cost more due to the added gold content which depends on the current market cost of gold. As usual, the skills of the dentist and lab technician will affect the fit of the crown and its longevity.
Until a decade ago, these were the most common type of crowns on the market. The crown consists of a metal substructure that can vary from a non-precious metal all the way to gold. Then layers of porcelain are stacked and backed on top of the metal. The end result is a very well fitting crown with a strong inner structure and an outer natural appearing porcelain structure that should match your tooth color. The fabrication is technique sensitive and requires an experienced technician. The metal has to have the proper thickness, proper shape, proper taper, and the outer porcelain layer needs to have a specific thickness. If anyone of these is less than ideal, the crown will not have a natural look and the porcelain will have a higher chance of fracturing. This is where paying a bit more for your crown will make all the difference.
One of the most common issues noticed by patients is the dark line at the margin. This is the metal that cannot be covered with porcelain. As your gum recedes the line becomes more obvious. There are certain ways to minimize the line. For example, gold substructure can be used instead of the typical darker metal. The yellow color is more natural and blends much better with the tooth which is yellower at the gum line. However, this will add to the overall cost.
The main disadvantage of porcelain is that it is brittle. Other than that, porcelain is very appealing and blends very well with teeth resulting in great aesthetic. There have been many different formulations to combat the brittleness of the material. The newer types have been promising and provide the strength that was missing to withstand mastication forces. Compared to metal/porcelain crowns, these are more technique sensitive when it comes to trimming the tooth. The dentist does need to pay attention to have the proper amount of tooth reduction. Also, the cementation is very technique sensitive and will greatly affect the longevity of your crown. Other factors play a role as well but it all starts with proper case selection.
As mentioned above, porcelain crowns are bonded to the teeth. Your dentist needs to judge if each situation is a suitable case or not. The benefit of bonding is that the added retention allows the tooth preparation to be much more conservative. Last but not least, the lack of metal will give you the best aesthetic at the margins, completely eliminating the dark lines associated with other crown types.
Full Zirconia crowns were introduced in 2009. These are very popular among dentist. Like any other crown types, these have their pros and cons. Zirconia crowns are made from a single layer material that is digitally designed, milled, and processed in an oven. As a result, Zirconia is very strong and very unlikely to fracture. Being digitally designed ensures that the crown has the proper thickness in all areas. The fit is very good if the dentist provides a well-prepared tooth with smooth finish lines.
You may ask why this crown type has not replaced all other types. Zirconia does not have a long track record. There is virtually no research done on zirconia. In the past, there have been many materials used that eventually proved to be less than ideal and are no longer utilized. Time will tell how promising zirconia will be.
As strong as zirconia may be, the aesthetics are not that great. Zirconia is generally white and has a lifeless opaque appearance. They are acceptable for back teeth that have less visibility but not so ideal for the front teeth. Surface stains can be applied to make them blend with the natural teeth but any applied surface stain will eventually come off and expose the true color of the zirconia. Have you ever noticed how your crown may appear so much whiter than the rest of your teeth after few years? Most patients believe that their teeth have darkened over the years but chances are that surface stains were used.
It depends what you mean by being the best. Each type has its advantages and disadvantages. There is no such thing as a best crown material. Every case is unique and needs to be evaluated. Talk to your dentist about the different options. He/she should be able to make that determination for you. Keep in mind that regardless of what material is used, unless your dentist and the technician pay attention to the preparation and fabrication process, the end result will not be great even if the proper material is selected.