What is the purpose of a crown?
A crown is essentially a protective shield or a strong "suit of armour" placed over a damaged tooth. In many cases, when a tooth loses its enamel coating, is hollowed by extensive decay or a large filling cannot continue to support the tooth, the tooth is exposed to damage from external forces. This is where the crown comes in. While a crown does enhance the aesthetics of the tooth, it is important to remember that the crown is designed to surround the tooth entirely, protecting it from the outside forces.
The crown can be considered to surround the tooth, similar to how metal hoops encase a barrel to protect it from splitting. Similarly, the crown serves to protect the tooth from fracturing by encapsulating the tooth.
The crown serves to protect the tooth externally, thereby increasing the longevity of the tooth for years to come. Additionally, a crown is used to support teeth that have worn down over time, restore the tooth's chewing ability, and ultimately, restore a complete and healthy appearance of the teeth that provides self-confidence.
Features of Zirconia Crowns
Zirconium itself is a unique material. One of the key characteristics of zirconium is its 'smart' structure. This characteristic is referred to as transformation toughening in the field of materials science, but it can be described simply as a self-protection mechanism. Microscopic cracks that begin to form within zirconium are compressed internally by the expansion of the zirconium's internal structure preventing the crack from progressing further. Therefore, it is able to withstand wear and tear similar to a metal restoration, yet remains a ceramic.
Another positive attribute of zirconium crowns is their compatibility with the human body. Oral tissue adapts well to zirconium, whereas some metals are known to cause inflammation of the gums or other soft tissue irritation. Additionally, zirconium has excellent thermal insulation properties. For example, when consuming something extremely cold such as ice cream, or something extremely hot such as soup, the temperature is not transmitted through the crown to the tooth nerve, resulting in significantly less post-procedure sensitivity.
How long does a zirconium crown last?
The average lifespan of a zirconium crown is approximately 15-20 years, based upon clinical study data and patient follow-up reports.
With appropriate oral care practices and routine dental check-ups, along with an effort to avoid habits such as bruxism (teeth grinding), it is likely that this estimated life span will increase to a near-lifetime investment. A research study reported that the overall success rate of zirconia crowns was approximately 98% after five years.
One of the most notable advantages of using zirconia as a dental restorative material is that it has been shown to exhibit increased resistance to fracture compared to metal-supported porcelains and is unaffected by oral fluids. As a result, it is reasonable to conclude that the primary determinant of how long a zirconia crown lasts is the combination of zirconia's biologic durability and the patient's oral hygiene practices; in other words, a well-maintained zirconia tooth can maintain both aesthetic and functional properties for decades.
When reviewing statistical data, it is clear that the likelihood of experiencing a problem within the first 5 years is almost nonexistent. Ninety eight percent of all patients continued to utilize their crowns with the same degree of satisfaction as the first day after five years. This success rate remained extremely high through the tenth year as well.
It is essential to accurately understand the concept of "lifespan". The general understanding is that what fails is not the zirconium itself. Zirconium does not melt, rust or deteriorate in the mouth. Typically, when a crown is said to have "failed", the failure is due to something that occurred with the patient's own tooth or gum beneath the crown. For example, gum recession may occur over time, or a new cavity may develop in a location that was not adequately cleaned below the crown. The material is very resilient, and extreme force would typically be required to break it in a lab setting. Therefore, the response to the question "How long does it last?" is essentially, "As long as you take good care of it."
What can affect the lifespan of a zirconia crown?
Teeth grinding (bruxism): Teeth grinding is the number one enemy of all types of crowns. When people grind their teeth, whether awake or asleep, they apply massive amounts of pressure to their crowns and eventually wear down the material or loosen the cement that holds it in place.
Poor oral hygiene: As previously mentioned, poor oral hygiene is essential to the longevity of any type of dental restoration. While zirconium itself will not decay, the portion of your tooth below the crown will continue to decay as normal and will create a pocket between the tooth and the crown allowing bacteria to collect. Bacteria will begin to cause gum disease and eventually lead to the loss of the tooth and/or the crown falling off.
Biting hard objects: There are many different habits that patients exhibit that are detrimental to their zirconia crowns such as chewing ice, opening hazelnuts, and biting pens. All of these activities are attempting to push the laws of physics and should be avoided.
Incorrect cementation of the crown: If the crown is cemented incorrectly it could possibly come loose, causing damage to the surrounding teeth.
Consumption of acidic or sugary foods/drinks: Consuming acidic or sugary foods/drinks regularly can accelerate the breakdown of the cement and the crown itself.
What are the different types of crowns and their longevity?
Dentists think of material selection as a weighing scale. One side has durability, and the other side has aesthetics. To determine the placement of zirconia in the balance, we need to look at other materials that have been used for years.
First, we have to mention the Metal-Supported Porcelains (PFM). These are considered the "old-timers" or "workhorses" of dentistry. There is a metal framework in the middle with a layer of tooth-coloured porcelain outside. They are very durable and can last fifteen years or more. However, they have some drawbacks when it comes to aesthetics. They don't allow light to pass through like natural teeth. And it has been reported that as the gum recedes over time, the grey colour of the metal can be noticeable at the bottom of the tooth. It is noted that the greatest advantage of zirconium is removing the potential of metal visibility.
Secondly, there are the traditional full metal or gold crowns. Leaving aesthetics aside, they could be described as perfectly mechanical. Gold teeth are so biocompatible that they rarely fracture and are also capable of wearing down the opposing natural tooth. In addition, gold teeth can stay in the mouth for twenty, thirty years or even a lifetime. Since no one wants to see a shiny yellow metal on their front teeth today, this is an option relegated to historical records. Zirconium is viewed as being created to provide a white and natural alternative to the durability of gold.
Glass ceramic crowns (such as E-Max) are thought to be the epitome of elegance. They allow a tremendous amount of light to pass through, making it nearly impossible to tell the difference between these crowns and natural teeth. Beautiful things are accomplished on front teeth. However, their structures are more fragile than zirconium. It was determined that they are more likely to crack under the larger masticatory forces present in back teeth. Thus, zirconium enters the picture here, providing a beauty similar to that of glass ceramic crowns but with a structure many times stronger.
Types of Zirconia Crowns
There are different forms of zirconium that may be used depending upon patient needs.
Zirconium types include:
Monolithic Zirconium:
Monolithic zirconium is made from a single block of zirconium and is the strongest of all forms of zirconium. Because of the strength, monolithic zirconium is generally limited to use in the posterior regions of the jaw (backside) because it has a greyish matte appearance and chalky white colour. However, current aesthetics allow for monolithic zirconium to be used in anterior areas of the jaw (front side). It is the most popular choice for the majority of dentists for their patients that grind at night.
High Translucency (HT) Zirconium:
HT zirconium is a type of zirconium that allows for better translucency of light than monolithic zirconium. This makes it appear more natural and gives it a more realistic look compared to other dental restorations. High Translucency zirconium is also able to give a more accurate representation of the natural gradient that exists between the gingiva (gum line) and the surface of the tooth.
Multi-Layered Zirconium:
Multi-layered zirconium is considered an aesthetic advancement. Multi-layered zirconium is manufactured to represent the layers found on a natural tooth. Multi-layered zirconium allows for a natural looking color gradation of the tooth. This means the area of the tooth closer to the gingiva will be darker, while the tip of the tooth will be lighter. Because of the layered nature of multi-layered zirconium, it is able to reflect light in a way that is nearly indistinguishable from a natural tooth. Due to the aesthetics provided by multi-layered zirconium, it is safe to use on both anterior and posterior regions of the jaw.
Porcelain Fused to Zirconia:
Porcelain fused to zirconia provides a strong zirconium base with a layer of hand-layered porcelain on top for maximum artistic control.
Comparing the different types of tooth crowns and how long they last
The various types of crowns available by stating that each type of material has its own characteristics, which determine how long the material will continue to provide stability for the tooth.
Types of Crowns
Most common types of crowns include:
Monolithic Zirconium:
This is considered the strongest form of crown due to being made from a single piece of zirconium. The advantage of monolithic zirconium is that since the entire crown is created from a single block of zirconium, there is no chance of porcelain cracking or peeling away. Monolithic zirconium crowns are expected to last 20 years or longer.
Layered Zirconium:
Layered zirconium crowns feature a strong ceramic interior, covered with layers of aesthetically pleasing porcelain. Aesthetics are excellent for layered zirconium crowns.
Metal-Supported Porcelain (PFM) Crown:
PFM crowns are also described as having an exceptionally good strength and longevity; however, the metal-supported porcelain crown falls behind zirconium in the area of aesthetics, and PFM crowns are subject to discolouration near the gumline.
Gold Crown:
Although gold crowns are the strongest and best in all areas except for aesthetics, they are not used for cosmetic purposes today because of their appearance.
Glass Ceramic:
Glass ceramic crowns are known to retain the "kingdom of aesthetics" for the front teeth, but glass ceramic crowns do not instill as much confidence as zirconium for back teeth.
Temporary Composite Crowns:
Temporary composite crowns are well-known as short-term solutions, either for financial or for temporary needs. Temporary composite crowns tend to darken quicker than other types of crowns, and they tend to be less durable.
Frequently Asked Questions
Can zirconia crowns last forever?
While we cannot give you a definitive "yes" to this question, we believe we have to say that in medicine there is no such thing as "for ever". Most statements claiming "lifetime warranty" are believed to be marketing tricks. However, zirconium is considered to be one of the most durable materials available today. Zirconium is also resistant to dissolution and corrosion in the oral cavity. Crowns made from zirconium can easily last 15 to 20 years when properly maintained. Replacement is rarely because the material has deteriorated but rather because of ageing of the gums or other structural changes within the mouth.
How long do zirconia crowns last on front teeth?
Because front teeth are subjected to less masticatory pressure than the back teeth, crowns placed on front teeth generally last longer. There are many patients who have had zirconium crowns placed on their front teeth for over twenty years. When crowns are changed on front teeth, it is usually not because of cracking or breaking, but rather because of aesthetic reasons due to recession of the gum over the years.
Are zirconia crowns suitable for all teeth?
Yes, it is said that they can be applied to all teeth without hesitation. As it is known that there are different types of zirconium too. It is said that a customised solution can be developed for each area by using the harder and more durable type for back teeth and the more transparent and aesthetically pleasing type for front teeth.
Can zirconia crowns be whitened?
No, it must be said that it is impossible to whiten zirconia crowns. Whitening gel lightens the colour by penetrating the pores of the natural tooth. However, it is observed that zirconium is a non-porous ceramic; therefore, the colour of the zirconium does not change with externally applied gel. Therefore, it is stressed that a careful choice of colour for the crown must be made. If whitening of the teeth is wanted, it is recommended that the whitening of the teeth be performed before the crowns are manufactured so that the colour of the crown can be adapted to the new whiteness.
Please contact us for more information.