Zirconia restorations are stronger, more durable and less abrasive than other ceramics.
Innovations in zirconia manufacturing have rapidly propelled zirconia to the go-to restoration material for many dentists. Zirconia tends to be stronger, more durable and less abrasive than other ceramics, and it’s now also being increasingly used for its aesthetic properties.
Dr Lawrence Neville is the Practice Owner and Principal Dentist at Spa Dental in Sydney. He has performed over 30,000 hours of clinical treatment during more than 12 years as a practising dentist. He now uses zirconia for the majority of his restoration implants for its superior strength and durability. However, he says there are some critical things dentists should know to ensure successful zirconia preparations.
Here, he reveals the key advantages of zirconia restorations, when to use zirconia restorations and when not to, and shares the five-step preparation workflow he uses for zirconia restorations.
Dr Neville points out that there are two key reasons why he chooses to use zirconia for dental restorations — strength and wear.
“The main reason we use zirconia is for its strength. It’s a really strong all-ceramic material,” he says. “The second advantage is its really low-wear properties. There’s a common misconception that because zirconia is really strong, it will wear down other teeth. But that’s completely wrong. Zirconia’s strength means the wear is actually a lot lower than a lot of the other ceramics.”
Traditional ceramic crowns are only layered on the surface, which leaves them vulnerable to unsightly chipping.
Avant has partnered with Aidite to solve that problem. Aidite’s innovative 3D Pro Zir uses a gradient layering manufacturing process for chip-proof construction. This achieves a new level in bio compatibility with strength at the incisal layer very similar to the strength of natural enamel — without the excessive abrasiveness of older products.
This means that 3D Pro Zir wears at the same rate as natural enamel, and is virtually chip proof at around 10 times the strength of traditional layered ceramic.
It is also very low-abrasive and wears at a similar rate to natural enamel while protecting adjacent dentition from abrasion. And its similarity to natural enamel also makes Avant Aesthetic Zirconia suitable for hand polishing and grinding for chair-side adjustments.
However, not all zirconia is created equal. That’s why Dr Neville says it’s important to have a conversation with your dental lab about the types of zirconia they are using.
“There are hundreds of types of zirconia, and there’s actually quite a lot of variability between them,” he explains. “One of the key things some dentists probably don’t really do very well is communicating with their dental lab about what type of zirconia the lab is using. Most dentists will simply order a zirconia crown, but they don’t know the type of zirconia they are using.”
Dr Neville is right on the money. There are indeed hundreds of zirconia brands on the market today, and dental zirconia is produced by five or six manufacturers around the world. It is often rebranded and on-sold by many different zirconia brands, so it can be difficult to identify the source and quality of zirconia your lab is using.
Avant solved this problem by partnering with Aidite — the leading zirconia producer in the world. The company operates a world-class facility in China, and exclusively uses high-quality dental zirconia sourced from the Tosoh Corporation in Japan. That is where all Avant Aesthetic Zirconia comes from.
Tosoh Corporation uses the latest hydrolysis processes and nano-technologies to produce the ultimate zirconia powder. The globally-trusted brand maintains complete control over the production process to ensure the highest purity and quality.
Uniform dispersion with superior sintering properties produces a fine crystal grain structure that achieves superior strength, fracture toughness and resistance to wear and ageing.
Dr Neville says zirconia has rapidly evolved over the last 10 years, and is now his material of choice for a wide range of restorations. But he points out that zirconia is not always his go-to material. He says it’s important to understand when zirconia is the best choice, and when it’s not.
“Most of our restoration implants are now made with zirconia,” he explains. “Zirconia is excellent for back-of-the-mouth posterior crowns. It also tends to be a good choice for single crown implants. You can also use zirconia for bonded bridges, and for more traditional bridges with abutments on either side.”
Dr Neville adds that while it is possible to use zirconia for inlays and onlays, it’s not necessarily his first choice of material.
“It’s a common misconception that you cannot use zirconia for inlays and onlays. You actually can use it. However, the preparation for zirconia inlays and onlays is very technique specific, so it would be my second choice in those cases. But if the dentist is comfortable with the preparation technique, zirconia can certainly be used for inlays and onlays.”
It’s also critical to note that undercuts or gutter preparations are unsuitable for zirconia restorations. Likewise, 90° shoulder and parallel wall preparations, and sharp incisal or occlusal edges are also unsuitable for zirconia restorations.
However, new developments in aesthetic zirconia are making it an increasingly attractive material for cosmetic work. It is now often used in veneers, but Dr Neville says it remains something of a balancing act.
On the plus side, he explains, new multi-layered monolithic zirconias offer higher levels of translucency, which translates to better cosmetic outcomes.
“The advantage of zirconia with some types of veneers is the brightness you can achieve with them. So if you have a patient who wants really bright, white veneers, zirconia is a good option.
“But as the translucency increases, the strength of the zirconia decreases. New monolithic zirconias have increased the strength of the material for aesthetic use, so zirconia veneers are strong and can be done quite well these days. But it’s still a balancing act. For that reason, zirconia is probably still not our first choice for veneers.”
While that’s certainly the case with many types of zirconia, Avant’s aesthetic zirconia is a little different. Ceramic is traditionally added to zirconia to increase its translucency. However, this process reduces the strength of the final product. Fortunately, our zirconia supplier — Aidite — has solved this problem. They are able to achieve 57% translucency with no added ceramic.
Aidite 3D Pro Zir uses multi-gradient layering manufacturing to achieve an industry-leading gradient colour transition.
This, along with a 16-shade colour matching system, means we can now deliver a completely new level in personalised aesthetics to match the product’s vastly superior strength.
It all comes down to the next-generation manufacturing process. Uniform two-way dry pressing ensures stable density and performance, and isostatic pressing creates an ultra-high isotropic pressure state. High temperature crystallisation is then achieved with step-by-step heating at a homogenous temperature field.
That is a massive step forward in the development of aesthetic zirconia for cosmetic use.
The right zirconia preparation is crucial to reduce chair time, and will help ensure you avoid fractures and remakes, and achieve the greatest patient satisfaction.
At Avant, we pride ourselves on communicating any issues or irregularities with your preparations and impressions. If problems are identified our technical team will contact you to discuss the most appropriate solution for each unique case.
We’ve created these useful zirconia preparation guidelines to avoid potential issues and wasted clinical time
Dr Neville explains that there are three key considerations dentists should think about when assessing patients for a possible zirconia restoration.
First, identify the position of the restoration in the mouth. Then consider the aesthetic goals for the treatment. Finally, examine the condition of the surrounding teeth.
“First up you’re looking at whether the restoration is at the front of the mouth or at the back of the mouth,” Dr Neville says. “Next, you’ll want to identify whether the restoration is aesthetic or not. Even if the restoration is at the back of the mouth, is the patient expecting a perfect colour match? In other words, how aesthetically driven is the patient, and how difficult will it be to match the colour?
“After that, you’re looking at the condition of the tooth and the surrounding teeth. Is the opposite tooth very worn? Does it have cracks? Why does the tooth need a crown in the first place? Are you replacing a big filling, or a crack? As far as possible, you’ll want to establish what has happened to the tooth in the past. That will determine what material you’re going to use.”
The correct tooth preparation is critical to the success of any zirconia crown or bridge restoration. If you don’t get it right, the crown or bridge will likely lack the proper retention, strength and wear resistance.
Once you’ve identified that zirconia is the best material to use for the restoration, it’s time to prepare the tooth. Dr Neville says it’s critical to determine the material type before moving onto tooth preparation because zirconia restorations require specific preparations to achieve optimal strength.
“Zirconia preparations generally need 1.5mm of clearance from the occlusal surface. That’s typically a little more than other ceramics,” he explains. “So if you decide to use zirconia after preparing the tooth, there’s a chance you may not have created sufficient occlusal clearance.”
Occlusion is a critical factor. They must be sufficiently spaced to allow rapid tooth excursions, otherwise you’ll risk putting too much stress on the opposing tooth.
Dr Neville cites a 2016 study that measured the strength of zirconia restorations at 0.8mm and 1.3mm of occlusion clearance. He says the study found there was a significant difference in strength between the zirconia that was under 1mm and over 1.3mm.
“The strength of the material really ramps up above 1.3mm,” he says. “That’s why we say zirconia should be 1.5mm, because you give yourself a little bit extra on top of that 1.3mm. That’s the key to zirconia prep.”
However, zirconia can be used in a much thinner layer at the lingual surface than other ceramics. “When it comes to load on the back of the lingual surface, we can bring it down to almost 0.5mm,” Dr Neville explains.
“Then we’re also making space for the ceramic on the surrounding tooth surface as well. That essentially lets the crown slide on top of the tooth. Traditionally that’s called shaving the tooth down.”
The importance of smooth edges in your tooth prep also cannot be understated. Smooth chamfer edges reduce stress on the crown and prevent fracturing.
Your dental lab should design broad contact areas on your crowns to prevent food impaction and the formation of caries. In order to achieve this, the path of insertion must be ideal with adjacent teeth.
Impressions — physical and digital — must show margins. Using a digital scanner will help you achieve the best outcome.
Dr Neville says tooth preparation can generally be completed with or without a prep guide, depending on the experience and preference of the dentist. “With experience, you can prepare the tooth without a prep guide. But if you do want guidance on how much you’re prepping, you can use a prep guide. You can make one yourself in your practice with some putty, or if you take a scan I’m sure your lab technician can help you make a prep guide.”
It’s also important to note that there are some subtle differences in how to prepare an anterior zirconia crown versus a posterior zirconia crown.
How to prepare an anterior zirconia crown
How to prepare a posterior zirconia crown
Once the tooth is prepared, Dr Neville takes digital scans for the dental lab to use to design and manufacture the zirconia restoration product. He says the scan also provides instant feedback on the success of the tooth preparation.
“We are fully digital and I find an advantage scans have over manual impressions is that the scan gives me instant feedback on the preparation. It will show me if I need to prepare an area of the tooth a little bit more, or conversely, if I’ve prepared the area a little bit too much. That feedback is very helpful for continuing to develop your tooth prep skills.”
Of course, the scans will also serve as a reference guide for your lab to design and manufacture the zirconia crown or bridge.
At the dental lab, a holistic digital system is used to design, mill, grind, stain and glaze the dental product. This ensures a faster, more cost effective, accurate and personalised outcome for each and every patient.
In the meantime, says Dr Neville, the dentist will usually put in a temporary crown that is usually made chair-side.
Shade matching is another important aspect of the zirconia preparation process, particularly in aesthetically-driven cases. Your lab should provide critical assistance with this, and will need as much information as you can provide.
“When it comes to shade matching, photos and as much information you can give the lab technician is important,” says Dr Neville. “That might include noting down any specific parts of the tooth that might be a different colour, and even drawing diagrams can help with that. The patient can also go and see the lab technician so they can get their own eyes on it as well.”
Dr Neville offers a warning about using potentially inaccurate shade matching guides provided by some dental labs.
“Most labs use a shade guide that’s made from plastic, not the actual zirconia material they are using,” he says. “Avant has a massive advantage in that area because Avant’s shade guide is actually made from the zirconia material itself. So you’re getting a like-for-Iike comparison, which should give you a much more accurate shade match.”
Avant Aesthetic Zirconia also takes shade matching a step further. With traditional multi-layering manufacturing there are visual steps between shades. However, our gradient-layer manufacturing removes those visible steps to create much smoother and more gradual transitions between shades.
Dr Neville adds that one of zirconia’s disadvantages can actually be used as an advantage in certain cases.
“Zirconia traditionally wasn’t translucent, which means the colour of the tooth underneath cannot shine through. So one of the advantages of zirconia over other ceramics is that you can use it to block out a discoloured tooth or a dark stump underneath. One of the reasons we would use zirconia at the front of the mouth is if someone has had trauma to the tooth or if they have a very dark tooth. We can use zirconia to block it out.”
Once the zirconia restoration product comes back from the lab, you should be ready for bonding. Dr Neville says there has been a lot of research conducted on zirconia bonding over the last decade, and there are some critical factors dentists should be aware of that are specific to bonding zirconia.
“Traditionally, the tooth was tapered by about four to eight degrees so it would be retentive. Basically, that means the crown could be cemented straight in,” he explains. “Nowadays, we’re moving towards bonding zirconia because it’s quite a lot stronger.
“Zirconia needs to be sandblasted with a micro-etcher that roughens the surface. We then tend to use a primer called MDP to create a layer between the ceramic and the resin-based composite you’re going to use to bond to the tooth.”
But Dr Neville warns that some labs and dentists may not be aware that sandblasting or air abrasion should occur chair-side directly before the zirconia restoration product is bonded.
“Sandblasting shouldn’t happen in the lab,” he says. “It should happen in your practice because you have to try the crown in to make sure it fits first. Then the crown needs to be taken out and cleaned, then finally you sandblast it. You do that while the patient is in the chair, because the strength of the bond will decrease about 15 minutes after sandblasting. So if the sandblasting is done in the lab and you’re not fitting it until a day later, then it’s a waste of time.”
Watch our free on-demand webinar: Zirconia Preparations – Critical Success Factors