By: Dr. David Rice
Lithium Disilicate vs Zirconia? When it comes to selecting the best material for your patient’s crown, you have options.
The question is, which option is best, when, and why.
At 550 MPa and excellent fracture toughness, Lithium Disilicate weighs in well.
Although I prefer to bond it, per ISO standards, you and I can bond – or lute E.max.
This quality is an excellent one, especially considering the two-decade clinical track record we have in addition to all the data the literature shows us.
With multiple opacities to work with, Lithium Disilicate offers us incredible aesthetics, even in a monolithic state.
We can choose to maximize the beauty of our underlying prep shade when we have it; we can choose to hide an unsightly prep shade when we do not.
Additionally, E.max offers us options to level up. When we want to stay monolithic, we have the ability to shade and glaze, where shading and glaze become a part of our E.max post-firing.
When we want to cut back our monolithic E.max and layer, we can predictably do that too.
This can be accomplished with both total and self-adhesive processes.
In full coverage crowns where we have little to no enamel, it often makes sense to work in the self-adhesive space with materials like SpeedCem Plus from Ivoclar.
When we have 3/4 crowns or crownlays with significant enamel on our margins, we can ideal strength and beauty by using a total adhesive process with materials like Variolink Aesthetic.
The win here is not only on the strength of the bond to enamel side, it’s on our ability to control the value of our final crown as materials like Variolink Aesthetic offer us a wide variety of value-based bonding cements.
This can be done using anyone’s RMGI. Luting with RMGI’s offers us speed and convenience with two caveat. We must have inherent material strength. E.max offers us that. We must have true retention form in our crown preparation.
Lithium Disilicate Disadvantages
Finding a true disadvantage is a real challenge with E.max, but if I must find one, it lies in the original strength – 550 MPa.
Translation – if you’re seeking an 800MPa restorative material for whatever reason, you won’t find it here.
We’re going to need to take a step back and define which Zirconia we are talking about:
👍 Strength: If you’re looking for pure strength, you’re looking for 3Y Zirconia. Manufacturer, dependent you’re in the 1000+ MPa range. The question is – why do you need 1000 MPa?
If you tell me you’re building a substructure for an implant-supported prosthesis, good choice.
If you’re telling me you’re looking for today’s topic – a crown – and you want the strongest material in dentistry – again – good choice.
👎 3Y Zirconia is not pretty. When it comes to crowns our opportunities for placement are typically limited to 2nd molars and patients who have zero aesthetic concerns.
If you’re choosing 3Y – or any Zirconia on a second molar, I want you to ask yourself why. My guess – you want to maximize strength because you’re on a second molar and you have limited clearance. Sound about right? I understand.
I want to remind you of the two qualifications we need to lute your crown, rather than bond your crown. The first is material strength – 3Y Zirconia satisfies that requirement. The second is true retention form in your preparation. I’m going to apologize for this data point as it will beg you to not lute in most second molar situations.
We need 4mm of height in our molar preparation to have true retention form in our prep. For the sake of completeness, we need 3mm of height on a premolar.
I share this not because 3Y Zirconia in itself is a poor choice for second molars, where you believed it was ideal. I share it because it’s only a good choice if you bond it when you do not have true retention form.
So my original question of why Zirconia on a second molar – is a question I always ask since typically one of the two reasons most dentists select it, isn’t satisfied.
👍 4Y Zirconia improves the beauty of the material.
👎 4Y Zirconia also decreases its strength.
👍 5Y radically improves the beauty of Zirconia.
👎 In reality, however, it also lowers its strength to E.max with one more added disadvantage
👎 5Y Zirconia is not as fracture tough as E.max.
👎 Add that to its decade and a half less history and call me biased, I can’t find a reason to use it.
I’ve carved this out as one can layer any Zirconia – theoretically. That said, although this can be done successfully, it does prove challenging for many ceramists as the firing temperature differences between the core and the layers are large.
I’d highly recommend learning more from Drs. Gordon and Rella Christensen for the best information. They are tremendous resources with tremendous data.
If I must use Zirconia (outside of substructures and the rare 3Y when aesthetics are not a concern at all) – my go-to is a hybrid called Zircad Prime or Zircad Prime Aesthetic.
Zircad Prime puts 3Y Zirconia in the cervical one-third to maximize strength; it puts 5Y Zirconia in the incisal/occlusal third to maximize beauty and hybridizes in between.
This union allows me to prep teeth more conservatively in most areas. It allows me to gain aesthetics. It allows me to lute or bond like E.max – and it allows me to build combination cases (with E.max) without compromise.
🥇 Lithium Disilicate is my workhorse. I use it for anterior and posterior crowns. I use it for partial crowns.
Off-topic, yet for completeness’ sake, I use it for inlays, onlays, and veneers.
Outside of the above-noted 3Y exceptions, I will occasionally add a hybridized Zirconia into a combination case primarily for the patient experience.
Meaning – if I’m inserting 10+ teeth and I know my patient’s ability to tolerate sitting in the chair is limited – and I want to lute my crown or crowns – although I can lute E.max, as I mentioned above – I prefer to bond it – and resultantly – I will mix materials.
Lithium Disilicate vs Zirconia: Dentists Takeaways
You and I have multiple material options for crowns today. Both Lithium Disilicate and Zirconia can offer excellent options.
The keys to success lie in understanding – when – what material wins – to help us deliver the best result.
Consult the data. Consider your patient’s experience. Create your best possible outcomes.
Photo by Anna Shvets