By: Dr. David Rice
As we all know, Zirconia is just one type of dental material at our disposal as dentists today.
Do you know what I love about my dental lab? They speak the truth, the whole truth, and everything around the truth. Thank you, Bonadent!
I was reminded of that as I spoke at Ivoclar Vivadent’s Innovation Tour stop in Houston, Texas, on “Biomaterials: The state of the union.”
Here’s a short story and see if you agree.
Most Commonly Used Indirect Dental Materials
The most commonly used indirect dental materials today are:
- Feldspar and Leucite Ceramics
- Lithium Disilicate/Silicate Ceramics
- Zirconia Oxide Ceramics
Shorter story is many dental labs today are driving you and I to just one of the above as our cure-all … with that one being Zirconia.
Types of Zirconia
Here’s Y that matters: Not all Zirconia is the same!
Take a look at the chart below, there are:
- 3Y: Substructure Zirconia or Full Contour Zirconia
- 4Y: Medium Translucent Zirconia
- 5Y: HT/Cubic Zirconia
What’s not on this chart for teaching purposes is that there are also hybrids that blend 3Y, 4Y, and 5Y.
Why Does the Type of Zirconia Matter?
So why does Y matter?
Check out the row labeled Y2O3. That’s the Y or “Yttria” content in each of the 3Y, 4Y, and 5Y. Look at how that increases in wt% from 3Y to 4Y to 5Y.
Now, look at the highlighted green tab that looks at light transmission.
What you’ll notice is as we progress from 3Y to 4Y to 5Y, we increase the light transmitted. In other words, we get more translucent. And, yes, we get prettier Zirconia.
Now, look at the highlighted blue tab that looks at the strength in two ways.
What you’ll also notice is that, as we make that same shift from 3Y to 4Y to 5Y, we lose strength, significantly.
3Y Zirconia is extremely strong. It’s also opaque. It’s also not pretty and, I’m guessing if you’re anything like most dentists, you remember the first Zirconia crown your lab sent your way. It likely fit great … and it likely looked terrible.
Then one day your lab did a better job, right? They sent you a Zirconia crown that fit great and looked great. I’m guessing you thought, “Thank goodness, they figured this Zirconia thing out.”
But did they? Or did they simply unplug 3Y and give you 5Y?
When they switched from 3Y to 5Y on you, did you change your preparation design back to your Lithium Disilicate prep? Or are you still prepping the same as you did when the rep came in and told you Zirconia is 1400 megapascal and you can prep it at .6mm?
Did they explain to you that, in addition to the megapascal measure of strength, there’s a second measure that matters even more for Zirconia?
A little something called fracture toughness. It’s the last blue highlighted row in the above chart.
Take a second look, because when you and I choose 5Y over the 3Y Zirconia, I’m guessing you’ve thought you’ve been placing when it comes to strength, you’ve lost half the fracture toughness!
And you know what’s more fracture tough than 5Y Zirconia? The Lithium Disilicate that the e.max lab told you to replace.
Slight squirrel chase here. The easiest explanation I can share for fracture toughness is this: You’re driving down the highway. A stone kicks up and dings your windshield. When the ding stays a ding, you’re fracture tough. When your ding cracks all the way across, you’re not.
Why Didn’t Your Lab Tell You The Whole Y Story?
So why did you not get the whole Y story? That’s a great question to ask your lab.
Either way, what matters is that, when you want the highest strength of Zirconia, you’re going to sacrifice esthetics, so inform your dental patient. When you want the most beautiful, you’re giving up strength.
Go back to your e.max prep and, if you want the most fracture tough version, go back to e.max all together. It outperforms 5Y and it has almost two decades of history to lean on every day.
I hope that helps! Reach out to me at firstname.lastname@example.org if I can answer any other questions for you.