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 just last week 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. 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 one of the above as our cure-all … with that one being Zirconia.
Here’s Y that matters: Not all Zirconia is the same.
Take a look at the chart below. There’s 3Y, 4Y, and 5Y Zirconia. What’s not on this chart for teaching purposes is that there are also hybrids that blend 3, 4, and 5Y.
So why does Y matter?
Check out the row labelled 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 and the highlighted blue tab that looks at strength in two ways.
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.
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 did that, 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 Zirconia 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 … the e.max your 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.
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 Zirconia, you’re going to sacrifice esthetics, so inform your dental patient. When you want the most beautiful Zirconia, 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 about Zirconia.