E.max cracking?

[rkm rdt]

Ditto!

So all your bridges must crack then?

 

[NicelyMKV]

Nope, but I have had the same question.

 

[corona]

bob , heres the answer . its a thinness thickness issue . increase your slow cool time to 3-5 minutes and you should not have any more problems . the crown is cooling down at different thickness /thinness therefore creating stress in the material . stress in material = crack. slow your cool .

 

[NicelyMKV]

I would like to talk more in depth about Emax CAD and Emax press. I personally thought the color and translucency of Emax CAD was superior to Emax press. I also felt like after crystallization, I had a more...... I don't know, defect free result? The surface was much more uniform etc. I keep hearing how much weaker Emax CAD is though. You are also severely limited in contour due to the way it has to be ground instead of cut. I wonder if there is more to the whole Emax press being overcooked in most press ovens and the reaction layer etc?

 

[CatamountRob]

Ok folks,then explain to me why I don't experience this problem with emax cad?

What many people don't realize is that the e.max (both CAD and press) produced for the Canadian market differs in formulation from that which is exported to the U.S. It contains 3% ground Narwhal tusk (by weight) which everyone knows has magical healing properties. What this means is Canadian e.max cracks, but then heals itself. It's not available in the U.S. due to the C.I.T.E.S. treaty.

 

[rkm rdt]

bob , heres the answer . its a thinness thickness issue . increase your slow cool time to 3-5 minutes and you should not have any more problems . the crown is cooling down at different thickness /thinness therefore creating stress in the material . stress in material = crack. slow your cool .

I would be inclined to agree with you however:

Bob said " After finishing we are seeing some units cracked."

So based on that, I don't think cooling is the problem. I think the heat is being created through friction of the finishing wheel.If I use an agressive approach with my white universal wheel, I can create cracks in the thin areas. I have only experienced this once with a thin veneer and am more carefull now.

Again this problem would occur with every bridge pressed if it was a fast cooling issue and only if the unit is returned to the furnace for additional bakes and glazing.

With a monolithic restoration however cooling is not at play here.

 

[rkm rdt]

I would like to talk more in depth about Emax CAD and Emax press. I personally thought the color and translucency of Emax CAD was superior to Emax press. I also felt like after crystallization, I had a more...... I don't know, defect free result? The surface was much more uniform etc. I keep hearing how much weaker Emax CAD is though. You are also severely limited in contour due to the way it has to be ground instead of cut. I wonder if there is more to the whole Emax press being overcooked in most press ovens and the reaction layer etc?

I agree,I am having less issues with emax cad. Diadem provides me with accurate margins comparable to press.

 

[cumino]

Curing the cracks @ 900 centgrade works fine...luckily only had to do it twice..... but in the furnace using glaze firing parameters...up to 900 and down with 2 mins of cooling...worked both times

 

[BobCDT]

Yes, or at least the crack is no longer visage under 20X mag. We did a few more and now we are firing under vac to 900 C and holding for 30 seconds. Also we have learned that it is necessary to submerge the margins in the Peg material.

 

[rkm rdt]

I find it quite rich to claim that emax cad is weaker than emax press considering the multitude of cracking issues I keep hearing about. Add to that the problem of delamination due to improper removal of the reaction layer and it is becoming apparent to me that the only advantage emax press may have is cost per unit.

 

[Kaypan]

Bob, which material generally cracks? HT or LT, or both? Been having some of these cracking problems at our lab also, but only with the HT ingots. Poor preps, thich/thin areas on monolithic molars would sometimes cause cracking problems. You get a "tug of war" in the material when it cools. As said by others here, filling up with peg material inside crowns and slow cooling to 550 celsius pretty much solved our problems.

 

[CatamountRob]

I find it quite rich to claim that emax cad is weaker than emax press considering the multitude of cracking issues I keep hearing about. Add to that the problem of delamination due to improper removal of the reaction layer and it is becoming apparent to me that the only advantage emax press may have is cost per unit.

That's just about enough from you, you.... you...nonbeliever.

.....someone get the Canadian another glass of Kool Aid.

 

[NicelyMKV]

Rkm, I didn't say it..... Ivoclar did

 

[BobCDT]

I would like to talk more in depth about Emax CAD and Emax press. I personally thought the color and translucency of Emax CAD was superior to Emax press. I also felt like after crystallization, I had a more...... I don't know, defect free result? The surface was much more uniform etc. I keep hearing how much weaker Emax CAD is though. You are also severely limited in contour due to the way it has to be ground instead of cut. I wonder if there is more to the whole Emax press being overcooked in most press ovens and the reaction layer etc?

Hi Jason,
I really don't have much experience with the e.max CAD. However, it's really easy to know when the press gets too hot. The surface of the restoration looks like an orange peel. Drop the temp 5 degrees and it goes away. The ivoclar presses seem to drift hot and need adjustment about onece a mounth. The Zubler and Dekema seem to stay on target much better.
Jason, the tests data provided by Ivoclar for flexure strength puts CAD at 360MPa and press at 400MPa. So, yes the press is stronge. But, not by that much. The fact, we really don't seem to hear of post cementation failures with either press or CAD.
From our experience, the reaction layer has not presented any problems.
Bob

 

[CoolHandLuke]

That's just about enough from you, you.... you...nonbeliever.

.....someone get the Canadian another glass of Kool Aid.

just for you RKM.

 

[CatamountRob]

From our experience, the relaxation layer has not presented any problems.
Bob

What's a relaxation layer? Didn't see anything about that in the manual.

 

[BobCDT]

I find it quite rich to claim that emax cad is weaker than emax press considering the multitude of cracking issues I keep hearing about. Add to that the problem of delamination due to improper removal of the reaction layer and it is becoming apparent to me that the only advantage emax press may have is cost per unit.

Honestly, cracking of emax press has really never been a problem for us. Until the last week. We press about 50 units a dat and have been really successful.
Bob

 

[rkm rdt]

When labs have to start fixing cracks in their crowns before sending them out then I think it's time to have an honest discussion that's all.....unless of course you have something to hide:suspicious:

 

[rkm rdt]

Rkm, I didn't say it..... Ivoclar did

Oh I know. I thought you brought up some good points and I wanted to start a debate .I find that you have to stir it up a bit inorder to get a response from the EMAX BROTHERHOOD around here.

 

[rkm rdt]

Honestly, cracking of emax press has really never been a problem for us. Until the last week. We press about 50 units a dat and have been really successful.
Bob

Bob, based on the responses today, I don't think you were the only one having this problem.In fact I have heard it from a couple of drs I had called on months ago.

You still haven't explained why you get cracking prior to glazing your monolithics.Where is the cooling process you think is the problem?