E.max cracking?

[NicelyMKV]

Rkm, are you getting decent occlusal anatomy with CAD?

Bob, you guys need to develop a tooth library optimized for the tooling strategy necessary to mill Emax Cad.

 

[CatamountRob]

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?

I don't think Bob wants to discuss this further.

So I'll ask you a question RKM. Do you think it's ethical to repair e.max in this manner. Maybe I missed it, but I don't recall seeing anything from Ivoclar regarding this technique.

 

[BobCDT]

I am thinking there are stresses built up in the glass where thick areas meet thin. All my failures exibited this configuration and the cracks went right through this seam. Then when grinding on the pressings the stress relieves itself and results in a crack. On other cases that crack during or after S and G I believe the problem to be a derivative of the same type of stress.
Not liking the concept of over firing e.max to heal or possibly just hide the cracks. So, I will continue to listen to all of you as well as communicating with Ivoclar tech support and keep on testing to come up with a crack free product every time. I have done many thousands of units and have really never had this problem. But that just another day in a dental lab!
We made some changes today. Moving forward we will be blocking out die to reduce the transition from thick to thin. I'll let you know how it goes.

Bob

 

[BobCDT]

Bob, which material generally cracks? HT or LT, or both?

Only happening with HT. but, we only use HT for monolithic on molars. So it provides no addional input that this is an HT problem.

 

[NicelyMKV]

I occasionally get that more translucent line in mine as well. I was told its where the crystals line up perfectly for some reason and lose opacity due to the less cross crossed pattern.

 

[NicelyMKV]

I had one crack once and fired it on the crystallization program for the hell of it. Repressed the original restoration though.

 

[NicelyMKV]

I still LOVE everything about composite....except.... well, that it's composite....

 

[BobCDT]

He all,
Thanks for the help today. I really think I'm on to a solution. I can't believe how many of you got involved in the thread.
Can we move this to e.max CAD vs. Press? Pros and cons.
I have been pressing glass since the inception of Empress. When e.max CAD was introduced I had a craplab mill and never got a usefull e.max CAD part out of it. So, I sent about 25 STL files to an outsource facility and honestly the fits were very inconsistent. After that I just figured pressing was less expensive and fit better. Am I figuring this correctly? What are you guys thinking produces the best end result.
Thanks again for all the help.
Bob

 

[BobCDT]

I occasionally get that more translucent line in mine as well. I was told its where the crystals line up perfectly for some reason and lose opacity due to the less cross crossed pattern.

We have seen this as well. Ivoclar gave me the same answers to what it was. We cut the restoration through the affected area and there was a space in the glass. A definite flaw.
B

 

[BobCDT]

We have seen this as well. Ivoclar gave me the same answers to what it was. We cut the restoration through the affected area and there was a space in the glass. A definite flaw.
B

In addition, I think it comes from putting two ingots in a ring and air may get trapped between the ingots. Just a theory.
B

 

[CoolHandLuke]

We have seen this as well. Ivoclar gave me the same answers to what it was. We cut the restoration through the affected area and there was a space in the glass. A definite flaw.
B

somethin fishy about that, bob. liquids tend to mix. unless this is emax of two COMPLETELY different densities (a la oil and water) the material is the same, so the glass should mix. unless of course you didnt have it at high enough temperature or hard enough force.

this is just what i know from material science class, not from my knowledge of emax (as i have absolutely none)

edit: or you were inserting the ingots cold.

 

[rkm rdt]

Rkm, are you getting decent occlusal anatomy with CAD?

Bob, you guys need to develop a tooth library optimized for the tooling strategy necessary to mill Emax Cad.

My tooth library is pretty basic,certainly not as detailed as CAP or Kastle Mills.

However ,since I receive the emax cad in the blue precrystalized state , I find it is quite simple to " enhance" my basic morphology.

 

[rkm rdt]

I don't think Bob wants to discuss this further.

So I'll ask you a question RKM. Do you think it's ethical to repair e.max in this manner. Maybe I missed it, but I don't recall seeing anything from Ivoclar regarding this technique.

I wouldn't go that far.
Certainly if it becomes a pattern, and nothing is solved, then we are negligent imo.

 

[rkm rdt]

He all,
Thanks for the help today. I really think I'm on to a solution. I can't believe how many of you got involved in the thread.
Can we move this to e.max CAD vs. Press? Pros and cons.
I have been pressing glass since the inception of Empress. When e.max CAD was introduced I had a craplab mill and never got a usefull e.max CAD part out of it. So, I sent about 25 STL files to an outsource facility and honestly the fits were very inconsistent. After that I just figured pressing was less expensive and fit better. Am I figuring this correctly? What are you guys thinking produces the best end result.
Thanks again for all the help.
Bob

I don't think there is a winner in a press vs cad/ debate. You can't mill a veneer for example, and even if you could , it wouldn't be cost effective when you can press all six ants at once.

I think each technique has it's advantages.

 

[desertfox384]

I didnt read through all the posts but when this happens to me its due to there being a big cusp with a lot of material meeting a thin occlusal area. Sometimes it wont take much to crack it, just a little bit of heat will do it. Do you have someone grinding on them? They need to be careful not to get it hot. Also Ivoclar told me that if you have a sharp corner like the ones we sometimes see on the occlusals of preps, it needs to be well covered by die spacer until the sharp edge is rounded off or else that will cause cracks as well.

 

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I had an emax monolithic crack, same place 4 times, I tried slow cooling, hold fix material, wow after waxing that sucker 4 times I could do it with my eyes shut, anyway whatever I tried didn't work until I called the dentist and asked if I could fill in the hole in the centre of the prep with a block out wax before I made it again, this worked out perfectly, no more crack. So am pretty sure that now and again you get a prep with weird geometry that stresses the crown when cooling. Is definitely a thick thin scenario, when I held the cracked units up to the light there was a thin area in the shape of a horseshoe with some bulk on the one side. I have been pressing FCC for a year now and only had this happen on this one case. Live and learn?