E.max cracking?

[BobCDT]

Hi,
We have been having more cracking of e.max than usual. After divesting all units look good. After finishing we are seeing some units cracked. Then more units after final stain and glaze.
Are any if you seeing this?
Any ideas?
Thanks,
Bob

 

[rkm rdt]

Can you be more specific Bob?

Vertical or horizontal cracks?

single line crack or crazing/multiple cracking?

No cracks after divesting but some after finishing? Are you creating heat during the finishing such as with a rubber wheel?

Can you post some pics?

 

[Affinity]

Hi,
We have been having more cracking of e.max than usual. After divesting all units look good. After finishing we are seeing some units cracked. Then more units after final stain and glaze.
Are any if you seeing this?
Any ideas?
Thanks,
Bob

Havent had it happen regularly, but I have healed cracks by covering the crown in peg putty and running it up to the magic temp.. not by the furnace so I cant tell you exactly, but its around 900' and it does work. Obviously this doesnt get to the root of the problem, so maybe not much help... haha I would think it has something to do with cooling the rings maybe.. What pressing furnace are you using?

 

[GarryB]

We have had some single line fractures after applying GC Lustre. Only 5 but still a worry.

Affinity, thats very interesting about "healing" cracks. How mant times have you done it? and if your not putting it in the furnace you must be using a torch? what kind of flame are you using?

As you say, it's not getting to the root of the problem but it's better than starting the whole job again at midnight!!

 

[charles007]

Bob, are you have problems with both Zubler and Ivoclar ovens ? are your guys devesting hot rings not using the Xcavator ? I'm assuming your techs are finishing correctly.. Haven't experienced any problems with emax yet with my ep5000, I did start using my NSK Aqua last year on most of my touchups with diamonds..
Bet it has something to do with heat, and not pressing..Please let us know the problem once you learn.....
Charles

 

[rkm rdt]

Perhaps Disturbed could share his wisdom on this ever increasing epidemic?popcorn

 

[BobCDT]

The cracking is only on monolithic posteriors. Single line crack. It's always the occlusal surface. Generally where the axial wall meets the occclusal surface on the inside of the crowd, But not always. In most cases the cracks seem to be curved around areas where thicker glass meets thinner glass.
My first thought was that is was thermal so we are slow cooling, to no avail.
Thanks,
Bon

 

[rkm rdt]

Can you explain your technique for finishing prior to glazing?

 

[BobCDT]

Bob, are you have problems with both Zubler and Ivoclar ovens ? are your guys devesting hot rings not using the Xcavator ? I'm assuming your techs are finishing correctly.. Haven't experienced any problems with emax yet with my ep5000, I did start using my NSK Aqua last year on most of my touchups with diamonds..
Bet it has something to do with heat, and not pressing..Please let us know the problem once you learn.....
Charles

It doen not seem to be related to any one press. It's occurring in all presses. Rings can be hand held before divesting.

 

[charles007]

Any techs using carbides while devesting & finishing..

 

[2thmakr]

Hi Bob,

Had some of the same issues a while back. Only on posteriors too, which usually had a couple things in common: unusually out of balance preps (missing corner due to fracture) and/or sharp line angles instead of a nice rounded prep. I did a few things to try to stop it and don't actually know which helped but it rarely happens now. On "out of balance" preps I adjust the crown contour so I am not hanging a bunch of material out there that creates a potential stress in cooling uneven mass. I also slow cool with a complete fill of the interior of the crown with refractory material, and as much as I want to rush it I let the investment cool before divesting. So far so good.

 

[RileyS]

Most of ours have been from crowns that were too thin and would crack where it thickens, or on crowns that our waxer would leave too high and lots of grinding to finish. Since I started checking all work before it is pressed we haven't had issues.

 

[BobCDT]

We just used some peg material (Object Fix by Ivoclar) on some of the cracked samples.
Ran the crown up in a porcelain oven to 900C with a 1 minute hold. Crowns no longer have cracks. Contact, occlusion are perfect. Fit is also good. Crowns look slightly over glazed.
Going to try another one with a 30second hold time. I'll let you know how it works out.
Bob

 

[EJADA]

The cracking is only on monolithic posteriors. Single line crack. It's always the occlusal surface. Generally where the axial wall meets the occclusal surface on the inside of the crowd, But not always. In most cases the cracks seem to be curved around areas where thicker glass meets thinner glass.
My first thought was that is was thermal so we are slow cooling, to no avail.
Thanks,
Bon

I have had this issue from time to time. Very frustrating. I have found if I block out the thick axial wall so the pressing is more uniform it helps. Make sure the minimal thickness is .8mm at least. And no sharp internal angles especially at areas where thick meets thin. Use some sort of insta peg and slow cool. These are what has helped me reduce this issue.
Good luck.

 

[rkm rdt]

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

 

[EJADA]

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

One of the GREAT mysteries.

 

[EJADA]

We just used some peg material (Object Fix by Ivoclar) on some of the cracked samples.
Ran the crown up in a porcelain oven to 900C with a 1 minute hold. Crowns no longer have cracks. Contact, occlusion are perfect. Fit is also good. Crowns look slightly over glazed.
Going to try another one with a 30second hold time. I'll let you know how it works out.
Bob

Bob are you saying you healed the crack?

 

[Affinity]

We have had some single line fractures after applying GC Lustre. Only 5 but still a worry.

Affinity, thats very interesting about "healing" cracks. How mant times have you done it? and if your not putting it in the furnace you must be using a torch? what kind of flame are you using?

As you say, it's not getting to the root of the problem but it's better than starting the whole job again at midnight!!

I think you misunderstood, I meant I wasnt BY my oven at the time, so I couldnt check the temp. Ive only done this once or twice, and only if it was a small internal crack.. I wouldnt recommend it as common practice, or as a solution obviously.. but it DOES work.. and it doesnt change the shape of the crown if you dont hold it very long.. like you said, its better than restarting the case..

 

[Affinity]

Do you keep track of your LOT numbers? I would hate to think you got a bad batch of material.. but I would say 95% of the time its human error.. Maybe someone got it too hot while finishing.. Having said that, ive tried to abuse this material and its hard to get it to crack....

 

[NicelyMKV]

I have had this issue from time to time. Very frustrating. I have found if I block out the thick axial wall so the pressing is more uniform it helps. Make sure the minimal thickness is .8mm at least. And no sharp internal angles especially at areas where thick meets thin. Use some sort of insta peg and slow cool. These are what has helped me reduce this issue.
Good luck.

Ditto!