Emax cracked

[EJADA]

Any thoughts? I just had an emax crack. I had already fired it twice. It was already cooled off. Minimal thickness was .5mm and all internal corners were rounded. The mesial wall was about 1.3mm and went right into a .5mm occlusal surface. This is where the cracked developed. I've only had this ever happen with thinner (under .4mm) crowns. Still, seems it should have been able to handle this. Totally baffled??? I need to redo this and make some adjustments as to how I approach it. Need input.

 

[odchamp]

Layered i guess, redo full contour and cut back to get the case finished, then analyse more later, just a thought.

 

[EJADA]

Good thought but it is full contour.

 

[marnero]

HT or LT? Have had the same happen a few times, mostly on HT. Seems like its the difference in thickness of the press material and the expansion/reduction when heated/cooled. I´ve started with long term cooling down to 550 celsius and always fill the crown entirely with Object Fix to get a more even distribution of the heat.

 

[EJADA]

Marnero; Thanks, It is an HT. Your thinking is same as mine. It's always nice to hear if similar situations are happening elsewhere. The couple of other units I've had this happen with were also HTs. I will try your advice.

 

[disturbed]

posterior i assume?
in the e max press manual it states not to go below 1.0 on posterior 1.5 on occlusal. I have done 0.8 transitions but with a thick/thin spot I always do a reduction coping or the thin spot will cool too quickly vs. the thicker area and crack.

1.0-1.5 minimum.lol:lalala:
we all stray from the manual from time to time, I have healed cracks like this on full contour by firing the crap out of them and getting them close enough to their melting temp but not so hot the margins round out and the crack fuses. checked under high power microscope.. melted the first 2 times i tried but once you get your oven dialed in it can be a life saver when you get funky cracks from thick thin spots or from trying to get your veneers to below manufactures recommendations.....

 

[NicelyMKV]

Can not go from that thick Of an area to that thin. I have had to block out areas before that were extremely thick meeting up with thin areas. Difference in cooling and expansion between large variances in thickness.

 

[EJADA]

Wow Thanks so much.. You all are really helpful. I am making the necessary adjustments right now. I will post this afternoon as to results if anyone is interested.

 

[Brett Hansen CDT]

I will echo some of the other comments. We get cracks in areas that go from thick to thin from time to time. I also believe that it has to do with a cooling issue. Nice to hear that others have seen the same things.

 

[charles007]

If this is common, this should have happened to me with-in the last 3 years ! I don't get ideal preps, far from it... I have HT's, but haven't pressed yet.

Question to all. I use the ep 5000 oven... any non Ivoclar oven users seeing cracks ? Any labs getting cracks with the 3000 or 5000 ovens ?

All Cracks head techs, how do you slow cool, and what grinding tools are you using ?

 

[EJADA]

Maybe this is mainly in the HTs, Hard to believe you haven't tried the HTs. They are awesome for full contour crowns. The have such a natural blending effect in the mouth.
The only ones I have had crack like this are HTs,full contour. But they all had the thick with a thinner area right next to it at an axial bend. I press in a ep600 and have pressed thousands in it. I've only had like three that this has happened to. I think that the minor modifications we discussed in this post will clear up the problem.

 

[ps2thtec]

Question to all. I use the ep 5000 oven... any non Ivoclar oven users seeing cracks ? Any labs getting cracks with the 3000 or 5000 ovens ?

All Cracks head techs, how do you slow cool, and what grinding tools are you using ?

Well, for all Crackheads, I've been pressing since Jan with 15yr old nonIvoclar
oven with no cracks,(just mispresses in beginning). I pull ring from press oven and place on steel brick to cool ring. Also use no cool on stain/glaze fire.
Everybody use the lower temps when pressingHT?
What about plungers? It was believed in the early days of pressing that alox plungers change the way the material cools which could cause cracks, hence hthe intro of disposable plungers.

 

[EJADA]

The cracks we are referring to are not during pressing they are during the staining or glazing. Just to clarify.

 

[Gaetano]

I used to get cracks in my full contour emax crowns and I remember how frustrating it was! I am guessing that most often it is on a lower molar? Perhaps an upper now and again... It has to do with the cooling and once I figured out how to compensate for the heat differentiation I have had almost 100% success. If you are cooling on a quartz peg you need to switch! I fire all of my emax on a pillow tray with a porc oven fabric on top to keep the pillow fuzz from messing with the glaze. Once I figured this out, I cant tell you how happy I was! It has honestly stopped the cracking. The thick to thin areas that you see on molars are often vulnerable to uneven temperature induced cracks and the way those pegs cool down was the culprit. Hope this helps you! If it does, let me know! !

 

[ps2thtec]

Well, for all Crackheads,
Also I use no cool on stain/glaze fire.

 

[odchamp]

Charles007, i have an ep 5000, no problems on cracking, and using the settings it came with.

 

[paulg100]

normally put mine on a little blob of object fix putty ontop of the peg. Maybe thats why i havnt seen any cracking issues.

 

[amadent]

normally put mine on a little blob of object fix putty ontop of the peg. Maybe thats why i havnt seen any cracking issues.

we do the same thing, we use wonder peg from dental creations

Greg Amendola MDT

 

[EJADA]

Well I'm happy to report that with the modifications you all suggested(IE;increase occlusal thickness to .8, thinned mesial wall a little,used more peg stabilizer with a slower cool down) the second crown was a total success.

Thanks again, After more than 30 years at the bench I still am learning and modifying what I do everyday.

 

[charles007]

normally put mine on a little blob of object fix putty ontop of the peg. Maybe thats why i havnt seen any cracking issues.

I do the same here also.....