Pressed emax crack

BDDS

BDDS

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We found multiple cracks clear through a pressed emax crown after glazing, our first issue with the product... removed from heat too soon at some point?
 
TheLabGuy

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Probably using carbides to finish the anatomy with and pressed too hard which created the heat needed to create micro fractures which usually aren't noticed until glazing..........that would be my guess. I haven 't noticed 'cool down' fractures on E.max like you might see with other porcelains, especially Empress Esthetic......maybe someone else might share their thoughts.
 
Al.

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Could somebody have used the wrong glaze?
 
Gdentallab

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could be the pressed copings are too thin and/or high pressure sandblast might cause microfractures.
 
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paulg100

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yeah ive never had any probs with emax through cool down stress. empress was much more sensitive in this regard.

As said above, its most likely a stress fracture from grinding which IS easy to do with emax if your not using the right stones/burs. Because of its hardness, heat builds very quickly.

Came across this on the ivoclar website, good chart for griding instruments.

http://www.ivoclarvivadent.com/zool.../IPS+e-max+-+Recommended+Grinding+Instruments

I use the diagen stones from bredent personally. They are expensive but as long as they are looked after they last AGES.

I still have some of my orginal kit from 2002! which i bought after doing 2 weeks at LVI.
 
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dmonwaxa

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Yes, Diagen are the best wheels for me. big wheel for sprue removal and the knife edge for rehsping mamelons. They cut easily, and i wet the pressing and stone when grinding to further reduce the heat.
 
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charles007

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What kind of firing peg did you use...has anyone in your lab have burned fingers?
Any carbides used on the crown? the one time I did, 557fg - slow to medium speed on a practice crown, I saw a crack- check, instantly.... and all the glazing in the world would not heal it.
Just how thin is it in that area?
 
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doug

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Carbides are a no-no, unless you're really careful and willing to accept the possible out come. Diamonds work very well in small doses.
 
BDDS

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Sounds like multiple issues ... too thin, AND she is using a carbide bur to cut in anatomy. They were'nt liking how they were turning out pressed full contour, so they started layering the buccal anatomy on posteriors. Is anyone else doing this?
 
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AL1

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I do it all the time, trying to make sure its not in a centric functional area.
 
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charles007

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Ask your tech to order some diamonds by Komet, in fine and med, HP & fG, to replace carbides, to fine tune EMAX.
I've never seen emax crack or check at all using moderate to slow speed.
 
sixonice

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As others have mentioned, I personally feel the Diagen "Turbo Grinders" cut Lithium Disilicate like butter and they will last a long time. Yes, they are more expensive than most, but they are the best. They do not create the heat that other grinding burs seem to create. You can get them through XPDent. They have a kit with all sorts of shades available. Creating excessive heat could very well be the cause of your problem and these Diagen's solve all your issues. Here is the website for more info: XPdent - Sintered Diamond Diagens
 
JeffT

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If you are using an ivoclar furnace (or get the firing prog from website) fire the crown on the (speed crystalization programme - 81) and most time the crack will heal. I have done this a few times and it has healed the crack.
worth a shot.
jeff
 
labman01

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At the lab I work at, I was glazing a posterior e-max crown and I noticed a fracture across the occlusal surface. To make matters worse it was a rush case that was due in couple hours. I adjusted the glaze parameters so the final temp was 880 Celsius, temp climb 45/min, and 1:00 hold, after it came down, the crown didn't have the fracture anymore.

This crown was finished by someone else, and possibly a carbide bur was used.
The temp 880 Celsius was chosen because the pressing oven presses the ingot around 910 Celsius(not positive on exact final pressing temp),but you follow the logic in choosing temp.

Hope this helps in rush cases, I'm not sure of the consequences of doing this. I would suggest, if you have time to always re-wax.
 
sixonice

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At the lab I work at, I was glazing a posterior e-max crown and I noticed a fracture across the occlusal surface. To make matters worse it was a rush case that was due in couple hours. I adjusted the glaze parameters so the final temp was 880 Celsius, temp climb 45/min, and 1:00 hold, after it came down, the crown didn't have the fracture anymore.

This crown was finished by someone else, and possibly a carbide bur was used.
The temp 880 Celsius was chosen because the pressing oven presses the ingot around 910 Celsius(not positive on exact final pressing temp),but you follow the logic in choosing temp.

Hope this helps in rush cases, I'm not sure of the consequences of doing this. I would suggest, if you have time to always re-wax.

Sounds like what you did there healed the crack. e.max presses at 915-925 C (in the Ivoclar press).
If you didn't fabricate the crown yourself, it will be tough to determine exactly how and why this happened. Experience has shown that sharp internal line angles, high-speed grinding and restorations that have very thick areas, to thinner areas can cause stress. All of them are easy fixes, I round out sharp internal lines angles, never grind with a high speed and thick-to-thin restorations I throw a slow cool on those to promote a nice, even cooling phase (thicker areas hold on to heat much longer than thinner areas creating a "tug-of-war" in the lithium disilicate during cooling).
Glad you got your case finished up and out on time and I agree that if you can, pressing it again would be the best route, but I like to find out why restorations may fail and take the steps to avoid them.
 
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