EMAX cracks

[David S.]

We are getting cracks in our emax after it is fired for stain and glaze. We are using Vacumat 6000.
Starting temp: 403 C
6 min dry time
50 rise
Vacuum comes on at 453
Final temp 735 C
Hold 1 min

We are at wits end trying to figure out what is going on. Don't know if they might be too thin or a thick and thin spot together.

 

[DMC]

I have never even seen an eMax crown in person.

Crazy, eh? Just not interested in that material at all.

Have fun! LOL

I am sure in a few seconds someone will help you.......

5,4,3,2....

 

[user name]

How thin? How long is your cool/opening time? Are the crowns being adjusted after pressing?

 

[Labwa]

Sounds like you should slow cool. maybe 550-500. I go real slow on all my e.max cooling.

 

[AL1]

If thin occlusal and thick axial walls you can get crack on the occlusal
you can sometimes heal crack by running up at a on a specific cycle,
Know labs that are doing that.
will post later.

 

[David S.]

How thin? How long is your cool/opening time? Are the crowns being adjusted after pressing?

I don't think there is a cool time it just opens. They are being adjusted after press but with a high speed and water. We do not have them thinner that 0.4mm.

 

[2thm8kr]

Are you using carbides to adjust?

 

[David S.]

Are you using carbides to adjust?

We use diamond burs to adjust.

 

[2thm8kr]

I don't think there is a cool time it just opens. They are being adjusted after press but with a high speed and water. We do not have them thinner that 0.4mm.

Posterior emax shouldn't be thinner than 1.2mm.

 

[Marcusthegladiator CDT]

Need pics and measurements..

 

[NicelyMKV]

Slow cool will help a lot. I had trouble with the metal pin style firing pins. They would stick to the Emax material sometimes and cause a crack when I pulled the crown off. When I say stick, I mean just barley noticeable, but enough.

 

[CoolHandLuke]

Posterior emax shouldn't be thinner than 1.2mm.

whoa...

seems unwieldily huge number to me

 

[2thm8kr]

whoa...

seems unwieldily huge number to me

If you're not getting enough occlusal reduction, you should be using a different material. Zr should be .5 mm, yes? Doctor is not giving this guy enough reduction for consistent success.

 

[sirmorty]

1.2 mm?
That's a dreamland.

 

[AL1]

Take crown up to 840 use everything else the same as stain and glaze, also fill
crown with object fix from ivoclar to prevent warping.

 

[CoolHandLuke]

we have good success with 3/4mm

 

[2thm8kr]

1.2 mm?
That's a dreamland.

I get it everyday. On the rare occasion I don't, Zr it is or reprep/ reduce opposing.

 

[user name]

I get it everyday. On the rare occasion I don't, Zr it is or reprep/ reduce opposing.

I get it from my accounts too. You have to let them know whats required for a specific material to be successful. Fortunately, when theres not enough room, e.max ceram blends well right down to a thin Zir coping.

If you don't have time to do it right, how will you have time to do it over?

 

[ps2thtec]

I don't think there is a cool time it just opens. They are being adjusted after press but with a high speed and water. We do not have them thinner that 0.4mm.

How fast it opens would be your cool. Leave the sager tray sit there a couple mins. before grabbing it.

I fire all posterior directly on the honeycomb tray, no peg. Never a problem, and if néeded , use a little superPeg putty on a wire MasterCeramist peg. Also cool for four min minimum.

 

[Patrick Coon]

Posterior Recommendations are: 1.5mm On occlusion and axial walls, 1.0mm at margins. These recommendations are for strength in the posterior.

As for the cracking, 0.4mm across the occlusion with probaly a much thicker cusp on either side would cause uneven cooling and cause a stress crack during cooling. Definitely adding a slow cooling to 500C/932F (if your oven is by temperature) or 7 minutes (if your oven is by time) would help, but at those thicknesses it may not solve it.

Also, I would not recommend using a high speed for adjustments, even with water cooling. At the thicknesses you are talking about it would not take much to create a thermal crack. And definitely no carbides. Stones and Diamonds only.

Hope this helps.