What causes this to happen?

[wwcanoer]

I've finally pressed my first Emax successfully! Dropped pressing temperature down 50°F and that seemed to be the answer.

I pressed an occlusal onlay out of HT A2. Hardly any reaction layer!!, fit perfect, made minor adjustments to the occlusion, and did initial stain firing.

On the glaze firing, it came out with a visible crack, and once handled turned into two pieces.

The prep had minimal angles, averages 1.5 to 2 mm thick. The white halo on the second picture is residue from from the pillow putty.

Anybody have any idea what causes something like this to happen?

 

[TheLabGuy]

The first thing that pops into my head when I see this is that you used a carbide to finish with.....did you? I've seen this on other labs cases, where they used a carbide to get in the grooves/fossaes/pits and have ground to fast and to hard, which results in a micro-crack, that becomes very evident during glazing. I know ivoclar states to use diamonds, but you can use carbides, but be very gentle, you're working with all-ceramic.......
The second thing it may be is that you cooled the restoration too quickly....I've seen this before on empress esthetic....simple fix, just add some cool time. Most likely though, it's your use of the carbide....hope that helps. I recently seen a Dentist post a picture on DT that was similar to what you posted that a lab sent them (the crack hadn't broke all the way through).

 

[wwcanoer]

Yep, I "cleaned" up my anatomy of a carbide 699 fissure. I will be repressing it next week, and I'll just have to remember, diamonds are a girl's best friend!

Thanks much!

Carol

 

[sixonice]

Yep, I "cleaned" up my anatomy of a carbide 699 fissure. I will be repressing it next week, and I'll just have to remember, diamonds are a girl's best friend!

Thanks much!

Carol

also, like another member posted above, with these thicker e.max cases, it never hurts to put a slow cool or longer term cooling program in your oven. the ivoclar ovens long-term cool is the "L" in the programming features. Put in like 575 Celcuis is your using the ivoclar oven OR if you have another furnace that uses time (minutes) for the long term cool, put in like 5 minutes. That will give you a much gentler cool time. with that thickness holding on to alot of residual heat after glazing, then the oven opening and cooling quickly, that may be stressing the lithium disilcate some.
also, watch for sharp internal line angles (which yours didn't appear to have). these act as predetermined stress points from within. finally adjust and finish at SLOW speed and light pressure to avoid micro-cracks. i would not use a high speed, ever!