Zirconia bridge fracture during stain cycle

[Ahmed Hazem]

Hello everyone,
I had a cross arch bridge a couple of days ago from the upper canine to the second premolar that I milled using a solid sintering stabilizer from millbox with the supports at the two ends of the bridge and the middle tooth of the three pontics, after sintering using the manufacturer instruction the bridge came out of the furnace perfect, it had some gingiva staining work I decided to do before cutting off the supports of the stabilizers, I put the bridge in the furnace to fire the stain with heat rate of 65 degrees to 760 degrees, the bridge came out I started to cut off the supports when the bridge fructured at the pontic beside the support, I used 4mm supports, any ideas what did I do wrong ?

 

[JKraver]

Hello everyone,
I had a cross arch bridge a couple of days ago from the upper canine to the second premolar that I milled using a solid sintering stabilizer from millbox with the supports at the two ends of the bridge and the middle tooth of the three pontics, after sintering using the manufacturer instruction the bridge came out of the furnace perfect, it had some gingiva staining work I decided to do before cutting off the supports of the stabilizers, I put the bridge in the furnace to fire the stain with heat rate of 65 degrees to 760 degrees, the bridge came out I started to cut off the supports when the bridge fructured at the pontic beside the support, I used 4mm supports, any ideas what did I do wrong ?

Pictures?
My suspects would be:
That there was a gentile drop somewhere.
The stabilization bar may not have been needed?
Did you disc the interproximals?

 

[JonnyLathe]

Your heat rate seems kind of high to be firing a bridge like that, I fire long span bridges at a 35° heat rate and don't get breaks. Oddly the only time I have gotten a break was when I tried putting a full arch in the porcelain oven and left the stabilizer on, I always take the stabilizer off before staining/glazing and don't have breaks.

 

[Ahmed Hazem]

Pictures?
My suspects would be:
That there was a gentile drop somewhere.
The stabilization bar may not have been needed?
Did you disc the interproximals?

Unfortunately I don't have photos, but yeah I did alittle bit disced the interproximals

 

[Ahmed Hazem]

Your heat rate seems kind of high to be firing a bridge like that, I fire long span bridges at a 35° heat rate and don't get breaks. Oddly the only time I have gotten a break was when I tried putting a full arch in the porcelain oven and left the stabilizer on, I always take the stabilizer off before staining/glazing and don't have breaks.

Thank you, I'll consider this in the next one.

 

[JonnyLathe]

Unfortunately I don't have photos, but yeah I did alittle bit disced the interproximals

You put a disc to the interproximals post sinter or pre?

 

[aidihra]

I use a heat rate of 20°C/min. I don't want to take any chances with large zirconia cases. I think that will fix your problem.

 

[Car 54]

Heat rate and not touching the interproximals post sinter. I do like the 20c a minute better for large bridges.

 

[AaronW12321]

So if it's a multi-strength or multi-trans puck with different zirconia compositions packed into one puck, you're going see fractures much more frequently, especially if its a massive area next to a thin area, due the different temps that the different zirc compositions sinter at. I know they all say they're suitable for full arch; they're wrong or lying.
The other problem with sintered zirc is that it doesn't convey heat very efficiently, so when you're cutting on it with a disc it's creating a intense amount of local heat. This heat changes small amounts of the zirc from tetragonal to cubic, which causes "lattice strain" or what I call torsion, internal stress.
You really want to use something thats all 1 type of zirc, multi shade is okay, but it should be all one Y type. If you do have to cut on the zirc after its sintered, be sure to do it with a tray of water and keep the zirc partially submerged. Also longer cooling on longer bridges, I let them cool to 250-300 in the porc oven instead of the normal 400-450 or whatever.

 

[Car 54]

@AaronW12321. What do you use for the bigger bridge and full arch cases?

 

[AaronW12321]

@AaronW12321. What do you use for bigger bridge and full arch cases?

Argen HT multilayer and Ivoclar prime (not esthetic)

 

[Car 54]

Argen HT multilayer and Ivoclar prime (not esthetic)

Thank you

 

[grantoz]

ahmed what you did wrong was not doing some kind of proper course on full arch zi pay the money and go and do a course somewhere if you are going to do grown up big boy bridges