Cracks Cracks N More Cracks

JVitto

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Hey Everyone, so ive read through a bunch of threads on cracks in your zirconia after sintering. After reading honestly I think Im more in the dark than before. Ive read it can be my milling machine, sintering beads, oven calibration, drying time and manner, ETC....... We have been milling for over a year with only minor issues. 2 days ago i had a #8 on a 8-9 splint crack right where the spruee was then a singe full contour crack on a cusp now this morning I had a 8-11 framework crack where the connector met the coping. We have a Roland DWX-51D, Brand New Burs, No Recent Power Outtages or Errors. We have a WhipMix Infinity ZR oven 6 months old. I use a toaster oven to dry 300 degrees for 20 min. We use Whipmix Vericore Zirconia. Any Ideas??? My beads are 7 months old and im using ZirkonZahn Colour Liquid Prettau Aquarell Please help..
 
JohnWilson

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Are you using the HTX?
 
JVitto

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yes we are but its not the HTX thats cracking. Also i forgot to say my hold temp is 1510 while sintering
 
Patrick Coon

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Hey Everyone, so ive read through a bunch of threads on cracks in your zirconia after sintering. After reading honestly I think Im more in the dark than before. Ive read it can be my milling machine, sintering beads, oven calibration, drying time and manner, ETC....... We have been milling for over a year with only minor issues. 2 days ago i had a #8 on a 8-9 splint crack right where the spruee was then a singe full contour crack on a cusp now this morning I had a 8-11 framework crack where the connector met the coping. We have a Roland DWX-51D, Brand New Burs, No Recent Power Outtages or Errors. We have a WhipMix Infinity ZR oven 6 months old. I use a toaster oven to dry 300 degrees for 20 min. We use Whipmix Vericore Zirconia. Any Ideas??? My beads are 7 months old and im using ZirkonZahn Colour Liquid Prettau Aquarell Please help..

None of our products, but a few things to consider:

1: When separating from disk, use a sharp carbide at high speed (20-25K rpm),and cut each bar (sprue) half way before cutting any one completely. This will reduce chances of bur chatter and vibration causing small cracks before sintering. And don't let them drop on to a hard surface, have a towel on your bench top so if they fall they land on something soft.

2: Don't use any disks to deepen embrasures, this can create small cracks that can propagate.

3: Reduce your drying temps and increase your drying times. We would recommend no high then 140C (284F). Single units at this temp for 5-10 minutes. Splinted restorations and bridges up to 4 units at least 25 minutes. Larger or bulkier restorations at least an hour.

Not sure any of these things are the cause, but I hope the suggestions help.
 
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Sda36

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Hi, I think your toaster oven temp may be a touch high. I've been using a coffee cup warmer for years now without issue. Fits a dish exactly and heat for about 45 min before sintering start.
b97e596fb28c33bea355fa8f14ed1cde.jpg
 
Sda36

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Also, cooling rate is really important to not induce stresses.

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Car 54

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My thoughts as above members,I think 300 degrees seems a little hot to me, steaming things? I'm at around 200 for 15-20 minutes for singles. Maybe I'm still to high?

Even though this was from a milling wet zirconia thread, it may be helpful? Then see 2 posts down, brayks post:
http://dentallabnetwork.com/forums/...to-mill-zirconia-wet.22557/page-3#post-238238

Agree with Patrick, have you changed how and what you're taking your sprues down with?
 
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Sda36

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Another question, did all these cracked units possibly come from the same block?

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Polarmolar

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How long is your sintering cycle ? Is this on full contour ? On copings I sandblast them out instead of using a carbide as it gets rid of any vibration. I like to ramp up my heat when I dry so from cold I'll raise it up slowly and won't throw them in at full 300C.


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JVitto

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None of our products, but a few things to consider:

1: When separating from disk, use a sharp carbide at high speed (20-25K rpm),and cut each bar (sprue) half way before cutting any one completely. This will reduce chances of bur chatter and vibration causing small cracks before sintering. And don't let them drop on to a hard surface, have a towel on your bench top so if they fall they land on something soft.

2: Don't use any disks to deepen embrasures, this can create small cracks that can propagate.

3: Reduce your drying temps and increase your drying times. We would recommend no high then 140C (284F). Single units at this temp for 5-10 minutes. Splinted restorations and bridges up to 4 units at least 25 minutes. Larger or bulkier restorations at least an hour.

Not sure any of these things are the cause, but I hope the suggestions help.


That is exactly how we remove from the puck. But drying is not the same i will reduce the temp for sure and see what happens thank u very much!!
 
JVitto

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Hi, I think your toaster oven temp may be a touch high. I've been using a coffee cup warmer for years now without issue. Fits a dish exactly and heat for about 45 min before sintering start.
b97e596fb28c33bea355fa8f14ed1cde.jpg



I agree im going to lower the temp Thank you very much
 
JVitto

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My thoughts as above members,I think 300 degrees seems a little hot to me, steaming things? I'm at around 200 for 15-20 minutes for singles. Maybe I'm still to high?

Even though this was from a milling wet zirconia thread, it may be helpful? Then see 2 posts down, brayks post:
http://dentallabnetwork.com/forums/...to-mill-zirconia-wet.22557/page-3#post-238238

Agree with Patrick, have you changed how and what you're taking your sprues down with?


Thank you for the link Im going to lower the temp
 
JVitto

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How long is your sintering cycle ? Is this on full contour ? On copings I sandblast them out instead of using a carbide as it gets rid of any vibration. I like to ramp up my heat when I dry so from cold I'll raise it up slowly and won't throw them in at full 300C.


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sintering cycle is 7c to 900 then 4c to 1510 then cool around 9.5 hrs
 
Joe

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I was going to say it sounded like your puck had a hairline fracture before milling. This happened to us a few times. If it's three different pucks, did a whole box get dropped? Other then that, it sounds like they are cracking when cutting out of the puck. That's where it usually happens.
 
Polarmolar

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sintering cycle is 7c to 900 then 4c to 1510 then cool around 9.5 hrs

That's a slow cycle it's probably getting damaged in the green state as I doubt the ramp times could cause that cracks at that heat rate. Check how you finish the green state , I've never had cracks that i didn't know I caused. Usually it's from rushing and fast sintering crowns.


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Getoothachopper

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Not related to the cracking issue I don't think ,,,,,,,, But 7 months with the same beads ? What colour are they now ! ,,,,,,,,I would have changed those out about 6 months ago :eek:
 
sidesh0wb0b

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Hey Everyone, so ive read through a bunch of threads on cracks in your zirconia after sintering. After reading honestly I think Im more in the dark than before. Ive read it can be my milling machine, sintering beads, oven calibration, drying time and manner, ETC....... We have been milling for over a year with only minor issues. 2 days ago i had a #8 on a 8-9 splint crack right where the spruee was then a singe full contour crack on a cusp now this morning I had a 8-11 framework crack where the connector met the coping. We have a Roland DWX-51D, Brand New Burs, No Recent Power Outtages or Errors. We have a WhipMix Infinity ZR oven 6 months old. I use a toaster oven to dry 300 degrees for 20 min. We use Whipmix Vericore Zirconia. Any Ideas??? My beads are 7 months old and im using ZirkonZahn Colour Liquid Prettau Aquarell Please help..
i use LOADS of vericore and have zero issues with it.
i will say a few things that have been said here already

1. 300 degrees in the toaster oven is a bit high. i warm mine at no more than 200for 20-30min. (full crank of the dial is about 28min for my oven)
2. for a tray of singles or small bridges, your sinter program is slightly different from mine..... 8deg/min to 900C and hold for 30min. then 3deg/min to 1525C and hold 2hr. be sure your cool down ramp is slow enough. mines 10deg/min to 400C. entire program takes about the same 9-10hr for me. ive yet to play with it to shorten it some because im crazy busy and it is working for me. (this is NOT my program for large bridge sintering FYI)
3. cut off may be where the cracks are coming from. be sure theres lots of care pre sinter on these cutoffs.
4. ive yet to find good beads that last much more than a month or two....and they are stupid expensive (searching for an alternative). might want to change those out.

if youd like to PM me, i am having great success with vericore and will help in any way i can.
cheers
 
Kam Yu

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Bought a mihm vogt cause of the reputation, started milling preshaded zr and didnt use any liquids and predried at 200 for 30 mins. Elements kept getting contaminated every few days. Called for support and was advised to dry at 300 for at least 30 mins. Now i have to be proactive and run a purge program every weekend. Haven't experienced any cracks or anything with drying at 300. But will probably drop down to 250 since so many are advising 300 is too high.
 
Sda36

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Hi Kam, you're probably fine as you didn't add any liquid to your zirconia. As far as I know, the risk is of steam expansion in the zirconia, from the liquids, being released too fast. JMHO

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