Advice on layering buccal cutback

T

tandob

New Member
Full Member
Sometimes when I am layering a buccal cutback on zirconia it pops off the in oven mid-fire due to contraction shrinkage. I do a washbake cycle and always condense and dry the porcelain thoroughly. I've found it happens more often when the buildup is thicker.

Does anyone else experience this problem? What are your techniques to mitigate it?
Any techniques to reduce firing shrinkage in general?

I am working with Vita VM9.

Thanks for any ideas
T
 
Sda36

Sda36

Active Member
Full Member
Hi, try and slow your heat rate climb, not sure where you're at with that but 25° C per minute is a good start. Predry 6 min at least, I also use a soak time of 1 min prior to heat rise. This is in case you use any internal stain medium of any sort in your build up technique. Zirconia is an Insulator, not a conductor as with PFM, it requires time and temperatures to respect that. Hope this helps, run a few test firings on sintered chips or un-used crowns to see if this helps you. You can also lightly blast your wash bake to remove any sheen to help wetting the surface and reduce asccotiated surface tension. Can't hurt. Best of luck.
 
OP
T

tandob

New Member
Full Member
Dear lord the Vita manual recommends 55C/min as rate of heating for VM9. I'll definitely bump it down and report back. My predry is currently 6 min as per manual. I'm not familiar with 'soak time', what is that?
T
 
Sda36

Sda36

Active Member
Full Member
Dear lord the Vita manual recommends 55C/min as rate of heating for VM9. I'll definitely bump it down and report back. My predry is currently 6 min as per manual. I'm not familiar with 'soak time', what is that?
T
That's a feature available on my Zubler furnace, just means it holds at start temp for 1 min while the muffle is closed fully. You can likely key in that on your furnace somehow.
 
OP
T

tandob

New Member
Full Member
Oh yeah my Vita furnace has programmable chamber opening positions for the predry. I just changed them to 3 min each fully open, 50% open, fully closed. Also change ramp up temp to 30C/min. Cycle length is now 30 mins but if it means no redos due to cracks, pop-offs or creeping margins then it's worth every second!
T
 
Sda36

Sda36

Active Member
Full Member
Oh yeah my Vita furnace has programmable chamber opening positions for the predry. I just changed them to 3 min each fully open, 50% open, fully closed. Also change ramp up temp to 30C/min. Cycle length is now 30 mins but if it means no redos due to cracks, pop-offs or creeping margins then it's worth every second!
T
You'll also want to set your cool time down as well, especially for bridges. 35 °C per minute is pretty safe. All the time spent is furnace time, not your productive time, surely you can find something else to do meantime 😉
 
OP
T

tandob

New Member
Full Member
You don't wait excitedly by your furnace like a child on Christmas for your restorations to finish firing?! 😆
 
Sda36

Sda36

Active Member
Full Member
You don't wait excitedly by your furnace like a child on Christmas for your restorations to finish firing?! 😆
Gave that up many years ago once things became more predictable, Thankfully!!
 
Contraluz

Contraluz

Well-Known Member
Donator
Full Member
Sometimes when I am layering a buccal cutback on zirconia it pops off the in oven mid-fire due to contraction shrinkage. I do a washbake cycle and always condense and dry the porcelain thoroughly. I've found it happens more often when the buildup is thicker.

Does anyone else experience this problem? What are your techniques to mitigate it?
Any techniques to reduce firing shrinkage in general?

I am working with Vita VM9.

Thanks for any ideas
T
You got some great advice here already! But, I would like to ask you at what temp you fire your wash? Is it more like a 'liner', at high temp or just a thin porcelain layer at 'regular' temp? For example, Ivoclar, and others, recommend a liner (Zirliner) firing at 960 C. And then do your wash cycle. This will improve the adherence of your stacked porcelain.
I've found it happens more often when the buildup is thicker.
You may be closing your furnace too quickly. An, on the other side of the spectrum, you may be over-drying your porcelain, before putting it into the furnace. Both can lead to cracks and 'lift-offs...)

M
 
rkm rdt

rkm rdt

Well-Known Member
Full Member
I never condense my porcelain.
I also minimize my cutback .
 
JMN

JMN

Christian Member
Staff member
Full Member
Sometimes when I am layering a buccal cutback on zirconia it pops off the in oven mid-fire due to contraction shrinkage. I do a washbake cycle and always condense and dry the porcelain thoroughly. I've found it happens more often when the buildup is thicker.

Does anyone else experience this problem? What are your techniques to mitigate it?
Any techniques to reduce firing shrinkage in general?

I am working with Vita VM9.

Thanks for any ideas
T
Thicker it is, the more 'agressively' it will shrink. It's all about percentages.

5% of 100 inches is 5 inches.
5% if 100 feet is 5 feet.

Same percentage but far more when there is more.
 
OP
T

tandob

New Member
Full Member
You got some great advice here already! But, I would like to ask you at what temp you fire your wash? Is it more like a 'liner', at high temp or just a thin porcelain layer at 'regular' temp? For example, Ivoclar, and others, recommend a liner (Zirliner) firing at 960 C. And then do your wash cycle. This will improve the adherence of your stacked porcelain.
My current washbake cycle paramaters are 2 min predry at 500C, 55C/min ramp rate, then 1 minute at 950C.

My technique is to apply a very thin layer of thinly mixed porcelain with modelling fluid around the surface to be stacked.
 
Contraluz

Contraluz

Well-Known Member
Donator
Full Member
My current washbake cycle paramaters are 2 min predry at 500C, 55C/min ramp rate, then 1 minute at 950C.

My technique is to apply a very thin layer of thinly mixed porcelain with modelling fluid around the surface to be stacked.
That would be the 'liner'. What I do after, as a wash, is wet the surface with glazing liquid (not past or material) and dip the restoration in porcelain powder of my choice or sprinkle it onto the frame. I usually add some characterization to the frame with staines or essence powders, before dipping/sprinkle it. That I then bake it about 20C above the regular dentin firing temp.
 
ps2thtec

ps2thtec

Well-Known Member
Donator
Full Member
My current washbake cycle paramaters are 2 min predry at 500C, 55C/min ramp rate, then 1 minute at 950C.

My technique is to apply a very thin layer of thinly mixed porcelain with modelling fluid around the surface to be stacked.

That two min. dry may be a little fast? I know the vita chart shows that, but. Posting the chart I made for my oven with VM9.
It’s what works for me and my oven. I never saw any pop off you described in original post.

532B6A12-0B32-42C9-9976-EB95CA1FC262.jpeg
 
OP
T

tandob

New Member
Full Member
That would be the 'liner'. What I do after, as a wash, is wet the surface with glazing liquid (not past or material) and dip the restoration in porcelain powder of my choice or sprinkle it onto the frame. I usually add some characterization to the frame with staines or essence powders, before dipping/sprinkle it. That I then bake it about 20C above the regular dentin firing temp.
That sounds like a great technique. I'm going to try that.


Also I baked the facial cutbacks I was having that problem with and the new firing parameters have solved the failure I was having due to shrinkage. Thanks guys
 
rkm rdt

rkm rdt

Well-Known Member
Full Member
Now get a Miyo kit and say goodbye to the layering technique.
 
Z

ztech

Active Member
Full Member
Vita recommends that you fire their porcelain with little condensing and definitely not dry. My judge to how wet it should be is when you can touch it and not leave finger prints on it, so relatively wet. The Vita parameters are what I use and except for really thick porcelain, I never have and issue. I suspect what you were doing was disturbing the wetting the raw porcelain has to the liner surface, when you dried the porcelain with the tissue. The grain size on the VM9 makes it easy to disturb the stack it you are not extra careful.
 
  • Useful
Reactions: JMN
OP
T

tandob

New Member
Full Member
Vita recommends that you fire their porcelain with little condensing and definitely not dry. My judge to how wet it should be is when you can touch it and not leave finger prints on it, so relatively wet. The Vita parameters are what I use and except for really thick porcelain, I never have and issue. I suspect what you were doing was disturbing the wetting the raw porcelain has to the liner surface, when you dried the porcelain with the tissue. The grain size on the VM9 makes it easy to disturb the stack it you are not extra careful.
Interesting. I'll dry firing it damp with the VM9 manufacturer recommended parameters.
 
sndmn2

sndmn2

Well-Known Member
Full Member
I use some Vita. I just use glaze as my liner. Run it up on a glaze cycle and shes good.
 
Guest Room
Help Users
  • No one is chatting at the moment.
  • Chat Bot:
    Room has been pruned!
    Chat Bot: Room has been pruned!
    Top Bottom