(Help!) Multi-Unit bridge issues.

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Hello,

Our lab is having a problem with manufacturing a 5 unit bridge that has one pontic in the middle. (actually, a lot of the multi-unit ones are being problematic...)

We use 3Shape for modeling, Zirkonzahn M5 to mill, and sintering with a Mihm-Vogt HTS-2/M/Zirkon-120.

We made a 5 unit bridge and it seems to fit the abutments in each die just fine, but wont fit perfectly when fitting it on a solid model with two abutments on each ends (4 abutments and a pontic in the middle).

It seems like it shrinks in ways that we weren't expecting and wanted to ask if anybody has had this kind of problem and how it was resolved.

Thanks.

- NDA -
 
CoolHandLuke

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mill it again in metal or wood or gypsum. if it works, its a zirconia problem. if not, its a CAD problem.
 
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What Zr are you using?
 
TheLabGuy

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Are you using any stabilizer bar during sintering?
 
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Double post.

Maybe the Mods can clean this up,or you could post again using all caps?
 
2000markpeters

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are you sinking the framework well into the beads?
 
2000markpeters

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Also make connectors thick
 
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Most of the time, this kind of issue with Zirconia specifically (doesn't apply in metal cases since no sintering),is due to sintering.
These bars, especially when there is curvature, will shrink and end up not fitting passively.

How you nest them is crucial. You need to have a stabilizer bar across the arch and to keep a good amount of Zirconia at the end of the sprues to act as a heatsink.
I don't have photos to share unfortunately, maybe someone can add to my comment.

Found some images on Google images: stab2-300x244.PNG 016-web-258x145.jpg
 
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2000markpeters

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stupid question, you have the correct shrinkage factor. Should be in the 10% range
 
2000markpeters

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Also your Argon must be 4.8 to 5 pure
 
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Are you using any stabilizer bar during sintering?
We were not, not this time. Our technician working on it said that he tried that method in the past and didn't seem to be effective enough.
 
Car 54

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Are you using a very slow cool rate, maybe 5c per minute?
 
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Most of the time, this kind of issue with Zirconia specifically (doesn't apply in metal cases since no sintering),is due to sintering.
These bars, especially when there is curvature, will shrink and end up not fitting passively.

How you nest them is crucial. You need to have a stabilizer bar across the arch and to keep a good amount of Zirconia at the end of the sprues to act as a heatsink.
I don't have photos to share unfortunately, maybe someone can add to my comment.

Found some images on Google images: View attachment 33468 View attachment 33469
At the moment, we are trying to conserve materials and thought, instead of doing the kind of stabilizer the way it is in your pictures, we are thinking of leaving materials around the top and bottom of the bridge...
We'll see what happens.

Bridge forum.JPG
 
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Single layer of beads.They should act like bearings so the bridge moves freely.

You shouldnt need any stabilizers with something that small.
 
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Single layer of beads.They should act like bearings so the bridge moves freely.

You shouldnt need any stabilizers with something that small.
Yea, that is what our technician thought. But it shrunk in a way that it would not fit properly on the solid model, it does fit into the dies.
 
2000markpeters

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Sorry I thought you were sintering sintered chrome restorations.For zirconia you do not need stabilizer bars. Use very small beads and place on top without sinking. We do full arches of zirconia like this without problems
 
GG - J

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Just to confirm they fit on all abutments as individuals but can’t seat bridge with All abutments in place on model ?

Being that you are trying to conserve material, I would milk it out of wax and see how the fit is as pointed out above
Seems to like it coUps be sintering problem
We have had similar issue on some bridges with a span of 6 units or larger
We have sent file out to Argen to mill and sinter
Bridges have come back with really good results
Not the most economic solution but better than not delivering work on schedule
 

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