Sintering shrinkage

tehnik

tehnik

Active Member
Full Member
Messages
506
Reaction score
12
Hello!


I am having a sintering problem with one specific job, that has two bridges. 4 unit and 3 unit. Both of them shrink mesio-distally... this means the pontics fit in the bridge one by one, but together not. I scanned the model again as I thought is was misaligned in the scanning software and the second time 4 unit bridge was ok but 3 unit not. I milled pmma test bridge out of the file and the pmma bridge seats perfectly. What can be wrong? I milled totally 4 bridges out of the milling block and other bridges were also OK. Is there something with the desing?
 

Attachments

  • Capture.PNG
    Capture.PNG
    61.6 KB · Views: 186
Patrick Coon

Patrick Coon

Well-Known Member
Full Member
Messages
1,174
Reaction score
565
My first thought is, have you input the shrinkage factor into the software correctly? A little bit off, may not be noticeable in single units, but would definitely show up more in bridges. And since there is no shrinkage in pmma, everything would look fine there.

My second thought is how are you placing them on the sintering tray? They should all be placed on the occlusion and supported (all units touching tray) to avoid warpage during sintering. If all units don't touch the tray, you should consider placing drops on the occlusion for support. Placing on facial or lingual is ok for anterior bridges (again if all units touch the tray) but with enough curvature you should place a lingual support bar to help control shrinkage.

I hope this helps.
 
tehnik

tehnik

Active Member
Full Member
Messages
506
Reaction score
12
I milled it again, added a bit more sintering beads ti the tray and yhe bridge is perfect.
 
tehnik

tehnik

Active Member
Full Member
Messages
506
Reaction score
12
So what to think of that? It was connected to 12 unit bridge. The bridge was actually on implants and two tooth and the bridge sat on the implants and rocked when I added prepared teeth to the model.
 

Attachments

  • IMG-20170804-WA0002.jpeg
    IMG-20170804-WA0002.jpeg
    47.2 KB · Views: 174
  • IMG_20170803_175020.jpg
    IMG_20170803_175020.jpg
    54 KB · Views: 174
CoolHandLuke

CoolHandLuke

Idiot
Full Member
Messages
10,078
Solutions
1
Reaction score
1,411
this is precisely the reason why those supports are supposed to be solid. you have created a support bar that effectively DOES NOTHING.

is it a huge waste of material? yes. but if you dont have to remake it, whats the big deal?

also you should know better than that, don't connect teeth to implants in a bridge.
 
tehnik

tehnik

Active Member
Full Member
Messages
506
Reaction score
12
As I am just milling what laboratories order, it is not up to me what to connect and what not. I will be doing the support solid next time. I am just wondering why was the bridge stable on the implants.... it was evetually fitted to the model btw.
 
Sevan P

Sevan P

Well-Known Member
Full Member
Messages
3,415
Reaction score
641
So what to think of that? It was connected to 12 unit bridge. The bridge was actually on implants and two tooth and the bridge sat on the implants and rocked when I added prepared teeth to the model.
What mill and cam was this done one? First thing j see is that the support bar is too thin for that style of arch. Thin support will cause warping as well. This is why the bottom of the support bowed inward.

Milling a solid center support will also cause problems as where it will sinter with more force and cause issues as well.

What cam was it done with.

Sent from my SM-G920V using Tapatalk
 
Brent Harvey

Brent Harvey

Well-Known Member
Full Member
Messages
411
Reaction score
188
What mill and cam was this done one? First thing j see is that the support bar is too thin for that style of arch. Thin support will cause warping as well. This is why the bottom of the support bowed inward.

Milling a solid center support will also cause problems as where it will sinter with more force and cause issues as well.

What cam was it done with.

Sent from my SM-G920V using Tapatalk
I agree 100% the equalizer/Support bar should be of equal mass to the bridge, this bridge looks like it has much more material than the support has.
 
tehnik

tehnik

Active Member
Full Member
Messages
506
Reaction score
12
Millbox with Roland. As said, the bridge was not crooked on the implant part.
 
tehnik

tehnik

Active Member
Full Member
Messages
506
Reaction score
12
So considering the mass, is this stabilizer good enough? the same job was bent, when I sintered it with solid stabilizer although the base was obviously straight. The thickness is 3 and height also 3 in the picture. I was thinking 2.5 and 2.5. These are settings in roland millbox.
 

Attachments

  • 1.PNG
    1.PNG
    107.3 KB · Views: 131
  • 2.PNG
    2.PNG
    253.3 KB · Views: 110
Last edited:

Similar threads

Top Bottom