Long Bridge Rocking

[Jennifer]

Hello All!

We've got an 8 unit and an 11 unit bridge that are giving us some trouble.

Our setup:
3shape scanner, D1000
Roland Mill, DWX-51D
Sintra Furnace

We tried milling in wax and we got a little bit of rocking. Zirconia with and without sintering connector rocked a lot.


We're milling with the CAP Z complete pucks and used the recommended program from CAP for long bridges. At this point we're not sure if it's a sintering issue, a designer issue or a software issue, or some combination of the three. The bridge seats perfectly on all the abutments except one on the end in both cases.

We're in contact with CAP about this as well, but wondered if we could get some help on the forum as well.

Update: CAP gave us a new sintering program which we tried with the 8 unit bridge. It seemed to work except for #7 where the margin is open, help! I've added a photo.

Thanks so much!

 

[H.Ross]

Rocking issues are mostly caused from how you place the sintered frame work, and in long span bridges, the milling or software strategy needs to keep sprue connecting both ends of the bridge together.

 

[Getoothachopper]

Are you sure the scan is good and a die or abutment wasn't seating correctly initially ? 'Just a thought'

 

[Sevan P]

How did you do the lingual support bar? Also what size sintering beeds, along with the sintering ramp times, hold time cooldown times and temps. Mainly if the scan was good. Usually it is the sintering end that messes things up. Also connectors and design can effect the out come.

Please provide more images of how you cammed the bridge. And more pics of the design.

 

[Car 54]

Try milling the same file out of PMMA (more rigid and accurate than wax),in which it should be rock solid. If all fits good, then you can take the scan/design and the mill out of the equation and focus on what others here are saying concerning spruing, connector design and sintering.

In your photo, it almost looks like #7 has lifted up, or tilted, warped in the sintering oven?

 

[Terry Whitty]

Have you tried a complete rescan and redesign or are you just milling the same file over and over?

Sometimes this will nail the problem as a small scanning or design issue can cause major headaches.

I know its a drag but i would definitely rescan and redesign, then mill in PMMA to verify..if all good..go for Zirconia.

 

[Sevan P]

Try milling the same file out of PMMA (more rigid and accurate than wax),in which it should be rock solid. If all fits good, then you can take the scan/design and the mill out of the equation and focus on what others here are saying concerning spruing, connector design and sintering.

In your photo, it almost looks like #7 has lifted up, or tilted, warped in the sintering oven?

I was just about to say mill it our of wax and see.

 

[RCKSTR]

Lingual support, with a stabilizer base (like sum3d offers) so the bridge can stand like an arch in the tray, no beads.

 

[Jennifer]

Wow, thanks so much for all the support! We're definitely taking all this advice into account and we're learning a lot!

At this point the game plan is to scan and design from scratch again. CAP let us know we should thicken our sprues on the lingual side connecting to the sintering stabilizer. We'll also be adding more sprues and making sure there's a sprue on each abutment tooth (last time we just did every other tooth).

Will update!

Thanks everyone!

p.s. I like your Dr Who pic Terry!

 

[Car 54]

That's who it is, Dr Who...good catch, Jennifer, have wondered about that one Thanks for keeping us posted.