Rocking, Rocking, ROCKING!

[wwcanoer]

I went through a short phase of rocking bridges also, and finally discovered this was what was causing the problems. I would take a length, about an inch, of my sprue wax wire off of a spool, straighten it, divide into how many many sprue pieces I needed, then attach it to the connectors, and cutting them down to length. In retrospect, I was dealing with "memory issues", but it took me about two weeks to figure out what had changed in my technique. Quit straightening the wire, problem went away

good luck, I hope you have already solved your problem!

Carol

 

[2thbob]

Make sure youre not using too much alloy... you want to cast your patterns and the runner bar only. If you have too much metal and are left with a button, youve shifted the heat-center in your ring. Without a picture its tough to show how thats a negative, But it does effect (or affect?) distortions. Also, when you attach your reservoir bar via feeders to your patterns, attach to your abutments first, then your pontic. AND, dont attach feeders to the interprox. Do it to cusp tips on each unit. otherwise you can get some microporosity in your unit to unit joint. Fits good as cast, but after its fired a rock can show up.

 

[Affinity]

i agree, the bridge in the picture looks like more metal than i want to finish down..

I also use the technique of one sprue on the pontic and rarely get rocking bridges. Just make sure that the bridge is not rocking in the wax, and it shouldnt rock in the metal, just wax slow, make sure to let it cool.

or just get some of primotec's light cured wax.. no brainer.

 

[crivasCDT]

Great techniques everyone....

We have a book called the Bredent Casting Technique According to Sabath which covers the entire casting spectrum and addresses all the issues mentioned here, and then some. The neat thing is that the information is presented in a to-the-point manner that can be taken from the page to the bench, fast! An excellent reference/training manual.
Bredent - Bredent Casting Technique Book

 

[desertfox384]

So everything is going great so far. Have been doing many bridges and 90% have came out great. I waxed a 9 unit, i think it was 3-11 and when i was pulling it off the model it warped between 3 and 4 (most likely due to a thin connector) but do any of you have a good trick for pulling off a bridge that big? i use a part of a latex glove which grips the wax OK and work it off slowly.

 

[charles007]

desertfox,
I usually grab the runner bar from both ends, etc, and just lift up, on cases that large. Don't ever intentionally make the connectors small, you can always thin them down in the finishing...... As you saw, small connector may have been where the wax flexed when you pulled off the model......
If you ever see a case that might have a draw problem, wax the abutments-just dip and seal margins. Then lay a metal bur, or hard plastic sprue rod, sticky wax over the inc-occlusal.....Lift off to see if it draws without breaking the dipped waxed coping......

 

[MsGabby]

I stopped using a razor blade years ago. If its heated up...it can distort or melt where You don't want. I use a wax filiment...basicly a very thin fishing line. Cuts real nice and super thin. After fine tuning margins etc... I reconnect the bridge with GC pattern . I never remove the wax ups from the dies until all is sprued and ready to invest. I make sure my sprues are the right gauge...the runner bar being the thickest. Works good for me.

 

[molarmaker]

Rocking Rocking Rocking

Hello this is my first post in this DLN been doing c&b a long time, and every ones advice is dead on, wish internet was around when I started, so here is my technique.I sprue with 8 Ga. plastic hollow sprues attached to a stick of carving wax as a runner bar and here is the key, investing using your nornal ratios and powder fill each pattern with investment then add 1 cc of liquid back to the mix and pour that in the ring don't use the vibrator or it will penetrate the thicker investment in the pattern making this useless, by this you overcome the different expansions you are trying to get

 

[dental1975]

Robert Berger said in a lecture that wax is still moving let it sit overnight or just sit it in front of a fan for a while

 

[labguy50]

Whether its a 3 unit or a roundhouse i never ever connect both sides of any pontic until im ready to sprue and invest. Wax it to one of the pontics so that the tolerance is so close that it looks like it is connected..finish waxing the case...add sprues to interproximals, seal the unconnected pontics with G Cera, attach runner bar with sticky wax on one or two sprues..connect the rest with G Cera...when removing from dies use crown holders or tweezers..etc. to gently pry fron the under interproximals while lifting at the same time ....works great at this end ...

 

[dmonwaxa]

When spruing for casting, does one attach connectors larger in diameter than the runner bar and lead sprues? Also how does that guage numbering thing work?

 

[dmonwaxa]

When spruing for casting, does one attach connectors larger in diameter than the runner bar and lead sprues? Also how does that guage numbering thing work? I always thought the smaller the number the larger the diameter and when spruing you go from large # to small # from the from the connectors so when the molten alloy enters the mold the sprue channels create a funnell like effect. I'm confused

 

[clearH2O]

When spruing for casting, does one attach connectors larger in diameter than the runner bar and lead sprues? Also how does that guage numbering thing work? I always thought the smaller the number the larger the diameter and when spruing you go from large # to small # from the from the connectors so when the molten alloy enters the mold the sprue channels create a funnell like effect. I'm confused

Smaller number is larger in diameter of sprue-wax. You can use #10 gauge for running bar attached the pattern, then goes up to #8 or even #6 (it means larger diameter) for the reservoir crossing bar. you are correct on funnel like effect. I hope my answer helps.

 

[clearH2O]

We talk about wax connector, sensitive, temperature, so forth... , I wanted to add once more cause may contribute to rocking. It is non-parallel insertion pattern.
Non parallel insertion may cause by undercut of the pattern or on larger bridge may cause by inter proximal tooth angles. At least 6 degree angle on prep-dies for wax pattern removal. A slight obstruction from inside wax pattern may let to wasting time re-doing. Warping of the bridge due to removal wax pattern before its completely cool is often, but trying to remove wax pattern on non-parallel insertion model is not unusual.
If this is the case, technician or lab must call Dr. for re-prep.

 

[dmonwaxa]

Smaller number is larger in diameter of sprue-wax. You can use #10 gauge for running bar attached the pattern, then goes up to #8 or even #6 (it means larger diameter) for the reservoir crossing bar. you are correct on funnel like effect. I hope my answer helps.

This sounds conflicting,

 

[labwoman]

One thing I also learned is the you cut the bridge after everything is sealed sprue the bridge with the bar then you stickywas the cut area. I have been doing this for a number of years and haven't had a bridge rock.

 

[clearH2O]

This sounds conflicting,

Hi dmonwaxa, I am sorry if I confused you. I ask you to take a look at TheLabGuy's wax picture.
1. number #10 gauge is the ~3mm sprue connected to the bridge wax pattern.
2. number #6 or #8 larger gauge is used on crossing reservoir bar of the pre-fabricated wax pattern
That is all. PM me I can send you more pictures I have if you needed.
thanks
clearh2o

 

[dmonwaxa]

thanks for clearing that up clearH2O

 

[paulg100]

im not a big metal guy but what a can say is that a cast span of 38mm is said to be the maximum to aim for if you require a highly accurate and completely passive fit.

It is then a matter of layering ceramic and picking up sections intra orally with ultra low expansion plaster and then post soldering.

This was concluded by a very highly respected tech in the UK who along with one of the countries leading dentists, published a book some years back.

They also teach that an open margin of more than 40 microns is clinically unacceptable, wonder how many of us are working to that popcorn. The dentist (wont name him) must be great fun to work for

 

[TheLabGuy]

This sounds conflicting,

This was the way I was taught......now if you want to sprue it at different places instead of at the connectors, that's fine, but the sprue/bar/resovoir leads sizes are very important to make sure you don't get any rocking.