Rocking, Rocking, ROCKING!

[desertfox384]

Hey all I'm new here but will get straight to the point.
Im tired of rocking bridges and have seemed to try everything with little luck. Let me give a quick detail of my technique. I use hot melted wax for initial application and hot melted wax for build up of copings. (I get absolutely perfect adaptation most of the time.) My waxer is set to 305 degrees all day. So for bridge wax up I'll wax up the copings add collars and trim margins then put back on model. Ill then wax in the pontics and finish. Now we check everything on solid model so ill now cut the bridge with a razor blade stick the wax pattern on the trimmed solid model and reattach it with duralay and ive also tried super glue. Many times it works. Many times it doesnt and ill end up with a tiny rock - and with very large bridges even though it seems great on the solid model theyll end up rocking after casting. I keep up on my water powder ratio's every day as well. My copings require very little work to get perfect fits. Oh I also most of the time use a direct spruing technique - For example a large plastic sprue with reservoir to pontic and wax leads coming from reservoir to abutments. Any suggestions? Im baffled.

 

[TheLabGuy]

Sounds like your spruing technique to me...........
Forget all that razor blade cutting with duralay/solid model nonsense........blahhh.
JUST Make sure your wax bridge looks good on your sectioned model, under scope make sure the margins where the pontic/abutment connectors didn't lift while waxing your pontic.
THEN...... take some 8 guage (3mm length),sprue that to your connectors.........
THEN...... take some 10 guage (same length as bridge),use that as a runner bar
THEN.......take some 10 or 12 guage for sprue leads to connect to the base former of the investment ring.

I never have bridges rock......too busy to have that type of nonsense going on.....good luck and tell us how it works.

 

[charles007]

If you use glue in the connector, try this.
Cut a cross in both sides of the cut connector with a sharp knife, blade......add glue in the connector, spray, let it set for a minutes or so, add sticky wax or soft wax over the glue so its very smooth....... If you don't cut the cross in the connectors, the glue really isn't sealed to both parts of the wax. This is why bridges warp when using glue !

Example of a 3 unit bridge,,,,,,,,cut one connector, as above,,,,,,seal margin, glue connector, spray, let set, add wax......... then cut the other connectors, seal other margin, seat die and glue- spray........ Let it dry for a few minutes.
Make sure you only see a "small space" between the connector before you add the glue......not a large cut !! just need a little daylight in your cut into the connector !
I use Renferts concrete glue, and Renferts pear shape reservoir sprues, and attach the reservoirs together with the same wax........
Use sticky wax and soft wax on the sprues to the coping.
With this technique, I go years without seeing warped bridges...
If you aren't sure if the bridge draws or not.......
Wax coping over the abutments only ,,,attach a bur- plastic sprue, with sticky wax,,,,,,let it set, and pull off to see if the bridge draws or not......

Feel free to call or PM......this technique is fool proof if you follow my technique carefully and don't play around with the wax......

Charles

 

[kcdt]

Sounds like your spruing technique to me...........
Forget all that razor blade cutting with duralay/solid model nonsense........blahhh.
JUST Make sure your wax bridge looks good on your sectioned model, under scope make sure the margins where the pontic/abutment connectors didn't lift while waxing your pontic.
THEN...... take some 8 guage (3mm length),sprue that to your connectors.........
THEN...... take some 10 guage (same length as bridge),use that as a runner bar
THEN.......take some 10 or 12 guage for sprue leads to connect to the base former of the investment ring.

I never have bridges rock......too busy to have that type of nonsense going on.....good luck and tell us how it works.

Don't forget to let the wax cool each time before you move on. Keep the thermal contraction to a minimum. The order as outlined here has worked well for me.
P.S. You may also be screwing the pooch going back and forth between models so many times. The way I was trained was to avoid drawing it off the die as much as possible.

 

[desertfox384]

Thank you very much everyone for the valuable info. The reason I started to fit bridges to the solid model is because of the sometimes vast differences in fit between solid and working models. Now that may be a problem in the model department which is out of my hands seeing as though it is not my lab to dictate.
I will try your technique next time Lab Guy - I do have some preformed runner bars i will try with the rest of your technique and we'll see how it goes! Thanks for the help everyone! I can see this site as being a lifesaver and a great way to improve my techniques!

 

[Al.]

I agree its probably your spruing or connecting technique. Rocking bridges are no the norm here.

I dip, then build everyting up, then add my pontic. Then cut one connection with a razor.

Then I cut back the dipping wax and reseal the margins.
Seat everything then I add a very small amount of wax on the connection , usually on the gin side.
I go on to working on other units to let that cool and shrink completely.
Then add a small bit again usually on the occ side. Let it cool then add the M @ D.
In other words, dont add alot of wax or duraly or glue to the connection area at once because it contracts and will warp your bridge.

I sprue 10 ga wax on every coping and pontic then when that completley cools I put a plastic runner bar on top. Tacking it down a little at a time.

Then pop the dies.

I wax everyting in one day so I have several bridges I wax at once. So I just pick up one model at a time and add bit of wax on each connection and have them all connected and sprued in a group in 10 to 15 minutes.

Long spans are unpredictable.
Up to 6 units though it should be rare to get rocks.

 

[charles007]

Hey all I'm new here but will get straight to the point.
Im tired of rocking bridges and have seemed to try everything with little luck. Let me give a quick detail of my technique. I use hot melted wax for initial application and hot melted wax for build up of copings. (I get absolutely perfect adaptation most of the time.) My waxer is set to 305 degrees all day. So for bridge wax up I'll wax up the copings add collars and trim margins then put back on model. Ill then wax in the pontics and finish. Now we check everything on solid model so ill now cut the bridge with a razor blade stick the wax pattern on the trimmed solid model and reattach it with duralay and ive also tried super glue. Many times it works. Many times it doesnt and ill end up with a tiny rock - and with very large bridges even though it seems great on the solid model theyll end up rocking after casting. I keep up on my water powder ratio's every day as well. My copings require very little work to get perfect fits. Oh I also most of the time use a direct spruing technique - For example a large plastic sprue with reservoir to pontic and wax leads coming from reservoir to abutments. Any suggestions? Im baffled.

desertfox,
On your next case, don't transfer to a solid model........And I hope your working model is accurate. VERY SOLID DIES !
I think your problems are starting with you make the transfer....... You are probably seeing a loose fit with your wax patterns on the solid model. Then you cut connectors on the most accurate model .....bet if you looked hard, you would see a little SPRING in the wax patterns on the solid !
My best bet, this is where the warp starts. OR a combo of problems in the spruing-tranfer......
Like others have said.......let the wax cool ! before going to the next step.

On really large roundhouses, its not a bad idea to wax to presolder.
Wax in 2 or 3 sections to presolder......... or use attachments . Nothing fits better than a soldered bridge.........

Lots of luck and let us know if these tips help.............

 

[kcdt]

I never had trouble with sectional dies 'cause I do my own model work....
The presolder isn't a bad idea either.
Does your lab by chance have a laser or plasma welder? Even better.

 

[dentor2010]

Most of the above mentioned suggestions are worth a try desertfox. The most important thing is to have patience with the wax. add in small quantities and give time for cooling. However there are other factors which are worth thinking of:
The longer the bridge the more the risk. Ney suggest every bridge to be seperated and soldered even if you don't see a rocking on the wax.

A Curved bridge and a curved running bar may also give problems. BEGO suggests sectiond and straight Running Bars. (see photo).

My teacher suggests never to follow the rapid burnout cycle. He even prefers Hygroscopic investment technique but I don't know if it is available for base metal alloys.

Recently I was told by a technician that there are special ovens where you put your finished and sprued wax-up. still on the model at around 35 deg. Celsius for 5-10 min and let it cool to room temperature slowly so that all the stresses built up in the wax are released evenly, and then you invest it. I don't know how much truth is in this. I haven't tried it.

Anyway keep your work standardized. Change one thing at a time to find the error.

And finally a question for everyone here. Have you ever seated a full mouth cast bridge (several copings and pontics) perfectly on your model before cutting the sprues?
I have heard about it, never succeeded. Up to 5-6 units are OK, longer I cut and solder.

 

[charles007]

dentor2010
Many years ago when roundhouse cases were very common to see in labs, we had what we called a horse shoe bar.....For those of you that haven't heard of the term, its a long sprue attached from the 2nd molar to the opposite 2nd molar....The sprue bar were not cut off until the case was in the bisbake or after degassing- glazing... These were put on the bridge to help prevent warpage in the firing.....
Yes I have seated a large bridge with the sprues still connected in the past. Probably not a very wise decision. The shear weight of the metal when seating could snap the dies off if there is any, or even the slightest draw problem or warpage. I would never do it today !
Now that I'm working with older docs, all of my large cases are done with attachments...... Good idea, pain to make..........

 

[charles007]

dentor2010
I like the idea of straight runner bars....I use to really have a hard time with the curved bars...... the memory thing....these bars a have a memory like an elephant.
I use a straight reservoir sprues for bridges or like you, a straight runner bar........ Curved runner bars are part of my past......... as will be hand waxing very soon...........


Charles

 

[kcdt]

I use plastic runner bars- the clear ones- to deal with memory issues.

 

[desertfox384]

Okay, so from all the info gathered this is what ill do with my next bridge.
-Wax up the copings and add collars if necessary
-Then i usually trim margins under scope and put dies back on the model. (i would normally pull off copings at this point to make sure they will pull off easy after i finish waxing the bridge, but now I think I wont do that. I thought it might cause stress to the bridge if they didnt pull off easy and maybe thats what was causing warpage).
-Wax up pontics and use sticky wax mixed with regular wax for connectors
-Reseal margins (i should do this while the bridge is still on the entire model right?) Its hard to trim the margins under a scope when its interproximal and under a connector but i think ill manage.
-attach sprue leads and let cool
-Attach to runner bar and invest

Have anything to add or subtract?

By the way- do any of you think using already melted wax is making things too hot?

 

[TheLabGuy]

Try it, I bet it works great........as someone else hinted too, don't "fast burnout" this. I've seen bridges back in the day warp due to the fast burnout technique. As for wax being too hot, just make sure you don't do a lot at any given time. Like Al stated, do it in stages, giving it time to cool and yes, you must manage grasshopper to get those margins interproximal (it can be tough sometimes) but you will do it. This will save you tons of time and you'll gain confidence back in your bridges again.....good luck.

 

[TheLabGuy]

Just in case you wanted to see in pictures.......This works great for me.

 

[charles007]

Rob, thats a sweet and fast technique to sprue BUT !!! can you cast that bridge at .3 in noble like me..........hehe

 

[TheLabGuy]

nope, you have me beat Charles...........i'm still .4 -.5......grrrr Someday Master Jedi!!!!!!

 

[rkm rdt]

That extra .1 comes in handy at refining time.

 

[SSDS]

I agree with lab guy's technique, desertfox 384 is using. The reservoir will pull at the pontic and cause the rocking. I use very similar technique to lab guy and have no issues with rocking bridges. Good Luck

 

[desertfox384]

Well I havent had much opportunity to try out the new technique except 2 3 unit bridges. I had perfect fits! One thing i noticed was i had no issues with margins pulling away from the die after i waxed in the pontic and i am giving the sticky wax the credit. Ive never used a sticky wax mix before and always had margins pull away but no more! Thanks again guys for the help. The chest pains are starting to subside.....