Holes in Pontic

[Uliana]

Hello!
We are new in casting Chroma Cobalt, we are getting holes in Pontic. Please see photos. Please advice what can be the issue?

 

[kimba]

where are you spruing?

 

[Uliana]

where are you spruing?

I sprued on lingual cusp if it is mandibular and for maxillary it will be on buccal portion


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[Uliana]

where are you spruing?

It’s bridge so I make runner bar in this case


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[Getoothachopper]

It's always good to go back to basics when you start getting these problems . Make sure the 'runner bar' is thicker than the thickest part of the bridge & is in the hottest part of the casting ring ( it needs to be the last part to cool as the bridge pulls metal from it )

 

[kimba]

agree with what getoothchopper said. also just to be clear , are the holes near the sprues?

 

[Uliana]

Bego supplier suggested not to put sprue on Pontic, is it correct? And we are getting holes only on Pontic.

 

[JMN]

Bego supplier suggested not to put sprue on Pontic, is it correct? And we are getting holes only on Pontic.

Nooo! Sprue to the pontic. I even double sprued on big ones. One to each buccal cusp.

Edit: The metal contracts as it cools and the bar and sprues are where you want it to draw metal from as it cools.

 

[GarryB]

As JMN says above...…..we use sprues with reservoirs on our big pontics (when we cast and not SLM) so when the metal cools it will pull from there and not the substructure.

 

[charles007]

The only difference in casting np and precious is using larger sprues with np.
Years ago I used runner bars and switched to direct spruing using sprues with reservoirs, not that its better, just faster.
Place your sprues at the correct angle. Got a feeling your runner bar was to small and or your direct sprues were to long, or both/suckback as stated by Getoothachopper.
In either case bad spruing technique !.......Hit the books on spruing.

 

[adl]

Hello!
We are new in casting Chroma Cobalt, we are getting holes in Pontic. Please see photos. Please advice what can be the issue?

Check out Bredent casting techniques. You’ll never go back to how you used to sprue.

 

[user name]

Make sure youre not using too much alloy. You want to complete your frame and most of the bar/reservoirs, but no more. If you have a button left over, it can be drawing allow from your bar and preventing the molten supply from going into your pattern.

Don't over heat the metal when casting. That causes unnecessary expansion.

I could tell you what I think of casting metal frames, but not without using the letter F.

Whiskey Tango

 

[JMN]

A well built sprue system will have the objects being cast jn the coolest part of the ring, or the part that will cool fastest if you prefer, and the spruegates, runner bar and feed from the button and then the button -in that order- in the parts that will cool slowest so that the desired parts wil be fed until they cool.

In practice it's near impossible to do right every time, but you can always get the gastes and bar/feedlines to be hotter than the cast parts.

With co/cr it is even more critical than normal to not overheat. If the remainder in the casting crucible does not come out like picking up a piece of foil it is being overheated. When using multiple ingots they may not look as if they have merged as HN ingots appear, and that is okay.

Another way to tell also, NP is overheated if you can see that the oxide layer broke/cleared.

Side note, if you are casting this by hand without welders glasses you are asking for trouble. Get some. You can acheive high enough energy output to cause irreperable retinal damage just like watching a weld.

Might be some useful info here for you as well, Al put up some nice sprue pics in this thread:
https://dentallabnetwork.com/forums...tics-orinto-thick-metal-supports-imake.15129/

If you find issues are still giving you a bad day, put up pics before you cut it off. Both sides, from bottom(metal entrance)/button and from the margin/metal stop side.

 

[Contraluz]

I always found the following Manuals useful. I can't individually post the links and some of the PDFs are too big. A couple of them come with a 'Troubleshooting chart':

http://www.ivoclarvivadent.com/en/p/all/products/alloys/successful-alloy-processing