Help with CTE-GC Initial users

[Affinity]

I am having a problem with cracking on my GC Initial MC. I am using Argedent 35SF, and almost every crown has cracked after the glaze.. Only after glaze or add-on firings, If I run it up again, it generally fixes it.. I had one that was fine all day friday, then come in monday, huge crack down the facial.

Now the hard part, GC manual says a CTE of 14.2 is "IDEAL" , yet this alloy has a CTE of exactly 14.2... What is going on? Im switching alloy to see if it fixes the problem.. but cant figure out what Im doing wrong... Cooling time?? I have my pro 100 set for a 3 min cool...

HELP

 

[corona]

it still sounds like a cte issue . is it only cracking with this alloy?? is it a verticle crack? horizontal crack? or just craze cracking everywhere?

 

[Al.]

Even if you fix it with slow or fast cool or different wax designs I would switch metals ASAP. Don't want a marginal combo but one that is forgiving with large or small frames and fast or slow cools.

I want an alloy that works well with single units or full arch splints with out fear of cracks. But on large pontics I scoop out the B and L to equal out the metal to porc ratios. Almost hollow pontics.

 

[wilkscm]

i had same problem even sent samples to belgium no solution changed to noritake never had problem with any alloy or firing cycle etc

 

[dmonwaxa]

Been using GC MC and Been using GC MC and ZR for 6 plus years and have never had a crack or any other issues. I believe as Al. stated above it could boil down to metal design. But I doubt from your experience thats the case. So what else? Contamination? From porcelain inadvertently being mixed. ie mc and zr. I use a different slab and brushes for either. Or make sure they're very clean.

 

[NicelyMKV]

This alloy has 56.5 % Pd content so it is imperative that fresh alloy be added each casting. Pd is an oxygen scavenger, so buttons can become easily contaminated after multiple castings and result in cracks, especially if torch casting and not induction casting.

That being said, the cool time is another possible problem. A three min cool time is not needed or advised for 14-14.2 alloys using MC. Extended cooling time is only advised when using alloys 14.5 or higher.

MC range of preferred alloys is 13.8 to 14.9, with 14.2 being ideal.

It is important to note that with Pd based alloys, that although the native/ fresh alloy may be listed at 14-14.2, after 1st casting CTE begins to drop, and if reusing a button 2-3 times without adding fresh, can drop down to 13 or lower, as CTE of pure palladium is 11. The extended cool time would only make cracking more extreme or increase occurrence of the cracking. Those trace elements that help regulate CTE and keep CTE at 14.2 are burned off in those first couple of castings.

One more reason to add fresh alloy, especially when using a Pd based metal.

 

[2thm8kr]

Well said Nicely!

 

[NicelyMKV]

I like MC

 

[dmonwaxa]

Jason, well said, but I took it for granted that's common knowledge. Yeah the long cool time is unnecessary. BTW I like GC also.

 

[Affinity]

I love the porcelain, and Ive been using it for over 7 years now.. Never had this type of problem.. Cracks are vertical and horizontal, had a molar with a vertical crack on buccal, had a bridge with crack the length of the pontic.. I always use a majority of fresh alloy, even with 100% fresh and brand new crucibles, i seem to have this problem. I have changed alloys to Argedent 65sf, see if less PD improves the situation.. I never really paid too much attention to the cooling time because I never had the problem before.. I used wirobond c (which is 14.0cte) for almost everything and it worked excellent, never a crack!, but unfortunately its NP.. the only thing I didnt like about it.. but the bond was amazing, especially at the margin..

Im going to rule out reusing old alloy, and metal design, only because it has happened on many cases.. I really think it is the cool time although the MC manual is a bit ambiguous about it, because it doesnt list a proper cool time.. I get a bit freaked out seeing red hot porcelain dropping immediately out of an oven.. I was always concerned THIS would cause the cracks.. I guess I was a bit ignorant thinking that if the CTE is what the man. deems 'ideal' that it should be ok regardless of cool time... but when you dont have problems, you dont pay attention to trying to solve them...

What about overheating the alloy during casting? I was spoiled with an induction casting machine and flawless casts for years but had to sell it, now im back to old skool, and learning from mistakes.. Im lettin 'er rip right at 'liquidus' phase, when it balls up.. maybe torch is too hot??

Thanks so much for the input guys, ill let you know how the new alloy works out!

 

[Affinity]

Well said Nicely!

Yeah you are seriously a weatlh of information on this site, along with Al of course, thanks so much.

 

[dmonwaxa]

My take is overheating may have the same effect as reusing buttons, because you may be vaporizing elements that have a low melting point. In my noob days I remember I overheated the metal so much it actually froze. And if you did get it to cast the metal was full of micro-porosity.

 

[NicelyMKV]

Make sure you keep the reduction zone of the flame against the alloy.

 

[corona]

just another thought ... out of the box . whats going on in the opaque stage .... are you using oil based opaqued or powder opaques ? what the opaqued coping look like after firing ? i still thinks its the cte giving you the checks in the porcelain , but check those opaques just to eliminate that from the story. good luck

 

[Affinity]

Ive tried both powder and paste opaque.. but good call.. I will see how the new alloy responds.. that is a definite possibility