Cracked up!

[JonB]

Addendum - when i got the HN crown back from the doc last week, I had the waxer wax a new coping to be cast out of fresh alloy and I stripped the cracked crown down to bare metal, refinished it, cleaned it, opaqued it and dried it on the hot plate for both coats of paste opaque (Noritake). It was then built up and cut in and glazed and held on the bench on the other crown running through the lab. The second one, I finished and gave to my ceramist who also used the hot plate. Both crowns were finished, glazed, polished and steamed and set on the bench for a day before I sent them out.

The doctor's assistant said they got them, and both were fine. No other cracks have since been reported.

 

[rkm rdt]

I have always designed my pfms with a lingual band.

 

[DMC]

I have had Docs that NEED a lingual band. They just don't reduce enough to have metal thinned out and opaque and porc. I try, but the porc breaks. Disto-Lingual 90% of the time.

Doesn't matter if it was PFM or PFZ. We added collars a few years ago for all cases with this guy, even the PFZ. Problem solved.

Maybe his impression technique is constantly giving me bogus info around that area?

Maybe we over-finished the metal and it was too thin at the margin?

 

[rkm rdt]

They concentrate on the buccal shoulder prep and reduce less on the lingual.The lingual band provides support for the porcelain and reduces overcontouring.It also eliminates that brutal porcelain to metal margin!!!!

 

[JonB]

In my experience, some alloys almost need a band, while others do not. Its a good idea to do regardless - but some docs object to showing a band. The alloys we've used in the past haven't exhibited the need for a band - except for the 75+6 on large bridgework that have thick pontics. Then its either slow cool or place a band.

 

[JonB]

update... still no more cracks!

 

[charles007]

I use Ex3 with Argelite 61 and I never degass/ oxidize .I just trim,sandblast and opaque.

I second this.. Used 61 and ex3 for over 15 years and not one check ... Its kind of like using Ivolcar pressing ovens and emax,,, never a problem...
Verticle check, CTE off ...end of subject...

Ask me how I know, I used Vita while other labs used Ceramco. If you didn't learn about CTE, cracks could be heard through the night and techs screaming through the day..

 

[JonB]

If Argen does not recommend degassing 61 - then you're fine. But if they do and you don't, you have departed from the recommended instructions with the alloy. You had better be a qualified and certified research facility if the stuff ever hits the fan and something goes south. in all the years I've been doing this, I've seen all kinds of things done "because that's the way it works in this lab" when it doesn't in others. All sorts of rationalizations for what we do. I think as things become more and more litigious - we'll have to learn how to follow the instructions just to protect our backsides.