Cracked up!

[JonB]

Did you hear about the guy who...


No jokes this time. A while back I wrote that i had a crack in a bridge show up a couple days after it was finished. It was fired out and I asked what everyone thought could have been the cause. We had covered everything from casting, to sandblasting, to finishing, to cleanup, to oxidization bake all the way through, including the CTE of the alloy and porcelains used. Everything has been in order and done properly. (i've been a ceramist for over 35 years and know my way around the bench - when working for other labs i was the most hated tech because i demanded proper framework design from the waxers and proper finishing techniques from the finishers.)

That said - Houston, we have a problem!

This is odd - really odd, and i wonder if something else is going on here...
We have a new dentist client, this dentist uses our 75+6 from Argen and does a lot of singles. This dentist does about $3000.00 a month with us. In the last two months, we've had about 6 crowns that were fine leaving the lab but have shown up in the dentists hands with a crack running up from the margin either on the buccal or the lingual or both. Only with this alloy and only with this dentist. I have 6 other dentists using this alloy doing a huge percentage of the work we do without a single complaint. No cracks at all.
Could it be internal lab sabotage? Could it be dental assistant sabotage? Or is there something fishy with a change in the alloy that we aren't aware? I'm going crazy here as it doesn't make much sense.

Also - we have been using Ceramco paste opaque for many years - ever since it came out - and had no problems at all with it. We use the original shade paste. Over the last 6 to 8 months I've noticed a greening that never used to happen - but mostly on the 75+6. I'm told by my Argen rep its the Ceramco opaque combined with the 6% silver content. But like i said, it never happened before. Does anyone know if Ceramco changed their formulas as well?

Using Noritake EX3 and just ordered a slew of Noritake opaques.

Any help or ideas or suggestions will be entertained.

 

[rkm rdt]

A vertical crack sounds like it may be an expansion issue.

What type of prep does this dr give and how much tooth reduction? Are his preps similar to the other drs with no problems? ...in other words ,are his copings thinner than the others?

Co-efficient of expansion may be effected by any differences.

 

[TheLabGuy]

The vertical cracks are most likely from placing the restoration onto the prep and the alloy actually flexes just enough that it cracks the porcelain. Probably seen more with long axial walls. However, that only perpetuates more questions, because what would cause that???? liquid/powder ratio with your study casts isn't correct, bad impression, maybe the H&H or two-step impression technique not being done correctly, light body isn't working the heavy body, or you're thinning the metal too much at the margin during finishing, so many things to consider but I'd be leaning more to the impression or impression technique at the end of the day. Oh wait, it's always your fault...lol

 

[JonB]

The doctor says the cracks are there when they open the box. It is mailed and takes two days to get there.
I can't get past thinking there is something wrong with the alloy/opaque interface - but I'm not having this problem with other doctors and I'm not having this problem with other alloys.

 

[pingvin]

What about the packaging? Postman playing football, throwing packages around...

 

[JonB]

Crowns sealed in a 1" plastic box with foam, models wrapped in bubble wrap, and then everything nested in a double layer of bubble wrap in a standard blue box. If the postman was kicking it around, I would think the models would at least have a few chips. No so though.
Good thought!

 

[TheLabGuy]

Are these being shipped out of state, possibly at 30-40,000 feet above sea level or by ground transportation?

 

[JonB]

Everything is shipped at about sea level. No flight time.
Thanks Rob!

 

[user name]

Is this problem unique to the method of shipping? Maybe theyre being exposed to some type of xray or micowave? Which ceramco opaques are you using? The formula has changed alittle with the IC line...~6 months ago or so.

 

[Al.]

Sometimes problems come then just as fast they go away with no explanation.

I wonder how often manufactors have bad batchs or lots we never know about.
They loose a certain supplier or use another one to save money for some trace material in their product.

Instead of doing a recall they just let us use it.

We got notice that Fugi Rock ep lost the supplier of a componant of the stone and it was reformulated and the color has changed a bit. If there wasnt a color change I bet they would have never notified us.

 

[CatamountRob]

In my nearly 30 yrs. at this, we had delayed crack issues twice, once we changed porcelains without checking to see if it was compatible with all our alloys (it wasn't) and once we changed alloys and didn't read the instructions to see that the oxidation firing was differant than are other alloys (it was). In each case, not everything would crack, if the coping was relatively uniformly thin, it wouldn't do it. Greater thicknesses of alloy exacerbate CTE issues.
Does this seem to happen more with bridges, implant crowns or in cases with more reduction?

 

[araucaria]

locating/anti-rotation grooves in the prep leading to CTE differential in the coping due to thickness changes ??
2c

 

[JonB]

No anti rotation grooves in any preps.

We follow the oxidation firing to the letter - as we have for the 20+ years we've used this alloy

I believe the opaque formula may have changed more so than the alloy - but either is possible.

UPS is handling the shipping and we're not having this happen on high noble or other doctors we ship to (unless they aren't telling me - and why would they not?)

--
I've tracked the lot numbers and not seen that that makes any difference, this has occurred over three separate lot numbers. I've replaced old crucibles with new ones. I've cast all fresh alloy and cast 40/60 mix old/new alloy - and no difference in frequency of the problem. We use Renfert Cobra 100 micron for divesting and 50 micron Cobra for pre-oxidation bake cleanup after finish. I've used A/O Rubi stones for years to finish and #1 & #2 burs inside for seating.
Possible contaminants from high speed NSK handpiece/air line seems unlikely as we'd see spots where oil or debris would show up in the oxidation. Same with anything coming out of the steamer. We have even ran batches of copings just in the ultrasonic instead of steam to see if any difference.

There is no one conclusive thing that jumps out. Seems like if i were finishing the margins too thin, it would be on the HN alloys as well - maybe more so since its a bit softer and more likely to deform.

In the past its been Ceramco paste opaque on 75+6 alloy with either Synspar porcelain or Noritake. We dropped the Synspar almost a year ago. Today will be the first day using the Noritake opaque on all cases.

 

[araucaria]

is one particular furnace being used for firing? firing pegs? one tech? is the aircon blowing fiercely on cooling jobs? Has the surgeon really just opened the box? How could sabotage produce such a consistent outcome?
Good luck finding a remedy, this is a fascinating problem.

 

[TheLabGuy]

Good luck finding a remedy, this is a fascinating problem.

I agree, been thinking about it since yesterday without any 'real' suggestion of a solution.

 

[rkm rdt]

The solution is to use the ex3 opaque with your ex3 porcelain.Your problem will go away.

 

[pingvin]

In the past its been Ceramco paste opaque on 75+6 alloy with either Synspar porcelain or Noritake. We dropped the Synspar almost a year ago. Today will be the first day using the Noritake opaque on all cases.

You were using paste opaque of one manufacturer and porcelain from another manufacturer??? I never heard this before.

A word about a problem I had with Noritake paste opaquer. All of a sudden tiny bubbles appeared on every case. Problem was traced down to the freezing of POBA in the delivery wan. Delivery guy would pack up the wan and park it outside in front of his house. I always order opaquers before the winter, but this time temperature drop was sever and all of a sudden.

 

[Flipperlady]

I think maybe casting is too hot/cold or whoever casts is cooling it down wrong (maybe too fast to keep on schedule.) Could be something as simple as a calibration or just looking over a shoulder or two for a few days.

 

[JonB]

Flipper - I had that problem when i did polycast dentures... but never seen it with real alloy.


I do the casting - cast at 1500 ring burnout, Harris auto torch with 10/20 mix, flame is concentrated at the reducing zone, the metal is puddled and thrown, allowed to spin down to full stop and then bench cooled - never quenched. Same way for all alloys. Rings are snipped out of investment under water to reduce dust, sandblasted completely clean with the Cobra 100 micron AO, steam cleaned, finished with A/O Rubi stones and White Koolie to reduce the sprue nub. Margins are left a little thicker and reduced with a #4 slightly dull HP bur to burnish them to the die.

@Pingvin - thanks for the tip on the opaques, i'll order before winter!

 

[Flipperlady]

Flipper - I had that problem when i did polycast dentures... but never seen it with real alloy.


I do the casting - cast at 1500 ring burnout, Harris auto torch with 10/20 mix, flame is concentrated at the reducing zone, the metal is puddled and thrown, allowed to spin down to full stop and then bench cooled - never quenched. Same way for all alloys. Rings are snipped out of investment under water to reduce dust, sandblasted completely clean with the Cobra 100 micron AO, steam cleaned, finished with A/O Rubi stones and White Koolie to reduce the sprue nub. Margins are left a little thicker and reduced with a #4 slightly dull HP bur to burnish them to the die.

@Pingvin - thanks for the tip on the opaques, i'll order before winter!

Jon,

I was wondering about the quenching, so that narrows it down. I'd now look at the metal itself and wonder if the burnout temp is what's wrong. The metal may be sensitive to a degree or two off. Too cool would produce dulled margins etc..... too hot could produce what you are looking at. I'm sure you check all of this. Could be flame is too hot. Maybe one less spin (or one more I forget Good luck!