PFM BRIDGE CRACKED

[sidesh0wb0b]

anyone consider that metal is generally porous? theres prob all sorts of bacteria in that metal from being in the mouth for 5 years.... might cause micro bubbles that in turn fracture that ceramic during firing. pics? we always have to ask...but seriously people PICTURES when you are asking questions about this stuff...

 

[CatamountRob]

anyone consider that metal is generally porous? theres prob all sorts of bacteria in that metal from being in the mouth for 5 years.... might cause micro bubbles that in turn fracture that ceramic during firing. pics? we always have to ask...but seriously people PICTURES when you are asking questions about this stuff...

You should be able to see that when you do an oxidation firing of the framework. It’s been my experiance that if you don’t have a nice even oxide, you can expect a problem.

 

[user name]

Save the headaches and do it in Zr.

 

[BLUE]

I did everything what I can do.

Way too complicated.

Thank you very much for all of your opinions.

Thank you

 

[2thm8kr]

Extract them and just go with a denture.

 

[grantoz]

user name nailed it .i did a full over full implant bridge in vmk the dentist changed his mind so many times we had to adjust the bridges so much too the point that the cte was all over the place cracks warping the works. i just gave up and did it in zi full over full layered its been in the mouth now 11 years no probs. by the way when i finished the zi implant bridges i weighed both the vmk and zi bridges there was only a few grams difference in the weights which was interesting as people always say zi feels heavy.

 

[Polarmolar]

GC has a opaque for helping fix shady metal issues, i would look into that as it's saved me a before.


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[Tayebdental]

I didn’t read all the posting if mentioned before( shame on me),it’s probably the glaze you are using if the cracks happened after stain and glaze. I wonder if you noticed the cracks during ceramic baking, in this case it is a different story.

 

[ztech]

A large bridge with a large amount of ceramics and metal will cool under tension if the alloy doesn't cool first. This will cause cracks that will appear shortly after the firing. Most of us as technicians will try to slow cool the large restoration and it will only make the problem worse. Although in this case you can't redesign the bridge, the best option would be to make the framework with areas of exposed alloy in non-aesthetic areas to allow faster cooling of the alloy. When I have this problem, I do opposite of what has been suggested here, I used the same program as single units, modifying the entry time to allow a more thorough heat up and the time at temp, to allow the mass to come to final temp. From there, i drop to lower table position without a slow cool same as single units.

 

[BLUE]

Thank you very much for your information.

Looks like everybody have their own ways to how to solve it.

 

[CatamountRob]

Thank you very much for your information.

Looks like everybody have their own ways to how to solve it.

You think that’s it? Just like that it’s over?? Finished?!? I don’t think so Blue....
We’re going to beat this to death, then hi-jack the thread and run off in 3 different directions..
Nice try, but this is DLN and it’s not done until we decide it’s done!

 

[aidihra]

Cracking on a long span bridge is always stressful. I noticed cracking usually happens where the pontics are too big/heavy, metal is too thin in some areas or not enough room between interproximals.

 

[Polarmolar]

You think that’s it? Just like that it’s over?? Finished?!? I don’t think so Blue....
We’re going to beat this to death, then hi-jack the thread and run off in 3 different directions..
Nice try, but this is DLN and it’s not done until we decide it’s done!

This will go on for years !! [emoji23]


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[CatamountRob]

I friggin’ love this place.

 

[JMN]

Cracking on a long span bridge is always stressful. I noticed cracking usually happens where the pontics are too big/heavy, metal is too thin in some areas or not enough room between interproximals.

And when the porcelain changes thickness too much too rapidly as well.

 

[sidesh0wb0b]

I friggin’ love this place.

crack kills

 

[charles007]

I used Vita and Creation porcelain for many years but rarely do pfms in the past 5-6 years.
Here's a few examples of checking.
Single unit molar with a vertical check line up from the margin = CTE off, mismatch of alloys.
Bridges having checking and more so on pontics = mismatch of alloys.
Porcelain to thick on mostly pontics can easily create checking even if the CTE in is the middle of the range !
Creation porcelain is pretty forgiven but you still need to keep your porcelain from being to thick if your on the lower or upper end range of the CTE of your alloy.
Many HN alloys have low CTE and I bet without seeing your bridge the porcelain is way to thick and the low cooling made the checking worse.
fyi whenever I strip porcelain off metal, I always refinish the metal as usual and sandblast, etc .
Not in the lab now but I think my glaze cycle is set at 1 minute or either no cool. Sorry, normally firing zirconia and can't remember for sure. Creation manual shows no slow cool on glazing cycle.
Question, is you porcelain thicker than 2mm + ...if so say no more.

 

[sndmn2]

You mention that the bridge cracked in the glaze bake. Is it an actual crack or is it craze lines in the glaze. Did you use a kind of glaze that you have not used before on this type of case and it didn't play well with material ? Just fishing.