My feldspathic porcelain crack after glazing

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Aditia KT

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Hello guys, do you know why my feldspathic very often gets crack after cooled ? Usually appears fter glazing and when it cooled the crack start appears ?
What i have to do ?
 
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grantoz

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lucite crystals change in size in the porcelain over multiple firings and then the cte goes out of wack with the refactory material and they are really weak thats why they invented lithium discilicate.
 
kimba

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I used to do a lot of inlay /onlays with feldspathic, and they would often crack on glazing if there was a thin section joined to a large. It was as they cooled so if you were quick you coud devest them before the stress propogation started to show itself. I have not seen that in normal veneers , but as Grantoz said look to CTE changing over multiple firings. Maybe check compatabiity if you are new to them , or have changed porcelain or refractory material.
 
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nrcastil

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It looks like you have a CTE problem. Check for CTE compatibility. The difference between the ceramic and the alloy should be in the range of 1 to 1.5 units of difference for good results. If CTE is in range just try to increase the cooling time by adding an extra or two minutes.
 
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Rockit1

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It looks like you have a CTE problem. Check for CTE compatibility. The difference between the ceramic and the alloy should be in the range of 1 to 1.5 units of difference for good results. If CTE is in range just try to increase the cooling time by adding an extra or two minutes.
Sounds like good advice…CTE and cooling rates. High Nobel alloys held heat like a heat sink and would crack if not cooled slowly.
 
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Dentalmike

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As kimba said. This can also occur with thin ceramic next to thick area. My fix for this was to CAREFULLY divest with burs and sometimes blasting with alumnus as well, to leave only minimal refractory attached to veneer, fill with peg putty and refire.
 

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