The problem is the different layers got different shrinkage. If you sinter the hole disk. The occlusal will shrink almost 2mm more than cervical in diameter. These materials only accurate on singles maybe 3 unit bridges. We tried everything even occlusal sinter supports.
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We had same problem. It started after one year of using furnace. Sulphur powder build up in chimney. When furnace closes the sulphur drops into furnace causing contamination of the zirconia. Removing chimney on top of furnace and steam clean works for us. Just steam clean once a month Run...
This furnace has a chimney on top. Take it out and steam clean once a month or when getting this contamination. Then run the cleaning cycle with leftover peaces of zirconia.
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