Dr. Beatrice Leung Dentistry Professional Corporation

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Does your crown fall out of your die easily?

I have completed this case many years ago.  But I never had the time to organize my pictures to showcase the steps taken.    But looking at this completed case almost  nine years later, you can see how I have completed my mandibular reconstruction first using cast based PFM restorations.  Then when I completed the maxillary arch, I used mostly zirconia material.  This change was a reflection of how I evolved during the last decade from using mostly cast based restoration to now mostly zirconia material.

There are many reasons for the switch; mostly to contain cost and to eliminate the possible metal display around the gingival margin. But if you ask me, I really do like how the margin of my metal copings fit around my preps, as well as how I like to use the metal coping to verify my occlusion.

Now with the trend of moving to digital dentistry and milling your restorations, the units still have great strength and adaptation to the margin.  But in general, I do find that the units tend to be oversized and lack the retention and stability I once saw with traditional cast based restorations.  I don’t know if this movement is because that we have moved from using water soluble cements like zinc phosphate cement to now bonded resin based cements.

Over the last decade, I have noticed that most fixed units (metal based or zirconia based) are not very retentive even if good preparation have been provided.   Once I told the lab technicians that I really like your metal work, but they are not retentive enough and I request to put less die spacers.  The comment he gave me was if I made them too tight, then some dentists cannot seat the restorations.

A good tight fitting restoration does mean more adjustments are needed both in the lab and chairside.  But when you are dealing with less than ideal preps, these tiny details will make a big difference to the overall success of the case.  I think we always expect the lab to deliver perfect restorations requiring very little adjustment.  And because of that, the lab may over adjust their procedures to ensure minimal adjustments on our end.

I know this is a very anecdotal observation with no scientific basis.  But I think the more seasoned dentists will know what I mean that a good casting is not supposed to fall out of your die easily.  When was the last time you saw that from your lab?

Thanks for reading.