I got an email today from a good friend and a relatively new CEREC user. His frustration was evident as he said that he was having issues with a case that would not seat. Being the ever inquisitive type especially with CEREC cases, I asked for the file. Upon opening the case I immediately knew what was the issue. In this particular case, there were two issues that were preventing the crown from seating.

In the first photo, if you look at the circled area, you will see the margin of the preparation rough and irregular. I’ll say this and its probably the most important thing with regards to the fit of CEREC restorations. The margins of the preparation need to be glass smooth. Polish your margins - whether with a hand instrument or rotary instrument, polish your margins.

The reason for this is that the margins are milled in Veneer Mode. Veneer Mode is a mode the tries to conserve porcelain, in other words it will prevent open margins. Veneer mode allows the CEREC machine to not Overmill the margins. The issue with Veneer Mode is that if your margins are not smooth the restoration will not seat. Do a search in the Digital Library section for Overmiling and Veneer Mode if you are not familiar with those terms.

The second issue I see Ive outlined again in red is the draw of the preparation. If I look at the preparation from the occlusal and try to define the insertion axis, you can see the yellow undercuts on the prep. This tells me that the preparation is too parallel. Now the 4.3 software will block out undercuts on the internal of the preparation - however, with this much of an undercut, you are asking for an inconsistent experience and fit which is exactly what happened in this case.

So to summarize, prep with draw and polish your margins. These two small changes will greatly improve the fit of your restoration. Obviously if you are still having issues like this, don’t hesitate to upload your own file for evaluation to www.cerecdoctors.com.

I would add a third comment. from your videos and my experience my seat problems have come when I did not have good margin clearance interproximal. I would say I need to look from the occlusal and see some space between both interproximal margins. hope this makes sense.