Switched zirconia, crowns too tight on dies

[John Caponigro]

Hi everyone. Our lab just recently switched the zirconia pucks we are using. Now, our crowns are too tight on the dies/models. We have assured that our cement gap settings in 3Shape have not changed since switching and that our shrink factor is correct during the milling process. I'm having to grind a good bit on the inside of the crowns so they'll seat properly. This is happening with traditional impressions as well as digitally printed models. I would appreciate any feedback and am hoping that someone can help me figure this out.

Thanks,
John

 

[Ryanlog24]

I would have a look at the settings on your sintering oven. Not all zirconias have the same requirements so its always good to check with the supplier with regards to optimal heating rates, peak temperatures, holding times and cooling rates.

 

[Patrick Coon]

Are you using a DME for the specific Zirconia, or a generic Zirconia when choosing your material in 3Shape? it could be that the new Zirconia you have chosen is Pre-Sintered slightly harder, which means if you are using a generic Zirconia in the material choice that you may need to increase the drill compensation a little more (maybe 0.1mm more - so if it was 0.5mm change it 0.6mm and see if that helps). Drill compensation is based on not only tool diameter, but also on material hardness. The harder the material, the more the tool will flex during the milling process, requiring the larger drill compensation. Conversely, the softer the material, the less the tool will flex, requiring a smaller drill compensation.

If your material manufacturer has a DME for their material, I would recommend using that, as they have already worked out the parameters for the material (drill comp, minimal thickness, connector size, etc.) and it will go through validation at the end to ensure you have (or at least let you know you didn't) meet the minimal requirements for the material. Doesn't mean you can't violate the minimal requirements on occasion, but it is a good reminder.

 

[MrNeverFixit]

the new puck should come with instructions. or if you use a high end sintering oven that can connect over to the internet, look for the firing settings/download.

 

[Muzz]

First think on shrinking scale and it settings in nesting software ???

Or measure sintered crown and compare that with measuring in design software...see is sintered crowns same dimension like the ones in modeling software....i will try from that...