One of the main reservations that some clinicians have had with regards to switching over to CEREC is that they feel that the preparations for all ceramic restorations are unnecessarily aggressive.  No doubt that you need an adequate thickness for traditional ceramic restorations to work well.  Naysayers argue that you can leave gold thin as 1mm, thereby conserving valuable tooth structure.   CEREC restorations by comparison have required 1.5 to 2.0 mm of occlusal reduction for the materials to have a chance at longevity.

Things however have started to change recently. Ivoclar has been testing emax at 1.0mm occlusal thickness.  This has worked well in their results and although they have come officially out and said that they recommend a 1.0 mm occlusal thickness, there is sufficient anecdotal evidence that a 1.0mm thick emax works just fine.

Conversations with our members has shown that many are pushing the limits of emax and leaving it 1.0mm thick and having no negative effects.

Perusing through the Vita Enamic brochure, I found this schematic a bit interesting.  Vita, with their new hybrid ceramic is actually recommending a 1.0mm thick reduction.  The nature of the material allows it to be left thin and we will supposedly have success with this.  I think this is going to have reverberating effects in the world of CAD CAM.  1.0mm thick occlusal reduction is a monumental step forward and for Vita to go out on a limb with this material and recommend 1.0 is significant.

Time will tell if our restorations will last as well at 1.0mm as they have done at 1.5.  However, I feel this is a step in the right direction.

Screen Shot from Vita Enamic Brochure

I have been in the CEREC world for over 6 years now.

There is a certain amount of stress involved with prepping enough for material integrity and not over prepping. One conclusion I have come to is that I and many of the rest of us were underprepping for PFM's and getting away with it frequently. However in many cases when "getting away with it" we were ignoring failures on the occlusion or accepting metal occlusion in thin areas. In reality those were PFM failures caused by prepping less than 1.5 mm.

So, I don't think we prep any more for CEREC crowns than we should for PFM's, but it is more important that we follow the rules for CEREC's because there are no partial failures with all ceramics.

John,
I agree with you and every CEREC owner agrees with you. But the perception amongst the non believers is that you have to prep aggressively for CEREC. So a company coming out and officially saying that 1.0mm is enough is a significant step forward.

Sam and John I could not agree with you more and would add that when we or others are "getting away" with less reduction they are also almost certainly ending with over contoured and/or too opaque restorations. As any top ceramist and they will tell you they want and need the same reduction, if not stuff starts to suffer and compromises are made.

I would like to add that CEREC preps are actually much more conservative than traditional crown preps. Buccal and lingual axial reduction is minimized and only
indicated if a prior restoration or decay is present. The days of endo, post and core with a full coverage crown because a cusp has fractured to the gingiva on an upper bicuspid are long gone. I have placed my CEREC finish line on the middle third of the buccal of a 1st bicuspid and the transition from enamel to ceramic is seemless, all while preserving tooth structure and avoiding endo. The only time that my preps resemble a traditional crown is when I am replacing a failed crown. MOD onlay or crownlay best describes my prep. I was sold on CEREC BECAUSE of conservation of tooth structure and preservation of biologic width. Prior to doing CEREC dentistry I needed endo on 50% of molars that needed crowns because I didn't have enough tooth structure. In the last 7 years of CEREC I have only needed endo on 2 teeth because of inadequate tooth structure. I am baffled at some of the posts that show traditional crown preparation for CEREC restoration. The more tooth structure that can be preserved the less likelyhood for endo in the future. I also have had very few CEREC restored teeth require endo post-operatively as compared to when I placed PBMs. I am convinced that buccal and lingual axial reduction in traditional crown preparation causes more pulpal damage than occlusal reduction. Sorry for the rant... This is my first post ever.