The Effect of CEREC Parameters on the Thickness of Porcelain
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One of the most commonly misunderstood parameters is the Occlusal Offset parameter. Â What the Occlusal Offset parameter does is above the height of contour, either adds or removes porcelain from the occlusal surface of the teeth. Â
 In our workshops, we have found that a negative occlusal offset often works best for individuals as it allows them to dial in their occlusion with minimal adjustment.  But the negative side effects of a negative occlusal offset are often ignored and misunderstood by CEREC users.  Think about this- If you turn on your analyzing tools and you click on Cursor Details- that is supposed to give you two measurements:  1- The Thickness of porcelain where the cursor is 2- The Height of Fissure- basically the thinnest spot on the occlusal surface in the central groove  Lets pretend for a second that your Height of Fissure reading is 1.5mm.  "Great" you think, because every CEREC trainer has taught you that you should be 1.5 mm thick in the central groove.  But are you really 1.5 mm thick?  We mentioned a negative occlusal offset works well.  For the sake of this discussion imagine you have a -200 occlusal offset.  What now is the true thickness of your porcelain?  Meaning, is the software taking into account the 200 microns of porcelain or .2mm of porcelain that the negative offset is going to remove?  So is your thickness 1.5mm or is it now decreased by .2 so your actual thickness is 1.3?  Its very easy- see for yourself.  Start a case- change the occlusal offset in your local parameters and see if your height of fissure changes.  Scary isn't it?  All this time you thought you had plenty of thickness yet you are thinner than you think you are by the amount of the occlusal offset.  Wanna blow your mind even more?  Think about the second parameter- the Spacer. What happens when you increase your spacer?  Shouldn't your porcelain get thinner?  Is this number reflected in the Height of Fissure?  Again, see for yourself.  Change the spacer and see what happens to the Height of Fissure.  The take away is that the HOF is a useless number. Ignore it completely because your actual thickness is always the HOF minus the offset and spacer.  And all this time you were thinking that 1.3mm HOF was more than enough in your designs. Â
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Yes that makes perfect sence. So you would need to raise the HOF to 1.7 with a -200 occlusal offset. To gain that amount you would have to reduce the prepped surface another 0.2mm more.
