The mill is maintained exactly as you described- this is not the source of the problem. I'm the kind that reads every manual for equipment. While a good suggestion, extreme tool paths are also not the problem. The issues have been of the what I'd call defective parts variety. It's been a long time since I worked with CEREC, but the fit was very good, even with the old zirconia we'd use for copings to stack. Without going off on a tangent, these two systems are like apples and oranges, but that doesn't mean that CEREC is bad at what it is meant for- single units and short span bridges. Regarding value, which is the true subject here, given the technicians' time involved- especially in a full arch- the cost just for the zirconia is significant. Pricing in the US is $468 for 25mm, $410 for 20, $360 for 16, so after tax you're over $500 for 25mm-I'm not here to exaggerate or spin this. We do a lot of zirconia, and the burs I'm using now get around 600 units- food for thought the next time you change when they hit 0%. The thing I keep in focus on the full arch zirconia subject is that the cad/cam labs will keep getting bigger, better, and cheaper, and the price of full arch zirconia production, i.e just to mill, green state finish, sinter, and cut and polish, will keep getting lower- this is inevitable. So, if I could send an STL file out and get a 12 unit bridge back ready to stain and glaze for less than what I could mill it out myself, then it's at least something to think about. There's a huge paradigm shift going on regarding production quality throughout the world, and let's suffice it to say that those burs I'm using that are milling 600 units are made in China and cost about 20% what a ZZ bur does. Regarding their zirconia- I've been there and seen the same. I agree completely with 'no comms is good comms' with any reps or support though! The lab business has always been tough, but don't be surprised when ZZ quality restorations are $15/unit or less out of Asia.