I have worked with the Cerec inLab for about a year now. Through trial and error and a variety of tests that I have done, it is my understanding that we need a certain type of prep design to be successful with this CAD/CAM system. It seems as though preps with nice shoulder's on them turn out pretty accurate to me. There is usually only a few minor adjustments to be made. However, with a knife edge prep I run into many issues. The margin isn't clear on the 3D model therefore it mills out horribly. What I would like to find out is if there is a way to make these preps work, and if so how? If there is anyone out there that can help please let me know!