Sometimes you have to take an impression and pour a model. Yes, I said it. I did a blog a while back regarding new users taking the stress out of the learning curve and doing a CEREC in two appointments. This way they don't feel so rushed with patients in the chair. They can scan in the mouth or take an impression.
Once in a great while, a patient just does not open enough to get the camera in the back of the mouth. These are the few times I have taken an impression, poured it up and then scanned off of a model. Another time that I will take an impression and scan off of a model is when I'm doing an implant and trying to make a soft-tissue model.
For those who will use a model for these scenarios, I have two suggestions to make your life a bit easier. The first is to use a scan stone from vita. It is a fantastic stone material that does not need to be powdered. I have been using it for my assistant training courses, and it works fantastic.
The only problem that I was noticing was that I would get bubbles in various areas when pouring the model. If those bubbles were on a margin, I was forced to pour another model until I got what I needed.
I found this in a Patterson catalog. You just spray into your models and it eliminates about every possible bubble I get when pouring. The day that I got it, I was pouring models for the class out of a silicone mold I have of the preps. My four-year-old daughter was visiting the office and said she wanted to help. I let her scoop up stone with a spatula and fill the mold that I sprayed with the Debubblizer while vibrating out any potential bubbles. I let it harden and the model was absolutely perfect. So I say get your hands on this stuff. It is so easy, a four-year-old can do it!!