How shall I know what kind of Ceramir block to use for different clinical situations—the T-block or the C-block?

The Ceramir CAD/CAM T- Block is often the best choice as you can individualize it with your cement. In addition, the block will due to its translucency blend in with the natural tooth.

The C-blocks will however be the best choice if there is a discolouration in the preparation that needs to be covered- the same thing is if you are working with an implant, and the abutment is grey/metal.