I will post tips weekly to give you ideas to use or try that I have found makes my working day less stressful.  Get yourself a bottle of 25% aluminum chloride solution.  When done prepping a tooth for a crown and you are ready to take an impression, dip a microbrush in the solution and rub it over the tissue and around the tooth.  This material will clean up the surface of the tooth and it makes the tissue relax so that it falls away from the tooth.  Plus it stops minor bleeding.  Rinse well with water and dry as you wish.  You now can take a better impression or digital picture for the lab or even for a Cerec crown.  A bottle costs aroud $30. and will last a year. I learned this in one of my dental study clubs and it works.  In many cases it eliminated using a cord.