I do not believe that a dental assistant should be able to scale unless they go to school and go through the dental hygiene program for two years and become  a R.D.H. I went through the assisting progam before going into the hygiene program. It is a totally different program. There is a reason we go to school two years to become a R.D.H.  I agree with a comment I read early  that said why cant hygineist do fillings and extractions if you are going to let assistants scale.  It takes us two years to learn the knowlede and skills to become a R.D.H.