If Dental Assistants were to provide scaling, polishing, injections, etc. this would all be under the license of the dentist and the dentist would be responsible for anything that results.  I personally am not comfortable with an assistant who does not have the experience or education of a dentist to perform such duties on myself.  This feeling is also held by many patients I have come into contact with.  Patients are paying to come and see a professional for their expertise.  Thank you.