There will always be the arguement that if a dental assistant is properly trained then he/she would be capable of providing basic scaling procedures effectively.  Let's just make sure that we consider the undeniable truth.  This arguement will be the exception, not the rule.  In the right scenario, in the right office, under the right supervision, with the proper procedures in place, an assistant may be able to perform the basic procedures.  The regulations in place are not there to cover the perfect scenarios, but to cover all scenarios.  Even the dentist can miss diagnose a patient and trained dental hygienist serve as a double check.  Also, there will be dental offices that push the envelope and allow, or even insist that the assistant perform more complicated scalings even though they do not have proper training.  Imagine the scenario where a hygienist calls in sick.  What percentage of the dental offices would allow the dental assistance to cover for the day as opposed to rescheduling the appointments?  Even if the answer is 1% (my guess is that this number would be much higher) then this should not even be considered.  Bottom line is that it is a disservice to the patients, period.