But first of all you should take care of your Patients satisfaction... bunch of positive opinions both those spread by mouth to mouth marketing and those put on you facebook or www site.. are the best customer satisfaction KPI ever.. (of course if you offer you services to individuals .. if your customer are companies like innsurance and they expect any "certificate" go for 15224 if not spend your money better and invest in good Patient<->MD/Medical stuff communication courses for all your team.
Good question stated above by Marc.
From my perspective implementing any QMS in small service company like 1-5 person, one location .. is waste of money (if not required by third party like insurance companies etc) For individuals your ISO etc cert means nothing , focus on quality reception processes, dental office processes , communication on each stage and safety. I am sure that outstanding opinions about your orthodontic practise is best magneto for new customers, for sure better then any paper on the wall.
sorry for typing mistakes (