How do you think your own dentist learned? This is a requirement of medical programs and they are supervised. And it takes a while because students are learning and they are likely other exams and what not they are doing. For privileged people like you this might be absurd but this is a well needed service for the underserved who go years without any dental hygiene leading to all kinds of medical issues. If you want to be an ass, do it on your own time but don’t shit in someone trying to make an impact.