Well, that's a very good question. A registered dental hygienist has gone to an accredited dental hygiene program for a minimum of two years to receive their education. Speaking from experience, you are definitely getting your money's worth with an RDH. Please ask the person cleaning your teeth if they are a Registered Dental Hygienist. If they are not, you may want to rethink who cleans your teeth.
Those were the hardest two years of my life; and the most rewarding. The people that I went to school with 10 years ago are my best friends today.
In my opinion, dental hygiene educators are the best in the educational system. They have amazing patience and tenacity when it comes to teaching us all we'll need to know when we go out into the world of dentistry. They taught me more about leadership and the power of education than any others.
Each state has their own rules about every little thing we are allowed to do and I encourage you to find out what that is. Simply search for your Board of Dental Examiners by state and they will give you all the information you need.
Dental hygienists also have their own professional association. Their website has a ton of information about dental hygienists, dentistry and your dental health.