Well an orthodontist speacializes in realigning the jw and all that. They usually put bracea on you to straighten everything out. A dental hygienist does the overall health of your teeth like cleaning, whitening, etc. And actually an orthodontist makes more.
Orthodontics deals with braces and all that, hygienist deals with cleanining and a dentist checks them for cavities and stuff.
and a dentist does tooth extractions, cavaties, caps, and stuff like that.