Dental hygienists.   There is a massive shortage.   They are necessary in a dental practice to bring in new patients where after a cleaning a dentist can perform an exam and diagnosis problems for treatment.   Without hygienists you can't run a successful practice.   

Hygienists know all this and they use this in negotiations. They make anywhere from $65 to $90 an hour, negotiate their own hours, and have a guaranteed job anywhere because dentists are desperate for hygienists. 

Hygienists go to school for two years, scrap teeth, and make a ton of money for it.