I'm a nontraditional who worked too and I avoided recs from employers. There's a reason why every school requires recs from science teachers. And most of them won't accept a rec from a lab class. Schools want to see your academic performance in a true science setting, which is the most relevant for dental school. Likewise, they don't give a rat's butt about your career performance in a business setting. (Why do you think MBA schools require mainly recs from employers and not teachers?) Make sure you submit the required science recs, otherwise it's a huge red flag. They'll think you were bad student and were desperate that you had to use non science teachers.
I also caution highly about sending more than the 4 that AADSAS accepts. Quality is better than quantity. Firstly, a lot of schools won't even accept additional recs and they'll be thrown into the shredder. Secondly, a bad rec will undermine any good recs in your file. An admission officer once told me about applicants who submit many just to increase the number and it winded up backfiring because the additional ones were either average at best or subpar.
I recommend 3 science teachers and 1 dentist. This will cover the schools that require 3 science recs. Trust me, 4 good recs will be enough.
It's like going to a restaurant. Would you rather see a menu of 10 items and all 10 are delicious choices? Or would you rather see 70 items with only 10 being delicious and 60 being mediocre? In the latter, the 60 subpar and unnecessary ones make it a bad restaurant.
