This is where it’s written in the help centerCould you provide the url link to the cic website where it says that you qualify to practice on the date you complete the minimum educational requirements of your occupation?
As for field of study, I am still confused between medicine and health sciences. People on this thread have suggested that our profession(3113) falls under health sciences but recently a colleague of mine selected medicine in his EE profile and got ITA. Personally, i don't think it matters much because somewhere in our profile we are asked the name of our degree(or something like that) and as long as it contains the word dental/dentistry, we're fine.
Coming to the date of license issuance, CIC/IRCC understands that in most 3rd world countries it takes months and even up to a year to receive the degree certificate from uni and the license from the state council, so they consider the date of internship completion.
http://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=1127&top=29