Correct me if I am wrong, but all letters sent to AADSAS go to every school you list when you submit. Most schools require the standard two science profs and one "other" letter, preferrably from the dental field. Then there are a handful that require three science profs, or want a non-science prof, or an employer, etc. AADSAS won't seperate those out for you, so have them send your standard packet with the three or four letters that you want every school to receive, then have the extras sent directly to those specific schools by your evaluators. An easy way to do this is to give the "extra" evaluators addressed, stamped envelopes for all of the schools that you need their letter sent to, and ask them to send copies to each of those schools. Also, remember that the less specific schools will accept extra letters, so you can even send a fourth letter through AADSAS to all of you schools, and it may even help your app.