call the schools and ask each one if they accept interfolio. i am pretty sure i have heard that a few dental schools require you to send all of your supplemental material through aadsas, and i don't think aadsas accepts interfolio because their website states that letters must arrive unopened, and i think interfolio opens the letters. i could be wrong though, definitly call and double check. any specific reason you don't want to just go through aadsas? you're paying big money for them to process your application, might as well get use out of it.