i donno who told you that it's easy but as far as what i have been hearing from everyone (from dentists to school staff), transfer is very very hard in dental schools and only granted in very rare circumstances.
first of all, each dental school has different curriculum and approach. for example, midwestern uses system based learning where instead of taking anatomy, biochem, etc. they will learn by each system (cardio system, etc.). so someone to trasnfer from one type of learning to another system will cause much confusion and transition will not be smooth at all.
also, dental schools have numbers of seats in class for a reason. they have it because they need to have certain numbers of chairs in sim lab or clinic for students (let's say there are 75 chairs so they have 75 ppl in their class). accepting 1 more person to that class will make one person from the class to share their chair with the new transferred student. this will not work out so there has to be an empty seat for that to happen.
although im not too sure how hard it is (my dentist has transferred from kansas dental school to UT houston in 70's, under very special circumstance with military and family reason), but im pretty sure in order for transfer to happen, you would need a very good reason, empty seat in the class for you to take, pretty good matches b/w ur curriculum and their curriculum (unless you don't mind starting all over from D1, but then you'll be wasting over 100k in money), and other factors which make it very very hard to happen