definitely be able to explain your research. if you've been a co-author on papers, go ahead and read them again. if you didnt write it, make sure you know the background and implications very well because the professors who interview you will try to poke holes and ask why not this? why this? if the research is unfinished, come up with your own hypothesis about what you expect will happen. think about some experiments you could design as next steps. other things i was asked about were career goal & why not just one or the other. find out who you're talking with before the interview day and what they do so you wont be caught off guard (one guy that interviewed me was in the same field and asked probing questions as if he didnt know anything about it and at the end he told me that it's his specialty.. lol).
i've been interviewed and accepted at a few dds/phd programs and as long as you know your research, you should be ok. most of my interviews went well unless the faculty was not a dds and only phd. those faculty tended to be more aggressive/trying to make you stumble than the ones who are not. for instance, i had one faculty straight up tell me that translational research is for researchers with weak scientific background (ouch!) and basic science is what i should study if i want to be successful. while i see the point they were trying to make about having a good foundation, chastising me for the lab i chose as an undergrad seems a little harsh.. but i digress.
tl;dr.. know the research cold going in and have a solid reason as to why you want to do the program
