I'm not sure if your school's pre-professional office offers mock interviews but, that really helped me get a feel for the types of questions that can be asked and pace of the interview.
From my own experience (I interviewed with UF last friday) be prepared to answer several questions about any part of your application. Think of possible questions like, "Why dentistry?", "Why _____ (school interviewing at)", Access to care questions where a big topic in my UF interview, any questions about red flags in your application. Student doctor also has a section for all the ds with questions people encountered at specific schools (http://studentdoctor.net/schools/?view=dental). Look at that. That should help you start to prepare.
Smile a lot. It will loosen up the environment. You will feel more relaxed as will your interviewers. Be knowledgeable and not arrogant (know it all) and you should not come across as cocky.
Hakuna mattata <- that should be your attitude. Interviews should be the least painful aspect of the process. Congratulations on receiving yours already. My application is still incomplete due to the committee letter and it is so frustrating!