I interviewed at UIC a month ago.
You don't have to write an essay.
There are two interviews, each lasting 30 min. Both of these interviews are one-on-one, by two different people.
The interviewer has a list of 20 questions where the interviewer will select about 4 questions. Therefore, everyone will get different questions. The questions are focused on accessing your personality and work habits.
The one question that you definitely will be asked is "why dentistry?"
You will get a tour of the school.
The day ends with a Q&A session with a panel of current d-students.
I thought the day was very well run and the school does a good job of trying to make you feel comfortable.