What is one of the specific questions they asked you?
why dentisty? why mcgill? have you applied into anything else? (DON'T SAY MEDICINE, if you say something like low or physics is usually a good thing since it shows that you have many intrests)
looked over typical interview questions on this site and school papers. checked the mcgill website for current reserch in dentistry
What impressed you positively?
very nice people and relaxing ambience
What are your general comments?
When you go there just remember that only 40 people get called for the interview so unless you really say something incedibly stupid you have great chances of getting in. Relax the importance of the interview is often exagerated, if you have good grades you will get in. Don't try to impress them, you will just look stupid. The questions are preety basic, if you read some coments on this website you will have no problem answering them. Don't look like you have memorized all the answers though, it is better to hesitate a bit. Prepare some questions for the interviewers- it really helps. Usually 2 of the 3 interviewers are students, so they know a phony when they see one- don't exagerate your desire to get into dentistry- be natural.