Remember who you are trying to impress, 35-65 year old dental professionals. Based on my interviews so far, I would lean toward the 65 year old end of the spectrum. These are not the 20 year old girls that you are usually trying to impress who love your slim slacks and skinny ties (which i think are much more flattering and personally wear on business casual occasions). My point is that I don't think this is the same crowd that watches project runway and will scoff at a three button suit as being "so nineties".
That is why it is important to dress conservatively, even if you think it looks boring. Though there may be one adcom who thinks a white suit, or in your case a grey cardigan is really special and distinctive and is going to accept you for being different, there are 99 who will write you off as unprofessional. That is the reason why politicians dress the way they do, they have done plenty of studies and determined that the way they dress instills confidence in the widest variety of people.
You can take your chances, maybe you'll get that random adcom who has the same taste as your girlfriend, but for me, I'm betting that I'll get one of the other ninety nine.