Whiten your teeth. Compared to the cost of a suit, flight, etc. it's worth it. Even just a $4 tube of the whitening toothpaste will make a difference over four to six weeks, along with cutting out coffee, soda, etc.
Question: With a navy (not blue, navy) suit, what color for belt and shoes? Black or chesnut? Black is more conservative but chestnut is more stylish. I'm leaning toward black just to be safe.
Those shoes in that second pic aren't really chestnut, they're burgundy/cordovan.
Anyway, I wore burgundy belt/shoes with my navy suit for residency interviews, primarily because I'm personally not a big fan of the black shoes with navy look. That said, some people more cautiously adhere to the "black shoes for interviews, period" dogma, and would consider black the only option.
Ultimately whichever you feel more comfortable/confident in. If I had to commit to one answer for you and not waffle, my blanket/generic recommendation would probably be black just because it's "safer." Consider this (admittedly silly) thought exercise:
Your interviewer will either have his finger on the pulse of semi-formal male attire, or he/she won't. It plays out 1 of 4 ways.
1. Stylish interviewer notices your black shoes with navy pants. Possibly isn't a fan, but understands sometimes interview etiquette trumps personal flair. No problem.
2. Stylish interviewer notices your burgundy shoes with navy pants. Appreciates your color choice. No problem.
3. Fashion-challenged interviewer notices your black shoes with navy pants. Or doesn't. If he does, he knows black = formal and thinks nothing more of it. No problem.
4. Fashion-challenged interviewer notices your burgundy shoes with navy pants. Is unduly insulted that you would have the audacity to wear non-black shoes to a professional school interview. Gets angry and punches you in the face, refuses to validate your parking, and puts you on the waitlist.
As you can see, the most negative outcome listed above is associated with the burgundy shoes.
All kidding aside, in the end this really doesn't matter very much. If you have any doubts, go with black to quash any worries you might have come interview day. You want to be focused on presenting yourself as a competent future doctor who is personable and friendly, not whether or not the interview approves of your sartorial color schemes.