“Leaking crowns? all porcelain dental crowns installed on my four front teeth”

Seeking help:

I recently had all procelain dental crowns installed on my four front teeth. When I floss two of them at the gumline, I can taste and smell a foul bacterial scent on the floss. The dentist poked around with a dental instrument and says they fit properly, but I disagree. None of my other teeth (crowned or real) produce the odor, so something isn't right. He told me x-rays won't necessarily show whether or not they fit, so is there a definitive way (i.e., special type of x-ray, MRI, etc.) to determine if the fit is correct?