Not a problem. I have a dress like that, and I wear it to travel all the time. The buttons on mine are steel.
Overalls *can* be a problem, though; the shoulder buckles are often just big enough to set off the detector. I always tell people not to put toddlers into overalls w/ metal buckles for travel -- it is one thing for an adult to be selected for addl. screening, but toddlers often don't handle it well.