K.L.
There are infant tooth brushes and toothpastes that are safe to swallow. They don't freshen breath the way a minty toothpaste would, but they remove debris on the teeth and gums, as well as begin to promote good dental hygeine.
I started brushing my son's gums at 4 months...he didn't even have a tooth until he was 7 months. He loves brushing his teeth! In the morning I let him do it himself (he really just chews on the toothbrush), but at night I actualy brush his teeth and gums, then let him chew on the toothbrush while I read his bedtime story.