Did your husband have a tooth/teeth removed in the area where the hard substance is breaking through? Sometimes, a little bit of broken-off bone can make its way out after an extraction (sometimes even years later). If it doesn't come out by itself fairly quickly, have a dentist remove it.
it came out the other day. i think he had root canal a couple of years ago. at that time, bone came out. now it's doing it again. i'm only assuming it's in the same area. but, i bet that's what it is. i had never seen it before.