Is it bad to have a gap between bridge and gum?

I have a porcelain lumineer bridge. I am missing a tooth so the bridge is only placed on my gums (no tooth underneath) and the bridge is connected to my two adjacent teeth. I recently noticed that behind the bridge, there is a small gap between where the bridge meets my gumline, just enough to fit a fingernail..Is that bad? In the front, it looks like the top of my bridge/below my gumline, it is dark...Not sure if it is discoloration on my bridge or if my gums have darkened.. :/