I was just talking to my dentist last week about babies' teeth, and she mentioned that teeth sometimes come in sideways and that it's nothing to worry about, and that it doesn't mean that the permanent teeth will be positioned that way.
It wouldn't hurt to mention it to your doctor if you're concerned or if it seems to be infected or particularly bothering your LO, though.
ETA: I just reread your post and realized that you're talking about something in the back of the mouth -- I would definitely consult your doctor about that, since they don't usually get molars until much later, around 2 years. It sounds like your LO is an early teether, but that's crazy-early for a molar!
DH+Me 1994 DS 2004 DD 2008 DDog 2014