As far as I can tell, this is a single rooted tooth. I suspect (or hope because it would be very cool) it being pretty old, since it is so dark in colour. It is not very pointy, so it doesn´t look like a carnivore tooth to me.
On the picture I think the sequence of the the positional relationship from front left to bottom right is labial, palatinal, mesial, distal. I'm leaning towards a mandibular incisor. I'm not sure if this could be a human tooth, but it fits size-wise.
It was found on a glacial freshwater lake in Germany. The right side of the scale is in cm.
I would be grateful if anyone has an idea about the owner of this tooth, or could point me in a good direction on how to further narrow it down.