My GTP tagged my hand one time on my knuckles. This caused his bottom tooth to pierce his bottom lip and hold it in a similar way as yours. GTP have some pretty long teeth and it did not appear that is would fix is self. I had to open his mouth and get his lip off his tooth and then all was well. With your having shorter teeth I think it is possible it will correct itself but you may have to help like I did.

Scared me to death when it happened. I thought he broke his jaw too.