Anyone else's baby chews there hands/fingers? Is it bad for them?😳

Phoebe • Mummy to casey 👶❤️17 years old 😋
This is all I see all day everyday, I'm guessing it's a way of self soothing but like thumb sucking can it be bad for there teeth? He sometimes gets sore and has blisters from over sucking 😔 any advice?