Sucking on fingers

When did you realize your child liked their fingers more than their pacifier? I’ve always heard it’s hard to break the habit if they suck on their thumb/fingers more than if it was a pacifier.

My son is 4 months and is constantly using his fingers more and more each day. I don’t know if he’s just exploring or if he is started to prefer them over his pacifier.

He will still take his pacifier but if it falls out or pulls it out of his mouth (I think unintentionally because it’s a wubanub and he’s always messing with the animal) he’ll just pop a couple of fingers in his mouth lol

My cousins daughter sucked her thumb until she was around 7 or 8 and does have dental issues because of it so I worry a little bit about being able to break the habit when he gets older.