Will pulling molars straighten a jaw?

my grandson had 4 molars pulled today. he has a slight underbite that he didnt have as a child. (his bottom teeth don't line up with his top ones, they come foreward a bit) he's now 18 & i just noticed the underbite a few years ago. he said he's been biting the back, inside of his mouth from having too many teeth in his mouth. my question is do you think his jaw will align with these 4 teeth out or will he need braces?