A.G.
I used to work for an orthodontist and yes sucking his thumb will effect his teeth. Here are some of the different things you can try to get him to stop. First you can wrap his thumb at night with medical tape and cotton balls. Make it really big so he can't suck on it. Or we would tell parents to put a sock on their kids hands and again wrap it with medical tape so they can't take it off at night. They usually only have to do this for a few weeks until the habit is broken. If he still finds a way to suck his thumb or you don't want to do these tricks we would also place a retainer in the child's mouth that enables them to suck their thumb. It works but it has to be glued on the teeth (so the child can't remove it) and can be scary for a child. Although I have done it on many kids and most of them are just a little scared at first but it takes like a minute to do the actual process of gluing the retainer in and then the kids are fine. And they stop sucking their thumb. So give some of these a try and if he still doesn't stop you might need to take him into the orthodontist.