C.M.
I can only give advice as a former thumb sucker. My mom made it a point NOT to make a big deal about my sucking my thumb even though many people told her on a daily basis, many times right in front of me, how and why she should make me stop. They told her to use tabasco sauce, nasty spices, put gloves and mittens on me, etc. She simply told them, "When she's ready, she'll stop." It was a comfort for me and I realize as an adult, I sometimes use food to fill that need but have realized gum works the same to thwart my oral fixation.
Anyway, at 13-years-old, with going to sleepovers with friends and getting more and more nervous about someone seeing me and trying to keep hiding it and afraid of being made fun of, I stopped- on MY terms when I was ready. I am now 33 and have a 2 1/2 year-old baby boy. I have no need or desire to suck my thumb and am thankful to my mother for allowing me that comfort when I needed it.
Oh also, about the teeth issue, I may be the exception to the rule but I have perfectly straight teeth. I NEVER wore braces or a retainer. Good luck!