A University of Iowa study says parents who let kids over two suck their thumbs or pacifiers should brace themselves for big dental bills.Dr. John Warren of the U-of-I’s College of Dentistry says research shows kids shouldn’t stick with their thumb or pacifier long term.Warren says they found that using a pacifier or sucking a thumb beyond the age of two led to changes in the way their teeth fit together. Warren says this study revises the traditional thinking on oral pacification for kids, which said kids could keep sucking until their permanent teeth came in.He says kids who kept up their habit after age two had problems with the alignment of their teeth.That could lead to braces or other expensive dental care down the road. Warren says if you have a choice, give your kid a pacifier before letting them suck their thumb, as the thumb sucking habit is harder to break.Warren says you should try and wean you child from the thumb or pacifier before they get too hooked on the experience, and ruining their teeth.