The American Academy of Pediatric Dentistry's "Policy on Thumb, Finger and Pacifier Habits" says: "Most children stop sucking on thumbs, pacifiers or other objects on their own between 2 and 4 years of age. However, some children continue these habits over long periods of time. In these children, the upper front teeth may tip toward the lip or not come in properly. Frequent or intense habits over a prolonged period of time can affect the way the child's teeth bite together, as well as the growth of the jaws and bones that support the teeth."