Thumb and finger sucking is a natural reflex that can begin in the womb. It provides them with a sense of security, helps them relax and sleep. It is normal for children to stop sucking thumbs and fingers between the ages of 2 and 4 years old.
Normal growth of the jaws, teeth and roof of the mouth can be affected if the habit continues after the permanent teeth have erupted. Pacifiers can cause the same effect as thumb and digit sucking. This may result in tooth crowding and protruding teeth.
It's important though to understand what sort of thumb sucking is likely to cause problems, because some thumb sucking is natural and will not lead to problems. Children who merely put their thumbs in their mouths are unlikely to cause any problems for themselves. It's where the thumb sucking is intense that there is likely to be a problem later on.
Our advice is that vigorous sucking should be discouraged from around the age of four and that you should watch carefully for any change in your child's teeth or mouth at around this time. If thumb sucking does continue after the first adult teeth have come through (normally around the age of 6 or 7), it may cause or contribute to teeth being pushed out of alignment, the development of a lisp in speech and possibly even an alteration of the shape of the jaw from a 'U' shape to a 'V' shape.