Your dentist can help.

For babies and young children, thumb sucking is a natural reflex. It gives them a sense of security and helps them fall asleep. However, when teeth begin to develop, thumb sucking or sucking on a pacifier can lead to dental problems.
Children who vigorously suck their thumbs are more likely to develop dental problems than children who suck their thumbs more passively. Vigorous thumb sucking can cause a child's baby teeth to shift, and correct alignment of a child's permanent teeth and proper growth of the mouth can be inhibited by persistent thumb sucking.

Children should not suck their thumbs or use pacifiers when their permanent teeth are coming in. Most children will naturally stop thumb sucking between the ages of two and four as they become more interested in their surroundings. But if a child persists in thumb sucking, a dentist, pediatric dentist or orthodontist can help.

A couple of tips...
Most children use thumb sucking as a means of comfort, parents can try to identify and then remove the cause of anxiety. Parents have also had success using praise and rewards to encourage their child to stop thumb sucking.
If you notice changes in your child's teeth due to thumb sucking or due to any reason, call us for a consultation.