Thumb Habits

Sucking on a thumb or finger is normal for infants and young children and most children stop on their own. However, if a child doesn't stop on their own, we do advise parents to discourage the habit ideally after age 3. Prolonged thumb sucking can lead to crooked teeth and bite problems affecting both baby teeth and permanent teeth that are developing, causing upper front teeth to tip outward and upper jaw to narrow in the back.

Be sure to use a positive approach and focus on praising your child when they are not thumb sucking. Initially, you could try limiting the time and location thumb sucking occurs, for example only at home or only while the child is in their bedroom to help them ease out of the habit. 

Pacifiers are no substitute for thumb sucking. They can affect the teeth essentially the same way as sucking fingers and thumbs. However, use of the pacifier can be controlled and modified more easily than the thumb or finger habit. If you have concerns about thumb sucking or use of a pacifier, consult your pediatric dentist.

A few suggestions to help your child get through thumb sucking:

-Instead of scolding children for thumb sucking, praise them when they are not.
-Children often suck their thumbs when feeling insecure. Focus on correcting the cause of anxiety, instead of the thumb sucking.
-Children who are sucking for comfort will feel less of a need when their parents provide comfort.
-Reward children when they refrain from sucking during difficult periods, such as when being separated from their parents.
-Your pediatric dentist can encourage children to stop sucking and explain what could happen if they continue.
If these approaches don't work, remind the children of their habit by bandaging the thumb or putting a sock on the hand at night. Your pediatric dentist may recommend the use of a mouth appliance.

Reference: http://mouthmonsters.mychildrensteeth.org/little-teeth-truths-is-thumbsucking-hurting-my-childs-teeth/