Thumb sucking in children has always caused embarrassment to many parents. The parents were more concerned over the social embarrassment caused by this habit rather than the actual physical damage caused by it. 
This silly habit as it appears to many parents not only causes abnormally arranged teeth but also implicates the mental state of the child.

CAUSES
Thumb sucking can either be a non-compulsive act or a compulsive oral habit.
 
Non-Compulsive act: 
As children grow, they pick up or drop habits depending on its acceptability. These habits are usually called non-compulsive habits or acts. Thumb sucking can be one such habit, which can be seen from birth to the age of 16. On an average most of the children stop this habit by the age 4. There are some children, however, who can continue the habit to as late as 12-15 years. In these children, thumb sucking is usually a way to relieve the frustration of hunger. 
 
Compulsive Act:
Thumb sucking can be called compulsive when it has acquired a fixation in the child to the extent that he retreats to the practice of this habit when ever his security is threatened by events, which occur in his world. Unlike the non-compulsive habit, the child tends to suffer from increased anxiety when he attempts to correct the habit. The habit becomes his safety valve to release emotional pressure, whenever it becomes, too much to cope with. Lack of love and affection by the parents towards the child plays a major role in making the child emotionally insecure and thus making him resort to habits like thumb sucking.

SYMPTOMS
If the habit is discontinued before the permanent teeth eruption, it can be considered harmless. 
 
Continuous thumb sucking leads to many ill effects. The main symptoms of this problem is shown by the teeth and they are:

Displacement of the child’s permanent teeth due to the   
uneven forces placed on the teeth by the thumb.