Thumbsucking

The sucking instinct is one of the strongest and most basic instincts. The purpose of this instinct, of course, is to ensure that the newborn is able to get sustenance from their mothers breast. The habit of thumb sucking is present even before a baby is born. In fact, many fetuses routinely suck their fingers or thumbs in-utero (in the mothers womb).

For an infant, sucking is associated with food, and since hunger is the one of the most disturbing states for infants and small children, the sucking reflex is soothing and distracting. As the child grows the association of sucking with food may diminish but the feeling of comfort derived from the action often stays with them for many years.

While thumb sucking is not psychologically damaging, and in babies is probably helpful in the normal formation of the mouth, if the habit persists beyond about 4-5 years old, it can have a devastating effect on the developing dentition and the bone of the jaws.

While the effects of sucking may vary, there are a few characteristic deformities that are very common to children who suck their thumbs for too long. Among them are:

"Buck" or protruding upper front teeth.
Retruded (the tops of the teeth pointing toward the tongue) lower front teeth.
Narrow high palettes (the roof of the mouth).

Pacifiers

Sucking a pacifier has the same effect on the dentition and surrounding bone as thumb sucking although it may be less pronounced due to the fact that that the pacifier itself is passive while a thumb may be pulled or pushed while sucking adding to the effect. Pacifiers may be preferred over thumb sucking simply because their access may be easily denied.