Whether it is sucking of the thumb, finger, or a  towel, prolonged placement of an object between the top & bottom teeth prevents them from growing towards each other. This may happen in children who cannot control their unhealthy habits; they are attached to the nice, warm and comforting feeling of their thumb or finger in their mouth. When the upper and lower front teeth are prevented from erupting towards each other, a big gap develops between the top & bottom front teeth, forming an open bite. Not only that, the upper teeth may be over-protruded, the lower teeth may be pushed too far in, and the cheeks may squeeze against the upper jaw, resulting in a V-shaped narrow upper dental arch. This deformed jaw results in crooked teeth.

The thumb-sucking habit should be corrected early, so that the jaw and teeth can develop normally. If the habit is stopped early, the child may avoid interceptive orthodontic treatment.

See also: Strange-looking new teeth