Thumb sucking is one of an infant’s natural reflexes.
It makes them feel secure and happy, and it helps them learn about their world. Placing a thumb or another finger in the mouth provides some children with a sense of security during difficult periods at other times when they are tired or asleep. However, prolonged sucking of the thumb use may cause problems with the proper growth of the mouth and the alignment of teeth.
These problems may be either the abnormal prosthesis of the upper jaw and its teeth (prognathism) or a gap between the anterior teeth when the child closes the mouth (open bite).
Of course, we should mention that if the child stops the harmful habit, the problem is usually restored without any intervention. But when the child continues beyond the age of 3.5-4, parents should intervene and discourage this habit. However, you should be careful because excessive pressure to stop can do more harm than good.