Causes of orthodontic problems

There are many reasons that lead to a particular form or forms of malocclusion or mal-position of teeth, including:

Genetics:
Often some orthodontic problems inherited from one generation to another.
It is possible for a child to inherit the shape and size of the jaw from one parent and inherits the shape and size of teeth of the other parent, leading in some cases to the lack of harmony between the size of the jaws and the size of the teeth. This problem might manifest in the form of crowding or spacing of teeth.

Early lost or extraction of milk teeth:
The milk teeth play an important role in maintaining the space for the soccer permanent teeth. If the milk teeth, for any reason, fall before the right time, the posterior teeth might drift causing a loss in the space which might lead to the impaction of a permanent tooth.

The congenital absence of one or more of the permanent teeth :
It is very common than one or more of the permanent teeth are congenitally missing. Mostly the upper lateral incisors which pose an esthetic problem considering the location of this tooth and it importance in the smile. The lower premolars (bicuspids) and the third molars (wisdom teeth) are affected too quite often.

Thumb Sucking:
It might lead to severe deformation in the upper teeth and jaw.

Tongue thrust the rest position of the tongue:
The tongue exercises a big force over the teeth while swallowing and speaking. If the tongue is mal-positioned while functioning or resting these forces might lead to mal-occlusion or mal-position of the teeth.
Breathing from the mouth might also cause some problems in the occlusion.