Baby teeth or milk teeth fall out to accommodate the full complement of 32 teeth in the growing jaw bone. The bigger, permanent teeth develop to fill the available space. There are 20 milk teeth which start appearing from six to eight months after birth and are all out by the time a child is about two and half years old.
As the child grows up, the jaw bone grows in size accommodating the larger and more permanent teeth. The permanent teeth actually begin to develop inside the gums as soon as the milk teeth appear. As a permanent tooth grows, it cuts away the root of the milk tooth. Thus, a milk tooth falls. The falling of milk teeth begins with the growth of the first permanent molar at the age of about six.