The best space maintainer for the early loss of upper primary incisor is the pin and tube maintainer, because :

 # The best space maintainer for the early loss of upper primary incisor is the pin and tube maintainer, because :

A. It is aesthetically acceptable 

B. It does not injure the upper lip 

C. It is easy to fabricate 

D. It allows lateral growth of the bone

The correct answer is D. It allows lateral growth of the bone.

The removable pin and tube space maintainer is designed to prevent space loss after the premature loss of a primary incisor. It allows for the natural lateral growth of the bone and provides sufficient space for the permanent tooth to erupt properly. This type of space maintainer is usually considered effective and well-tolerated by patients. While aesthetics and ease of fabrication are also important considerations, the primary purpose of a space maintainer is to preserve the space for the permanent tooth and support proper oral development.