Why are some people have a translucency at the bottom of their front teeth? i wanna know the exact cause?

Dentin: For many, the dentist in the center of the tooth does not extend down to the very tip, resulting in just a thin layer of enamel. Enamel is translucent and that's why it appears a little darker.

Incisal translucency: This is the normal anatomy of a tooth and is called incisal translucency. The enamel thins out at the edge of the frontal tooth and also there is no underlying dentin.