Why aren't US doctors using hydroxyapatite/coral for chin or jaw implants?

I believe that facial implants made from coral/hydroxyapatite are not FDA approved in the United States.  This is most likely the main reason that surgeons here are not using them.  

In our practice, we have been using Silastic chin implant for 25 years and have an excellent success rate with them. The  are easy to place, and easy to remove. They provide excellent smooth augmentation to the chin.

  I can't speak for any other plastic and cosmetic surgeon but I have performed many cheek and chin implant surgeries for over 25 years.  These types of implants are not new and have been used before here in the US. Implants that become part of the bone are extremely difficult to be removed or simply can't be removed making them, in my humble opinion, far less desirable than silastic implants.  Infection rates for facial implants are very low, so that would not be a motivation for using these types of implant material.