What are the risks (long term and short term) of using Cadaver Bone Graft before Dental Implant?

First, one needs to understand how bone works to begin with.  Bodies need calcium to function, so cells "digest" bone to free it up.  Other cells lay down bone where it previously was taken, a sort of "circle of life."  A graft simply creates a scaffolding to lay down bone.  Long term the graft (no matter what material is used) is gone, it is replaced with host bone.  Some materials take longer to turn over, so bone is normally best.  Your situation LIKELY is best done by extracting the infected tooth, grafting to preserve bone VOLUME (needed for an implant) and then placing an implant when healed.

All bone graft materials are sourced for certified and licensed bone banks.  The graft materials are usually irradiated and the chances of transmission of disease is almost nil.  Infection is possible as with any implantation of foreign material.  There are other synthetic materials that can be used or even your own bone harvested from your mouth.  You need to discuss all the options with your dental surgeon and come up with the best plan for you.

As long as your dentist uses a certified and recognized bone bank, your risks are minimal. Your surgeon can also get some bone from your own mouth to graft into the extraction socket. You need to know your options. There are various grafting materials (cadaver, coral, ceramics, membranes) that work as well as cadaver bone and you should know your options.