Extraction and bone graft on back molar, 4 days post op, large bone pushing out, is this normal? (photo)

It appears as a plate of bone that must have been detached at the time of extraction and unfortunately became necrotic. Such dead bone is referred to as a sequestrum and is now protrudes through the gum. See your dentist / surgeon for further help. Nothing complicated here, but needs to be dealt with. Good luck , Dr. Daniyar

This does not look like the bone grafting particles/granules the dentist/specialist used at the time of treatment.  This looks like a "bone sequestration."  Sometimes during the extraction, trauma can be induced to the surrounding bone, caused by pushing/pulling to remove the tooth.  If too much trauma and force is used the bone that holds/surrounds the tooth can be "fractured."  Hence this is what it appears to be.  The fractured bone fragment lost its blood supply/circulation and has died... and what ends up happening is the body forces it through the gums in order for it to exfoliate or be removed.  It may take a couple of weeks for this process to finalize and fully heal.  Typically, there isnt much pain with this other than the annoyance of tongue rubbing against it and feels real rough in the mouth.  I would recommend you see the person who did the surgery - he may be able to remove it with certain techniques.  Home care should include using warm salt water rinses (1 tsp salt + 1 cup of warm water) to help maintain the area is clean and to also promote gum healing.  Sorry, these sequestrations do occur, they are relatively easy to treat, but just need time for the body to heal. Hope this helps

Most likely, it's a small piece of bone that essentially died and is making it's way through the gums. It needs to be removed so the gums can continue to heal over the socket.