ALLOGRAFT HISTOLOGY

How freeze dried bone allografts heal and potentially fail.

The second molar was extracted and grafted with mineralized freeze dried bone allograft approximately six month prior to this radiograph. Allografts have been shown to not be osteoinductive or osteogenic but little effort has been made to understand how allografts heal. Antigenic ossification appears to a be a plausible examination for how allografts heal.

At implant placement, a pebble like surface texture was found made up of trapped mineralized freeze dried bone allograft particles.

Histologically, the surface pebbles were comprised of granules of mineralized freeze dried bone allograft particles. The remaining bone shows allograft particles trapped in sclerotic bone. In all cases of freeze dried bone allograft inflammatory cells are present. In this core sample, foreign body multinucleated giant cells are noted. Freeze dried allografts produce sclerotic bone which is a pathologic type of bone. Sclerotic bone is found in other bony lesions such as arthritic joints and calcified arteries. Sclerotic bone is formed as a result of inflammation. Allografts produce an inflammatory response because the tissue is not tissue typed and no effort is made to match the donor and host. The result is the host trying to push out the allograft material. What the host cannot expel is then encased in mineralized tissue with virtually no vitality in order to isolate the foreign material from the host. Very rarely are osteoblasts or osteoclasts found is sites grafted with freeze dried bone allografts.

From the same allograft core sample foreign body multinucleated giant cells are found as a chronic inflammatory reaction persists.

This photomicrograph is taken from a deeper part of the core sample. Evan when the graft particles have been expelled from an area, the resulting bone is sclerotic bone with virtually no osteoblasts or osteoclasts. The lack of osteoblasts and osteoclasts result in bone that cannot be remolded and will remain fixed in time and unable to adapt to changes in load.

This is a high power photomicrograph from the same core sample. It shows an allograft particle covered with a few abnormal osteoblasts. The morphology, physiology and function of these osteoblasts are abnormal and they function similarly to the mineralization of arteries.

This is a photograph of an extraction socket grafted with freeze dried allograft after 4 weeks. The graft particles can be seen being exfoliated out of the extraction socket.

This is an extraction socket 8 weeks after grafting with freeze dried bone allograft and granules are still being exfoliated. Freeze dried bone allografts are non resorbable. The mineralized component of allografts are either exfoliated or trapped in sclerotic bone indefinitely.

This is a series of photomicrographs from a study on animals using freeze dried bone allografts. NVB refers to non vital bone and is the residual allograft material. B is for new bone. At 3 weeks, in this animal, the majority of the allograft is still in the extraction socket. In the 6 week sample most of the allograft has been expelled and the socket is filled with a few graft particles and mostly soft connective tissue. The 12 week sample shows the remaining graft material clustered at the crest and the epithelium closed. This sample will retain the encapsulated allograft material in a similar fashion as the preceding human sample. Freeze dried bone allografts are non resorbable, are not osteoinductive and not osteogenic in humans. There is no indication that freeze dried bone allografts are even osteoconductive. It is our opinion, that freeze dried bone allografts heal by way of antigenic ossification to a foreign object producing sclerotic bone.

This radiograph shows a molar site grafted with mineralized freeze dried bone allograft after approximately 10 years. The bicuspid site was grafted with Socket Graft showing at 2 months. Allografts and low temperature zenografts (Bio-Oss) contain foreign proteins that are not biocompatible. The biocompatibility of a graft material can be seen radiographically. When a molar is extracted, the interradicular bone is resorbed and the body bunches up the graft material into a round bolus surrounded by a radiolucent halo(small arrows). A biocompatible graft material will fill the socket and bone will regenerate and for a time period will leave the outline of the extraction socket retaining the interradicular bone.

The site grafted with allograft is poorly mineralized with the surface of the ridge covered with granules of allograft encased in granulation tissue after 10 years. The bicuspid site grafted with Socket Graft and presents with a mineralized surface. When grafting with an allograft or zenograft there is no way to know how well the graft material will be tolerated by the host and the result will vary from sclerotic bone formation in a well tolerated graft to granulation tissue in a poorly tolerated graft with an intense inflammatory response in complete graft rejection.

Tooth #3 was extracted and grafted with freeze dried bone allograft. The radiograph shows the presence of sclerotic bone.

Implant placement with sinus lift was performed with apparent success. However approximately 3 years post implant placement shows complete failure of the graft. The implant is still integrated in the area of the sinus augmentation. How sclerotic bone fails will be covered in subsequent memorandum.