The matrix or scaffolding is usually the visible part of the graft material itself. There are a variety of different graft materials to choose from and each has their own purpose and application, however the basic function of the matrix is that of "osseoconduction". This is the ability to guide cells along the "scaffolding" so that the patient's own bone can eventually be deposited around the scaffolding.
The scaffolding can either be synthetic substitute bone, cadaver bone, bone from another species, or the patient's own bone. The latter offers the added benefit of having some of the other parameters, such as Cells and Signaling Molecules included, however, it does often require an additional surgery to obtain this bone.
The Cells:
The most important cells necessary are the adult stem cells, platelets and bone cells, such as osteoblasts and osteoclasts. The resident stem cells will start dividing rapidly in response to injury in order to increase their number and then morph into bone-building cells (osteoblasts). The platelets will release a variety of signaling molecules which regulate the different stages of the regeneration process. Some newer bone graft materials are more cellular based and have stem cells already included, in addition to the scaffolding
Courtesy: Christina Beck (2008), Max-Planck Gesellschaft)
Signaling Molecules:
The signaling molecules have some very important functions in the healing events. They signal stem cells to divide and morph into specific bone cells, they also direct cells into the proper location via a process called chemotaxis and, finally, some of them offer an adhesive substrate to which other cells can "stick", such as fibronectin and vitronectin.
Time:
This is the most often overlooked parameter in bone grafting and healing. We often try to push the limits of nature by accelerating the treatment and often times using grafted sites too prematurely. This may work out in certain cases, however, fact of the matter still is that any type of bone healing, whether it is an injury or a grafting scenario, it takes TIME for all the molecular events to complete until we have organized and above all load bearing bone.
Perhaps with the increased use of recombinant growth factors, stem cell technology, and laser applications, we will be able to accelerate this bone regeneration cycle somewhat, but more research needs to be done until this can be utilized with confidence and predictability.
Bone Grafting has certainly become the "Buzz Word" in Implant Dentistry in the last decade or so. The reason for this is that more often then not, we need to do some kind of grafting either in association with the placement of a dental implant or even before we can place any dental implants. We can not place dental implants if there is not enough bone volume available to accommodate a dental implant of proper dimensions, so what we usually have to do is grow bone in the deficient areas.
Before we get into the technicalities of bone graft methods and bone graft materials, however, I feel it is prudent to spend a little time on the basic physiological concepts of the bone regeneration cycle. Everytime we perform a grafting procedure or even just place a dental implant, we invariably "create" an injury to the bone structure. Therefore, we need to look at the wound healing physiology before we can embark on the actual tissue engineering part.
There are four parameters or prerequisites, which need to be present in order for tissue regeneration to proceed successfully and predictably:
- A matrix or scaffold
- Cells
- Signaling molecules
- Time
The Matrix or Scaffold:
