Frequently Asked Questions (FAQ's)
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We have assembled information to address frequently asked questions we receive about our bone grafting systems. The Information and opinions supplied is based largely on the clinical experiences of our users. Where applicable, we reference the literature. Please keep us informed of your innovative applications and submit to us any questions.
1. What are some of the intra-oral applications for autogenous bone grafting that have utilized the Maxilon bone grafting systems?
The most common applications in clinical practices are localized alveolar reconstruction, coverage of implant dehiscence/fenestration at the time of surgery, and sinus lift augmentation procedures. Other applications being explored include: periodontal defect reconstruction, extraction socket alveolar preservation, coverage of lower second molar distal roots in older patients that undergo third molar surgery, alveolar cleft reconstruction, osteotomy defects and apicoectomy defects. With the cost-effective ease of rapidly harvesting autogenous bone, many clinical applications will benefit.
2. What do you consider the best intra-oral site for harvesting bone with Maxilon's bone grafting systems?
Any accessible cortical surface is fair game for harvesting bone. When small amounts of bone are needed, the flap at the primary surgical site can often be extended to harvest bone. When greater amounts of bone are needed, the lateral ramus, external oblique ridge area is a easily accessible site that yields moderate amounts of bone. Other sites include the mandibular symphysis, the maxillary tuberosity, and the zygomatic process of the maxilla.
3. How long does it take to harvest the bone?
It takes about 15 minutes to access the lateral ramus donor site, harvest 2 cc of bone, and close the donor site. Common procedures such as alveolar defect reconstruction and sinus lift augmentation can be completed easily in less than an hour.
4. What is the consistency of the graft material?
The XBR graft material is in the form of thin convoluted shavings, and with their randomized form, there is a relative increase in the graft volume in comparison to the original bone volume that was harvested. The interstices created by the shavings form a porous matrix that is filled with blood from the bone's surface as the shavings are being harvested. The exposed collagen promotes coagulation of the blood and binds the graft together with a firm mortar like consistency. This allows the graft material to be easily handled and packed securely into place. These shavings, in comparison to particulate grafts from ronguers or bone mills, do not have any sharp edges. This allows the material to be placed securely in position as compared to chip-like particles. And without sharp edges, the graft is more gentle on the flap and from our clinical experience, allows the flap to adhere to the graft and minimize the tension across the wound closure.
5. Have patients become more comfortable about consenting to bone grafting procedures?
Patient acceptance based on our clinical experience and the experience of our users has been very high. It is much easier to discuss the risks and benefits and for a patient to feel comfortable with a procedure that planes a thin layer of bone vs. issues with other grafting approaches: other autogenous grafts ( pieces of bone from the chin and jaw, iliac grafts), allogeneic and xenogeneic preparations (dealing with patient concerns of disease transmission), and alloplastic materials (long term success rates). Most patients are very comfortable with the concept of using their own bone and the low morbidity of the harvesting procedure.
6. Is a barrier membrane required?
In our experience, we do not routinely include a membrane, unless, there is 1) difficulty achieving closure, or 2) there is scar tissue with no periosteum present.
A blood clot alone that occupies a volume does not provide any cues to direct the destiny at that site. In the case where bone regeneration is needed, the membrane excludes the soft tissue elements and allows re-population of the site by osteoprogenitor cells from the recipient bed.
In the situation where a autogenous bone graft with blood in its interstices is placed, the fate of the region is far more clearly defined and the role of a membrane is less clear. By not including the membrane, other favorable conditions are present:
a. The cambium layer of the periosteum is in contact with the graft and provides a rich source of osteoprogenitor cells.
b. The outer surface of the graft is in close proximity to a blood supply, and revascularization is not impeded by the membrane
c. Additional procedures are not required to remove the membrane
d. The added expense is not included in the procedure.
It is up to the clinician's personal discretion whether to use the membrane. In our experience, we do not include the membrane unless there is difficulty achieving wound closure.
7. Are the cortical bone shavings from the Maxilon instruments comparable to cancellous (marrow) bone as a graft material?
The blade transforms the block form of cortical bone into convoluted shavings with blood in its interstices. This porous, interconnecting matrix allows a rapid response of revascularization comparable to cancellous grafts.
In addition, the cortical shavings provide several important elements for bone healing at the grafted site. These include osteoprogenitor cells and a source of precursors and bone morphogenetic proteins. Below these concepts are expanded in more detail.
Revascularization1,2 Cortical blocks of bone require an initial phase of extensive bone resorption (physical space needs to be created) before there can be significant revascularization of the site and bone deposition. By rendering the cortical bone in the form of convoluted shavings, a porous interconnecting blood-filled matrix is formed. This stable substratum allows rapid ingrowth of capillaries and the deposition of bone on the graft's large surface without the need for significant resorption to initially take place. This is an important similarity to cancellous bone in that it provides easy accessibility for revascularization and a high surface area to promote bone deposition. Significant bone formation cannot occur until the vascular supply is re-established.
Cell population. Although the density of osteoprogenitor cells is less in cortical bone grafts, a significant number of the osteoprogenitor cells line the haversion vascular channels of cortical bone. Because of the relatively atraumatic approach to harvest the graft (low heat, minimal contamination, no osmotic gradients, no desiccation of the graft) many cells probably remain viable at the time of harvest. However, once any graft is placed in the recipient bed, cells beyond about 300 microns of their blood supply are unlikely to remain viable.
Osteoprogenitor cells from the host bed are a significant source of cells for healing. For example, in guided tissue regeneration techniques, allogeneic (freeze dried cadaver bone), xenogenic ( bovine bone) sources, and alloplastic grafts
(HA, tricalcium phosphate), these acellular methods only provide a osteoconductive scaffold the sole source of osteoprogenitor cells is from the tissue bed.
Precursors The shavings of cortical bone, with blood in the intersticies of the matrix, provide many of the necessary precursors for bone formation. In addition, as capillaries invade the graft and osteoclasts resorb the bone surfaces, bone morphogenetic proteins are liberated from the graft3. These osteoinductive factors recruit primitive mesenchyal cells that accompany the infiltrating vessels to become bone forming cells. With the very high surface area to volume, the porous matrix of convoluted shavings is analogous to a drug delivery system for these factors in many respects.
Burchardt, H. The Biology of Bone Graft Repair. Clin Orthop. 174:28-42 April 1983
Albrektsson, T. Repair of Bone Grafts – A Vital Microscopic and Histological Investigation in the Rabbit Scand J Plast
Reconstr Surg 14:1-12, 1980
Marx, R.E. Biology of Bone Grafts OMS Knowledge Update, 1:RCN3-17, 1994