Dr. Suneel Chagger


Bone grafts from Intraoral Donor Sites

Introduction and Principles

Bone is a continuously modifying dynamically depositing, resorbing and remodelling. This is the basis through which bone grafting works.
The two types of bone grafts frequently used are:
1. Autografts -recipients own
2. Allografts. -from another member of the same species.
Ideal bone grafts are osteoinductive/conductive, biomechanically stable, disease free and contain minimal antigenic factors as usually is autograft bone. Allografts as well as not having these properties, have delayed vascular penetration, and union can be delayed or incomplete. They are osteoconductive but slightly osteoinductive. The structure of grafts vary:
a) Cortical- +density=-angiogenesis=-osteoblasts+osteocytes=graft becomes weaker initially due to more ostoecyte activity.
b) Cancellous -density=+angionesis=+osteoblasts-osteocytes=graft becomes stronger due to more osteoblast activity.
Therefore graft selection is important as it influences the structure and integrity of the substituting bone, aswell as the interface contact that effects the speed of vascular ingrowth.
Healing occurs in three distinct stages
1. Early Inflammatory- haematoma =+inflammatory/fibroblast cells infiltrate =+ neurovasculature formation =+ mesenchymal cells.
2. Repair- fibroblasts =+ callus. This is quite soft for up to seven weeks and so the union must be properly immobilized and protected to prevent fibrous union.
3. Remodelling- over years. Mechanical forces influence osteoblast/clast activity laying and resorbing bone to balance out stresses and through creeping substitution necrotic bone is replaced with new.

Intraoral donor sites

The most common sites for intraoral bone grafts are
1) mandibular symphysis- Membranous grafts revascularise more rapidly than endochondral types which have a thicker cortical component(1)
2) mandibular ramus.
Misch(2) et al reported in a comparison of symphysis and ramus grafts, that out of 31 patients symphysis patients were concerned regarding the compromise to the chin shape and contour, had greater postoperative sensory disturbance and greater chance of infection(2/31). The ramus had poorer access, grafts were thinner and cortical. To note. there were only 50 grafts performed and there were 22% more patients having sympyhsis graft, and conditions such as Patient compliance, immune control, and surgical sepsis may have varied all the results should not be conclusive.
3) mandibular/lingual tori - these occur quite infrequently but can be used and may even benefit the patient if they are large and effect speech, dentures etc.
4) Zygomatic bone -. Kainulainen(3) et al concluded that this was a safe donor site for
smaller defects based on a study on 20 cadavers. A total of 22 perforations into the sinuses were observed from ct scans in nearly half the specimens. Patient morbidity/discomfort as well as the operator skill requirement was also not considered when reaching the conclusion.
5) palate.
Graft structural composition depends on the manner by which it is extrapolated or prepared e.g. bone chunks, rings, chips, crushed, powdered (bone trap), mixed. Each has its own advantages and disadvantages and user preference.


Selection criteria

The selection criteria for donor source depends on the size/shape of the defect and on the availability of bone. These can be determined by the use of x-rays (OPT,PA,CT) and ridge mapping. Bearing in mind
1.the donor block should be away from teeth apices(5mm) and the inferior borders,
2. The third molars could prevent adequate harvest
3. The ID canal is away from the site.
4. Magnifications from x-rays are calibrated.
A Sethi et al(4) used the symphysis for 1-6 implant for small defects (2-4 mm), and the ramus for 1-2 implants with larger defect (6mm width and/or 4mm height). This is generally accepted by many authors who have also cited the high success rate of local block grafting. Dr D Schwartz-Arad(5), based on a study of ten patient files concluded” Intraoral bone block grafting is a predictable operation with a high success rate for longspan augmentation, up to complete jaw augmentation/ extensive bone reconstruction of the maxillary alveolar ridge“ . Although this was only studied till up to the implants were placed, only four of the ten files reviewed were totally uneventful.







Surgical principles

The fundamentals of surgery is the planning. The post tooth position must be determined so that we have a goal at aim for. This can be done by means of models with teeth on them and templates/stents. Surgery should always start at the recipient site in order to confirm the size and shape of the defect. Post operative management includes the use of antibiotic, anti inflammatory, cold packs and steroids to kerb pain and swelling

Soft tissue management

1. Bevelled incisions full thickness and divergent releasing incisions help to relocate the flap and maintain blood supply. The maxilla -remote palatal, The mandible - crestal. Papillaes maintained and released past adjacent teeth. .
2. Complete and tension free interrupted sutures- Periostium on the flap can be scored and periosteal released, or a soft tissue graft attached to allow stretching.

Access to graft sites:

a) Symphysis i)small grafts require sulcular incision between the canines.
ii)Larger require full thickness flap from ginivalmargin distal of the formina, (which is exposed and protected), Both are reflected to the lingual border.
b) Ramus Avoiding buccal and lingual nerves raise flap along the ridge distal and around the 2nd molar to expose the lateral ramus and the external oblique ridge.
Hard Tissue management
1. Evaluate the size of the defect and from where the graft is going to come.
2. The recipient bed is perforated with a small round bur and contoured to improve and accept the graft contact.
3. Symphysis grafts- fine fissure bur, and chisels. The superior osteootomy must be angulated downwards atleast 5mm below the apices and the inferior margin above and parallel to the inferior border.
Ramus is also initially marked for the 3d donation with fissure and round burs. The lower being a groove made by a large round bur above the ID canal.
4. Graft is removed, placed quickly, and stabilized with titanium screws. A membrane or particulate bone can be used if there are minor deficiencies.




Clinical applications

Grafting procedures will become more and more frequent as training/research and patients desire to have more aesthetic and stable implants increases. Areas where bone deficiencies or poor quality bone prevent the ideal placement of an implant which may lead to an unaesthetic or unstable implant/crown can now be rectified through knowing when to use specific grafting techniques with the science of graft healing and providing a more satisfactory results.

References

(1) Misch CM, Misch CE. The repair of localized severe ridge defects for implant placement using mandibular bone grafts. Implant Dent. 1995;4:261-67.

(2) Misch CM. Comparison of intraoral donor sites for onlay grafting prior to implant placement. Int J Oral Maxillofac Implants. 1997;12:767-76.
(3) V T Kainulainen, G K B Sàndor, C M L Clokie, A M Keller, K S Oikarinen The zygomatic bone as a potential donor site for alveolar reconstruction--a quantitative anatomic cadaver study.Int J Oral Maxillofac Surg. 2004 Dec ;33 (8):786-91

(4) Sethi A, Kaus T. Ridge augmentation using mandibular block bone grafts: preliminary results of an ongoing prospective study. Int J Oral Maxillofac Implants. 2001;16:378-88.

(5) Dr. Devorah Schwartz-Arad Intraoral Autogenous Block Onlay Bone Grafting for Extensive Reconstruction of Atrophic Maxillary Alveolar RidgesJ Periodontol 2005;76:636-641