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BONE GRAFT INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com


CONTENTS -Introduction - History - Definition - Types of Bone Graft - Forms of Bone Graft - Autografts - Allografts - Synthetic Bone Grafts -Sinus Bone Graft - Bone Graft Handling - Goals of Reconstruction - Summary and Conclusion - References www.indiandentalacademy.com


INTRODUCTION Bone grafting is a dynamic phenomenon. A successful bone graft is applied, heals, becomes incorporated, revascularizes and eventually assumes the form desired. In their early application, bone grafts were considered a mere strap lattice, and the results were measured primarily by the graft’s ability to withstand the mechanical stresses that surrounded them. Today, bone grafts are viewed as biologic structures. Of course, mechanical stress, shear stress (extrinsic and intrinsic), contouring, and remodeling are also important in the long term and are the part of the healing process of a bone graft. Different forms of bone grafts vary on the basis of the function that they must perform. www.indiandentalacademy.com


Grafts that must withstand the shear pressure of mechanical stress is usually a large cortical bone graft. A bone graft intended for contouring, to expand the biologic boundaries of the skeleton, and to change the three dimensional configuration of the face is usually of the corticocancellous variety; these are soft bone grafts that can be contoured and allowed to heal, vascularize, and augment existing bone to produce the desired shape. Corticocancellous bone grafts are applied to fill a discontinuity defect and require a carrier. There are many carriers used for such applications. Almost all bone grafts used currently by thousand of surgeons around the globe are autogenous. Such autogenous bone grafts constitute the best biologic bone grafting system for the human body. They vascularize bone grafts, they heal; and they withstand mechanical stresses in due time. The more compact the bone graft is, the less the chance of complete and rapid vascularization. The less compact the bone graft is, the more rapid the revascularization and www.indiandentalacademy.com healing.


Whatever specialized group of surgeons uses bone grafting, whether on the face, the mandible, or the extremities, the principles are the same. The techniques and indications differ, but the contra indications may be the same (e.g. bone grafts cannot be applied in areas that are heavily bacterially contaminated). Topical application of antibiotics is gaining momentum, particularly the use of antibiotics in small pellet form to obtain the maximal effect with the least disadvantage. We cannot really finish the introductory remarks without noting two recent advances. The first is the use of vascularized bone grafts, which have their own vasculature. These can be implanted with microsurgical technique and allowed to heal appropriately. In certain parts of the body, it may still be advantageous to allow a bone graft to vascularize (e.g., in areas where mechanical stress and shear stress are needed to ensure normal function). www.indiandentalacademy.com


The second aspect is the use and understanding of allografts. Allografts are becoming a more accepted form of bone grafts. The majority of large allografts assume a near normal function in individual who lack certain areas of the body that have been resected for oncologic problems or for other reasons. It is frequently possible for these areas to be replaced, and the patient can resume normal function. However, these large bone grafts do not really completely vascularize as allografts.

Finally, bone grafts could not have become extensively popular, easy to implant, and widely utilized around the globe, without the use of rigid fixation systems. The rigid fixation systems brought a necessity for understanding biomaterials and metallurgy. Whether the metal used is stainless steel, titanium, or vitallium, these systems provide mechanical strength that is 200 times that of a natural bone. These systems are gettingwww.indiandentalacademy.com smaller and smaller, to the extent that a system introduced in 1990 utilized screws measuring 0.8 mm.


Prospects for the future include the possibility that when certain parts are needed, they can be fabricated within the same biologic system as an autogenous bone graft and then reapplied, particularly in discontinuity defects. This may benefit the patient with skeletal problems undergoing oncologic treatment or the patient with postoncologic deformities, as well as patients with post traumatic defects.

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HISTORY OF AUTOGENOUS BONE GRAFTING In 1682 VanMeekren transplanted canine skull bone to calvarial defect. Von Walter 1882 described use of corticocancellous bone graft. Ollier 1867 reported transfer of periosteum and bone and concluded that both must be alive to account for osteogenesis. Barth in 1893 he revealed that several days after bone graft transfer, the graft is dead. He felt that the graft worked via gradual resorption and replacement of dead bone by creeping substitution of dead graft by viable bone growing into it from living bone in contact www.indiandentalacademy.com with it. This is currently called as Osteoconduction.


Axhausen in 1907 demonstrated in an experiment that periosteally covered bone grafts exhibited osteogenesis from surface cells surviving at the periosteum. Phemister in 1914 concluded after a series of studies that some osteogenic cells on surface of bone graft survive by diffusion of oxygen and nutrients from the recipient bed. It was later done by Ham and Gorden in 1952 and Hancock 1963. Gallie & Robertson 1918, agreed that survival of cells on bone graft is important, and that rate of survival was better with cancellous bone than with cortical. Mowlem in 1944 and later in 1963, used cancellous bone grafts and demonstrated its superiority over cortical bone grafts. www.indiandentalacademy.com


Okland and associates in 1985 put forward that survival of surface cells in autogenous bone grafts is much more superior to freeze dried autogenous grafts, allografts, inorganic bone and its substitutes.

ALLOGENIC BONE GRAFTING History: Bone induction principle was described by Urist for allogenic bone in 1953. This induction was mediated through an acid-insolube protein complex (BMP) derived from the grafted bone that directs differentiation and activity of host osteocompetent cells towards bone formation. Urist and Burwell in 1968 and later in 1969 that early use of allogenic bone either fresh or frozen and dried. Urist in 1968 also described that allogenic bone is replaced by new host bone. www.indiandentalacademy.com


Definition A graft is a substance, foreign to the region of the body in which it is placed, which is used to replace, augment or fill a defect created by surgery, trauma, disease and developmental deficiency. Graft is a living tissue, transplanted to a different site, that continues to live and function in the new environment. If the tissues does not survive the relocation, it is technically an implant rather than a graft. Graft (according to GPT) : Tissue or material used to repair a defect or deficiency.

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Indication for Bone Grafting 

Jaw resection following malignancy / other pathology

Extensive trauma

In orthognathic surgery

As an onlay material in facial aesthetic surgery

As a composite cartilage – bone graft in the reconstruction of the TMJ (growth center)

Large bony defects created by cysts and tumors

In preprosthetic surgery as an onlay

In preprosthetic surgery as a fill in material

In cleft patients.

In implantology e.g. : sinus lift procedure

In periodontal surgery

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Radiographic Assessment Presurgically -

Radiographs to assess the bone density at recipient and doner site.

-

Radiographs to rule out aberrant anatomy and gross pathology.

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Arteriograms for free grafts

Post surgically -

Increased or normal radio density at the grafted site.

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Irregular margins coinciding with osteoclastic activity www.indiandentalacademy.com


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At the end of healing phase : No radio density

-

Scintography exhibits hot spots in areas of increased bone activity – bone deposition.

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C.T. Scans show good resolution and clarity

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In M.R.I., shows up as high intensity images in both T1 and T2 scans.

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M.R.I. can detect marrow activity and is helpful in predicting initial changes.

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TYPES OF BONE GRAFTS Auto graft : Bone graft transplanted from one site to another from patients own body. Xenograft / Heterograft : Bone taken from another species. These can be both cancellous or cortical Composite : Bone grafts are made partly allograft or heterograft and partly autograft. Allograft : Bone transplanted from one individual to another genetically unrelated individual of same species. Isograft : Bone graft transplanted from one person to another genetically related individual of same species. The donors are designated as Autologous, Heterologous, Allologous, Isologous with respect to the recipient. www.indiandentalacademy.com


FORMS OF BONE GRAFT 1.

Non-vascularised

2.

Vascularised

3.

Cancellous

4.

Cortical

5.

Corticocancellous, has properties of both types

Other types of grafts such as slurry bone, particulate bone, bone pastes are small fragments of bones of different sizes compacted together. The easier the penetration of blood vessel into the graft to revascularise it, the less mechanical stress that graft can take. More solid the bone graft is in its form to withstand mechanical stress with appropriate stress shielding, the harder it is to revascularise, incorporate and be viable bone. www.indiandentalacademy.com


CORTICAL BONE Cortical bone can produce good mechanical filling of defect, and give good functional result, although it takes longer time to revascularise . Cancellous bone also fills defect but its healing is faster. They have some clinical limitation. They are used primarily in areas of great mechanical stress,and hence its proper fixation is important for the stability of graft and for its proper function. It allows the graft to survive with or without complete viability. This form of graft is useful in long bones, not very effective when used in facial skeleton membranous bone site. It used for discontinuity repair, to improve existing contours, expand on the boundary to give patient a normal aesthetic look.

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CANCELLOUS BONE This is used to get fusion and for correcting discontinuity defects. They can be utilized in any type of wounds i.e., contaminated or clean. These usually do not have mechanical strength desired for reconstruction of larger defects. Because of large open areas in the grafts, revascularisation takes place very well. Thus new cellular regeneration, remodeling and substitution, of new bone occurs, as old bone is removed.

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CORTICAL

CANCELLOUS

Cortical bone grafts revascularise slowly. They are not permeated by the blood vessels until 6-7days and graft is not completely vascular till 12months. This delay may be due to the need to open, by the osteoclastic activity, the existing Volkmanns canals and Haversian system. It may also be due to smaller no of endosteal cells available for the end to end anestamosis.

There is end to end anestomosis of host with grafted vessels. This together with the process of in-growth into the marrow spaces takes place with in 2 weeks. This revascularization also allows the grafted cells and host cells, induced by osteogenic cells, to differentiate into osteoblasts. They surround isolate dead bone and account for increased radiodensity of graft initially.

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The process of repair is initiated by osteoclastic activity. Here osteoclastic activity ceases following the completion of the task of walling off the remaining necrotic bone. This mixture of new necrotic bone remains until the metabolic and the catabolic phases of repair are complete. Here we have viable and non viable bone

In time decreased radiodensity is seen, as a result of removal of necrotic bone. Also increased radio density is due to increased no. of surviving transplanted cells. The no. of viable cells are more also because of ability of more cells to be nourished by diffusion from surrounding host. The process of repair is initiated by osteoblastic activity.

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This bone graft decreases in mass and in porosity, thus it is weakened by 50% from 6 weeks to 6 months to 2 years following grafting, the mechanical strength is equal to normal bone.

Here only new bone remains and the necrotic bone is removed. Here we have only viable bone. Although in cancellous bone the augmentation of new bone and its homogenecity result in initial increase in strength, in time mechanical strength return to normal due to osteoclastic activity and decreased osteoblastic activity

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Bone Graft

Cancellous

Cortical Cortico – Cancellous Autograft

Allograft

Xenograft Source HIP, RIB, TIBIA Cranium

Clinical application varied Clinical outcome Accepted (special)

Not useful

Satisfactory www.indiandentalacademy.com

Standard Procedure


The bone used for grafts should have a structure and form so that when it is placed in the recipient bed, it will proceed through the natural process of healing. Cortical bone contains pure cortex dense bone. It is usually layered and the only open space for revascularisation is that of nutrient blood vessels.Hence it is used for weight bearing areas. Cancellous bone provides more open spaces for faster revascularisation, but it lacks mechanical strength, particularly when used for weight bearing areas. However corticocancellous provides the advantage of both. Bone grafts can be developed into blocks, chips, and paste. Block of bone developed is used such that the defect is outlined on the donor site, donor bone cut to the specification needed and graft corresponds exactly to size and shape of the defect. www.indiandentalacademy.com


Bone chips are harvested as particulate bone. There is no structure to such grafts. The defect must be well stented and healing takes place as the pieces of bone become incorporated. Rapid vascularization of grafted tissue is then ended by solidification, then only can it withstand weight and forces. Only disadvantage is that it takes about one year for its completion. Bone paste is used as a carrier to bridge the defect to be closed. Thus bone paste if made slurry can be packed in the defect. . Some authors say addition of microfibrillar collagen (avitene) gives form to paste, thus making it more easy to handle. This also takes about, at least one year to become solid to withstand mechanical forces. It should have sufficient rigidity to withstand mechanical pressure during healing phase.

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I Autograft The most preferred bone graft, sites mainly being rib, iliac crest as the primary source. This refers to bone tissue transferred from one site to another in same individual. Clinically these grafts can be further classified on the basis of SITE OF ORIGIN 

Iliac

Fibula

Rib

GROSS ANATOMY 

Cortical

Cancellous

Corticocancellous www.indiandentalacademy.com


Bone marrow aspirate

Vascular autografts

Free tissue transplants

Pedicle flaps

PHYSICAL FORM 

Paste

Morsel

Chip

Strip

Block

Segment

Match stick www.indiandentalacademy.com


1. Block Bone Grafts Devoid of Periosteium The piece of bone contain both cortical and cancellous bone. It is shaped to fit a defect either before or after the bone has been removed from the donor site subperiostially. This type of graft is useful for a.

Repairing a saddle nose.

b.

Restoring continuity of the mandible

c.

Filling skull defects

d.

Restoring the zygomatic prominence.

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Block Graft

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2. Osteoperiosteal Grafts These bone grafts have the periosteum attached. They are obtained from the flat medial surface of the tibia and from the iliac bone.

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3. Cancellous Bone Grafts The best source for these type of grafts is the ilium. These grafts are useful for a.

Filling in surface bone defects

b.

Interposing between separated bony fragments

c.

Filling gaps beneath and between larger bone grafts

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The chips are usually packed at the junction between larger bone graft and the host bone. The advantages of chip cancellous bone grafts include a.

They seem to be more resistant to infection

b.

Regeneration occurs more rapidly than with other grafts

4. The Split – Rib Graft This type of graft has been recommended by Hongacre and Destefano (1975) for large cranial and facial defects in children as regeneration of bone occurs in the donor site.

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5. Fibular The free vascularised fibular graft was the first free graft used clinically. The advantage of it in long bone defects are strength, length and growth plate. As it is purely cortical it can withstand daily stresses. The disadvantages of this graft are that vascular pedicle is as short as 1 cm. This means that there must be appropriate vasculature close to the recipient site. It is used basically for long bone defects.

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In 1973, Taylor described its use as a reconstructive method. It is used for reconstruction of mandibular deformities, craniofacial defect, long bone defects etc. The advantage is its curvature, thickness of vascular pedical length upto 8 cm. This can be raised as a composite flap, myoosseous and osseocutaneous flap. Disadvantage: damage by perforating the peritoneal cavity. The anatomy is such that either superficial or deep circumflex iliac artery can be used as vascular supply for flap closure.

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II Allografts This is the principle alternative to autogenous bone. Allograft or alloimplant refers to bone which is harvested from one individual and transplanted into another within same species. These bone tissue implants provide the form and matrix of bone tissue, but no viable bone cells are transplanted. Some of articular chondrocytes may remain viable if handled carefully.

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1 Freeze dried bone allograft FDBA This is not a synthetic bone,but it is a human bone,harvested from fresh cadavers it is then sterilised,freezed and dried .It works primarily through conduction, thus over a period,it will resorb and bone graft is replaced.These are commonly used in sinus bone grafting procedures.

Barrier membrane (Gortex)

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This is probably the most frequently used alloimplant. It is used mainly as a composite graft (i.e., in combination with marrow from the recipient). In orthopaedic surgery, it is used to fill defects resulting from the extirpation of bone tumors or cysts or as an adjunct in spinal fusions. It is also used extensively by periodontists to fill alveolar defects and by oral surgeons for reconstruction in the maxillofacial region. However, lyophilized bone has been shown to retain its antigenicity, and in applications where larger segments of bone are required with ability to withstand stress, the results have been very unfavorable, showing incomplete incorporation and decreased ability to withstand torsional stress. Longitudinal cracks have also been observed when freeze-dried bone is rehydrated. It is suggested that freeze-dried bone be supplemented with generous amounts of autogenous iliac bone

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2 Demineralised bone matrix It is a subset of alloimplant bone, which can be used as an implant material. Preparation and dimineralisation of bone further reduces antigenicity and makes bioactive proteins in bone matrix more available for interaction with local cells. This demineralised bone matrix has been used to induce bone formation and produce healing. It was shown by Glowacki and coworkers that some of its use is in craniofacial reconstruction; although its use is mostly in orthopedic procedure. In contrast to deproteinized bone, demineralized bone retains its osteoinductive properties and has been used by Mulliken et al for reconstruction in the craniofacial region. It is acknowledged, however, that the use of radiation for sterilization diminishes osteoinductivity, and other ways to sterilize the implant are being investigated

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DBX速 Demineralized Bone Matrix Putty

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Deproteinized Bone Such bone preparations lack osteoinductivity. Despite one report in which good results are claimed, experimental results indicate the failure to incorporate deproteinized bone into the host skeleton. Chemosterilized (AAA) Bone

Autolysed,

Antigen-Extracted

Allogeneic

This particular alloimplant has been described and is being used by Urist and Dawson. Cadaver bone is harvested as soon as possible, after death, and processed so that the BMP is preserved while nearly all the stainable intralacunar material is enzymatically digested. It is then freeze-dried. The breaking strength is claimed to be about one half that of whole, undemineralized wet bone. The highest success rates come from operations on young children with a high proliferative bone growing capacity. www.indiandentalacademy.com


III Xenografts As noted earlier, the use of xenogeneic transplants has been abandoned by most surgeons, although sporadic reports of their use continues. The genetic transplantation differences between human tissue and that of other species (e.g., bovine), are such that the fate of such grafts is their eventual sequestration without any new bone formation.

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IV Synthetic bone grafts Alloplast These are expanding variety of synthetic or non tissue bone graft. These includes biologic and synthetic polymers; ceramics, matrix proteins and metals. Combinations of some of these materials may replace autograft and allograft bone materials. The various alloplasts used for reconstruction or augmentation in the craniofacial maxillary region include. 1.

Solid or mesh metals such as titanium and its alloys, 316 L stainless steel, and Cr. Co-Mb alloys.

2.

Solid or porous polymicrons such as silicone rubber, proplast.

3.

Hydroxylapatite

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Selection of an alloplastic material for reconstruction involves two considerations. 1. Physical properties dictate how such materials may be adapted to the deficit and whether any functional load can be applied to it. 2. Biocompatibility of the material will determine whether the alloplast, in its loaded or unloaded clinical adaptation, will be tolerated by the tissues.

Use of such implants has been investigated as substitutes for autogenous grafts and allogenic implants. Attempts were directed toward creating a porous material that would allow in-growth of bone. For the fabrication of porous implant materials, several materials were tested by implantation in the femurs and tibias of dogs, in the form of cylinders 1.0 cm long and 0.5 cm in diameter. Among the materials tested, hydroxyapatite and calcium carbonate showed complete in-growth at 8 weeks with “normal appearing and normally www.indiandentalacademy.com mineralizing osseous tissue.� Furthermore, it was observed that in 1 year the calcium carbonate skeleton had been resorbed.


CLASSIFICATION POLYMERS BIOLOGI C collagen fibrin SYNTHETIC Polylactic polyglycolic acid polymers CERAMICS Calcium phosphate Hydroxyapatite Tricalcium phosphate Calcium Sulphate METALS Titanium alloy

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BONE MATRIX PROTEINS Osteonectin Osteopontin Fibronectin Osteocalcin GROWTH FACTORS Bone morphogenic protein factor 1 to 7 Transforming growth factor Insulin like growth factor I & II Fibroblast growth factor Platelet derived growth factor Epidermal growth factor Retinoic acid

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Requirements 1.

Non immunogenic

2.

Strength and resilience to restore hard tissue form where function is required.

3.

Bend ability, mold ability or carvability to allow for intra operative adaptation.

4.

Stable and non-reactive surface whether loaded or not.

5.

Modulus of elasticity similar to that of connective tissue at the implant tissue interface.

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HYDROXYAPATITE It is an alloplastic material. This is a mineral substance, basically a ceramic which is similar to cortical bone in its composition. It is inorganic, stable, non absorbable and non biodegradable. They are osteoconductive and not osteoinductive (ie) they will induce bone formation when placed next to viable cells, but not when surrounded by non bone forming tissue like skin.

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Hydroxyapatite implants were tested by Holmes, who implanted them in the mandibles of dogs in which 2-cm defects were treated with implants placed in metal cast trays. At 4 months, bone extended into the implant for a distance of 3-5mm. At 4 months, the entire length of the implant had been bridged in many of the porous channels. At 6 months, all the channels had been filled with lamellar bone with well formed osteons. At 12 months, the architecture of the implant was notably diminished, and 88% of the implant area had been replaced by regenerated bone. It is noteworthy, however, that similar defects created in the mandibles of two dogs by the author and left without an implant were also completely bridged with regenerated bone at 6 months. In a more recent paper, Holmes tested experimentally the possibility of cranial reconstruction with porous hydroxyapatite. The final composition of the implant was 39.3% hydroxyapatite matrix, 17.2% bone in growth and 43.5% soft tissue in growth. He concluded that a satisfactory contour can be obtained and the implant can function at least in part as a bone substitute www.indiandentalacademy.com


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CALCIUM PHOSPHATE

Calcium phosphate has also been tested under the form of a ceramic biodegradable implant called “Synthos� (Miter Inc., Worthington, Ohio). This material can be carved into the desired shape and provides a uniform distribution of large interconnecting pores from 100 to 300 microns in size. Testing in the mandible, iliac crest, and inferior orbital rims of dogs was undertaken. Progressive invasion and replacement of the implant with bone were observed.

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ACRYLIC RESINS Acrylic resin is available as a two component system; a powder of small PMMA spheres and beads and a liquid monomer. The polymerization is strongly exothermic (max. Temp. 120oC). Disadvantages of solid, heat cured acrylics include -

Difficult handling

-

Problems with thermal, electrical and X-ray conductivity.

Uses include dental implants, submucosal augmentation, contour correction, cranial defect correction, orbital wall and floor defect correction, intra ocular lenses

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SILICONE RUBBER

Widespread use of this material is due to its biocompatibility and excellent physical characteristics such as. -

Thermal stability

-

Oxidative stability

-

Retention of flexibility through wide temperature changes.

Basic building block is dimethylsiloxane with contributions from other organic side chains i.e., Vinyl and Phenyl condensation polymerization produces a high molecular weight molecule that has a highly polar Si-O-Si backbone.

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Disadvantages include low tear resistance and that it is thrombogenic Preformed silicone rubber implants with or without polymer fabric can be used to augment chin, zygomatic and nasal deficiencies including reconstruction of the dorsum, nasal tip and columella as a custom implant. The disadvantage here being that it exhibits “Memory�. Therefore it must conform to bone contour in the relaxed state. Fluid silicone is clear, colourless odourless and has an oily lubricant feel to it. It may be injected to lift depressed scars, unless they are bound down by strong fibrous adhesions. Vertical and oblique brown lines in the glabella region and nasolabial folds can be lifted. Sunken facial contours can be augmented. Depressed defects of the dorsum of nose, defects of nasal tip etc. may be treated. Augmentation in a flattened hemifacial contour is www.indiandentalacademy.com possible with this material too.


POLYETHENES -

Group of polymers made from ethane type monomers and include polyethylene and polypropylene.

-

Porous sponge form can be used in reconstruction in non load bearing areas as in the middle ear. Also used to correct facial and skull defects, reconstructing the external ear, the trachea and rebasing the vocal folds.

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POLYTETRAFLUROETHYLENE (TEFLON) - Tetrafluoroethylene gas at high temperature and pressure. - Non carcinogenic, resistant to corrosion, non adherent and can be sterilized. - Used for repair of orbital floor fractures. Available in sheet that are 1.245 mm thick . - Injectable form consisting of pure . particles of 50-100um. suspended in 50% glycerin solution is used in paralyzed vocal cords.

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PROPLAST

Porous low modulus implant material available in 3 forms basic material that forms the porous matrix of proplast is prefluorocarbone polymer. Advantages of proplast over solid polymers 1. Improved stabilization, on or in bone, in virtue of rapid tissue in growth rather than only fibrous encapsulation. 2. A low modulus characteristic similar to that of soft tissue which allows it to be bent or molded to appropriate contours. 3.

Easy wettability

4.

Light weight www.indiandentalacademy.com


5.

Radiolucency

6.

Ease of curving

7.

Stable at very high temperatures, therefore can be sterilized by autoclaving 3 times.

8.

Proplast sheeting of 1-3mm permits repair of defects of irregular depth.

Disadvantages 1.

Macrophage response

2. Increased incidence of infection if contamination occurs during emergency 3.

Decreased pore size and therefore tissue in growth of the materials if loaded or compressed www.indiandentalacademy.com


. Contra indications 1.

As an implant by itself in weight bearing or articulating bony surface, where compressive loading is likely (TMJ).

2.

Over sinus cavities

3.

Where there is insufficient underlying bone or soft tissue to prevent collapse in the event of external pressure.

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4.

In patients with systemic disorders that may compromise tissue in growth or normal wound healing.

5.

In recent areas of infection.

6.

Available in block, preformed or customized implants for chin, mandible, premaxilla, zygoma, orbit and nasal augmentation.

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POLYURETHANES -

Implanted in the form of rigid foams for bone replacement and as bone adhesions.

-

Consists primarily of varied arrangements of polymeric molecules that share a common structure of urethane group

-

Polyether polyurethanes are capable of long term implantation with no significant physical changes.

Malar augmentation Mandibular repair Orbital Floor repair Surface scan model Complex fracture analysis Fetal heart model www.indiandentalacademy.com


POLYAMIDE -

Is used successfully

in facial augmentation..

-

Can be used alone or in combination with autogenous tissue in growth as an onlay material for the chin, maxilla, nasal dorsum.

Disadvantages Difficulty in contouring and handling and in placement of the material during surgery.

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CALCIUM PHOSPHATE CERAMICS . - These are polycrystalline ceramics, and either in porous or dense forms, serve as permanent bone implants showing no tendency to resorb in vivo. - These are are hard tissue prosthetic materials that interact with and may ultimately become an integral part of living bone. Limitation : -

Brittle, low impact resistance and relatively low strength.

-

Biocompatible

- Lack of local systemic toxicity. They bond directly to bone without the need for porosity. www.indiandentalacademy.com


APPLICATIONS Osteo Gen is clinically indicated for the contouring and improvement of alveolar ridge deformities, support and filling of tooth sockets and cyst defects following extraction or removal, and, for the filling and repair of marginal, periapical, and periodontal alveolar bony defects. The granular material is mixed with sterile water or the patient’s blood to form a putty like material. This material is then transferred to the osteotomy.

When OsteoGen is implanted into a defect that has been demonstrated to have healthy vascular circulation, it serves in part as a material that physically occupies an empty bony void. Thus, a physical connection is achieved between all sides of the bony void. As this occurs, the void fills with natural body fluids from each side of the bony void. OsteoGen then serves as a material platform that allows www.indiandentalacademy.com osteoblasts and other cellular material to invade the bony void.


OsteoGen granules serve as a osteoconductive material allowing new bone to be slowly created over several months. An osteoconductive material such as OsteoGen is defined as a material that does not inhibit the necessary cellular material from invading the bony void to lay down new bone. In fact, on osteoconductive material serves as a physical platform for the osteoblasts to move into the bony void to lay down the new bone. A second advantage of OsteoGen is that, as new bone is laid down, the OsteoGen material resorbs. The resorption process of OsteoGen occurs progressively over a six to eight month period; however, depending on the size of the defect and the patient’s age, a large percentage will have resorbed some time between three to five months. The net results is that the void is predominately filled with bone, not a “Bone filling and Augmentation material”. OsteoGen is avoidate in three sizes: 0.75 gm, 1.50 gm and www.indiandentalacademy.com 3.00gm.


TefGen-FD Regenerative Membrane, designed for use in treating osseous and periodontal defects with guided tissue regeneration. It is available in a size of 25 mm x 30 mm x 0.2 mm. It finds application in Periodontics, Implantology and Oral Surgery where particulate bone graft is indicated. It is available in quantities of 0.5cc and 1cc.

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THE SINUS BONE GRAFT

The first use of bone grafting of the maxillary sinus, to increase bony depth and bulk of osseous tissue for prosthodontic reasons was in the 1960s by Boyne. Grafting of maxillary sinus was used at that time to increase the bulk of bone for later maxillary posterior ridge reduction to obtain optimal prosthodontic inter arch distance. However some patients presenting for conventional complete maxillary and mandibular prosthesis had bulbous or enlarged tuberosities that was impinging on the inter arch space, and therefore it was impossible to construct a complete denture.The removal of bone from mandible is not feasible, and therfore removal of bone from the maxillary tuberosity was the option www.indiandentalacademy.com


To correct this condition, a Caldwell Luc opening was made in maxillary antrum, the sinus membrane was elevated, and then an autogenous particulate marrow cancellous bone (PMCB) graft was placed in the sinus floor. Approximately 3 months later, the bone of tuberosity could be reduced along with excess soft tissue. Additional osseous structure had been obtained by the previous grafting procedure.

Bone grafting of the maxillary sinus for metallic implants -

Blade implants

-

Root form implants

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Blade implants - During late 1970’s grafting was undertaken for patients who had large, pneumatized antra and needed blade implant for construction of fixed ,semi-fixed, or removal prosthesis for edentulous areas of posterior maxilla. Autogenous PMCB was usually used as a grafting material and after a period of three months, blade implant was placed.

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Root form implants With the advent of titanium root form implants, it became obvious that many possible, posterior maxillary reception sites for implants were deficient in vertical bone height and width. Various practitioners then undertook different surgical techniques to enter the antrum to elevate the sinus membrane and to place various types of bone graft

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Three anatomic locations were utilized to enter the antrum. 1.The classic superior position of the Caldwell Luc opening, located just anterior to the zygomatic buttress. 2. A mid maxillary entrance, between the level of the crest of the alveolar ridge and the level of the zygomatic buttress area.

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3. A low position along the anterior surface of the maxilla, practically at the level of the existing alveolar ridge. Of the three locations, the third area became quite popular because it gave a quick access to the sinus floor and enabled the practitioner to make an antral window to impact the buccal osseous plate into the antrum, expediously implant the bone graft material, and close the incision.

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Indications for maxillary subantral augmentation 1.

Implant placement in areas of insufficient bone volume or decreased inter arch space.

2.

Oro-antral fistula repair.

3.

Alveolar cleft reconstruction

4.

Le fort I down fracture with inter positional grafting

5.

Cancer reconstruction for craniofacial prosthesis

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Guidelines to follow for sinus grafting for dental implants may also include. 1.

Alveolar ridge bone height of less than 10 mm

2.

Less than 4mm of residual bone width

3.

No history of pathosis

4.

No significant history of sinus disease

No anatomic limitations presented by anatomic structures or scarring after previous surgery

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Contraindications to maxillary subantral augmentation General medical contra indications 1.

Radiation treatment to the maxillary region

2.

Sepsis

3.

Severe medical fragility

4.

Uncontrolled systemic disease

5.

Excessive tobacco abuse

6.

Excessive alcohol or substance abuse

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Local factors that may contra indicate subantral augmentation 1.

Maxillary sinus infections (empyema)

2.

Chronic sinusitis

3.

Alveolar scar ablation

4.

Odontogenic infections

5.

Inflammatory or pathologic lesions.

6.

Severe allergic rhinitis.

Healing period for the graft Because severe atrophy results in an unfavorable vascularization of the maxillary alveolar process and the adjacent maxillary sinus, the grafting material should be allowed to heal 1 to 2 months longer than normal. www.indiandentalacademy.com


Treatment Planning for Sinus Grafts Treatment planning for dental implants must be based on prosthetic considerations and, in all but the most simple cases, should involve a complete dental restorative workup. In most cases, this will minimally involve the following : 1.

Facebow-mounted, articulated casts placed in centric relation.

2.

Diagnostic wax up.

3.

Presurgical equilibration or restorative measures

4.

Surgical stent manufactured by using a surveyor.

5.

Radiographic or computerized tomographic verification www.indiandentalacademy.com


Use of Allografts for Sinus Grafting The development of the sinus elevation procedure originates from the clinical reports of Boyne, James and Tatum, who recognized the need to supplement bone inferior to the maxillary sinus to enable clinicians to perform alveolectomies and subsequently place implants. Their efforts led to the development of a technique whereby the external wall of bone, surrounding the maxillary sinus was perforated with a careful osteotomy. In Tatum’s technique, the osseous wall and underlying membrane were infractured medially and pushed in a superior direction.. The space created by this infracture was filled with an autogenous bone graft. Boyne and James made no attempt to retain this external wall of bone, when dissecting the sinus membrane away from the underlying bone. www.indiandentalacademy.com


Allografts Most of the cases are limited to the use of one specific type of allograft. is demineralized freeze dried bone, without any other supplements. The choice of the demineralized material over the mineralized sources was merely to add an extra degree of safety to the material. The material has been used successfully for bone grafting both in periodontal defects and around implants for reasonable amount of time. It also gives a patient the option to avoid a secondary site from which bone is harvested. (hip, chin, etc), which may be more traumatic than placement of the implants.

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As in all procedures, there are conditions that are not conducive to the use of an allograft for sinus augmentation. The main situation would be in those patients who lack adequate bone in the premaxillary area to support implants under loading (patients who have fewer than 7 mm of bone from canine to canine). While the antral augmentation might be successful, all the forces of occlusion will be generated on the sinus placed implants, ultimately causing overload and failure. The second contra indication would be inadequate buccopalatal width of bone, in association with the deficiency in height, adjacent to the maxillary sinus. Finally, patients who have fewer than 4 to 5 mm of bone and wish to have the implants placed at the time of sinus augmentation would best be treated with a large block inlay graft, which could receive the implant simultaneously. Major vertical height advances, which are difficult, are also bestwww.indiandentalacademy.com treated with autogenous block grafts.


The bone resorption process that occurs following tooth loss is four times greater in the maxilla than in the mandible. The bone loss encountered in the posterior regions of the edentulous maxillary arch is higher than in the posterior mandible due to the pneumatization of the maxillary sinus. Furthermore, the maxillary cortex is thinner and the trabecular structure is less dense than in the mandible ; the posterior maxilla usually exhibits the poorest bone quality. Hence, the quantity and quality of bone necessary for implant supported restorations are less likely to be available in the maxilla. For these reasons, dental implants placed in the posterior maxilla are likely to have higher failure rates than implants placed in the anterior maxilla or mandible. Different bone grafting materials have been used for this purpose, including autogenous graft that the iliac crest and chin region, allo-grafts such as freeze dried demineralized bone, and alloplasts such as porous hydroxyapatite and non-porous hydroxyapatite. www.indiandentalacademy.com


Sinus bone grafting with hydroxyapatite

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Sinus Grafting with Calvarial Bone The cranial vault has always been an extremely valuable source of bone grafts. Facility in harvesting, a simple post surgical period, and solid construction make calvarial bone an ideal material for reconstruction of the cranial or facial skeleton. Although bone from the cranial vault had been used as early as 1980 as part of an osteocutaneous flap by Konig and Muller, the first autogenous cranial bone graft was apparently performed by Dandy in 1929. Tessier, however, was the first to popularize the use of the calvarium as a donor site of grafts for cranial and facial reconstruction.

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Harvesting of the cranial bone grafts The harvesting is done in the parietal region, generally on the right side (nondominant hemisphere) behind the coronal suture, and approximately 3cm lateral to the sagittal suture or midline of the skull.

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Grafting of the sinus floor The construction is homogenous only if the sinus cavity is partitioned in its inferior part by a large graft that rests on the sinus walls and becomes the roof of the cavity to be filled. Thus, the sinus graft starts with the positioning of a large rectangular strip of cranial bone 10 to 15mm above the floor. Before its insertion, the vertical side of the graft is thinned with a bur, and several holes are made to facilitate its revascularization

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Tibial Cancellous Autograft for Sinus Grafting Various donor sites and bone harvesting technique are used for the augmentation of the sinus floor prior to the placement of osseointegrated implants, but seldom has the proximal lateral tibial graft been utilized, despite its excellent accessibility and availability. When the bone volume or bone quality is extremely deficient, tibial graft is recommended.

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Healing The cancellous autogenous bone graft contains endosteal osteoblasts, which can survive the transplantation process when handled appropriately. Also transplanted are a host of growth factors, which provide the stimulus for mesenchymal cell differentiation into osteoblasts, and growth promoters, which accelerate bone production by these newly differentiated cells. The cancellous graft heals by a combination of formation of new bone by the transplanted osteoblasts, followed by the formation and remodeling of new bone by the cells recruited from the periphery. The cortioccancellous block graft provides transplanted osteoblasts and growth factors as well as structural rigidity, which is frequently required when implants are placed simultaneously. However, the cortical portion of the graft is slow to revascularize and thus may be more prone to infection. The structural rigidity of the graft allows accurate implant placement, independent of the thickness of the sinus www.indiandentalacademy.com floor.


The healing of these bone grafts follows a course of events that starts with basic wound healing and follows with bone remodeling. Phase I bone healing includes osteoid production and cellular proliferation. Phase 2 includes remodeling of the disorganized phase 1 osteoid and replacement with lamellar bone. In autogenous grafts, surviving osteoblasts and other cells are responsible for primary bone production. These transplanted cells survive through diffusion of nutrients during the first 4 days of transplantation, during graft revascularization. The amount of bone eventually produced by the transplanted cells is directly proportional to the density of the surviving endosteal osteoblasts.

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Autogenous Bone Combined with Demineralized Bone Demineralized bone is bone that has had its mineral removed through an acid treatment and then is washed and lyophilized until reconstituted for use. When autogenous bone is demineralized, the remaining organic substrate contains bone morphogenetic proteins. Because the amount of autogenous bone available from the jaws may be limited, demineralized bone can be combined with autogenous bone to expand the graft’s volume. This combination of autogenous bone expanded with allogeneic demineralized bone is a useful method for obtaining phase I bone formation from the autogenous bone graft as well as phase II bone formation from the demineralized bone, and establishing the bulk of the graft.

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Subnasal Elevation and Augmentation Procedure. Surgical scrub is performed in the usual manner for the placement of implants. After the surgical team scrubs, the patient is draped. For intra oral preparation of the surgical site, a Chlorhexidine antiseptic scrub and rinse can be used. Iodophor or Chlorhexidine antiseptics can be used for preoperative extra oral scrubbing of the skin. Infiltration anesthesia has been successfully used, however a more significant regional anesthesia occurs when the secondary division of the maxillary nerve (V2) is blocked. With this technique, anesthesia of the hemimaxilla, side of the nose, cheek, lip and sinus area can be achieved.

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Proper angulation of the needle prevents penetration into the nasal cavity through the medial wall of the pterygopalatal fossa. A full thickness incision is made on the crest of the maxillary ridge, from the distal end of the canine region to the distal end of the contra lateral canine region. A nasal undercut region is typically formed at the junction of the lateral and inferior piriform rim that often corresponds to the area of placement for implant (canine area). The nasal mucosa in this region is elevated with a soft tissue curette in a manner similar to that used for elevation of the mucoperiosteum in subantral augmentation procedures. Depending on the depth of the impression behind the piriform rim, the nasal mucosa is elevated approximately 3 to 5 mm and then augmented with graft material.

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For subnasal augmentation, approximately 5 ml of cortical and trabecular autogenous bone is harvested from the mandibular symphysis and ground in a mill. This bone can then be mixed with freeze dried bone allograft (if necessary to expand the volume) in 50 : 50 ratio and compressed into a 1 - and 3 -ml tuberculin syringe. The mixture is applied from the posterior regions of the nasal space to the most anterior labial region of the nasal spine and piriform rim. When subnasal augmentation is performed in conjunction with iliac graft reconstruction of the maxilla, a 2- to 5- mm septal reduction is performed in the anterior septum, taking care to avoid tears of the mucosal lining of the nasal septum. A block graft that is 5 to 7 mm in height is fixed with one or two miniscrews placed laterally; these can be left permanently if facial augmentation is performed over them. This provides enough stabilization for standard implants. If additional ridge width is necessary, block grafts from the anterior mandible or ramus can be used by fixation to the buccal aspect of the anterior maxilla. After maturization of the graft, the appropriate sized implants can be placed. www.indiandentalacademy.com


Prior to suturing, the periosteum of the mucosal flap covering the graft is horizontally scored with a scalpel to allow tension free wound closure. The primary crestal incision and the vertical relieving incisions are closed with 3-0 chromic or silk sutures in either an interrupted or continuous mattress fashion. This area should be permitted to heal for 4 to 6 months before implant placement. In addition, the provisional partial denture or complete denture should be adjusted to avoid contact with the grafted area.

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Complications augmentation

associated

with

maxillary

Intra operative complications •

Membrane perforation

Fracture of the residual alveolar ridge

Obstruction of the maxillary ostium

Hemorrhage

Damage to adjacent dentition

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sinus


Early postoperative complications •

Wound dehiscence

Acute infection

Implant failure / loss

Graft loss

Exposure of barrier membrane

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Late postoperative complications •

Graft loss

Implant loss or failure

Implant migration

Oroantral fistula

Chronic pain

Chronic sinus disease

·

Chronic infection

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BONE GRAFT HANDLING It is essential that the viability of the bone in the period between its harvest and its placement be maintained. There are 4 important factors affecting graft cell viability .

1.

Tonicity of storage medium

2.

Temperature of storage medium

3.

Sterility of bone cell handling

4.

Trauma of bone handling.

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1. STORAGE MEDIA Distilled water and other hypotonic solutions are contraindicated as bone cell storage media. These hypotonic solution diffuse through the cell membrane resulting in swelling of cytoplasm, leading to cell death by physical rupture. Hypertonic solution are also contra indicated as they draw the free water away from cytoplasmic bone cells. Blood and blood soaked sponges should not be used as clotted blood has many membrane toxic intermediates of platelet aggregation and fibrin clot formation including lysozyme, fibrin split products, osteoclastic, chemotactic, factors etc. Also the blood soaked cells undergo a certain degree of drying, causing cell death. Saline is a good storage media, however the cellular activity is reduced after saline immersion because bone cell growth factors are washed out of cells stored in saline. www.indiandentalacademy.com


Tissue culture media, is an ideal storage medium. These are isotonic balanced solution buffered at Ph. 7.42 and have organic and inorganic cell nutrients. The advantage of tissue storage media is that they maintain absolute cell viability, cell activity and do not deplete intra cellular bone maintenance and growth factors. 2. TEMPERATURE Chilling to point of physical freezing, maintains better cell viability. Heating a storage medium is detrimental to survival as it causes direct membrane and intra cellular protein coagulation with enhanced toxicity from exogeneous agents. The media is kept refrigerated at 4oC until its use. It is then allowed to warm towards room temperature until placement.

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3. STERILITY OF HANDLING Incorporation of just a small inoculum of microorganism can result in either clinical infection or subclinical graft cell death yielding little bone. If overt contamination occur, graft should be discarded, with another harvest taken. Graft can be irregular with storage medium and finally antibiotic solution. Never autoclave irradiate or treat it with any disinfectants or soaps.

4. ROUGH HANDLING Bone cells are relatively resistant to rough handling by compression or shearing forces. However excessive trauma by crushing or when particulated into very small pieces, has caused inflammation within tissue bud. Therefore trauma should be minimal and tissue handling should be done with utmost care. www.indiandentalacademy.com


BIOLOGICAL MECHANISMS IN BONE GRAFTING

New bone formation occurs through three biologic mechanisms

1.

Osteogenesis

2.

Osteo conduction

3.

Osteo induction

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1. Osteogenesis : Is the production of new bone by proliferation, osteoid production and mineralization by transplanted osteocompetent cells. It is the main mechanism exploited by surgeons to graft large loss defects and it accounts for the greatest amount of bone formed by the graft. 2. Osteoconductive : Is the production of new bone by the proliferation and migration of local host osteocompetent cells along a conduct. The conduct may be local vessels, epincurium allogeneic bone or certain alloplasts the HA blocks. This accounts for a small amount of the bone derived in bone reconstruction. This bone usually originates from the endosteum of the host bone ends or residual periosteum.

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3. Osteoinduction: Is the formation of bone by connective tissue cells trans formed into osteocompetent cells by inductive agents usually proteins such as bone morphogenetic protein (BMP), skeletal growth factor and osteogenin. This mechanism accounts for a small amount of the bone produced by bone graft systems. This is an important mechanism in inducing the recipient connective tissue fibroblasts about the graft into a periosteum which accounts, partily for its longevity. Bone regeneration is responsible for healing of a bony graft consisting of autogenous particulate bone and cancellous bone marrow. The amount of bone produced in the graft is dependent on the cellular density of the transplanted cancellous bone.

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The critical bone transplant density as suggested by simmons at the donor site is 2000 osteoblasts /mg of bone and Frieden stein has reported that 1 106 osteocomponent cells/ cum are needed within the recipient tissue bed for the formation of new bone. The principle is basically to use cellular cancellous bone, harvest a sufficient quantity of it and compact it into a high cell/unit volume for maximal bone formation. It is for this reason the ilium is the preferred donor site (4 times ostogenic cellularity of either cortical bone sources and twice that of other cancellous bone sources) 8-10cc of cancellous bone for each 1 cm of defect is a simple yardstict one can fellow to ensure sufficient harvest of donor bone. The bone can be compacted in by simple syringe compression or hand instrument compression.

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The transplanted cellular bone mainly the endosteal osteoblasts on the cancellous surface, proliferate and produce new osteoild. This bone produced is a cellular woven type of bone with little structural organization. This is the first phase of bone and this soon undergoes resorption and replacement to be replaced by a second phase bone which is derived from the local cell population of the host and is more structural. This phase is also responsible for the longevity of the bone ossicle. Both the naturation of the bone oesicle as well as its volume maintaining endosteal and periosteal systems determine not only the longevity of the graft but as its ability to remodel under applicances and even to osteointegrate dental implants. It is also seen that the height and width of the graft obtained at the time of its placement to the maximum it will ever be as the osteocompetent cells proliferate and produce osteoid within the limits of the cancellous bone volume. www.indiandentalacademy.com


GOALS OF RECONSTRUCTION / CRITERIA OF SUCCESS There are certain goals toward which reconstruction should strive. These are : 1. Restoration of bone continuity This, especially, in respect to the mandible helps in three ways namely. a.

Mandibular continuity restores much of the mechanical stability to the function of mastication, speech and deglutition. Residual musculature, adaptation of accessory muscles and the muscle of facial expression provide adequate and sufficient function. b. The patients self image improves. Thus he become more willing to return to a normal life style. c. Bony continuity of any part of the facial skeleton adds to more normal contours and appearance, thereby providing foundation upon which more enacting cosmetic procedure may be performed. www.indiandentalacademy.com


2.

Restoration of osseous bulk : A thin and volume deficient transplant is often associated with certain problems such as

a.

They are prone to fractures

b.

Usually do not supply sufficient contour.

c.

Rarely support a prosthetic appliance

Osseous bulk is achieved by adhering to the biologic principles of graft healing i.e. i.

Sufficient quantity of cellular cancellous graft materials should be placed.

ii.

Should be firmly fixated into a vascular and cellular tissue bed free of contamination. www.indiandentalacademy.com


3. Restoration of alveolar bone height Sufficient alveolar bone height is essential for the retention and stability of conventional prosthesis and is necessary for implant systems to osteointegrate effectively. Good alveolar bone height is accomplished in the dissection to prepare the soft tissue for the graft. The dissection must free all scar within the space of the mandible to a this overlying mucosa (1-3mm), without perforation into the oral cavity. This is achieved by blunt dissection in this area with the instruments spread parallel to the ridge or crestal scar, or by sharp dissection palpating the maxillary dentition as a guide to tissue thickness, or by dissecting under guidance from another member of the surgical team who has placed a gloved hand within the oral cavity. 4. Bone maintenance Maintenance of the bone ossicle throughout the left time of the www.indiandentalacademy.com patient is one of the most important aspects of a successful


Lack of bone formation or b. Resorption of their non viable mineral matrix in the first 6 months. Grafts that fail in the second phase will show resorption with in 6-18 months. Grafts that maintain or increase their radiographic mineral density beyond 18 months almost always maintain their aside throughout the patients lifetime and can be considered successful. 5. Elimination Soft tissue deficiencies Residual soft tissue deficiencies often restrict tongue and lip function and create unseating forces, and prevent a seal for prosthesis. Such soft tissue deficiencies are eliminated either prior to bone graft tissue flaps or after bone grafting with releasing procedures using SSE or dermal grafts. www.indiandentalacademy.com


6. Restoration of facial contours It is essential that facial form and function be restored and it is only after this is done that cosmetic onlay grafts, contouring procedures and scar revisions care staged. ALLOPLASTIC CRIBS All have features of biologic encapsulation non resorbability and biologic inadaptability. 1. Dacron coated polyurethane crubs. -

Radiolucent therefore do not obscure post operative radiographic of graft consolidation.

-

Easily cut for contouring and shaping.

- Moderately flexible material but rigid enough to maintain its shape. -

Pore size is small butwww.indiandentalacademy.com large enough to allow capillary in growth.


2. Titanium : more rigid Metal, obscures complete radiographic visualization of the graft. -

Bio-lateral material

-

Bendable and trimmable, more easily than other metals.

1. Stainless steel Very rigid difficult to cut or contour, and is there customized for each patient.

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Bone substitutes 1. Polymers : PMMA bone cement PMMA / PHEMA 2. Bioinert alumina ceramics 3. Bioactive glass ceramics 4. Bioactive non glass ceramics 5. Corals – Biocorals - Coralline HA 6. Hydronyapatite Replam and interpore Osprovit 200 – 600 mm pores Cenos 80

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7. Tricalcium phosphate Cevos 82 TCP Calciresorb 8. HA and TCP Iriosite Ostilit 9. CaCo3 (calcite) 10. Collagen 11. Collagen and particulate ceramic – collapat 12. Collagen and particulate ceramic – collagraft and ceraver osteal produces 13. Carbon fiber implant

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14. Ti mesh cylinder and fibremetal rods.


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Summary and conclusion The essence of a successful bone grafting is the variable transplantation of osteocompetent cells. These cells must be sufficient in number and recipient tissue bed must be sufficiently cellular and vascular to develop and maintain a self remodeling bone. Numerous grafts and its harvesting techniques have been proposed. there is no real difference in the osteogenic potential of osteocompetent cells from any of the popular donor sites. The use of cortico-cancellous bone grafts for reconstruction was proposed as it has a higher biomechanical rigitidy. Autogenous bone grafts are used for various purposes like bridging gaps in orthognathic surgeries and in preparing the implant sites. The advantage of these graft is that large open areas will yield to revascularisation easily hence bringing about new bone formation. Various techniques of harvesting bone either black or particulate bone by the use of trephine has www.indiandentalacademy.com advantages over open technique as morbidity and gait disturbance chance are low.


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