University Hospital of MuensterDepartment of Cranio-Maxillofacial Surgery

Director: MD, DMD, DHC, PhD U. Joos

Vertical bone augmentation: methods and prognosis

Master Thesis

Master of Oral Medicine in Implantology

International Medical CollegeMedical Faculty

Of the Westphalian Wilhelms-University of Muenster

Submitted by:

Chulmin BaeSeoul, Korea

2008

Table of Contents

Executive Summary ................................................................................. 3

I. Introduction .......................................................................................... 4

II. Materials and Methods ....................................................................... 5

III. Results ................................................................................................ 6

IV. Discussion .......................................................................................... 19

V. Conclusion .......................................................................................... 21

Executive Summary

Vertical bone augmentation: Methods and Prognosis

Project objectives

2

To review all the existing methods for the vertical augmentation used in dental

implant and evaluate the prognosis and complication according to the different methods.

Materials and methods

The comprehensive overview of English literature is done through the Pubmed site

and the literatures related to various bone augmentation techniques is outlined. The key

word for the search was vertical augmentation and dental implant .The limitation for

this review was 10 years and dental journals.The number of literature reviewed was

167 and the databases were Medline and Pubmed , with non-peer-reviewed articles

eliminated as much as possible.

Results

Several techniques have been developed to treat insufficient volume, but only four

of the most commonly performed are described. Three are frequently used: (1) sinus

floor elevation and (2) bone block graft, involving either a cortical or cortico-cancellous

graft and (3) GBR .The fourth is the technique of bone distraction, which is still in

development and may show promising results in the future because of its great

biological pertinence.

Depending on the implantation site, the morphology of the bone defect and the

quantity of bone to be repaired determine the techniques used in oral surgery.

Conclusion

Many different techniques for reconstruction of bony defect exist for effective bone

augmentation. The approach is largely dependent on the extent of the defect and specific

procedures to be performed for the implant reconstruction It is most appropriate to use

an evidence-based approach when a treatment plan is being developed for bone

augmentation cases.

Key words: vertical augmentation, dental implant, bone substitute, bone graft,

membrane

I. Introduction

As the prevalence of implants has increased, so has the challenge to augment the

remaining osseous structure to house those implants. Therefore, lots of different

methods for vertical bone augmentation have developed and the purpose of this article

is to review the existing methods and prognosis of that according to these respective

methods.

3

Several techniques have been developed to treat insufficient volume, but only four

of the most commonly performed are described. Three are frequently used: (1) sinus

floor elevation and (2) bone block graft, involving either a cortical or cortico-cancellous

graft and (3) GBR .The fourth is the technique of bone distraction, which is still in

development and may show promising results in the future because of its great

biological pertinence.

The expectations of dimensional gain and bone quality are unique to each technique,

as well as the potential complications. Distraction osteogenesis has had the greatest

potential for vertical gain, while guided-bone regeneration and monocortical onlay

grafting achieve similar results and bicortal onlay graftin has better results than

monocortical and GTR .

The choice of procedure is to be based upon the patient's existing anatomy, degree

of vertical deficiency, and willingness to participate in treatment.Volume insufficiency

at the maxillary and mandibular incisors is usually related to a lack of thickness, while

molar sectors more often present with height. Depending on the implantation site, the

morphology of the bone defect and the quantity of bone to be repaired determine the

techniques used in oral surgery. The following question should be considered: in light

of the current information available, is a particular therapeutic approach adapted to

reach the treatment objectives?

II. Materials and Methods

The biggest surgical challenge clinically is to augment lost bone vertically. The

purpose of this article is to review currently available techniques for achieving greater

vertical dimension before implant placement. A literature search was conducted using

Pubmed to find all articles published between 1998 and 2008 regarding vertical bone

augmentation. Following the literature search, all articles were reviewed and

summarized in this review article of vertical bone augmentation. The results of the

research showed that guided-bone regeneration, monocortical onlay grafting, bicortical

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onlay graftig ( 3D bone augmentation) and distraction osteogenesis have the potential to

be applied to augment deficient areas vertically.

The comprehensive overview of the English literature is done through the Pubmed

site and the literatures related to various bone augmentation techniques is outlined. The

key word for the search was vertical augmentation , bone substitute, bone graft,

membrane and dental implant .The limitation for this review was 10 years and dental

journals.The number of literature reviewed was 167 and the databases were Medline

and Pubmed , with non-peer-reviewed articles eliminated as much as possible.

The focus was done about the pre-existing methods for vertical augmentation and

the prognosis of the respective methods. So single clinical trial methods are excluded

and the mothods which was done by different clinicians and institutes are included. As

many as possible, most of the methods are reviewed and the methods and prognosis of

the methods are reviewed and described.

The general aim of the present review was to test the hypotheis tha there is no

difference between the method of vertical augmentation and the material used to that

purpose. And more specific objectives were to determine whether and when

augmentation procedures are necessary and which is the most effective augmentation

technique for the specific clinical indication.

III. Results

The technique for reconstruction of bony defects that are reviewed in this paper

included the use of particulate bone grafts and bone graft substitute, barrier membranes

for GBR(guided bone regeration) , autogenous and allogenic block grafts, and the

application of distraction osteogenesis

Biology of bone regeneration

Bones and teeth are the only structures within the body where calcium and

phosphate participate as functional pillars. Despite their mineral nature, both organs are

vital and dynamic. The histogenesis of bone is directly from mesenchymal connective

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tissue (intramembranous bone formation) or from preexisting cartilage (endochondral

bone formation). Intramembranous bones are found in the mandibulo-craniofacial

complex, ilium, clavicle, and scapula. The intramembranous bone formation pathway is

used when intraoral bone augmentation techniques are used by the surgeon

Bone is composed of the outer cortical layer and the inner cancellous layer. The

dense haversian systems of cortical bone provide skeletal strength. Interposed between

the cortices is a three – dimensional lattice network of trabecula that acts as a resorvior

for active bone metabolism. This bony architecture is dynamic with a continous

remodeling to repair and shape the bone to ensure renewal of form and function.

The principles of osteogenesis, osteoconduction, and osteoinductio can be used to

optimize therapeutic approaches to bone regeneration. Osteogenesis has been described

as the direct transfer of vital cells to the area that will regenerate new bone.

Osteoconduction embraces the principles of providing the space and a substratum for

the cellular and biochemical events progressing to bone formation. The space

maintenance requirement for many of intraoral bone augmentation procedues allows the

correct cells to populate the regenerate zone. Osteoinduction embodies the principles of

converting pluripotential, mesenchymal-derived cells along an osteoblast pathway with

the subsequent formation of bone. This concept was established in 1965, with

heterotopic ossicle formation induced by the glycoprotein family of morphogens known

as the bone morphogenetic proteins(BMPs). Therapeutic bone reconstruction

approaches use some or all of these principles in an attempt to maximize the clinical

bone augmentation results.

1. Bone augmentation with barrier membrane technique

In 1988, Dahlin et al. showed that bone could be reconstructed around implants

using the principle of guided tissue regeneration(GTR). The concept of GTR was

established by Nyman et al. in 1982 with the aim of reconstruciong deep periodontium

destroyed by periodontal disease.

The biological principle is based on the healing rate of different periodontal tissues

and the necessity to prevent colonization of the damaged site by tissues that might

inhibit healing. Bone has a unique capacity for restoring its original structure. Any bone

lesion create osteoinduction. In fact, osseous or neighboring cells release growth factors

and bone-inducing factors such as bone morphogenic proteins(BMPs)

This induction leads to cellular reactions in osteoprecursor cells, which are found in

the periosteum and in endosteal and medullary spaces. These cells differentiate into

osteoblasts, which can promote bone formation.

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This bone regeneration capacity has some limitations. It can fail in some situation:

lack of vascularization, mechanical instability, defects that are too large, and

competition with inhibiting tissues.

Utilizing a membrane can thus be a key step in the GBR technique. The membrane

isolates the osseous site that requires reconstruction and allows free expression of the

osteoinductor potential, without the influence of external factors such as the mucosal

connective tissue that can inhibit this potential.

Thus, a Teflon membrane(expanded polytetrafluoroethylene, e-PTFE) is placed to

create a barrier between the epithelial and connective tissue of the oral mucosa and the

bony defect. Osseous and desmodontal cells can then colonize the healing site and

promote the formation of new tissue, which leads to a new attachment. This technique

was referred to as guided bone regeneration(GBR)

This technique has widened the indications for implant placement. However, several

questions arise as to the duration of membrane placement, the aspect and transformation

of newly formed tissue, tissue maturation, and the quality of implant osseointegration in

regenerated osseous tissue.

Membranes

Non- resorbable membranes

The use of non-resorbable expanded polytetrafluoroethylene membrane in the

reconstrucion of bone defects was first developed for periodonal regeneration by a

Scandinavian team. These are GTAM (GoreTex augmentation material) membranes

made of e-PTFE fibers. These membranes offer different properties, such as flexibility,

an effective cellular barrier and the maintenance of adequate space. However, the most

important property is biocompatibility, and thus the abscence of cytotoxicity at the

healing site, and to osseous cells in particular.

Successful vertical ridge augmentation with the GBR technique, using titanium

reinforced e-PTFE membranes, was shown in human and animal studies. Both studies

demonstrated up to 4 mm of vertical augmentation was feasible without the use of any

grafting material under the membranes. Addition of grafting material to the GBR

technique increases the amount of achievable vertical regeration.

Non-resorbabe barriers are available as e-PTFE, titanium reinforced e-PTFE, high-

density PTFE, or titanium mesh.The e-PTFE membrane has been studied extensively in

animals and humans and is considered a standard for bone augmentation. The high–

density PTFE membranes are entirely cell occlusive, show minimal inflammation when

exposed to the oral cavity, do not integrate with the tissue for membrane stabilization,

and were effectvie in a rat mandible model and in human case reports. The use of

titanium mesh as a barrier maximazes graft containment and eliminates the space

maintenance collapse problems that are associated with conventional membranes. In

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circumstances where the defect is too large to generate a biomechanically stable central

scaffold, bone formation is limited to the marginal stable zone with central zone of

disorganized loose connective tissue. Thus, combined use of bone grafts or bone

replacement substitutes with barrier membranes are advocated in bone regeneration of

larger defects.

Resorbable membranes

To overcome some of the limitation of non-resorbable membranes, such as the need

for a second surgical procedure for their removal with the added risk of loss of some of

the regenerated bone further to flap reflection, they largely have been replaced with

bioabsorbable membranes. Bioresorbable membranes currently in clinical use fall into

two broad categories: natural or synthetic. Natural products are made of various types

of collagen of animal origin. Synthetic products are made of aliphatic polyesters,

primarily poly(lactic) and poly(glycolic) acid copolymers. They differ in their mode of

resorption: collagen products undergo enzymatic degradation, whereas synthetic barries

are degraded by hydrolysis. However, commmunicatio with the oral cavity accelerates

their resorption rate, and thus , reduces prolonged contamination of the regenerated

bone matrix. Although collagen barriers offered improved soft tissue response, they

lacked the abilityt to maintain adequate defect space. Collagen barriers promoted human

osteoblast proliferation and alkaline phosphate activity. Degradation of synthetic

copolymers elicited a soft tissue inflammatory response that resulted in resorption of

some of the regenerated bone. In addition, there is high variablity and lack of control

over the rate of membrane resorption, which is influlenced by factors such as the local

pH and material composition.

Bioabsorbable barries have been developed in synthetic polymer forms(Epi-Guide,

Resolut, Atrisorb, Guidor, Ossix)( including polygalctin 910 mesh(vicryl), collagen

(Biomend, Biomend extended, Colla tape, Colla cote, Collaplug, RCM, Bio-Gide),

calcium sulfate(Capset), or intact connective tissue( Alloderm).

One of the collagen membranes (Bio-Gide) had a barrier function in animal studies

up to 4months. These collagen products (colla tape, colla cote, colla plug) are used only

for initial graft material containment and clot stabilization because of their rapid 1 to 2

week resorption time. A polymer membrane (Guidor) was evaluated and found to be

successful in humans for use as a GBR barrier in combination with particulate grafting.

Because of a lack of rigidity, in all but the smallest defects, most of these bioabsorbable

membranes must be used in combination with a graft material for space maintenance in

bone augmentation applications.

Choice of membrane depends largely on the required duration of membrane

function for tissue regeneration(~ 6 months) . The volume of regenerated bone generally

is more encouraging with non-resorbable e-PTFE membrane than with bioabsorbable

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membranes. When no premature membrane exposure occurred, nearly complete defect

fill resulted. However, in 16% of the collagen membrane cases and 24%of the e-PTFE

cases, membrane exposure was present at the time of suture removal; ultimately, 44% of

the e-PTFE membranes had to be removed prematurely.

Perforation of the cortical bone layer has been advocated in GBR, because it was

postulated that this increases the vascularity of the wound and releases growth factors

and cells with angiogenic and osteogenic potential. Although no evidence exists in the

literature regarding a performance advantage, numerous membrane fixation products

exist for improved graft containment and minimization of membrane micromotion.

Membrane micromotion was hypothesized to decrease the regenerative response by

forming a layer of soft tissue under the membrane. Products that are available to

stabilize membranes include non-resorbable mini screws and tacks and bioabsorbable

tacks made from polylactic acid.

Membranes associated with bone grafts

Sometimes, reconstruction of large bone defects may require the use of a bone graft.

When applied to the graft, a membrane preserves and maintains the graft.

Bone grafts fall into four general categories: autograft, allografts, xenografts, and

alloplasts. The use of these materials in regnerative procedures is based on the

assumption that they posses osteogenic potential (contain bone-forming cell), are

osteoinductive (containing bone- inducing substances), or simply are osteoconductive

(serve as a scaffold for bone formation). Autogenous bone harvested from intraoral or

extraoral sites is the most predictable osteogenic organic graft for osseous tissue

regeneration.

1) Autogenous bone

Extraoral sites, such as the iliac crest, provide adequate quantity of graft material

with excellent osteogenic, osteoinductive, and osteoconductive properties, but have a

high morbidity related to second surgical sites. With the limited availability of intraoral

sites, donor site morbidities, and inadequate quantity of the harvested bone, the use of

other grafting materials has been advocated whenever possible.

Even though the particulated autograft is the gold standard for most craniofacial

bone grafitng, including the treatment of dental implant-related defects, autografts have

recognized limitation, such as donor site morbidity, increased cost, potential resorption,

size mismatch, and an inadequate volume of graft material.

2) Allogenic bone

There are several clinical reasons explaining the failure of DFDBA to induce new

bone formation. One of them is DFDBA does not contain enough BMP/NPC and

moreover, osteoclasts need mineralized bone to initiate the process of resorption. The

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other thing is osteoclast cannot fix to implanted bone, as this bone is already

demineralized. Grafted bone can eventually be resorbed by macrophages: however, this

proces is time –consuming and macrophages cannot initiate a new osteogenesis process.

The conclusion was that combining allogenic bone does not add any value to GBR. It is

thus increasingly evident that DFDBA is more osteoconductive that osteoinductive. Its

use does not seem to be justified. Also, although the risk for disease transmission

essentially is non-existent, concern still exist for some patients and estimates for the risk

were reported.

3) Alloplastic material

Alloplastic grafts include dense and porous hydroxyapatites, tricalcium phosphastes,

a mixture of both materials and a derivatives of natural coral. It is available in different

forms: resorbable or non-resorble, particles or block, porous or non-porous. These

synthetic bone graft materials are osteoconductive and have no intrinsic potential for

osteogenesis or induction. Additionally, there is no practical restriction to the available

quantity of graft, and the risk for disease transmission and need for harvesting bone

tissue are eliminated. Calsum sulfate (Capset) and calcium phosphate compounds

(Cerasorb) are attractive alternatives to autografts because of their biocompatibility,

handling characteristics, porosity, different rates of dissolution, chemical and physical

resemblance to bone mineral and potentially unlimited supply at a modern cost.

Grandular porous HA (Biogran) has been considered a unique alloplast, in that it is

formed by the hydrothermal chemical conversion of sea coral form biogenic carbonate

to HA. The second generation of calcium phosphate bone cements has shown promise

in implant dentisty.

4) Xenograft

Xenografs are animal bone substitution materials. Bovine hydroxyapatite(BH),

which is the most widely used and reported xenograft material is chemically treated to

eliminate any trace of organic material and conserve the mineral part. Owing to its

natural origin, this bone offers great similarity to human bone. The material is 60 to

70% porous per volume unit, which facilitates osteoblast migration and stimulates better

vascularization. The crystal size is 10nm and the granule size is 0.25- 1mm. Bovine

hydroapatite completely integrates within regenerated bone and resorption of bovine

hydroapatite is active but seems to be very slow. Finally the long-term fate of BH is still

unknown, since the literature is not conclusive on whether the material is completely

resorbed with time or not.

Bovine hydroapatite fulfills most of the expected objectives from the use of a bone

substitues materal with robust scientific documentation, and can thus be considered as a

material of choice. Even though the long term results with Bovine hydroapatite are still

uncertain, the incomplete or abscence of resorption does not prevent implant

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osseointegration or high implant survival rates in different clinical situations. However,

bovine bone still deserve further evaluation in large controlled studies.

Method of GBR

The implant and membrane can be placed seperately or simultaneously, depending

on the size of the bone defect and the possibility of achieving primary implant stability.

Simultaneous implant and membrane placement

Simultaneous implant and membrane placement is indicated when:

1. Crestal width is insufficient

2. Ideal implant positioning leads to exposure of one of its faces and

3. The implant is placed in an extraction socket.

Staged implant and membrane placement

This technique is used when implant placement is required, but primary implant

stability is difficult to achieve. Membranes, used alone or combined with bone grafts,

remains totally covered for 9-12 months, depending on the size of the bone defect.

Success depends on factors such as

- the volume of regenerated bone: if this volume is insufficient, it will induce

technical difficuties because of a risk of membrane collapse

- the real possibility of bone cells invading the space created by the membrane,

without being inhibited by other cells, and in particular cells from the mucosal

connective tissue.

- The type of bone defect: vertical augmentation is a difficult process, which is

sometimes impossible to achieve

- Membrane placement time without any exposure: a period of 8-12 months is

necessary

- The density of the newly formed tissue: there is a significant relation between

membrane placement time and the density of the newly formed tissue.

Post surgical GBR complications

The major complication of GBR is membrane colonization by pathogens and an

infected membrane cannot remain covered and is rapidly exposed. The causes for

premature exposure is inadequate surgical protocol, anatomic defect factors, prosthetic

irritation and host factors (uncontrolled DM, alteration of the immune system, stress or

smoking).

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2. Block grafting approaches

Although the evolution of alloplastc and allogenic materials and GBR techniques

seems to be promising, information on the healing processes involved and predictable

prognosis in comparision with autogenous bone is still lacking. The superiority of

autogenous bone has been demonstrated with respect to other bone substitues on a

biological, immunological, and even medico-legal basis.. Several donor sites have been

described , such as the cranium, tibia, ribs, maxillary tuberosity, palatal bone, torus,

zygomatic arch, iliac crest and mandibular sites. Resorption observed for the latter

seems to be lower than for the other sites.

The primary location for harvesting intraoral block grafts include the external

oblique ridge of the posterior mandible, symphysis, and ramus. With bone defects > 2

cm, an extraoral autogenous bone harvest from the iliac crest, cranium, or tibia is used

often. In addition to to the ease of intraoral harvest, grafts derived from

intramembranous bone have less resorption than endochondral bone. For the less

resorption, membrane could be used with block bone grafts. Another concern related to

the grafted block bone is retained vitality of the block autografts. Block grafts are

harvested as corticocancellous or cortical bone autografts. The revascularization fo

corticocancellous block grafts takes at much faster rate than in cortical bone

autograftsand at a slower rate than particulate autografts. Revascularization of block

grafts enables maintenance of their vitality, and , hence, reduces chances of graft

infection and necrosis.

1) Monocortical approaches

This technique is traditional block bone graft method and success of this method

ususally depends on the stabilization and intimate contact of these block grafts to the

recipient bed. This can be achieved with the use of bone fixation screws or the

simultaneous placement of dental implants. Aggressive recipient bed preparation with

decortication, intramarrow penetration, and inlay shaping also has been supported,

because of increases in the rate of revascularization, the availability of osteoprogenitor

cells, and the increased rate of remodeling. The healing of autogenous block grafts has

been described as „ creeping substitution“ where viable bone replaced the necrotic bone

within the graft and is highly dependent on graft angiogenesis and revascularization.

Although results have improved from the initially reported 50% failure rate, graft

resorption, complication, and implant survival rates are still a concern for these full-arch

grafting procedures. A recent study showed 17% resorption of mandibular block grafts

used in combination with particulate autograft and xenograft for vertical ridge

augmentation, with an average gain of ~ 5mm.

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2) 3D reconstruction technique using special instrument

( Microsaw, dentsply Friadent)

The concept of this methods lies in that increasing the surface of the grafted bone

has a positve influence on new bone formation and regeneration. This method uses a

combination of a thin block graft and particulate small pieces of cancellous and cortical

bone. The thin cortical block acts as an autogenous biological membrane for

stabilization of the small pieces of particulate bone. From a practical point of view, the

bone graft is placed in two layers of different shape: the first layer consists of a thin

bone blcok that creates the alveolar crest shape, giving it form and volulme. This block

graft is screwed at a distance from the recipient site rather that in close contact, leaving

a free space between the graft and the atrophic alveolar crest. The space between the

block graft and the recipient site is then filled wih mandibular cancellous and small

particulate bones, which possess high revascularization and regeneration potential. This

leads to an ideal graft, with a high regenerative capacity comparable to iliac bone and an

osseointegration potential close to that of the mandible. The bone could be harvested

from ramus, chin and mandibualr edenturous areas.

Fig) Preparation of bone blocks and access windows

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3. Distraction osteogenesis

Distraction osteogenesis is a surgical process for reconstruction of skeletal

deformities. It involves gradual, controlled displacement of surgically created fractures

which results in simultaneous expansion of soft tissue and bone volume. It is the ability

to reconstruct combined deficiencies in bone and soft tissue that makes this process

unique and invaluable to all types of reconstructive surgeons. Gavriel Ilizarov, a

Russian orthopedic surgeon, is credited with developing the armamentarium and

describing the biologic basis of this process for the management of orthopedic limb

deformities. The concepts described by Ilizarov have been adapted and modified for use

in maxillofacial surgery. Although the majority of surgical experience with distraction

technology has been in orthopedics, early results indicate the process to be equally

effective in facial skeletal reconstruction. It is now possible to apply distraction

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technology to deformities of the jaws and dentoalveolar process. Development of

miniature, internal distraction devices have made this clinically feasible and practical.

The Process of Alveolar Distraction Osteogenesis

The process of alveolar distraction osteogenesis involves mobilization, transport,

and fixation of a healthy segment of bone adjacent the deficient site. A mechanical

device, the alveolar distraction device, is used to provide gradual, controlled transport of

a mobilized alveolar segment. When the desired repositioning of the bone segment is

achieved, the distraction device is left in a static mode to act as a fixation device.

Displacement of the osseous segment results in positioning of a healthy portion of bone

into a previously deficient site. Because the soft tissue is left attached to the transport

segment, the movement of the bone also results in expansion of the soft tissue adjacent

the bone segment. At the original location of the segment is left a regeneration chamber

which has a natural capacity to heal by filling with bone. This propensity of the

regeneration chamber to heal by filling with bone instead of fibrous tissue is a function

of the surrounding, healthy cancellous bone walls and location within the skeletal

functional matrix. As a result of the gradual distraction, the alveolar housing, including

the osseous and soft tissue components are enlarged in a single, simultaneous process.

Alveolar Distraction Device

Development of miniature, internal distraction devices has made transport of

alveolar segments possible. The alveolar distraction device has been developed for

reconstruction of alveolar process deformities using the distraction osteogenesis

process. The implantable components of the alveolar distraction device consists three

components.

When placed into a properly formed segmental osteotomy, the distraction device

allows for controlled elevation of the segment resulting in coronal displacement of the

alveolar crest. The transport slowly displaces the overlying soft tissue producing

expansion. A regeneration chamber is established in the portion of the osteotomy that is

perpendicular to the transport axis. The portion of the osteotomy that is parallel to the

transport acts to maintain alignment of the segment. After the desired amount of

transport has been achieved, the lead screw is left in place until bone healing occurs

across the sliding component of the osteotomy. The regeneration chamber fills with

bone of several weeks.

As a result of the distraction process the volume of both bone and soft tissue has

been increased. The reconstructed site is them suitable for further rehabilitation with

osseointegrated implants, prosthetic pontic placement, or movement of a tooth with

orthodontics.

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Indications:

Primary indications

- Combined deficiencies in bone and soft tissue.

- Compromised wound healing environment.

Secondary indications

Alternative treatments

Expansion of the alveolar housing for:

   -   Create site for dental implant placement

   -   Improve ridge esthetics for pontic

   -   Improve periodontal environment of adjacent teeth

   - Expand alveolus for orthodontic tooth movement

 Limitations

- Must have a minimum quantity of bone

- transport and anchorage segment must have adequate strength to withstand

- forces of mobilization and transport

- Expansion occurs only in the direction of transport.

- Patient must cooperate with activation process

Complications

- fracture of transport segment

- fracture of anchorage segment

- premature consolidation

- undesirable transport vector

Objectives of Distraction Process

- expansion of bone and soft tissue volume

- displacement of bone into deficient site

Conclusion of distraction osteogenesis

Distraction osteogenesis is a proven technique for vertical augmentation of the

alveolar crest. The surgical procedure requires some standardized techniques to avoid

failures. Owing to the preparation of the alveolar crest as for a fracture, the direction of

the osteotomy determines the subsequent prosthetic outcome. This technique utilizes the

natural healing capacity, which requires high patient compliance and a strict recall. The

biological regeneration of new bone shows a negligible rate of infection and wound

healing disturbances, which do not influence the success rate of the implants.

4. Other developing approaches

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There have been lots of attempts to develop a new method for bone augmentation

and most of them would be molecular, cellular, and genetic tissue engineering

technologies. The molecular approach using BMPs has received the most attention over

the past decade. BMPs are differentiation factors that are part of the transforming

growth factor superfamily. Although BMP- 2 has ben approved by the FDA for spinal

fusion application, for human intraoral application the carriers and dosage of BMP- 2

and -7 are still regulatory review and investigation. Another promising growth factors

now being evaluated actively is platelet-derived growth factor(PDGF).

Another growth factor approach is to use patient’s own blood, seperating out the

platelet-rich plasma(PRP) and adding this concentrated group of autogenous growth

factors to the grafting material. The addition of PRP to autograft showed a more rapid

and dense bone formation compared to autograft used alone for bone augmentation. An

improvement in bone formation when PRP is added to other graft materials has not been

demonstrated clearly. Still now, there was no reliable evidence supporting the efficacy

of acitve agents, such as PRP in conjuction with implant treatment.

5. Complication of Bone augmentation technique

Complications in bone grafting procedures are relatively rare, but may be severe and

of concern for the patient, because they may jeopardize the whole procedure and

somtimes leave a situation worse than that at the start. This requires careful

communication with the patient and written consent. Bone grafting procedures require

extensive surgical training and have a relatively flat learing curve. Soft tissue surgery is

as important as bone surgery and should be considered during proper preoperative

planning. A subsequent protocol involving antibiotic prophylaxis, chemical plaque

control, anti-inflammator y agents and postoperative care must be followed. Major risk

factors such as smoking, mechanical irritation dut to temporary restoration, and patient

non-compliance have to be eliminated.

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IV. Discussion

There is evidence that nonresorbable and resorbable barriers allow statistically

significantly more bone regeneration than no barrier and the choices between

nonresorbable and resorbable usually depend on clinician’s preference and the special

need related to the cases.

Bone substitutes (Bio-Oss and Cerasorb) might be effective as autogenous bone

grafts for augmenting extremely ridge and sinuses. Therefore, they might be used as a

replacement for autogenous bone graftss, although these preliminary findings need to be

confirmed by large multicenter trials.

A vertical alveolar defect reconstructed with a mandibular graft in the form of one

cortical sometimess represents a poor site for osseointegration of titanium implants

because of the low revascularization potential of cortical bone. A partculate bone graft

seems to yield better revascularization, giving good quality regeneration of the

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augmented area. Based on the reasons for biological grafting previously described,

vertical boe augmentation is performed in a 3D form by combining thin mandibular

cortical blocks with particulate bone grafts. Thick blocks from the ramus area are cut

longitudinally with the Microsaw into two thin pieces with the same surface area. These

two thin blocks are used to rebuild the two walls of the future alveolar crest (buccal and

palatal, or occlusa and vestibular) and stabilized with osteosynthesis screw. The

remaining space is filled with particulate and cancellous bone. The method for 3D

reconstruction seems to be a good alternative to the reconstruction of vertical defects

with one cortical block or with membranes using the GBR technique. Relatively low

rate of complications, the good bone regeneration and the big gain of vertical

augmentation make it promising and encouraging.

Osteodistraction is a proven technique for vertical augmentation of the alveolar

crest. The surgical procedure require some standardized techniques to avoid failures.

Owing to the preparation of the alveolar crest as for a fracture, the direction of the

osteotomy determines the subsequent prosthetic outcome. This technique utilizes the

natural healing capacity, which requires high patient compliance and a strict recall

protocol. The biological regeneration of new bone shows a negligible rate of infection

and wound healing disturbances, which do not influence the success rate of the implants

Osteodistraction and various GBR techniques are able to regenerate bone in a

vertical direction; however, there is insufficient evidence to indicate whether one of

these technique is preferable. Osteodistraction is of little use in the presence of thin

ridges but may allow more vertical regeneration. Complication with GBR techniques

are common and in some cases determined the failure of the augmentation procedure.

Clincians and patients should carefully evaluate the benefits and risks in relation to the

desired outcome when deciding whether to use vertical ridge augmentation techniques.

BMPs used in conjunction with Bio-Oss and resorbable barriers may promote bone

formation in need of ridge augmentation.

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V. Conclusion

Many different techniques exist for effective bone augmentation. The approach is

largely dependent on the extent of the defect and specific procedues to be performed for

the implant reconstrcution. It is most appropriate to use an evidence-based approach

when a treratment plan is developed for bone augmentation cases.

Successful vertical ridge augmentation with the GBR technique, using titanium

reinforced ePTFE membranes, was shown in human and animal studies. Both studies

demonstrated up to 4 mm of vertical augmentation was feasible without the use of any

grafting material under the membranes. Addition of grafting material to the GBR

technique increases the amount of achievable vertical regeration

Autogenous bone still represents the gold standard in reconstruction surgery. The

results are mostly predictable and reproducible. Biomaterials with their osteoconductive

property are used only as a space maintainer. Autogenous block grafts harvested from

the mandible can be very useful for reconstructing complicated defects. A 3D

reconstruction of vertical bone defects seems to represent a better alternative than an

onlay graft with thick cortical bone.

20

Finally, from a purely biological standpoint, distraction seems to be the surgical

procedure best adapted to the problem of volume augmentation of bone and

surrounding tissue. In fact, distraction is a biological process that takes into account

local signaling and can locally induce the formation of a volume and structure adapted

to bone loading that will allow implant osseointegration with an appropriate reaction to

local stress and strain.

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