Jan Lindhe. Clinical Periodontology

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ALVEOLAR BONE FORMATION •

877

Fig. 38-14. Microphotographs showing submerged membrane-covered roots. (a) Membrane has collapsed, leaving

a narrow space adjacent to the root surface (arrowheads). The formation of bone underneath the membrane is negli

gible, but a thin layer of new cementum covers the root surface between the arrows. (b) Root covered with a

mem

brane (M) which has maintained considerable space adjacent to the root surface. New cementum is seen on

the root

surface from the notch (N) to the arrow, and considerable amounts of new bone (NB) have formed

underneath the

membrane. Note that in the area below the notch (N), new bone (NB) has also formed on top of the

original buccal

bone plate where bone has not existed before.

healing in osseous defects or to augment atrophic

alveolar ridges has been evaluated in a number of

experimental and clinical studies (Boyne 1970,

Thompson & Casson 1970, Steinhauser & Hardt 1977,

Fazili et al. 1978, Baker et al. 1979, Mulliken &

Glowacki 1980, Curtis & William 1983, Swart & Allard

1985, Block et al. 1987, Cullum et al. 1988, Hupp &

McKenna 1988). However, there are several reports

indicating that this type of treatment fails to predict-

ably produce bone fill and augment alveolar ridges (

Korlof et al. 1973, Curtis & Ware 1977, Steinhauser &

Hardt 1977, Taylor 1983, Davis et al. 1984, Jackson et

al. 1986, Hupp & McKenna 1988). Often the bone

grafts do not attach to the graft site through bony

attachment and there is bone resorption and bone loss

associated with grafting procedures. As a conse-

quence, much of the intended volume is lost, and

frequently the defects heal with a fibrous connective

tissue instead of bone.

CONCEPT OF GUIDED TISSUE

REGENERATION (GTR)

The principles of guided tissue regeneration (GTR)

have been developed on the basis of a number of

experimental animal studies on periodontal regenera-

tion (see Chapter 33). In one of these studies (Gottlow

et al. 1984), barrier membranes were placed over

crown-resected roots in monkeys. The membrane-

covered roots were then submerged. Following 3

months of healing, it was noticed that, in situations

where the membranes were collapsed, leaving a nar-

row space adjacent to the root surface, new cementum

had formed on the root surface, but the amount of

newly formed alveolar bone was negligible (Fig. 38-

14a). On the other hand, in situations where the mem

branes had not collapsed, leaving a wider space

adja

cent to the root surface, considerable amounts of

new

bone had formed in addition to the new

connective

tissue attachment to the root surface,

even in areas

where bone had not existed before (Fig.

38-14b). This

observation suggested that the GTR

principle may be applied successfully in bone

regeneration as well by creating a secluded space

which can only be invaded

by cells with bone-forming

capacity from existing

bone.

Animal studies

Alveolar bone defects

The application of the GTR principle for bone regen-

eration (guided bone regeneration (GBR)) was first

investigated by Dahlin et al. (1988) in an experimental

study in rats. Transmandibular defects 5 mm in di-

ameter were surgically created bilaterally, while the

test sites were covered on either side of the defect with

a barrier membrane to allow the exclusive ingrowth

of tissue from the mandibular bone, at the same time

excluding the fibrous tissue of the area from prolifer-

ating into the defect. The control sites were left with-

out the placement of a membrane. On the test side,

almost complete bone healing was demonstrated both

on defleshed mandibles and in histologic prepara-

878 • CHAPTER 38

Fig. 38-15. (a) Test defects of critical size with membranes blocking the proliferation of undesired cells into the de

fect, resulting in complete bone regeneration after 6 weeks. (b) Control defects with residual transmandibular de

fects after 9 weeks due to the invasion of soft tissues into the defect space.

Fig. 38-16. 2 x 3 mm standardized defect produced at

the inferior border of the mandible of a rat. A gutta-per-

cha point (arrow) is placed to indicate the original level

of the inferior border.

Fig. 38-17. Microphotographs of control (a) and test (b) jaw bone defects 6 months following surgery. Some new

bone has formed in the bottom of the control defect (arrow) while the remaining part contains muscle and connec

tive tissue. The gutta-percha point (G) indicates the original inferior border of the mandible. In the test defect (b),

covered with a membrane (M), the newly formed bone (NB) is filling out the defect and has reached the gutta-per-

cha point (G), indicating the original level of the inferior border of the mandible.

tions after 6 weeks (Fig. 38-15a). Control sites, on the

tissues were invading the defects, hindering the bone-

other hand, demonstrated residual transmandibular regenerating cells from occupying the wound space

defects, although somewhat diminished in diameter

(Fig. 38-15b).

after 9 weeks due to the fact that surrounding soft

Similar results have been reported in an experimen-

ALVEOLAR BONE FORMATION •

tal model in rats where standardized mandibular de-

fects were covered with a bio-absorbable membrane

(

Kostopoulos & Karring 1994a). The mandibular ra-

mus of the rats was exposed on both sides and a 2 x 3

mm defect was created at its lower border (Fig. 38-16).

A gutta-percha point was placed to indicate the origi-

nal level of the border. On one side the defects were

covered with a resorbable membrane, while the con-

tralateral sides remained uncovered. The jaws were

subjected to histologic analysis. In addition, defleshed

specimens were prepared. These specimens revealed

minimal bone fill in the control defects (Fig. 38-17a),

while all test defects healed to or close to the gutta-

percha point, indicating the original inferior border of

the jaw (Fig. 38-17b). Likewise, the histologic analysis

showed that bone regeneration in the experimental

specimens occurred gradually over 7-180 days,

amounting to 85% of the initial defect depth at 180

days (Fig. 38-18). In the control defects only some bone

regeneration occurred within the first month follow-

ing surgery. Bone regeneration in the control spec-

imens amounted to 48% of the defect at 180 days. The

rest of the control defect was filled with muscular,

glandular and connective tissue (Fig. 38-17a).

Bone regeneration adjacent to implants

Titanium dental implants were inserted into the tibial

bone in rabbits in such a way that three to four coronal

threads were exposed on one side of each implant

(

Dahlin et al. 1989). At the test sites the implants were

covered with a Teflon membrane, whereas at the con-

trol sites the implants remained uncovered. The over-

lying soft tissues were then sutured to obtain complete

closure. Histologic analysis after 6 weeks revealed

that, in the test sites, new bone was completely cover

ing the exposed threads of the implants, while the

threads of the implants at the control sites were cov-

ered by connective tissue. In a similar study in dogs (

Becker et al. 1990), titanium implants were inserted

in such

a way

that some of their threads remained

exposed. Again, before closure of the wounds with a

mucoperiosteal flap, the test sites were covered with a

Teflon membrane, while the control sites remained

uncovered. Following a healing period of 18 weeks,

the specimens were subjected to clinical, radiographic

and histologic examination. For the majority of the test

implants, new bone was covering the previously ex-

posed implant threads. The average gain in bone

height was 1.37 mm for the test and 0.23 mm for the

control implants. In the control sites, loosely adherent

connective tissue was covering the exposed threads.

Immediate implant placement

The effect of GTR on osseointegration of titanium

implants inserted into fresh extraction sockets was

investigated by Warrer et al. (1991) in an experimental

study in monkeys. The experimental sites were cov-

ered with a Teflon membrane, while the controls re-

mained uncovered at the time of complete wound

closure. Following 3 months of healing, histologic

Fig. 38-18. Diagram showing the regeneration of bone

in experimental and control defects. The columns indi-

cate the remaining defect area, not filled with bone at

various observation times. It can be seen that bone for-

mation in the control defects is arrested after 1 month,

while new bone continues to fill out the experimental

defects.

analysis of the experimental sites revealed complete

bone regeneration to the top of the implants and com-

plete osseointegration. However, when exposure of

the

membrane had occurred during healing, less bone

regeneration was observed and the coronal part of the

fixtures was not osseointegrated. The controls also

exhibited incomplete osseointegration. The authors

concluded that osseointegration may be achieved pre-

dictably on dental implants placed into extraction

sockets and covered with a membrane, provided the

membrane is kept without communication to the oral

cavity during healing. These results are in agreement

with the results of other experimental studies in dogs

(

Becker et al. 1991, Gotfredsen et al. 1993), where

titanium dental implants were placed in fresh extrac-

tion sockets or where HA-coated implants were

placed in stimulated sockets before coverage with

PTFE membranes (Caudill & Meffert 1991, Caudill

Lancaster 1993). Again, substantial amounts of new

bone formed under the membranes, while minimal

amounts were seen in control sites.

A comparison of e-PTFE membranes alone or in

combination with platelet-derived growth factor

(

PDGF) and insulin-like growth factor (IGF-I) or

demineralized freeze-dried bone (DFDB) in stimulat-

ing bone formation around immediate extraction

socket implants was investigated in dogs by Becker et

al. (1992). Following 18 weeks of healing, the his-

tologic analysis revealed that e-PTFE membranes

alone or e-PTFE membranes combined with PDGF/

IGF-I were equally effective in promoting bone

growth

around the implants. Bone regeneration in the

DFDB-

treated specimens was highly variable and did

not

improve the efficacy of the Teflon membranes. The

authors concluded that, on the basis of these results,

the clinical use of DFDB must be questioned.

A study in monkeys has indicated that bony defects

similar to those occurring around failed implants can

88o •

CHAPTER

Fig. 38-19. Microphotographs of bone defects around implants covered with membranes (M). The defect seen in (b)

was grafted with hydroxylapatite (arrows). Both non-grafted (a) and grafted (b) defects are filled with bone which

extends coronally to the implant, to the level of the membrane (M).

Fig. 38-20. Microphotographs of

bone defects around implants

treated without membranes. (b)

Defect grafted with hydroxylapa-

tite (arrows). (a) Non-grafted de-

fect shows incomplete bone fill,

while new bone has formed in the

grafted defect (b) to the top of the

implant. Some hydroxylapatite

particles (arrows) are seen in the

soft tissue coronal to the implant.

Fig. 38-21. Microphotograph showing that the space be

tween the membrane (arrowheads) and the original

border of the mandible (arrows) is filled with new

bone,

and the naturally existing curvature is eliminated.

also be successfully treated with membranes (Gotfred-

sen et al. 1991). Standardized bony defects were pre-

pared in the alveolar ridge of edentulous areas in

monkeys. A titanium dental implant was then placed

in the middle of these defects. In each monkey one

defect was covered with a membrane. Another was

grafted with hydroxylapatite particles before cover-

age

with a membrane. A third defect was grafted with

hydroxylapatite only and a fourth defect, serving as

control, was covered only by the raised tissue flaps.

Histologic analysis after 3 months of healing showed

that all bony defects treated only with a membrane

(

Fig. 38-19a) and the majority of those grafted with

hydroxylapatite and subsequently covered with a

membrane were completely filled with bone (Fig. 38-

19b). The defects treated with hydroxylapatite alone

(

Fig. 38-20b) and the control defects (Fig. 38-20a) often

demonstrated incomplete bone fill in the defects.

Thus, the placement of hydroxylapatite in the defects

in addition to membrane coverage did not improve

the

healing results.

Localized ridge augmentation

The principle of GBR was applied in localized ridge

augmentation in dogs (Seibert & Nyman 1990). Surgi-

cally created alveolar ridge defects in the mandibles

dogs were covered with e-PTFE membrane alone,

ALVEOLAR BONE FORMATION • 881

Fig. 38-22 a,b. Microphotographs showing new bone formation (NB) between the membrane (arrows) and the

mandibular border. A rupture in the membrane, seen at high magnification in (b), has allowed soft connective tis

sue to invade the space underneath the membrane, thereby preventing osseointegration between the newly formed

bone and the surface of the micro-titanium implant.

Fig.

38-23.

After elevation of a musculo-periosteal flap exposing the mandibular ramus (a), a non-porous Teflon

capsule is placed with its opening facing the mandibular ramus (b).

or treated with a combination of membrane placement

and porous hydroxylapatite (HA) blocks, functioning

a space keeper, or with a combination of membrane

and

tissue growth matrix (porous PTFE). Tissue

growth

matrix as well as porous HA blocks were also

used

without membranes. In the control specimens,

neither

membranes nor implants were placed. His

tologic

analysis after 55-90 days of healing revealed

that in the

specimens covered only with membranes,

bone had

filled out the entire space underneath the

membrane.

At the sites where a membrane and HA

were used,

bone had also filled out the entire space.

However, the

pores of the HA adjacent to the subsur

face of the

membrane were only partially filled with

bone. Bone

deposition was mainly observed in the

apical and

middle part of the implant. The control specimens

without membranes showed no new bone

formation.

Vertical augmentation of the mandible at its inferior

border using a bioresorbable membrane adapted to

create a secluded space for ingrowth of bone tissue

was evaluated in a study in rats (Kostopoulos & Kar-

ring 1994b). Following exposure of the mandibular

ramus, a standardized titanium microimplant serving

as a space maker and a fixed reference point was

inserted in the naturally existing curvature at the in-

ferior border of the mandible. The implant consisted

two parts, a threaded and a non-threaded part,

separated by a stopper ring. One side of the mandible

was covered with a bioabsorbable membrane, in such

way that a space was created in the curvature be-

tween the membrane and the inferior border of the

mandible. The contralateral sides remained uncov

ered

and served as controls. After 6 months of healing the

specimens were defleshed and prepared for his

tologic

analysis. The control specimens revealed mini

mal

bone formation and the naturally existing curva

ture at

the inferior border of the mandible had persist-

ed. In

contrast, the test specimens revealed consider-

able

bone formation and the non-threaded part of the

titanium microimplants was osseointegrated (Fig. 38-

21). However, in specimens where soft tissue from the

environment had escaped underneath the membrane,

bone formation was reduced and osseointegration of

the implants prevented (Fig.

38-22).

In order to evaluate the potential to produce bone

with GTR in a space where bone has not existed before,

an experimental model was developed by Kostopou

los

et al. (1994). Non-porous, rigid, Teflon capsules of

identical size were placed on the lateral surface of the

Fig. 38-24. Microphotographs of Teflon capsules 2 months (a) and 4 months (b) after placement on the mandibular

ramus. After 2 months (a) the capsule (C) is about half filled with bone, while after 4 months (b) new bone is filling

out

the entire capsule. R: Remaining capsule space.

Fig. 38-25. Microphotograph of Teflon capsule (C) prior to removal after 6 months (a). The capsule is completely

filled with bone. (b) Bone tuberosity present at the mandibular ramus after removal of the capsule.

Fig. 38-26. Radiograph showing the bone tuberosities

(arrows) formed on the lateral aspect of the ramus at

both sides of the mandible.

mandibular ramus of rats in such a way that the open

part of the capsules was adjoining the lateral surface

of the mandibular ramus which was either covered

with periosteum or denuded (Fig. 38-23). The his-

tologic analysis revealed that new bone formation

gradually occurred in the capsules (Fig. 38-24a). At 120

days, the capsules were filled out or almost filled out

with bone amounting to five to six times the original

width of the mandibular ramus at both the pe-

riosteum-covered and the denuded sides (Fig. 38-24b).

However, up to 60 days following surgery the amount

of generated bone was significantly greater at the

periosteum-covered sites than at the denuded sites.

The authors suggested that a secluded space created

adjacent to an existing bone surface, covered or not

with periosteum, will inevitably be filled with newly

formed bone.

The stability of such bone tuberosities produced by

GTR in areas where bone has not existed before was

evaluated by Lioubavina et al. (1997). Non-porous

Teflon capsules were placed on the lateral surfaces of

the mandibular ramus of rats. At one side the pe-

riosteum was preserved, while the other side was

denuded. Histologic analysis of some of the animals

after 6 months showed that the capsules were com-

pletely filled with bone (Fig. 38-25). The capsules in

the remaining animals were removed by a second

operation at 6 months and the structure and size of the

bone tuberosities were evaluated histologically and

radiographically until 1 year following removal of the

capsules. The bone tuberosities diminished slightly in

size immediately after capsule removal, after which

882 . CHAPTER 38

ALVEOLAR BONE FORMATION • 883

Fig. 38-27. Buccolingual section of a defect covered by a

barrier membrane after 2 months. Complete bone fill in

the secluded space beneath the membrane yields

pri-

mary spongiosa.

(From Schenk et al. (1994))

Fig. 38-28. Transformation of the primary spongework

into cortical and cancellous bone. After 2 months, the

peripheral spongiosa is somewhat denser than the cen

ter. (From Schenk et al. (1994))

time no further resorption was observed (Fig. 38-26).

This observation indicates that bone formed by GTR

stable over the long term.

Healing of GTR-treated bone defects

An experimental study in a canine model (Schenk et al.

1994) provided detailed information about the se-

quence and pattern of bone regeneration in surgically

created, membrane-protected defects in the alveolar

ridge. This histologic documentation confirmed that

bone regeneration in membrane-protected defects fol-

lowed closely the pattern of normal intramembrane-

ous bone growth in extraction sites and a development

through a similar sequence of maturation steps. Fol-

lowing initial organization of the blood clot, protected

by the membrane, regeneration was initiated by depo-

sition of woven bone along

new vascular structures

origi-

nating from the three surgically created bony walls that

defined the defect margins. This

primary spongiosa

was

characterized by blood vessels originating from marrow

spaces (Fig. 38-27).

Secondarily, the network of woven bone was rein-

forced by concentrically deposited parallel-fibered

la-

mellar bone,

which resulted in the development of a

new cortical structure at the periphery of the defects

(

Fig. 38-28). Finally, the onset of bone remodeling with

the formation of

secondary osteons

could be observed

the newly formed bone close to the defect margins

(

Fig. 38-29). The duration of the maturation process

obviously exceeded 4 months in the large defects cre-

ated, since small remaining defects were still found in

the midcrestal portion of the defect after 4 months

(

Fig. 38-30).

Subsequently, a similar second study was per-

formed in dogs as well (Schenk et al. 1994) to address

questions about osseointegration of titanium implants

into regenerated bone and the remodeling process of

regenerated bone under functional loading conditions.

In this study, complete bone fill was demon

strated in

the defects after 6 months of healing, which

histologically represented regular compact and can-

cellous bone perfectly suitable for the osseointegra

tion

of implants. Hence, all the implants inserted

yielded

primary stability. An intimate viable regener

ated bone

to implant contact was demonstrated in the

histologic

preparations. Secondary osteon formation

and signs of

ongoing remodeling were found in close

proximity to

the implant interface. Formation of bone

trabeculae to

"support" the implant was also identi

fied in the more

spongy region of the regenerated

alveolar bone. The

bone remodeling process, however,

was not influenced

by functional loading of the im

plants. On the other

hand, regenerated control sites

with no implant

placement exhibited a rarefied bone

structure

characterized by a thin cortical layer and

sparse bone

trabeculae. Hence, it may be stated that

the

incorporation of titanium implants into newly

regenerated bone may provide the necessary stimulus

to activate bone maturation and remodeling.

Human experimental studies

At present, most of the information regarding the

biologic events which lead to new bone formation is

derived from animal studies. Results regarding bone

formation collected in animal studies have to be ap-

plied with proper caution in humans. In particular, the

time sequence of the various steps ultimately leading

to the formation of mineralized mature bone in man

884 • CHAPTER 38

Fig. 38-29. Cortical bone formation and

secondary

spongiosa

after 4 months. A compact bone layer in the

periphery including haversian remodeling confines a

cancellous bone in the center with well-defined trabecu

lae and bone marrow. (From Schenk et al. (1994))

is different from that in all experimental animal sys-

tems known. A few human specimens, often har-

vested under poorly controlled conditions, contribute

relatively little to the understanding of the biologic

events of bone regeneration in humans.

A model system was designed to obtain human

specimens of regenerated and also newly generated

alveolar bone for the study of the biologic events

under a variety of conditions (Hammerle et al. 1996).

A mucoperiosteal flap was raised in the retromolar

area of the mandible of nine healthy volunteers. Fol-

lowing flap reflection, a standardized hole was drilled

through the cortical bone into the bone marrow. Con

gruent test cylinders were firmly placed into the pre-

pared bony bed, yielding primary stability;

/2-2 mm

of the test device were submerged below the level of

the surrounding bone, leaving 2-3 mm above the bone

surface. The bone-facing end of the cylinder was left

open, while the coronal soft tissue-facing end was

closed by an ePTFE-membrane. The flap was sutured

to obtain primary wound closure. In order to prevent

infection, penicillin was prescribed systemically and

oral rinses of chlorhexidine were administered. After

2, 7 and 12 weeks, one test device, including the regen

erated tissue, was surgically harvested, while after

16,

24 and 36 weeks, respectively, two devices were

har

vested and processed for soft or hard tissue

histology

or histochemistry The tissue generated

after 2 and 7

weeks (Fig. 38-31) presented with a

cylindrical shape,

whereas the specimens harvested

at 12 weeks and

thereafter resembled the form of an

hourglass. Speci

mens of 12 weeks and less

regeneration time were

Fig. 38-30. The barrier membrane separates an outer

gingival compartment from the compartment that is

mainly accessible from the marrow space. In the latter,

a well-vascularized connective tissue derived from

bone marrow forms a periosteal envelope along the

bone surface. (From Schenk et al. (1994).)

almost entirely composed of soft tissue, while speci-

mens with a regeneration time of 4 months and more

were composed of both soft and increasing amounts

of mineralized tissue (Fig. 38-32). It was concluded

that the model system is suitable for studying tempo-

ral dynamics and tissue physiology of bone regenera-

tion in humans with minimal risk of complications or

adverse effects for the volunteers.

In a retrospective re-entry study (Lang et al. 1994a),

the bone volume regenerated using non-bioresorbable

membrane barriers was assessed. Nineteen patients

with jaw bone defects of various sizes and configura-

tions were included. Combined split-thickness/full-

thickness mucosal flaps were elevated in the area of

missing bone. The size of the defects was assessed

geometrically. Following the placement of Gore-Tex

augmentation material as a barrier, the maximum pos

sible volume for bone regeneration was calculated. At

the time of membrane removal (3-8 months later), the

same measurements were performed and the percent

ages of regenerated bone in relation to the possible

volume for regeneration determined. In six patients in

whom the membranes had to be removed early, be-

tween 3 and 5 months, due to an increased risk of

infection, bone regeneration varied between 0 and

60%. In 13 patients in whom the membranes were left

for 6-8 months, regenerated bone filled 90-100% of the

possible volume. It was concluded that successful

bone regeneration consistently occurred with an un-

disturbed healing period of at least 6 months.

ALVEOLAR BONE FORMATION •

885

Fig. 38-31. Histologic section of a 7-week specimen,

comprising non-mineralized connective tissue in the

shape of an hourglass. Note the covering e-PTFE mem

brane.

Fig. 38-32. Histologic section of a 9-month specimen.

The height of the mineralized tissue has reached the

top 20% of the cylinder space area.

CLINICAL APPLICATIONS

As a result of the animal studies elaborated above,

several clinical applications of the principle of

"guided

tissue regeneration", in conjunction with the

treatment of oral defects prior to or concomitantly

with the placement of oral implants, have been devel-

oped to produce predictable treatment outcomes.

These include:

•

Alveolar bone defect closure

•

Enlargement or augmentation of alveolar ridges

•

Alveolar bone dehiscences or fenestrations in

asso

ciation with oral implants

•

Immediate implant placement following tooth ex-

traction.

Alveolar bone defect closure

A clinical example is described in Figs. 38-33a-i. The

defect is self-limited and presents with well-defined

bony borders.

An ankylosed retained canine (Fig. 38-33a) had to

be removed (Fig. 38-33b), leaving a cavity the size of

cherry which extended into the edentulous ridge of

tooth 23 (Fig. 38-33c). An e-PTFE membrane was

tightly adapted to cover the palatal defect completely (

Fig. 38-33d). After 6 months, the membrane was re-

moved (Fig. 38-33e), and a bed for a one-stage trans-

mucosal implant was prepared (Fig. 38-33f). The cen-

tral bone core of the ITI hollow screw implant was

processed histologically (Fig. 38-33g). Regular intra-

membraneous bone formation with woven bone and

remodeling processes evidenced by the apposition of

lamellar bone was seen. Fig. 38-33h-i documents the

clinical and radiographic appearance of a stable im-

plant 8 years after the placement into the regenerated

bone. It should be mentioned that no bone substitutes

have been used as fillers or scaffold in this self-con-

taining defect.

Enlargement or augmentation of alveolar

ridges

In areas with a partially resorbed alveolar ridge, the

bone volume is often insufficient to contain an im-

plant. Therefore, enlargement of the alveolar ridge is

frequently necessary prior to the placement of an

implant.

As opposed to a self-contained jaw bone defect

guaranteeing the maintenance of the secluded space

into which exclusively osteogenic cells may prolifer-

ate, such a space will first have to be created for the

enlargement of atrophic jaw bone crests.

A series of case reports and clinical studies (Nyman

et al. 1990, Buser et al. 1991, 1993, 1995a,b, 1996a,b)

were initiated to develop a surgical protocol resulting

in predictable treatment outcomes of localized ridge

augmentation and, later on, to validate the technique

(

Buser et al. 1994). In all these trials, ePTFE membranes

were closely adapted to the bone surfaces and fixed

with fixation screws or pins, while the space under the

membrane was provided by means of specially de-

signed supporting screws (Memfix0, Straumann In-

stitute, Waldenburg, Switzerland) (Buser et al. 1994).

In order to prevent membrane collapse, autogenous

bone grafts were also used as support under the mem

branes. The clinical experience regarding optimal

treatment outcomes was presented in a methodologic

886 • CHAPTER 38

Fig. 38-33. Alveolar bone defect closure. (a) Orthopantomogram of an ankylosed retained maxillary canine. (b) Fol-

lowing flap elevation the crown of the ankylosed canine (23) is prepared free from its bony coverage. (c) A large de-

fect extending into the edentulous ridge of tooth 23 is visible. (d) The self-containing defect is covered with a mem-

brane barrier (e-PTFE). (e) At removal of the membrane after 6 months the defect has been filled with new bone. (f)

Implantation of a hollow cylinder implant (ITI) is now possible. (g) Histologic preparation of the central bone core

the implant bed showed woven bone undergoing remodeling. (h) Clinical appearance of the crowned implant in

position of tooth 23, 8 years after implant placement. (i) Radiographic documentation after 8 years showing im-

plant stability

report (Buser et al. 1995a,b). The essential criteria for

success were:

Achievement of primary soft tissue healing to

avoid

membrane exposure by utilizing a lateral

incision

technique

Creation and maintenance of a secluded space un-

der the membrane to avoid collapse of the mem-

brane by utilizing appropriate membrane support

with or without autogenous bone grafts or osteo-

conductive substitutes

Stabilization and close adaptation of the membrane

to the supporting bone to prevent the ingrowth of

competing non-osteogenic cells into the defect area

by utilizing fixation screws or pins

Allowance of an adequate healing period of at least

7 months to obtain complete bone regeneration

and

bone maturation.