16

Localized Ridge Augmentation Using Guided Bone Regeneration in Deficient Implant Sites

Daniel A. Buser, Dieter Weingart, and Hans-Peter Weber

The use of osseointegrated implants anchored in the jawbone with direct bone-implant contact has become an increasingly important treatment modality for the replacement of missing teeth.1,2 To expect a predictable long-term prognosis for osseointegrated implants, a sufficient volume of healthy bone should be available at possible recipient sites. Thus a careful presurgical evaluation is essential to obtain the necessary information about the quality of the bone, the vertical bone height, and the orofacial bone width. When this analysis reveals that the width of the alveolar ridge is insufficient at desired implant locations, reconstructive surgery is needed if endosseous implants are to be used. One augmentation technique is based on the principle of guided tissue regeneration using barrier membranes, which was initially developed for periodontal regeneration.3,4 A comprehensive text on guided bone regeneration in implant dentistry has been published by Buser et al.5

This principle has been tested for the regeneration of bone tissue in different types of bone defects as well as around dental implants.4–23 These studies have in common that barrier membranes were placed over bone defects and closely adapted to the surrounding bone surface, creating a secluded space between the bone and the membrane. With the placement of a barrier membrane, preference is given to bone-forming cells that originate from adjacent bone to populate and regenerate these defects with bone, since competing soft tissue cells from the mucosa are excluded from these defects. Control sites without membranes demonstrate incomplete bone regeneration and the presence of soft tissue within the defects. For the regeneration of bone defects using barrier membranes, the term guided bone regeneration (GBR) is preferable since this term describes the purpose of the membrane application more precisely than does the term guided tissue regeneration (GTR).

In combination with the placement of endosseous implants, two different applications of GBR are possible: (1) the simultaneous approach using membranes to regenerate bone defects around an inserted implant; and (2) the staged approach using membranes for localized ridge augmentation and placement of implants 6 months later into the newly regenerated alveolar ridge in a separate surgical procedure.

The clinical testing of GBR in patients for implant indications started at the University of Bern in 1988, and the potential of both treatment options was demonstrated.11,12 From these early experiences it could be concluded that the biological principle of GBR for ridge enlargement is predictable. However, factors such as soft tissue management, placement of membranes with the provision of sufficient space for bone regeneration, primary flap closure, and postsurgical infection control influence the prognosis to a great degree and must be optimized.

Consequently, the surgical procedures were refined and technical modifications developed to improve the predictability of the GBR technique.21–23

In implant patients with an insufficient bone volume, the surgical approach to be chosen depends on three selection criteria. If the intrasurgical status demonstrates: (1) an implant cannot be inserted with primary stability; (2) an implant cannot be inserted in an appropriate position from a prosthetic point of view; or (3) the peri-implant bone defect would be relatively extended, the simultaneous application of a barrier membrane, and an implant would have certain risks. Therefore, the staged approach is preferred in these situations since it reduces the risk for compromise or failure of the result.

The goal of the staged approach is a localized ridge augmentation and subsequent placement of endosseous implants into the newly formed alveolar ridge after a healing period of 6 months.

Based on current experimental and clinical knowledge, a healthy individual with normal healing capacity and an alveolar bone (defect) site rendering the opportunity for vascularization and colonization with bone-forming cells is a good candidate for GBR procedure. Additionally, the following clinical and/or technical prerequisites need to be fulfilled for predictable success with ridge augmentation procedures.

Appropriate Barrier Membrane

An appropriate membrane to serve as a barrier is necessary. The mostly used e-PTFE (Teflon) membrane (GTAM, W.L. Gore and Associates, Flagstaff, AZ) is a nondegradable mem-

155

156	D.A. Buser, D. Weingart, and H.-P. Weber
brane. The structure of this membrane does not allow the	tension-free wound closure with appropriate mattress and
penetration of cells through the membrane, which is an im-	interrupted sutures. Furthermore, a perioperative medica-
portant factor for its success as a physical barrier. Numer-	tion with nonsteroidal anti-inflammatory drugs and the lo-
ous experimental studies in animals have demonstrated that	cal extraoral application of cold packs in the surgical area
this membrane material is bioinert and allows complication-	are useful to reduce postoperative swelling.
free tissue integration, provided that submerged healing
without direct contact to the oral cavity can be achieved
(for review, see Buser et al.5). Biodegradable membranes	Membrane Adaptation and Fixation
have also been tested in animals and humans with success-
ful outcomes for periodontal indications.24–28 In these in-	to Surrounding Bone
dications, the use of biodegradable membranes gains from
the advantage of avoiding a second surgical procedure for	Close adaptation is necessary to achieve a sealing effect to
membrane removal. However, the advantage of using	prevent the ingrowth of soft tissue cells derived from the gin-
biodegradable membranes for implant indications is not	gival connective tissue because these cells are able to com-
considerable since most surgical sites have to be reopened	pete with bone-forming cells in the created space underneath
anyway, either for abutment connection (simultaneous ap-	the membrane. In addition, stabilization of the membrane is
proach) or for implant placement (staged approach).	useful for maintaining close adaptation of the membrane to
Biodegradable membranes may have an advantage over	the bone during wound closure. Clinical applications with the
nondegradable, bioinert membranes for implant indications,	specially designed mini-screws (Memfix System, Institut
with further research needed for outcomes.	Straumann AG, Waldenburg, Switzerland)21–23 or pins29,30
	have documented their effectiveness for membrane adapta-
Primary Soft Tissue Healing	tion and stabilization.
It has been clearly demonstrated in clinical applications and	Creation and Maintenance of
confirmed in experimental studies (for review, see Buser et
al.5) that a closed healing of the regeneration site is a pre-	Secluded Space
requisite for a predictable result. When a soft tissue dehis-
cence occurs, the exposure of the membrane leads to its	A membrane-protected space allows the ingrowth of angio-
contamination with bacteria from the oral cavity and fre-	genic and osteogenic cells so that bone regeneration is undis-
quently to an infection in the membrane site within 2 to 3	turbed by competing nonosteogenic soft tissue cells.14 It is
months, when the membrane remains in place. Since in-	important to differentiate between space-making defects, such
fected membranes cited have an increased risk for a com-	as an extraction socket with intact bone walls, and non–space-
promised surgical result, early membrane removal is gen-	making defects. Non–space-making defects, including sites
erally recommended in cases of soft tissue dehiscences.23	for localized ridge augmentation, are more demanding be-
Therefore, an appropriate flap design has to be chosen for	cause the membrane is not supported by local bone walls. In
predictable achievement of primary soft tissue healing.	these defects, standard e-PTFE membranes are susceptible to
Placement of a barrier membrane changes the conditions	partial collapse caused by the soft tissue cover during heal-
for the healing of a soft tissue wound. In the presence of a	ing.14,23 Therefore, membrane support for space maintenance
barrier membrane, the soft tissue flap is separated from the	is important.
bone. As a consequence, the primary soft tissue healing de-	Attempts have been made to solve this clinical problem in
pends mainly on a sufficient vascular supply of the soft-	recent years. One possible solution is the use of stiffer mem-
tissue flaps, and the soft tissue wound cannot be supported	branes (i.e., reinforced e-PTFE membranes with titanium
by granulation tissue derived from the underlying bone.	mesh) as recommended for periodontal indications.31 How-
Clinical experience has demonstrated that crestal incisions	ever, clinical testing must demonstrate if stiffer membranes
do not allow the predictable achievement of primary soft-	also have value for ridge augmentation procedures. Mem-
tissue healing. The modified incision technique using a lat-	brane-supporting devices such as mini-screws21–23 or pins29,30
eral incision on the palatal aspect with a combined split-	have been used. The surgical results were improved, but par-
thickness and full-thickness flap design clearly reduced the	tial membrane collapse lateral to the support posts still posed
frequency of postoperative soft tissue complications. Other	a problem. It became obvious that an appropriate filling ma-
important factors for primary soft tissue healing are care-	terial was needed in non–space-making defects. Autogenous
ful handling of the soft tissue flap using fine surgical in-	bone is still considered the material of first choice for bone
struments and retraction sutures during surgery as well as	defect grafting.32,33 Consequently, autografts were used to

16. Localized Ridge Augmentation

further optimize the ridge augmentation procedure. It was expected that the combination of autogenous bone grafts and e- PTFE augmentation material would improve the outcome of ridge augmentation procedures because the autograft would not only serve as a membrane-supporting device to maintain the created space but also act as an osteoconductive scaffold to accelerate bone regeneration.

It is important to understand the biological behavior of autografts with respect to graft incorporation and repair and the differences between cortical and cancellous autografts. These details have been intensively studied in numerous experimental studies in orthopedic surgery (for review, see Burchardt32,33). Cancellous autografts are rapidly revascularized, and they are completely repaired by creeping substitution. In contrast, revascularization of cortical autografts is slow and occurs through existing haversian canals. Remodeling of cortical autografts is also slow and results in a mixture of necrotic and new viable bone.

Based on this biological knowledge of graft incorporation and graft repair, corticocancellous block grafts placed in the center of the augmentation area and combined with smaller bone particles surrounding the block graft were subsequently used. This surgical approach is based on two assumptions. First, the cortical portion of the graft facing to the buccal aspect of the crest is used to reestablish the missing buccal cortex. Although this new cortex will be a mixture of necrotic and new viable bone, it offers good mechanical stability and is less susceptible to resorption than cancellous bone. Second, the cancellous portion of the graft is placed in direct contact to the host bone in the area where the implant will be placed during second surgery. The host bone surface is perforated during the surgical procedure to activate bone formation and to open the marrow space, allowing fast ingrowth of blood vessels. It can be expected that this portion of the graft will undergo rapid revascularization and graft remodeling. In addition, the preparation of an implant bed during second surgery will further activate bone remodeling in this area. These assumptions, however, are based on orthopedic literature, and histologic details of graft incorporation and repair underneath barrier membranes are not yet documented. Experimental studies evaluating these aspects are currently in progress.

Corticocancellous block grafts can be harvested either in the retromolar area of the mandible or in the chin, where the cortical layer normally has an appropriate thickness of 2 to 3 mm. The harvesting is uncomplicated and feasible within the extension of the same surgical flap. The block graft should be appropriately applied to the recipient site. First, rigid fixation of the graft is important. A bone-graft fixation screw should be used because it allows precise positioning of the graft and prevents micromovements of the graft underneath the membrane during healing. Second, the block graft must be placed with its cortical layer facing buccally and the can-

157

cellous portion of the graft in direct contact of the host bone, as discussed previously. Based on more than 6 years of experience with the combination of 3-PTFE membranes and autografts, treatment outcome can clearly be optimized in both maxillary and mandibular sites,21–23 as demonstrated in the clinical examples presented at the end of this section. When autografts and the GBR technique are combined, the membrane has a double function. First, it serves as a physical barrier to protect the created space against nonosteogenic cells derived from the mucosa. Second, the membrane serves as a graft preservation device, protecting the autograft from postoperative resorption. It has been documented that autogenous bone graft applied in ridge augmentation procedures without membranes show resorption of up to 50% after 6 months of healing.34 Resorption in ridge augmentation cases has not been observed when bone grafts were protected by a membrane. This clinical observation has been confirmed in patients undergoing vertical alveolar ridge augmentation utilizing autografts from the iliac crest.35 As an alternative to autografts, mineralized and demineralized freeze-dried bone allografts have been used as a membrane-supporting device in ridge augmentation procedures as well,15, 36–40 and some of these publications have presented encouraging clinical results.37,39,40 Allografts have the advantage that no harvesting procedure is necessary. However, histologic details of allograft incorporation and their substitution underneath barrier membranes and adjacent to implants are not sufficiently known for each material at present and need further investigation to provide information concerning their predictability for clinical outcomes.

Healing Time

A last factor important for achieving predictable results is a sufficiently long healing period. It has been demonstrated that sites of early membrane removal attain less gain in bone height.41–43 However, the exact healing period for ridge augmentation procedures with the GBR technique is not known at present. A histologic study involving extended defects in the alveolar ridge in foxhounds revealed almost complete cortical and cancellous bone repair and an onset of bone remodeling after 4 months of healing in membranecovered defects.14 These defects are surgically created and no osteoconductive filler was used. The study confirmed that bone regeneration and bone maturation is a timedependent process, even in an animal known for its rapid healing. Based on this fact, a healing period of 9 months has been used during the development of this technique for ridge augmentation procedures in large bone defects. Clinical experience has proven this length of time to be efficacious.12, 21–23 However, it can be speculated that the healing period may be shortened when membranes combined

158	D.A. Buser, D. Weingart, and H.-P. Weber
a	b

c

d

FIGURE 16.1 Staged approach of guided bone regeneration. (a) Schematic overview of staged approach to augment a deficient alveolar ridge. Note lateral split-thickness/full-thickness incision and wound-closing technique. (b) Patient with missing right lateral incisor. Compromised width of alveolar site. (c) Mucoperiosteal flap

elevated; deficient alveolar bone site does not allow placement of implant. (d) Corticocancellous bone block graft secured with bone fixation screw. Small autologous bone chips are arranged around block graft.

with autogenous bone grafts are used because of the excel-	over a simultaneous approach in large bone defects in the alve-
lent osteoconductive properties of autografts. This expec-	olar process. First, it provides a larger bone surface available
tation has been confirmed in more than 30 cases with a heal-	to contribute to new bone formation, because no implant is in-
ing period of 6 months.	serted in the defect area. With a simultaneous approach, the
	inserted implant reduces the exposed bone surface and its mar-
Summary	row space as a source of angiogenic and osteogenic cells. Sec-
	ond, the implant positioning can be optimized from a pros-
	thetic point of view because the implant is placed when the
Over the past several years, the ridge augmentation procedure	new crest is already reestablished. Following confirmation of
using e-PTFE membranes and autografts has proven to be an	the treatment outcome, this allows a much easier preparation
efficient and predictable surgical technique.21–23 This tech-	of the recipient site and a better initial stability for the implant.
nique uses a staged approach, which has numerous advantages	Third, the staged approach offers advantages with respect to

16. Localized Ridge Augmentation	159
e	f

g

h

FIGURE 16.1 Continued. (e) GTAM membrane adapted and secured with miniature fixation screws (Memfix System, Institut Straumann AG, Waldenburg, Switzerland). (f) Primary flap closure with Gore-

bone maturation because new bone formation is activated twice by the local release of growth factor.44 The first activation occurs during membrane surgery, when the cortical layer is perforated prior to graft placement. The second activation occurs during implant placement, when the implant recipient site is prepared in the newly formed alveolar crest. Finally, it can be assumed that better bone apposition to the titanium surface can be achieved with a staged approach because the “travel distance” for osteogenic elements to the implant surface is much shorter. Thus the staged approach should be the treatment of choice for large bone defects in the alveolar process, whereas the simultaneous approach can be used in

Tex sutures. (g) Postoperative follow-up at 7 months. (h) Reopening surgery, Memfix screws and membrane removed.

Continued.

smaller defects. The question of whether bone regenerated using the barrier technique is “for real” has recently been answered in two dog experiments.14, 45 These studies have shown that the newly regenerated bone closely resembled the structure of preexisting alveolar bone,14,45 and osseointegration of unloaded and loaded implants in these regenerated bone sites occurred identically as for preexisting bone.45

Case Reports

Figures 16.1 and 16.2 show illustrative examples from case reports.

160	D.A. Buser, D. Weingart, and H.-P. Weber
i	j

k

l

m

FIGURE 16.1 Continued. (i) Result of alveolar augmentation in an occlusal view. Site prepared for ITI Hollow-Cylinder (HC) implant in ideal position. (j) Implant placed to correct vertical level (i.e., shoulder apical to cementoenamel junction of neighbor teeth). (k) HC implant in proper axis direction for screw-retained restoration with screw access in the cingulum area of the future crown. (l) Final restoration (porcelain-fused-to-metal) in place. (m) Radiographic control.

16. Localized Ridge Augmentation	161
a	b

c

d

e

f

FIGURE 16.2 Simultaneous approach of guided bone regeneration. (a) Schematic overview on simultaneous approach for alveolar ridge augmentation. Note incision technique as in staged approach. (b) Implant placed in area of lower left first molar. Note buccal alveolar dehiscence. Surrounding bone is perforated with a small round bur to promote bleeding and a source for cells with bone-forming po-

tential. (c) Autologous bone particles obtained from implant bed preparation (bone core) placed in area of dehiscence. Small closure screw placed in implant. (d) GTAM membrane adapted as “poncho” over implant and secured with two Memfix screws. (e) Primary wound closure. (f) Postoperative follow-up at 1 month.

Continued.

162	D.A. Buser, D. Weingart, and H.-P. Weber
g	h

i

j

FIGURE 16.2 Continued. (g) Reopening surgery at 6 months. (h) Result of augmentation. Small implant closure screw replaced with transmucosal healing cap. (i) Postoperative follow-up 3 weeks after reopening surgery. (j) Radiographic control 1 year after crown insertion.

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