clinical and histologic assessment of lateral …...of a variety of ridge deformities.2,3 the...

Clinical and Histologic Assessment ofLateral Alveolar Ridge AugmentationUsing a Synthetic Long-TermBioabsorbable Membraneand an AllograftNicolaas C. Geurs,* Jonathan M. Korostoff,† Philip J. Vassilopoulos,* Tae-Heon Kang,†

Marjorie Jeffcoat,† Robert Kellar,‡ and Michael S. Reddy*

Background: Guided bone regeneration (GBR) is a widely usedprocedure for augmenting alveolar ridge width prior to placementof endosseous implants. Various graft materials and barrier mem-branes (non-resorbable and bioabsorbable) have been used inGBR. The aim of this study was to assess the performance ofa new bioabsorbable, synthetic polyglycolic acid/trimethylenecarbonate (PGA/TMC) barrier membrane with an increased ab-sorption time in conjunction with a combination of assayed demin-eralized bone matrix and cortical cancellous chips uniformlydispersed in a thermoplastic biologic carrier.

Methods: At 72 potential implant sites in 38 subjects, ridgewidth at the crest and 4 mm apical to the crest was measured be-fore and 6 months after a GBR procedure using the long-term(LT) PGA/TMC membrane and an allograft in a thermoplastic car-rier. Before placement of endosseous implants, 48 biopsy speci-mens were obtained from the augmentation sites and analyzedhistomorphometrically.

Results: The GBR procedure increased the mean ridge width atthe crest from 2.4 to 5.2 mm. This 216% change from baseline wassignificant (P <0.001). The mean width 4 mm apical to the crest in-creased from 4.4 to 7.5 mm, a significant (P <0.001) 174% change.The histomorphometric analysis showed that the biopsy speci-mens consisted, on average, of 57% bone (36% graft materialand 21% new bone) and 43% soft tissue and space.

Conclusion: Our findings suggest that the LT PGA/TMC barriermembrane, used in conjunction with an allograft, provides lateralalveolar ridge augmentation comparable to that achieved withother materials without the necessity for bone-graft harvesting ora second procedure to remove the barrier membrane. J Periodon-tol 2008;79:1133-1140.

KEY WORDS

Alveolar ridge augmentation; bone regeneration;polyglycolic acid/trimethylene carbonate.

Without intervention, alveo-lar ridge resorption follow-ing tooth loss seems to be

inevitable and irreversible; it oftenoccurs quickly, especially within thefirst 6 months after a tooth is lost.1,2

Typically, resorption takes place atthe expense of facial or buccalbone, leading to the developmentof a variety of ridge deformities.2,3

The associated loss in ridge widthmay preclude placement of endo-sseous dental implants and, there-fore, represents a major challengein implant dentistry.3

Several methods for augmentingthe alveolar ridge in preparation forimplant placement have been de-scribed. Among these techniques,guided bone regeneration (GBR)has probably generated the mostinterest.4,5 The concept of GBR isbased upon the use of a barrier mem-brane to exclude rapidly growing softtissue cells from a bony defect and,more importantly, to maintain aspace for the slower process of boneformation.4 Bone grafts or bone sub-stitutes are commonly used in GBRprocedures to provide support forthe barrier membrane, for additional

* Department of Periodontology, University of Alabama at Birmingham School of Dentistry,Birmingham, AL.

† Department of Periodontics, University of Pennsylvania School of Dental Medicine, Philadelphia,PA.

‡ W.L. Gore & Associates, Inc., Flagstaff, AZ.doi: 10.1902/jop.2008.070595

J Periodontol • July 2008

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space maintenance, and/or for their osteoconduc-tive/osteoinductive properties.

Historically, most initial GBR procedures, espe-cially those in patients not undergoing immediateimplant placement, used autogenous bone and a non-resorbable barrier membrane composed of expandedpolytetrafluoroethylene (ePTFE).6-8 This approachresulted in adequate lateral ridge augmentation andfavorable long-term survival of subsequently insertedimplants.5,9-12 Despite these encouraging results,there are drawbacks to using autogenous bone andnon-resorbable ePTFE membranes for GBR. Al-though the use of autogenous bone ensures biocom-patibility and provides viable osteogenic cells, it alsonecessitates a separate bone-harvesting procedure.8

In some cases, bone must be obtained from an extra-oral site by a surgeon with the appropriate expertise.Furthermore, the need to remove the membrane, ifnot done in conjunction with implant placement, addsan additional surgical procedure to the treatmentprotocol. The added time, expense, and potentialmorbidity are recognized impediments to patientacceptance of such procedures. Premature exposureand possible premature removal of non-resorbablemembranes have been associated with diminishedresults.5-7,9 Because of these drawbacks, the mostrecent GBR research has included a strong focus onaugmentation procedures using different bone graftmaterials (allogenic, xenogenic, and alloplastic) incombination with bioabsorbable barrier membranes.Promising results with these materials have been re-ported in animal studies13,14 and human clinical in-vestigations.15-17

Barrier membranes made of bovine or porcinecollagen18,19 or synthetic polymers,3,14 including amembrane composed of polyglycolic acid/trimethy-lene carbonate (PGA/TMC§),20,21 are the most widelystudied bioabsorbable materials for GBR. Collagenhas several desirable properties, including its hemo-static, chemotactic, and cell-adhesion functions,22

and has yielded favorable results in clinical trials ofGBR for ridge-width augmentation.23 However, asnoted by Bunyaratavej and Wang,18 collagen’s fastabsorption rate remains a concern to most clinicians.This issue provoked the development of a new bioab-sorbable, synthetic membrane of 67% PGA and 33%TMC that was designed to remain intact for 16 to 25weeks.

A prototype of the long-term (LT) PGA/TMCi mem-brane was compared to a collagen membrane in aGBR study in dogs.24 In this investigation, teeth wereextracted, and osseous defects were created. Defectswere filled with a demineralized freeze-dried bone al-lograft in a thermoplastic gelatin matrix alone (con-trol) or covered with a collagen membrane or an LTPGA/TMC membrane. Three months later, the dogs

were sacrificed, and representative tissue sectionswere prepared from the defects and subjected to his-tomorphometric analysis. Sites covered with a PGA/TMC membrane showed a significantly higher per-centage of bone regeneration and less soft tissue rel-ative to sites covered with collagen membranes.Control sites showed deformation of regeneratedbone resulting from collapse of the overlying perios-teum. These findings provided initial evidence of theeffectiveness of the combination of an allograft andthe PGA/TMC membrane for GBR in edentulous areas.

The purpose of the current study was to evaluatethe efficacy of LT PGA/TMC membranes when usedin conjunction with a combination of assayed demin-eralized bone matrix and cortical cancellous chipsuniformly dispersed in a thermoplastic biologiccarrier¶ for GBR of lateral ridge defects in humans.The specific aim of the study was to assess the quan-tity and quality of augmented bone achieved withthese unique materials by means of clinical and histo-logic criteria.

MATERIALS AND METHODS

Subject PopulationThis two-center study was conducted at the Universityof Alabama at Birmingham School of Dentistry andthe University of Pennsylvania School of Dental Med-icine from November 2003 through March 2005. Indi-viduals who participated in the study required anendosseous implant in at least one healed bony sitethat exhibited adequate ridge height but insufficientridge width (defined as £5 mm on bone sounding)for implantation. Subjects with medical conditionsor lifestyle factors likely to affect healing were ex-cluded from the study, including those with uncon-trolled diabetes, immune disease, history of alcohol ordrug abuse, current smokers, or individuals deemedto be a compliance risk. Fifty-one subjects (41 menand 10 women; mean age: 53 years; age range, 24to 77 years) with 98 potential implant sites were en-rolled into the investigation. The protocol was ap-proved by the institutional review boards of theauthors’ universities, and all subjects provided writteninformed consent.

Ridge Augmentation ProcedureA treatment plan for placement and restoration ofdental implants was derived by a team of surgeonsand prosthodontists of the graduate programs in peri-odontology and prosthodontics at both centers. Asurgical guide was fabricated to facilitate accurate

§ Gore Resolut XT Regenerative Membrane, W.L. Gore & Associates, Inc.,Flagstaff, AZ.

i Gore Resolut Adapt LT Regenerative Membrane, W.L. Gore & Associates,Inc.

¶ Regenaform Moldable Allograft Paste, Exactech Dental Biologics,Gainesville, FL.

Ridge Augmentation Using a Synthetic Bioabsorbable Membrane Volume 79 • Number 7

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implant placement and to ensure that pre- and post-augmentation measurements were taken at the sameanatomic location. All subjects received an antibioticagent (cephalexin, 2 g, or if allergic, clindamycin, 600mg) 30 minutes before the ridge-augmentation sur-gery. The surgical procedure was performed usinglocal anesthesia and intravenous sedation, when indi-cated. A crestal incision was made above the treat-ment site, and full-thickness flaps were reflected toallow access to the site. Potential implant-placementsites were located with the surgical guide. The testsites were located with the surgical guide identifyingthe implant sites, and ridge width at the crest and4 mm apical to the crest of each future implant sitewas measured with ridge-mapping calipers. An LTPGA/TMC membrane was shaped with a fabricatedtemplate and fitted to the area requiring augmenta-tion. The membrane was tailored to cover the ridge,allograft, and ‡3 mm of native bone while remaining‡1 mm from any adjacent teeth.

Prior to placement of the allograft, the bone defectwas decorticated with a high-speed drill using a #2round bur with perforations made at 4-mm intervalsin the cortical plate. Periosteal release was performedto allow for tension-free closure over the membraneand graft. The thermoplastic nature of the biologiccarrier of the allograft allows for manipulation andmodeling of the graft for ;2 minutes, after which itsets up to a rubbery consistency with dimensional sta-bility. The material was shaped to dimensions thatprovided adequate augmentation of the defectiveridge, set in place, and covered with the trimmed LTPGA/TMC membrane. To keep the surgical proceduresimple and because of the dimensional stability of thegraft, no pins and/or tacks for supporting and/or an-choring the membrane were used. Primary wound clo-sure was achieved with a combination of continuousinterlocking mattress and interrupted ePTFE sutures.#

An analgesic agent was given according to the clini-cian’s and subject’s preference. An antibiotic wasprescribed as a continuation of the premedicationregimen and consisted of cephalexin, 500 mg, every8 hours for 7 days or clindamycin, 300 mg, every8 hours for 7 days. Subjects were instructed to rinsetheir mouths with a 0.12% chlorhexidine mouthrinsetwice daily for 2 weeks. Sutures were removed, andhealing in the operative sites was confirmed at a2-week postoperative clinical examination.

Implant ProcedureEndosseous implant surgery was performed ;6months after the ridge-augmentation procedure.Full-thickness flaps were reflected, and study siteswere identified with the original surgical guide. Ridgewidth measurements at the crest and 4 mm apical tothe crest of each site were repeated. A biopsy speci-

men of one treatment site per separate augmentationsite was obtained using a 2-mm trephine inserted to adepth of 6 mm in the same position and at the sameangle planned for the endosseous implants. Speci-mens were stored inside the trephine, which wasplaced in formalin and subsequently processed forhistomorphometric analysis. Placement of the endo-sseous implants was done in accordance with the au-thors’ standard protocol.

HistomorphometryThe trephines containing the biopsy specimens wereembedded in polymethylmethacrylate, and a sectionfor analysis was cut from the middle of the block. Thesections were treated with Paragon stain that showedvital bone as dark red, non-vital bone as light red, andmarrow spaces, soft tissue, and cells as variousshades of blue. An image analysis system** was usedto determine the proportions of vital and non-vitalbone in the specimens.

Calculation of Ridge Width Changes andStatistical AnalysisThe values for ridge width change at the crest and4 mm apical to the crest were calculated by subtract-ing the values for the initial ridge width measurementfrom the corresponding values obtained 6 monthslater at the time of implant placement. A one-sidedStudent t test was used to evaluate the change in ridgewidth. A P value <0.05 was considered to represent asignificant difference between ridge width before and6 months after placement of the allograft and LT PGA/TMC membrane.

RESULTS

Fifty-one subjects with 98 potential implant sites wereenrolled in the investigation at the two study centers.Thirteen subjects subsequently withdrew from thestudy because of health problems, including cancer(two subjects) and temporomandibular disorder(one subject); financial reasons (two subjects); or un-known reasons (eight subjects). Thirty-eight subjectsreturned for the 6-month assessment and implantplacement; 48 ridges were augmented in this group.Thirty subjects had one, six subjects had two, andtwo subjects had three ridge augmentations. Thus,the reported comparisons between ridge width valuesat the initial evaluation and 6 months later were basedon measurements at 72 sites in 38 subjects.

Clinical ObservationsAt flap reflection for placement of the endosseous im-plants, no LT PGA/TMC membranes or remnants ofthese membranes were observed. Figure 1 showsthe mean – SD values for ridge width at the crest

# CV-5 Gore-Tex Suture, W.L. Gore & Associates, Inc.** Nova Prime, Bioquant Image Analysis, Nashville, TN.

J Periodontol • July 2008 Geurs, Korostoff, Vassilopoulos, et al.

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and 4 mm apical to the crest before and 6 months afterthe GBR procedure. For ridge width at the crest, therewas a mean increase of 2.8 – 1.7 mm (range, 0 to7 mm). This change was significant (P <0.001). Forridge width 4 mm apical to the crest, a mean increaseof 3.1 – 1.9 mm (range, -0.5 to 7 mm) occurred. Thischange from baseline was statistically significant(P <0.001). The change in ridge width for all individualsites is represented in Table 1. It shows the distributionof the individual sites with the change that was ob-served from baseline. Only a few sites demonstratedno gain in width at the crest, and all sites showed anincrease in width at one of the measuring points. Fig-ure 2 shows a representative mandibular lateral ridgeaugmentation performed with the LT PGA/TMC mem-brane in conjunction with a combination of assayeddemineralized bone matrix and cortical cancellouschips uniformly dispersed in a thermoplastic biologiccarrier. Figure 3 represents another case with theridge before and 6 months after augmentation.

HistomorphometryForty-eight treatment sites were included in the histo-morphometric analysis. Every ridge area that was

augmented contributed one bi-opsy site. The analysis of the com-position of the 48 specimens foundthe following (mean – SD) propor-tions: 36.2% – 15% graft material,20.6% – 8.8% new bone, and49.9% – 17.3% soft tissue andspace. The mean proportion oftotal bone (residual graft and newbone) was 56.8%.

Figure 4 shows representativehistologic sections prepared fromthe biopsy specimens. Histomor-phometric analysis demonstratednew bone formation. The generalfindings show evidence of remod-eling and new bone surroundingthe implanted bone fragments.Marrow tissue was consistently ob-

served. Active remodeling of the allograft was evidentby the presence of osteoid and osteoblasts. The newbone appears woven and has viable osteocytes. Insome sections, the remodelingof theallograft fragmentswas almost complete.

ComplicationsOne subject complained of temporomandibular jointpain after the surgery. It was found to be a preexistingcondition of a temporomandibular disorder that wasnot reported by the subject upon enrollment. One sub-ject reported paresthesia that resolved spontaneouslywithin a month. Two fistulas were noted at postoper-ative evaluations and resolved after antibiotic treat-ment.

Membrane ExposureOverall, membrane exposure occurred at 30 of the 72study sites (42%). Eight (11%) of the exposed mem-branes necessitated premature removal. When amembrane became exposed, the subject was in-structed to locally apply 0.12% chlorhexidine to thearea twice a day. The membranes that were removedshowed localized signs of infection. All infections re-solved without further intervention after membraneremoval. Table 2 summarizes the ridge width changesfor the different exposure status.

DISCUSSION

This study evaluated the effectiveness of a new bioab-sorbable, synthetic LT PGA/TMC membrane used inconjunction with a bone allograft to augment alveolarridge width in healed bony sites in preparation forplacement of endosseous dental implants. In a major-ity of the treated cases, there were significant in-creases in ridge width at the crest and 4 mm apicalto the crest relative to presurgical values. Because

Figure 1.Mean (– SD) values (N = 72 sites) for alveolar ridge width at crest and 4 mm apical to the crestbefore augmentation procedure and 6 months after ridge-augmentation procedure.

Table 1.

Distribution of Sites in Relation to theChange From Baseline (mm)

Change <1

1 to

<2

2 to

<3

3 to

<4

4 to

<5

5 to

<6 6+

At the crest (n) 6 12 22 9 12 5 6

4 mm apical tothe crest (n) 6 8 20 11 10 9 8


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we measured the ridge at two locations, our assess-ment indicated that augmentation occurred alongthe entire ridge, thereby further enhancing the poten-tial implant sites. GBR using an LT PGA/TMC mem-brane and an allograft was reported to provideeffective ridge augmentation in dogs.24 However, toour knowledge, the present study represents the firsthuman clinical investigation of this technique. Theresults are in accordance with those of the animalstudy24 and indicate that this particular membraneand allograft material effectively promoted increasesin ridge width in healed bony defects for which delayedimplantation was planned.

The allograft used in this study has several advan-tageous characteristics. The gelatin matrix in whichit is suspended is thermoplastic and sets to a rubberyconsistency. After setting, it has dimensional stabil-ity. These features facilitate the subsequent place-ment of the membrane because graft displacementis avoided, and tacks are not required to stabilizethe membrane. Most important, using an allografteliminates the need for a procedure to harvest au-togenous bone for grafting. Studies in animals14

and humans22 showed that allografts could provideresults comparable to those achieved with autoge-nous bone.

Figure 2.A) The ridge after reflection of the flaps. B) The cortical perforations. C) The thermoplastic allograft in place. D) The membrane adapted over thegraft. E) Primary closure with ePTFE sutures. F) The ridge 6 months after the ridge augmentation.


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Collagen was the first bioabsorbable membrane ma-terial to be widely used in GBR. Collagen membraneshave been used in combination with autogenousbone,23 xenografts,17 hydroxyapatite,15 and otherbone substitutes22 and have been associated withsuccess rates comparable to those achieved withnon-resorbable ePTFE membranes.13,18,19 Suchfindings support the use of a bioabsorbable barriermembrane for the regeneration of bone. Moreover,the use of a bioabsorbable membrane may decrease

the risk for a membrane infec-tion if a soft tissue dehiscenceoccurspostoperatively.3,7 How-ever, there are drawbacks tocollagen membranes. Becauseof its relatively short absorptiontime, collagen loses its barrierfunction within 2 or 3 months;7

therefore, it may not providesufficient time for completionof the bone-regeneration pro-cess. There is also some evi-dence that collagen does notadequately exclude soft tis-sue.24 Finally, some subjectsrefuse treatment involving pro-ducts derived from animals onthe basis of religious and/orethical beliefs.

The limitations of colla-gen membranes provoked thesearch for a bioabsorbable poly-mer substitute for collagen inGBR that began in the late1990s. Lekovic et al.3 evalu-ated the efficacy of a membranecomposed of glycolide and lac-tic acid polymers for alveolarridge augmentation after toothextraction in 16 subjects. Bonegrafts were not used in thatstudy. Compared to controls,sites in which the membraneswere placed exhibited signifi-cantly less horizontal ridge re-sorption. In a case report,Miller et al.21 used bioabsorb-able polymer membranes fromtwo manufacturers in conjunc-tion with autogenous bone toaugment the alveoli of a patientwho lost two teeth after beingkicked in the mouth during asoccer game. Six months later,both sites were completely re-generated with hard tissue that

had the histologic appearance of normal bone. Melloniget al.14,25 conducted a two-part histomorphometricassessment of a prototype bioabsorbable PGA/TMCmembrane used for GBR in large, dehiscence-type de-fects in dogs. When the membrane was used without agraft material, the investigators failed to observe an in-crease in ridge width relative to untreated sites.25 Incontrast,when themembrane was used incombinationwith an allograft, it resulted in a mean alveolar ridgewidth that was more than twice that detected at control

Figure 3.A) The ridge after reflection of the flaps. B) The ridge 6 months after the ridge augmentation.

Figure 4.A) Histologic sections. Low-power view of a trephine and bone core taken from an augmented ridgeafter 6 months of healing. The trephine is filled with bone fragments and newly remodeled bone (red).B) A higher-power view of section A showing bone fragments (bf) in the trephine (T) that haveevidence of remodeling, new bone (NB) surrounding the demineralized freeze-dried bone allograft,and marrow tissue (M). C) Histologic section study showing an osteoid seam (arrows) lining newlyremodeled bone (NB) around the bone fragments (bf). The new bone appears woven and has viableosteocytes. T = trephine. D) Histologic section showing almost complete remodeling of bone fragments(bf) and replacement with new bone (NB). Viable osteocytes are visible in the bony matrix, andadipocytes are present in the marrow-like tissue (M). (Paragon stain; original magnification: A, ·2.5;B, ·10; C and D, ·25.)


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sites (4.6 versus 2.0 mm).14 Values for bone contact,bone height, and area of newly formed bone were alsomarkedly higher than those from controls (70% versus6%, 6 mm versus 2 mm, and 12 mm2 versus 6 mm2,respectively). The authors considered these resultscomparable to those provided by the combination ofa non-resorbable ePTFE membrane and an allograft,although they also noted that the prototype PGA/TMC membrane they studied may have absorbed tooquickly.14 The LT PGA/TMC membrane used in thecurrent study has a substantially longer retention time.

Our investigation was not a comparative trial, butour results may be examined in relation to the findingsof two clinical studies6,23 that also evaluated changesin ridge width after GBR. In a series of 40 subjects,Buser et al.6 used corticocancellous autografts, bonechips, and non-resorbable ePTFE membranes toaugment the ridge in 66 potential implantation sitesnarrower than 5 mm. Before the augmentation proce-dure, the mean ridge width, measured 2 mm apical tothe alveolar crest, was 3.5 mm (range, 2 to 4.5 mm).When the ePTFE membranes were removed 7 to13 months later, the mean width was 7 mm (range,5 to 10 mm). Subsequent placement of titanium im-plants was successful in all 40 subjects. The mean in-creases in ridge width achieved by Buser’s group werevery similar to those of our study. However, they usedthe standard GBR method, which, unlike the tech-nique we used, required a bone-harvesting procedureand frequently a second operation to remove themembrane. In the study conducted by von Arx andBuser,23 autogenous block grafts, anorganic bovinebone mineral, and collagen membranes were usedfor horizontal ridge augmentation of 58 sites in 42 sub-jects. The mean ridge width at the crest was 3 mm(range, 0.5 to 5 mm) before the GBR procedure and8 mm (range, 6 to 10 mm) after an average of 5.8months (range, 4.5 to 13.5 months). Although themean gain in ridge width (4.6 mm) was greater thanthat attained in our study, the augmentation tech-

nique used by von Arx and Buser was much morecomplex than our method and required harvestingof block grafts from the symphysis or the retromolararea. Moreover, we regard the ridge widths obtainedin our series (5.2 mm at the crest and 7.5 mm apicalto the crest) as adequate for the subsequent place-ment of endosseous implants.

On average, our histomorphometric analysisshowed that the 48 biopsy specimens consisted of57% bone (allograft material plus new bone), 20%new bone, and 43% soft tissue and space. A histomor-phometric study by Brunel et al.15 of specimens ob-tained 8 months after a GBR procedure using acollagen membrane and a synthetic hydroxyapatitegraft material yielded similar results: 49% for meanbone surface area and 39% for medullary space sur-face area. They reported that this defect fill madeplacement of implants possible in all 14 sites studied,and only one of the implants failed during a 7-yearfollow-up period.

Membrane exposure has been associated with di-minished results.26 In this study, 42% of the sites wereexposed. When an exposure did not lead to the removalof the membrane, the meangain in ridgewidthwas sim-ilar to the sites where themembrane remained covered.The premature exposure of these membranes, whenmanaged with the protocol for prevention of infectionby using local application of 0.12% chlorhexidine, didnot lead to diminished results. During the healing ofthese sites, the integrity of the membrane remained in-tact for an extended period of time postexposure. Themaintenance of the integrity of the barrier function maybe beneficial. However, this does add a managementconcern for these sites and should be avoided. Prema-ture removal of the membranes because of infectionnegatively impacted the gain in width.

CONCLUSIONS

Definitive evidence that the extentofbone regenerationachieved with the LT PGA/TMC membrane is compa-rable or superior to that associated with other materialscan come only from randomized controlled studies. Werecognize this as a limitation of the current study. How-ever, our results indicated that GBR procedures involv-ing this membrane in conjunction with a bone allograftproduce lateral ridge augmentation sufficient for place-ment of endosseous implants in healed bony sites. Ad-ditionally, such an approach provides several benefitsfor patients relative to the use of non-resorbable mem-branes in combination with autogenous bone. It is lessinvasive, less painful, less expensive, and facilitates thecompletion of treatment in a shorter period of time. Col-lectively, these properties suggest that the use of the LTPGA/TMC membrane along with a bone allograft repre-sents a reasonable alternative to previously describedlateral ridge-augmentation procedures.

Table 2.

Ridge Width Changes for MembraneExposure Status

At the

Crest (mm)

4 mm Apical to

the Crest (mm)

n

Mean

(SD)

Range Mean

(SD) Range

Exposed andremoved

8 1.75 (1.4) 0.5 to 4.0 2.0 (1.5) 0 to 5.0

Exposed, notremoved

22 3.1 (1.8) 0 to 7.0 3.3 (1.8) 0 to 7.0

Covered 42 2.9 (1.7) 0 to 6.5 3.3 (1.9) -0.5 to 7.0


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ACKNOWLEDGMENTS

The authors thank W.L. Gore & Associates, Inc., forfinancial support for this study and the preparationof the manuscript. The authors also thank Renee J.Robillard, scientific writer, W.L. Gore & Associates,Inc., and Elizabeth Bolton, editorial support, Univer-sity of Alabama at Birmingham, for writing and edito-rial assistance. Dr. Geurs has received lecture feesfrom Exactech Dental Biologics, the company thatprovided the biologic carrier used in this study. Atthe time this study was conducted, Dr. Kellar wasProduct Specialist at W.L. Gore & Associates, Inc.,and held vested stock in the company. Drs. Korostoff,Vassilopoulos, Kang, Jeffcoat, and Reddy report noconflicts of interest related to this study.

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Correspondence: Dr. Nicolaas Geurs, Department of Peri-odontology, University of Alabama at Birmingham Schoolof Dentistry, SDB 412, 1530 3rd Ave. S., Birmingham, AL35294-0007. Fax: 205/934-7901; e-mail: [email protected].

Submitted November 19, 2007; accepted for publicationJanuary 2, 2008.


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clinical and histologic assessment of lateral …...of a variety of ridge deformities.2,3 the...

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