Flapless implant surgery: an experimental studySeung-Mi Jeong, DDS, PhD,a Byung-Ho Choi, DDS, PhD,b Jingxu Li, DDS,c

Han-Sung Kim, PhD,d Chang-Yong Ko,e Jae-Hyung Jung, DDS,f Hyeon-Jung Lee, DDS,f

Seoung-Ho Lee, DDS, PhD,g and Wilfried Engelke, MD, DDS, PhD,h Wonju and Seoul,South Korea, and Göttingen, GermanyYONSEI UNIVERSITY AND GEORG-AUGUST UNIVERSITY

Objective. The purpose of this study was to examine the effect of flapless implant surgery on crestal bone loss andosseointegration in a canine mandible model.Study design. In 6 mongrel dogs, bilateral, edentulated, flat alveolar ridges were created in the mandible. After 3months of healing, 2 implants in each side were placed by either flap or flapless procedures. After a healing period of8 weeks, microcomputerized tomography at the implantation site was performed. Osseointegration was calculated aspercentage of implant surface in contact with bone. Additionally, bone height was measured in the peri-implant bone.Results. The mean osseointegration was greater at flapless sites (70.4%) than at sites with flaps (59.5%) (P � .05). Themean peri-implant bone height was greater at flapless sites (10.1 mm) than at sites with flaps (9.0 mm) (P � .05).Conclusion. Flapless surgery can achieve results superior to surgery with reflected flaps. The specific improvements ofthis technique include enhanced osseointegration of dental implants and increased bone height. (Oral Surg Oral Med

Oral Pathol Oral Radiol Endod 2007;104:24-8)

When soft tissue flaps are reflected during dental im-plant surgery, bone resorption of varying degrees al-most always occurs in the crestal area of the alveolarbone.1,2 Flapless implant surgery may be useful, there-fore, for minimizing bone resorption. In general, clini-cians have described flapless implant surgery as a pre-dictable procedure,3,4 but such reports include clinicalobservations without well defined parameters for suc-cess or proper controls. In an attempt to provide morerigorous data, the present study was undertaken to

Supported by a research grant from Yonsei University Wonju Collegeof Medicine (YUWCM 2006-11).aAssistant Professor, Department of Dentistry, Yonsei UniversityWonju College of Medicine, Wonju.bProfessor, Department of Oral and Maxillofacial Surgery, College ofDentistry, Yonsei University, Seoul.cResearch Assistant, Department of Dentistry, Yonsei UniversityWonju College of Medicine, Wonju.dAssociate Professor, Department of Biomedical Engineering. Col-lege of Health Science, Institute of Medical Engineering, YonseiUniversity, Wonju.eGraduate, Department of Biomedical Engineering. College of HealthScience, Institute of Medical Engineering, Yonsei University, Wonju.fGraduate, Department of Oral and Maxillofacial Surgery, College ofDentistry, Yonsei University.gAssociate Professor, Department of Periodontology, Ewha Women’sUniversity.hProfessor, Department of Oral Surgery, School of Dentistry, Georg-August University, Göttingen, Germany.Received for publication Aug 21, 2006; returned for revision Oct 2,2006; accepted for publication Nov 9, 2006.1079-2104/$ - see front matter© 2007 Mosby, Inc. All rights reserved.

doi:10.1016/j.tripleo.2006.11.034

24

examine the effect of flapless implant surgery on crestalbone loss and osseointegration in a canine mandiblemodel.

MATERIALS AND METHODSAnimal model

Six adult female mongrel dogs, each weighing morethan 15 kg (range 15-20 kg), were used in this exper-iment. The protocol was approved by the Animal Careand Use Committee of Yonsei Medical Center, Seoul,Korea.

Edentulated flat ridge inductionAll surgical procedures were performed under sys-

temic (5 mg/kg ketamine and 2 mg/kg IM xylazine) andlocal (2% lidocaine with 1:80,000 epinephrine) anes-thesia. All mandibular premolars were removed to es-tablish space for implants. After 1 month of healing,bilateral flat alveolar ridges were surgically produced.Briefly, a mucoperiosteal flap was raised to expose thealveolar bone. Burs were then used to flatten the alve-olar crest under sterile saline irrigation so that an ap-propriate width of bone would be available for implantplacement. The mucoperiosteal flap was replaced andsutured, and the resulting edentulated flat alveolar ridgewas allowed to heal for 3 months.

Implantation procedureTwo dental implants (length 10 mm, diameter 4.1

mm; Osstem, Seoul, Korea) were placed within the

edentulated ridge in each side of the mandible (Fig. 1).

OOOOEVolume 104, Number 1 Jeong et al. 25

The implants in each side were randomly assigned to 1of the following 2 surgical techniques: 1) implantationafter making a 5-mm-wide circumferential incision inthe gingiva at the center of the implant site (flaplessgroup); 2) implantation after elevating a mucoperiostealflap to expose the alveolar ridge (flap group). Care wastaken during this procedure to place the 2 implants atthe same height and to avoid perforation of the corticalplates, both lingual and buccal. Abutments were con-nected to the implants, and the implants were not sub-merged. Antibiotic therapy was administered 1 hourbefore surgery and once daily for 2 days after surgery.

Microcomputerized tomographyAnimals were killed 8 weeks after implantation, and

bone blocks containing the implants were excised. Re-sected bone specimens were fixed for 48 h in 10%buffered formalin and then stored in 70% ethanol. Amorphometric study, using microcomputerized tomog-raphy (microCT) (Skyscan 1076; Skyscan, Antwerpen,Belgium), was used to quantify the bone around theimplants. Microtomographic slices were acquired ateach 35-�m interval, and computerized 3-dimensional(3D) reconstruction was performed by accumulatingtraces of each implant, following the method describedby Akagawa et al.5 These settings have been recentlyused for accurate analysis of titanium implant os-seointegration.6 Osseointegration was calculated aspercentage of implant surface in contact with bone.Additionally, bone height in the peri-implant bone wasmeasured as the distance between the alveolar crest andthe bottom surface of the implant.

Statistical analysisWilcoxon signed rank test for paired samples was

used to calculate statistical differences between the

Fig. 1. Clinical feature after implant placement. A, Implantplaced without a flap. B, Implant placed with a flap.

groups.

RESULTSHealing after implant placement was uneventful in

all animals. Upon gross examination, the bone aroundthe implants was more abundant at flapless sites than atflap sites (Fig. 2). The results of microCT image anal-ysis are presented in Table I. Average bone height wasgreater in the flapless group (10.1 � 0.5 mm) than inthe flap group (9.0 � 0.7 mm) (P � .05) (Fig. 3).Average osseointegration was significantly greater inthe flapless group (70.4 � 6.3%) than in the flap group(59.5 � 6.3%) (P � .05) (Fig. 4). The flapless grouphad significantly better vertical alveolar ridge heightand more bone/implant contact than the flap group.

DISCUSSIONIn recent years, there have been reports that flapless

implant surgery is a predictable procedure with highsuccess rates if patients are appropriately selected andan appropriate width of bone is available for implantplacement.3,4 The aim of the present study was toexamine the effect of flapless implant surgery on crestalbone loss and osseointegration compared with flap im-plant surgery. The study showed that when implantswere placed without flap elevation, both the amount ofosseointegration and bone height around the implantswere significantly greater than in implants placed with

Fig. 2. Photograph of the mandible showing bone loss aroundthe implants. A, flapless site; B, flap site.

Table I. Parameters (mean values and standard devia-tion) of bone-to-implant contact and bone heightaround dental implants when placed either without orwith a flap

Flapless group Flap group P values

Bone-implant contact (%) 70.4 � 6.3 59.5 � 6.3 �.05Bone height (mm) 10.1 � 0.5 9.0 � 0.7 �.05

flap elevation. This enhancement is probably due to the

OOOOE26 Jeong et al. July 2007

Fig. 3. Three-dimensional microCT showing the bone (yellow) around the implants (gray). A, Implant placed without a flap.

B, Implant placed with a flap. Buccal, buccal side of the alveolus; lingual, lingual side of the alveolus.

flap.

OOOOEVolume 104, Number 1 Jeong et al. 27

preservation of bone vascularization. When teeth arepresent, blood is supplied to the bone from 3 differentpaths: the periodontal ligament, the connective tissueabove the periosteum, and inside the bone. When atooth is lost, the blood supply from the periodontalligament disappears, and blood is supplied only fromsoft tissue and bone. Cortical bone is poorly vascularizedin contrast to marrow bone. When soft tissue flaps arereflected for implant placement, the blood supply from thesoft tissue to the bone (supraperiosteal blood supply) isalso removed, leaving only poorly vascularized corticalbone without a part of its vascular supply, ultimatelyprompting bone resorption during the initial healingphase.7-9 The preservation of bone vascularization whenno flaps are reflected may help optimize bone regenerationaround implants, as suggested by the improved osseointe-gration we observed after flapless surgery.

According to the Branemark protocol, an incision inthe mucosa or the mucobuccal fold was made, and thena flap was reflected to expose the underlying bone. Theimplants were placed, and the flap was sutured back inplace.10,11 The rationale for this method is to keep theincision line away from the implants, thereby possiblypreventing infection.12 In the present study, however,peri-implantitis did not occur in the flapless group.

Most studies have histologically evaluated thebone structure around the implant. It is well recog-nized, however, that partial evaluation of some sec-tions is not sufficient for overall evaluation of thebone structure. This study attempted to evaluate the3D bone structure around the implants, using mi-croCT. In 1989, Feldkamp et al.13 introduced anx-ray microCT system to create 3D images. More re-cent developments have allowed the creation of higher-resolution 3D images and quantitative measurements ofthe trabecular bone structure.14 MicroCT was validatedas a method for 3D assessment and analysis of cancel-lous bone by Muller et al.15 in 1998, who compared themorphometric results of conventional histomorphom-etry to microCT scans. Those authors demonstrated thestrength of 3D representation of trabecular bone archi-tecture compared with conventional 2D histology andfound excellent correlation of the indices assessed. Re-cent studies have proposed the application of microCTto dental implant research.16,17 In the present study,microCT was used to perform a detailed quantitativeanalysis of the entire implantation site.

To our knowledge, this is the first report to providecontrolled experimental data concerning the influenceof flapless implant surgery on osseointegration and theheight of newly formed bone around implants. Flaplessimplant surgery improved both the osseointegration ofdental implants and the bone height around implants

Fig. 4. Three-dimensional microCT overview of the bone-to-implant contact area (red) around the implant surface (gray).A, Implant placed without a flap. B, Implant placed with a

after surgery. Our data, therefore, support the concept

OOOOE28 Jeong et al. July 2007

that flapless implant surgery may be more effectivethan surgery with flap reflection in improving implantanchorage.

REFERENCES1. Ramfjord SP, Costich ER. Healing after exposure of periosteum

on the alveolar process. J Periodontol 1968;38:199-207.2. Wood DL, Hoag PM, Donnenfeld OW, Rosenfeld LD. Alveolar

crest reduction following full and partial thickness flaps. J Peri-odontol 1972;42:141-4.

3. Campelo LD, Camara JR. Flapless implant surgery: A 10-yearclinical retrospective analysis. Int J Oral Maxillofac Implants2002;17:271-6.

4. Becker W, Goldstein M, Becker BE, Sennerby L. Minimallyinvasive flapless implant surgery: a prospective multicenterstudy. Clin Implant Dent Relat Res 2005;7(Suppl 1):S21-7.

5. Akagawa Y, Wadamoto M, Sato Y, Tsuru H. The three-dimen-tional bone interface of an osseointegrated implant: a method forstudy. J Prosthet Dent 1992;68:813-6.

6. Kuroda S, Virdi AS, Li P, Healy KE, Summer DR. A low-temperature biomimetic calcium phosphate surface enhancesearly implant fixation in a rat model. J Biomed Mater Res2004;70:66-73.

7. Pennel BM, King KO, Wilderman MN, Barron JM. Repair of thealveolar process following osseous surgery. J Periodontol1967;38:426-31.

8. Wilderman MN, Pennel BM, King K, Barron JM. Histogenesisof repair following osseous surgery. J Periodontol 1970;41:551-65.

9. Wilderman MN, Wentz FM. Repair of a dentogingival defectwith a pedicle flap. J Periodontol 1965;36:218-31.

10. Branemark PI, Hansson BO, Adell R. Osseointegrated implants

in the treatment of the edentulous jaw. Experience from a 10-yearperiod. Scand Plast Reconstr Surg 1977;16(Suppl):1-132.

11. Albrektsson T, Branemark PI, Hansson HA, Lindstrom J. Os-seointegrated titanium implants. Requirements for ensuring along-lasting direct bone anchorage in man. Acta Orthop Scand1981;52:155-70.

12. Casap N, Tarazi E, Wexler A, Sonnenfeld U, Lustmann J. Intra-operative computerized navigation for flapless implant surgeryand immediate loading in the edentulous mandible. Int J OralMaxillofac Implants 2005;20:92-8.

13. Feldkamp LA, Goldstein SA, Parfitt AM, Jesion G, KleerekoperM. The direct examination of three-dimensional bone architec-ture in vitro by computed tomography. J Bone Miner Res1989;4:3-11.

14. Ruegsegger P, Koller B, Muller R. A microtomographic systemfor the nondestructive evaluation of bone architecture. CalcifTissue Int 1996;58:24-9.

15. Muller R, Van Campenhout H, Van Damme B. Morphometricanalysis of human bone biopsies: a quantitative structural com-parison of histological sections and microcomputed tomography.Bone 1998;23:59-66.

16. Rebaudi A, Koller B, Laib A, Trisi P. MicroCT scan: microcom-puted tomographic analysis of the peri-implant bone. Int J Peri-odont Restor Dent 2004;24:316-25.

17. Sennerby L, Wennerberg A, Pasop F. A new microtomographictechnique for noninvasive evaluation of the bone structurearound implants. Clin Oral Implants Res 2001;12:91-4.

Reprint requests:

Prof. Byung-Ho ChoiDept. of Oral and Maxillofacial SurgeryCollege of Dentistry, Yonsei UniversitySeoul, South Korea

hoibh@yonsei.ac.kr