5 Professor and Chair, Department of Periodontics, Dental

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1 Biologic Width Around Different Implant-Abutment Interface Configurations. A Radiographic Evaluation of the Effect of Horizontal Offset and Concave Abutment Profile in the Canine Mandible Santiago J. Caram, DDS, MS 1 /Guy Huynh-Ba, DDS, MS 2 /John D. Schoolfield, MS 3 / Archie A. Jones, DDS 4 /David L. Cochran, DDS, MS, PhD, MMsci 5 /Urs C. Belser, DMD, Dr Med Dent 6 Purpose: The purpose of this experimental study was to analyze radiographically in a dog model how different implant-abutment interface configurations influence alveolar crestal bone changes. Materials and Methods: Six different experimental implant-abutment connections were evaluated in six mixed-breed dogs. The following parameters were tested: absence of microgap, microgap proximal to bone crest, and microgap distant from bone crest. In addition, two different cervical abutment profiles, one straight and one featuring a supracrestal concavity, were evaluated. Implants were based on a cylindrical full-body screw design and made from coldworked grade IV commercially pure titanium. The diameter (at thread tips) measured 4.1 mm, whereas the inner diameter was 3.5 mm. Standardized periapical digital radiographs were obtained for comparative analysis at baseline and at 3, 4, 5, 6, 7, 8, and 9 months after implant placement. Radiographs were randomized and calibrated for linear measurements. For statistical analysis, mixed-model repeated-measures analysis of variance was used. Results: All implants integrated successfully and remained stable during the entire period of the study. Radiographically, when comparing groups with straight profiles, crestal bone remodeling in group C (one-piece design) was significantly less than in group A (matching diameters) and B (nonmatching diameters). In fact, implant group C showed the least crestal bone remodeling of all groups. When comparing groups with a concave profile but different microgap configurations, all three designs demonstrated bone loss with no significant differences among the three groups. Conclusion: A nonsubmerged one-piece implant design demonstrated the least amount of bone remodeling of all groups. Implant-abutment connections with a concave profile established crestal bone levels immediately apical to the concavity regardless of the microgap variable. Int J Oral Maxillofac Implants 2014;29: doi: /jomi.3068 Key words: alveolar bone loss/etiology, dental implants, horizontal offset, platform switching, supracrestal concavity In 1981, André Schroeder advocated a one-piece implant design, which did not involve a microgap and allowed soft tissues to heal right after surgery in contact with the transmucosal aspect of the implant. 1 This trend showed an early attempt to resolve some of the technical and biologic shortcomings of the implant approach. Since then, high success rates have been reported; however, current implant protocols are forced to achieve not only osseointegration but also high levels of soft tissue stability and esthetics. 2 7 Great effort has been made to understand the physiologic wound healing process implicated with implant 1 Postgraduate Assistant Professor, Department of Prosthodontics, Dental School, National University of Cuyo, Mendoza, Argentina. 2 Assistant Professor, Department of Periodontics, Dental School, University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA. 3 Biostatistician, Department of Periodontics, University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA. 4 Professor, Department of Periodontics, Dental School, University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA. 5 Professor and Chair, Department of Periodontics, Dental School, University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA. 6 Professor Emeritus, Department of Fixed Prosthodontics & Occlusion, School of Dental Medicine, University of Geneva, Switzerland. Correspondence to: Dr Santiago Caram, Department of Periodontics, Dental School, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA. Fax: santicaram@hotmail.com 2014 by Quintessence Publishing Co Inc Volume 29, Number 5, 2014

2 treatment. Crestal bone changes and their impact on soft tissue architecture are the most unpredictable and undesirable consequences of implant therapy, especially in the anterior maxilla. Hypotheses about the etiology of crestal bone remodeling around dental implants can be categorized into three main proposals. The first hypothesis states that it is a mechanical factor that will disturb the surrounding tissues when occlusal forces are transmitted through the prosthetic component to the implant. This will create compression and tension forces at the crestal bone, causing a peri-implant tissue response The second hypothesis advocates that it is a peri-implant inflammatory cell infiltrate caused by bacteria located at the implant/abutment microgap that will trigger the crestal bone changes. According to several authors, the microgap formed between abutment and implant promotes microbial contamination, which leads to an inflammatory reaction at the soft tissue level and eventually will cause bone remodeling Ericsson et al showed in their study a consistent inflammatory cell infiltrate area facing the fixture-abutment junction that they called abutment ICT. This abutment ICT was approximately 1.5 mm high and 0.5 mm wide, and its apical border was located approximately 1 mm from the alveolar bone crest. The authors suggested that this 1 mm could be a protective mechanism used by the host to prevent further deterioration of the implant osseointegration. 16 Others showed that it was the inflammatory infiltrate (inflammatory front) movement toward the alveolar bone that caused a net loss of tissue. Results indicated that proinflammatory mediators such as interleukin 1 (IL-1) and tumor necrosis factor (TNF) have the capacity to activate pathways leading to tissue destruction and bone resorption. Thus, it was not only the bacterial leakage through the epithelium and their byproducts that caused direct damage over the tissues, but also the host cell defense response Garant demonstrated the destructive consequence of the immune system inflammation when adjacent to periosteum and bone. 17 A dense neutrophil infiltration was induced proximal to the palate bone in a rat model, which in 24 hours developed rapid bone damage. Bone was characterized by periosteal disruption and osteoblast and osteocyte necrosis. This is in agreement with data collected from histologic sections of autopsy cases in which an inflammatory reaction induced by the subgingival plaque led to attachment loss and bone remodeling. 20 The inflammatory concept supports the rationale of a one-piece implant design in which the microgap is located far enough from the crestal bone to prevent an inflammatory cell infiltrate near it. By relocating the microgap, a machined surface is created to allow soft tissue attachment. 21 The third hypothesis on crestal bone remodeling states that it is an adaptive response of the biologic width to the local condition and is not related to stress factors or inflammatory factors. Berglundh et al reported that a minimum thickness of mucosa is required; otherwise, crestal bone remodeling will take place. 22 Even though soft tissue on an implant resembles closely soft tissue on the natural dentition, a protective mechanism may be less efficient and less dimensionally stable. The mucosal attachment to a titanium implant is composed of an epithelial component and a connective tissue component. The function of both is to protect the underlying osseous tissue from irritants coming from the oral cavity. Gould et al reported an epithelial attachment mechanism via hemidesmosomes and basal lamina. 23,24 Hansson et al analyzed the interface zone between the implant and epithelium with the aid of scanning electron micrographs in an animal model. They confirmed the presence of hemidesmosomes connecting the epithelium cell to titanium as well as an absence of an inflammatory reaction. 25 This is in agreement with other studies as well. 1,26,27 It can be concluded that the epithelium-implant interface has many features in common with the epitheliumtooth interface. On the contrary, connective tissue composition and cell arrangement differs when it is in contact with tooth structure (cementum) or implant structure (titanium). Due to the lack of cementum and connective tissue fibers attached to the implant surface, connective tissue lies closely adapted to the titanium surface, consistently separated by a 20 nm wide proteoglican layer. 25 Listgarten et al observed a more or less parallel orientation of collagen fibers to the implant surface, and there was no evidence of any fiber insertions into the surface irregularities of the smooth or rough titanium. 28 Berglundh et al reported the same parallel fiber configuration of the connective tissue when facing an implant abutment surface. 29 The same group reported differences in the volume of cellular components in connective tissue when comparing teeth and implants. Peri-implant connective tissue contains more collagen fibers and fewer fibroblasts than connective tissue related to teeth. The importance of this difference is not fully understood, but it may compromise the sealing ability of the connective tissue as well as the epithelial attachment leading to peri-implant bone remodeling. The aim of the proposed research project was to evaluate radiographically the peri-implant tissue response around different implant-abutment interface configurations when compared side by side. Implantabutment designs proposed in this study created two different soft tissue adaptation variables and three different microgap interface variables. The International Journal of Oral & Maxillofacial Implants 1115

3 Group A Group B Group C Group D Group E Group F A B C D E F Straight matching Straight nonmatching Straight one-piece Concave matching Concave nonmatching Concave one-piece Fig 1 Straight designs: group A, straight/matching; group B, straight/nonmatching; and group C, straight/one-piece. Concave designs: group D, concave/matching; group E, concave/ nonmatching; and group F, concave/one-piece. Fig 2 Scanning electron microscopy images of implant prototype designs (groups A to F). MATERIALS AND METHODS Overview of Transmucosal Abutment Designs Six different experimental implant groups were evaluated in this study (groups A to F; Figs 1 and 2). The transmucosal component (abutment) of all groups measured 4.5 mm high and had different designs for crestal bone assessment after healing. The first abutment design, group A or straight/ matching design (S/M), had straight parallel sides aligned with the external edge of the implant body. The second abutment design, group B or straight/ nonmatching design (S/nM), had straight parallel sides with a smaller diameter than the implant body. The diameter discrepancy between implant and abutment created a horizontal offset microgap of approximately 0.5 mm. In group C or straight/one-piece design (S/ OP), the transmucosal portion of the implant had straight parallel sides aligned with the external outline of the endosseous portion and no interface (microgap) between the implant and abutment. Abutments in groups D and E differed from previous groups by having a supracrestal concavity in the most apical portion. This concavity was 1.5 mm wide and 0.5 mm deep. In group F, the transmucosal portion of the implant had a supracrestal concavity with the same dimensions and location as the previous groups, but again with no interface (microgap) between the implant and abutment. In group D or concave/matching (C/M) design, abutments matched the diameter of the implant body, creating an aligned connection with the external edge of the implant. In addition, an inward concavity was milled in the abutment proximal to the microgap. This concavity duplicated the dimension and configuration of the inward area obtained from connecting an abutment and implant in group E (C/nM). The apical part of the inward area in group D was approximately 0.20 mm from microgap (see Figs 1 and 2). In group E or concave/nonmatching (C/nM) design, the abutment matched the diameter of the implant body at the coronal part. However, at the apical connection part, the diameter was reduced, creating an inward bevel. This not only created an inward area but also a horizontal offset microgap mimicking the currently marketed bone-level implant (Straumann). A concavity was formed coronally by the abutment and apically by the top part of the implant platform. In group F or concave/one-piece design (C/OP), the transmucosal portion had an inward concavity that was milled in the same fashion as the ones created in group D. Overview of Implant Designs and Surfaces Implants were based on a cylindrical full-body screw design and made from cold-worked grade IV commercially pure titanium (Straumann). The diameter (at thread tips) measured 4.1 mm, whereas the inner diameter was 3.5 mm. Two different implant designs were used for this study: one-piece and two-piece. Both were tested in a nonsubmerged surgical protocol. For the two-piece implant design, group A (S/M) and group D (C/M), a modified Bone Level Implant body (Straumann) with a horizontal or slightly slanted platform was fabricated. This implant design allowed the production of abutments with a more solid margin, ensuring a clinically acceptable connection interface. In group B (S/nM) and group E (C/nM), an endosseous Bone Level Implant body (Straumann) was used. Bone-level and bone level modified implants measured 8 mm in length, and their surface had a modified sand-blasted/acid-etched titanium surface (SLActive, Straumann). The platform of the implants was defined to be clinically positioned 1 mm below 1116 Volume 29, Number 5, 2014

4 a b c Fig 3 (a) Alveolar ridge; (b) implant bed orientation; (c) implant with abutment placement. the crestal bone level for all two-piece implant groups. On the other hand, one-piece implants (groups C and F) (Straumann) were specially fabricated for this study. The endosseous portion duplicated the dimensions and thread design of the two-piece implant group and had an SLActive surface as well. The supraosseous portion (transmucosal portion) consisted of a machined surface. The rough-smooth border was defined to be clinically positioned 1 mm below the crestal bone level. Overview of the Experimental Design Prior to beginning this animal study, the protocol was approved by the Institutional Animal Care and Use Committee at The University of Texas Health Science Center San Antonio. For this study, six male, mixedbreed canines were used in which mandibular right and left first, second, third, and fourth premolars (P1, P2, P3, P4) and mandibular left and right first molars (M1) were extracted (month 3). At month 0, implant placement was performed, and baseline standardized radiographs were taken. After 3 months of healing, standardized radiographs were taken, and preformed titanium crowns were screwretained to the top part of the abutments at 32 Ncm. Radiographs were taken every month for a period of 6 months. Dogs were fed a soft diet, and implants were cleaned once a week with chemical and mechanical plaque control. Extractions Extractions were performed in an operating room under general anesthesia and sterile conditions. For tooth removal, the surgical site was disinfected with 10% povidone-iodine solution. 2% lidocaine HCl with epinephrine 1:100,000 was administered as a local anesthetic. A full-thickness mucoperiosteal flap was elevated. Premolars (P2 P4) and molars (M1) were sectioned to help prevent tooth fracture and disruptive forces over the alveolar process. Teeth were extracted as atraumatically as possible. Interrupted sutures were used to allow approximation of the wound margins and to permit healing. Sutures were removed after a period of 10 to 14 days. Similar protocols had been used by investigators in the same dog model. 30 Implant Placement At month 0, one implant from each group was placed in each side of the mandibular premolar and molar area under the same surgical conditions as when tooth extraction had been performed. Before surgical intervention, polyvinyl siloxane impressions were made for the fabrication of a radiographic stent and parallel beam guiding device. Crestal incisions were performed to maximize keratinized tissue on each side of the incision. Mucoperiosteal flaps were reflected on both the lingual and buccal side. The crestal osseous ridge was flattened with a large bur under copious irrigation with chilled sterile physiologic saline solution. Edentulous spaces were measured with a caliper to help distribute an even distance between implants (Fig 3). Implant site preparations were planned in the center of the alveolar ridge with a torque-reduction rotary instrument at 500 rpm using chilled saline. A strict bur-sequence protocol was followed according to the implant system recommendations. Parallel pins/depth gauges were used at all times to help assess correct implant bed orientation (see Fig 3). Each group was randomly allocated to the six implant beds prepared for implant insertion. This assured no bias from the operator. One-piece implants were inserted until roughsmooth border levels were 1 mm below the crestal bone of the alveolar ridge. All two-piece implants were inserted until platform levels were 1 mm below the crestal bone of the alveolar ridge. Abutments were previously mounted, screwed in place, and tightened to 35 Ncm by the manufacturer. Wound closure was The International Journal of Oral & Maxillofacial Implants 1117

5 performed using horizontal mattress and interrupted sutures. All groups followed a nonsubmerged protocol. To minimize loading and irritation on the implant area, dogs were fed a soft diet for 2 weeks. Mechanical and chemical plaque control was carried out three times per week with a soft sponge in combination with a 0.2% chlorhexidine gel. Sutures were removed after 10 to 14 days. Radiographic Procedure One week after implant placement, postoperative standardized digital periapical radiographs were obtained to serve as baseline for further comparative radiographic analysis (month 0). After 3 months of unloaded implant healing, dogs were anesthetized, and a second series of digital periapical radiographs were obtained for further comparative analysis and assessment of complete seating of titanium crowns. Follow-up radiographs were obtained every month for 6 months. Prosthetic Phase After month 3, control radiographs were taken, and at the same clinical intervention, prefabricated singleunit screw-retained titanium crowns were inserted onto all implant groups. All dogs were included in the loading protocol. Abutments (A, B, D, and E) and the top part of the one-piece implants in groups C and F had an external octagon for prosthetic connection that allowed for a screw-retained crown insertion. Prefabricated milled crowns were specifically designed and produced for this study (Straumann). The dimensions of the crowns were such that they would not need adjustments and they would closely approximate the opposing maxillary dentition. Crowns were positioned and aligned for screw tightening at 35 Ncm. Restorations provided partial or relative loading to all implant groups: axial loading by mastication of food and nonaxial loading by tongue and cheek. Radiographic Measurement Acquisition Digital radiographs were randomized, and a number was assigned to each to ensure the examiner was blind. Image J Software (National Institutes of Health [NIH]) was used to perform measurements. Every radiograph was calibrated using the known distance between the most apical two threads (pitch = 0.8 mm). 31 Measurements were made from the reference point of each group to the first bone-to-implant contact (fbic). The reference point for implant designs A (S/M) and B (S/nM) was the implant/abutment microgap. For implant design C (S/OP) the reference point was the smooth/rough border of the implant. In the concave group (D, E, and F), the reference point was the most inward point of the concavity. Statistical Analysis Alveolar bone levels were compared at each radiographic time interval using a mixed-model repeated measures analysis of variance (ANOVA) to obtain estimated means for each implant type and time, with each set of mean comparisons for a radiographic time based on the estimated pooled variance for the time. Bonferroni-adjusted Student t tests were used to identify significant implant-type mean differences for crestal bone levels at each radiographic time. RESULTS Seventy-two implants were placed, and all implants healed uneventfully. At baseline, successful integration was confirmed, as assessed by standard clinical and radiographic examination. No complication during the loading phase was observed. All screw-retained crowns were delivered and provided functional loading for the entire period of the study. No crowns were loosened, lost, or required replacement. All implants remained stable during the loading period. Radiographic Analysis The 72 implants placed in this study were evaluated at placement day, crown insertion day, and 4, 5, 6, 7, 8, and 9 months postinsertion. The distance from the first bone-to-implant contact (fbic) to the implant reference point was measured on both the mesial and distal of the implants. Forty-eight of 1,152 measurements could not be acquired because four radiographs (with the six implant groups in each) were excluded as unreadable. Radiographic analysis was performed using the mean of the paired mesial and distal measures. At implant placement, the bone crest was 0.5 to 1.0 mm coronal to the implant reference point, confirming implant position at baseline. These results were recorded with a positive value. When the fbic was apical to the implant reference point, the distance measured was recorded with a negative value and was observed at all other time points. No significant mean differences were observed at the implant placement time point. First, the implant-abutment interface variable (matching, nonmatching, or one-piece) was analyzed. Within the straight abutment profile group, the periimplant crestal bone level in implant group C (S/OP) showed statistically significantly less bone remodeling than implants in group A (S/M) and group B (S/ nm) at months 3 and 4 postinsertion and at month 6 with group B. The estimated mean radiographic distances from the implant reference point to fbic at 6 months postinsertion based on mixed-model ANOVA were mm for group C, 0.15 mm for group A, and 0.28 mm for group B, while the estimated pooled 1118 Volume 29, Number 5, 2014

6 Table 1 Mean Bone Changes from Placement to 6 Months Postloading Time/ Implant type Mean change (mm) 95% CI SD Lower bound Upper bound F value P Type differences Placement A NS B C D E F Crown delivery A C > E (P =.003) B C > F (P =.002) C D E F Month 1 A C > D (P =.008) B C > E (P =.023) C C > F (P =.014) D E F Month 2 A C > F (P =.032) B C D E F Month 3 A C > A (P =.014) B C > B (P =.034) C C > D (P =.002) D C > E (P =.036) E C > F (P =.001) F Month 4 A <.001 C > A (P <.001) B C > B (P =.001) C C > D (P <.001) D C > E (P <.001) E C > F (P <.001) F Month 5 A NS B C D E F Month 6 A C > B (P =.003) B C > D (P =.001) C C > E (P =.014) D C > F (P =.008) E F CI = confidence interval; NS = not statistically different; SD = standard deviation. The International Journal of Oral & Maxillofacial Implants 1119

7 Matching Nonmatching One-piece Distance (mm) C B A 0.5 Placement Crown Months post crown delivery Fig 4 Average of mesial and distal BIC distances above implant reference points: implants with straight abutment profile. Matching Nonmatching One-piece Distance (mm) D E F 0.5 Placement Crown Months post crown delivery Fig 5 Average of mesial and distal BIC distances above implant reference points: implants with concave abutment profile. A D No significant differences B E No significant differences C Significant differences (P =.008) F Fig 6 Comparison of crestal bone remodeling according to the implant-abutment profile (straight vs concave). variance resulted in a standard deviation of 0.28 mm being apportioned to each implant type for the purposes of 6-month mean comparisons (Table 1 and Fig 4). On the contrary, the same implant-abutment interface variables with a concave abutment design did not show significant differences among them (D = E = F). The estimated mean radiographic distances from the implant reference point to fbic were 0.39 mm for group D, 0.23 mm for group E, and 0.24 mm for group F (Table 1 and Fig 5). Second, the evaluation of the implant-abutment profile variables (straight vs concave) was performed. Matching implant-abutment connections (A and D) did not show a significant difference between them. A similar finding was observed when comparing nonmatching implant-abutment connections (B and E). However, the straight one-piece implant design (C) showed statistically less crestal bone remodeling than the concave (F) design (P =.008) (Table 1 and Fig 6) Volume 29, Number 5, 2014

8 DISCUSSION In implant dentistry, there were two well-investigated implant-abutment connection designs, a two-piece implant design with peripheral microgap (butt-joint) and straight profile and a one-piece implant design without microgap and a straight profile. However, a new implant-abutment connection was introduced in the market in 2006, promoting less crestal bone remodeling and a more stable peri-implant soft tissue. This design was called platform switching, and it was defined as a smaller-diameter prosthetic abutment that engages a larger-diameter implant platform, creating a mismatch between the two components and establishing a microgap distant to the periphery of the implant. 32 Nonetheless, a new implant-abutment connection variable, a concave profile, was also created with an unknown possible beneficial effect on the periimplant tissues. In this study, prototype test implants were fabricated to combine all current microgap and abutment profile variables. Group A (S/M), group C (S/ OP), and group E (C/nM) can be related to commercially available implant systems that have been tested in the literature. The radiographic results on matching implant-abutment connection design (A and D) showed less crestal bone remodeling after 6 months postloading than what has been reported in other studies. 30,33 The authors assumed that premounted and torqued abutments on implants, both delivered in a sterile ampoule from the manufacturer, created an ideal condition resulting in minimum crestal bone remodeling. Furthermore, the abutment extended into the implant with a Morse taper type connection, which is different from the historic two-piece implants with a butt-point in which the abutment sits on top of the implant and is secured with an internal screw. Also, it was decided that there would be no disconnection of abutments during the entire period of the study to avoid contamination of the implant screw access or damage to the soft tissue, which would affect the twopiece implant design groups. 33 Knowing that minimum crestal bone remodeling would result from this decision, implants were positioned 1 mm subcrestal to force a more challenging situation to all groups equally. Subcrestal bone-implant positioning has been reported in previous studies. 30,34,35 In the straight profile groups, as expected and in accordance with other studies, the one-piece implant design showed minimal amounts of bone remodeling. 30,31,36 Furthermore, the one-piece design (group C, S/OP) demonstrated less bone remodeling than did groups A (S/M) and B (S/nM) at all time points examined. At some time points, however, this difference did not reach a significant level, likely because the abutments were not loosened and retightened. 30,33 Bone remodeling around the concave groups (D, E, and F) showed that crestal bone levels stabilized and were coincident with the apical portion of the concavity, regardless of the presence of the microgap or whether it was proximal or distant to the crestal bone. The hypotheses of crestal bone remodeling associated with a one-piece implant design that lacks a microgap and inflammation seem to be in accordance with the results of the present study. 16,22 On the contrary, when a concavity is present, crestal bone remodeling occurred and stabilized apical to the concavity regardless of the microgap. 34,35 This finding is supported by the hypothesis of an adaptive response of the biologic width to the local condition; however, it should be noted that bone loss occurred in all implants with the concave design. The biologic width reference in this case may not refer to the traditional sense of linear soft tissue dimensions. Rather, the biologic width dimension may in this case be related to the quantity or amount of soft tissue (most likely the connective tissue) that surrounds the implant. In other words, the concavity might improve the protective mechanism of the peri-implant soft tissue by allowing more connective tissue to surround the transmucosal component of the implant. Nonetheless, results on this experimental animal study should be validated with a higher level of scientific evidence. CONCLUSION A combination of all possible implant-abutment variables was clinically and radiographically tested. All implants integrated, and there were no biologic or technical complications. Similar to previous studies, the one-piece nonsubmerged implant design with a straight profile demonstrated the least crestal bone remodeling. The concave implant-abutment profile groups did not show statistical differences among them; however, crestal bone loss occurred around all implants with a concave design with the bone level systematically stabilized apical to the concavity. ACKNOWLEDGMENTS The authors greatly acknowledge Sonja Bustamante, HT (ASCP), histotechnologist at the University of Texas Health Science Center at San Antonio (UTHSCSA), for her valuable support throughout the study. The authors also would like to thank the members of the Laboratory Animal Resources, UTHSCSA, for exemplary care of the animals. In addition, the authors would like to express their gratitude to Marcel Obrecht and Michel Dard, Institut Straumann, Basel, Switzerland, for manufacturing the prototype implants. This investigation was supported by a grant from the ITI Foundation for the Promotion of Oral Implantology (ITI Grant no ). This paper was presented on April 16, 2010, The International Journal of Oral & Maxillofacial Implants 1121

9 during the ITI World Symposium research competition held in Geneva, Switzerland. The authors reported no conflicts of interest related to this study. REFERENCES 1. Schroeder A, van der Zypen E, Stich H, Sutter F. The reactions of bone, connective tissue, and epithelium to endosteal implants with titanium-sprayed surfaces. J Maxillofac Surg 1981;9: Buser D, Mericske-Stern R, Bernard JP, et al. Long-term evaluation of non-submerged ITI implants. Part 1: 8-year life table analysis of a prospective multi-center study with 2359 implants. Clin Oral Implants Res 1997;8: Buser D, Weber HP, Bragger U, Balsiger C. Tissue integration of one-stage ITI implants: 3-year results of a longitudinal study with Hollow-Cylinder and Hollow-Screw implants. Int J Oral Maxillofac Implants 1991;6: Buser D, Weber HP, Lang NP. Tissue integration of non-submerged implants. 1-year results of a prospective study with 100 ITI hollow-cylinder and hollow-screw implants. 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