The International Journal of Oral & Maxillofacial Implants, 06/2005

Purpose: This study was designed to evaluate the healing process in horizontal alveolar ridge distraction of the narrow alveolus in dogs. Materials and Methods: Six beagle dogs weighing approximately 9 to 10 kg were used in this experiment. Horizontal alveolar ridge distraction was performed in the right mandible, where the premolars had been extracted 12 weeks previously. Twelve days after the completion of distraction, the lengthening apparatus was removed. The distracted site was evaluated at 12 and 24 weeks after the removal. Results: At 12 weeks, thin woven bone was observed at the distracted site growing from the surface of the original lingual cortical bone toward the transport segment. At 24 weeks, the distracted site had fully changed into new mature lamellar bone, but the transport segments had been almost completely resorbed. Discussion: Horizontal alveolar ridge distraction was performed successfully in beagle dogs even though the apparatus was removed 12 days after the completion of distraction. The most important feature of this technique is the resorption of the transport segment. Conclusion: Horizontal alveolar ridge distraction can be a beneficial technique for augmenting the alveolar ridge horizontally in the buccolingually reduced alveolar process before the placement of implants. Keywords: alveolar ridge augmentation, alveolar ridge distraction, distraction osteogenesis

Purpose: The objective of the present study was to histologically evaluate barrier durability and host tissue response of new prototype collagen membranes in comparison to clinically available collagen and synthetic polymer membranes. Materials and Methods: The experimental study was conducted in 20 rabbits with 4 different healing periods of 2, 6, 12, and 28 weeks. Following surgical exposure of the calvarium, 6 circular bone defects (diameter 4 mm, depth 1.5 mm) were drilled into the outer cortex. After the bone had been removed, each defect was covered with 1 of 6 different membranes: 3 collagen prototype membranes, a Bio-Gide collagen membrane (BG), a glycolide-lactide-trimethylene carbonate Osseoquest membrane (OQ), and a polylactide Atrisorb membrane (AS). Histological analysis was performed following staining with toluidine blue and transversal sectioning of the calvarial bone. Results: All collagen membranes showed similar tissue integration characterized by fibrous encapsulation with differentiation of a periosteumlike tissue upon the external bony surface. One prototype collagen membrane displayed clearly longer membrane integrity. The evaluated synthetic membranes demonstrated extended barrier durability but also exhibited inflammatory foreign-body reactions. Discussion: Recent experimental investigations have shown that degradation of collagen membranes may begin within days to weeks of membrane placement. This was confirmed in the present study. However, 1 of the chemically modified collagen prototype membranes exhibited prolonged membrane integrity in the absence of an inflammatory tissue response. Conclusion: Further investigation of the prototype membrane that showed prolonged membrane integrity to evaluate its potential in GBR procedures is needed. Keywords: aliphatic polymers, bioresorbable barrier membranes, collagen, membrane degradation, tissue reactions

Purpose: The goal of this study was to determine the relationship between fracture surface morphology and applied stress level for dental abutment screws loaded in cyclic fatigue. If a correlation between fracture surface and load level can be determined, then the fracture surface analysis could be used as a tool to assess the mechanism by which a screw failed and the magnitude of the load at which it failed. Materials and Methods: Test implants were loaded with static and cyclic forces. In the cyclic test, the load versus the number of cycles was plotted as a curve for biomechanical analysis. The fracture surfaces of the failed screws were observed and recorded using scanning electron microscopy (SEM). Results: Two fracture phases, a smooth region and a rough region, were observed on the fracture surface. After identifying the boundary between the 2 regions, the smooth region ratio (SRR), the ratio of the smooth phase area to the area of the whole fracture surface, was measured using digitized SEM images. The mean SRRs were 0.60 ± 0.03, 0.66 ± 0.03, and 0.75 ± 0.03 when the tested implants were subjected to dynamic loading of 60%, 55%, and 50% ultimate failure loading (UFL), respectively. Linear relationships were found between the SRR values and loading magnitude and between SSR and number of cycles. Discussion: The smooth area on the fracture surface can be used to assess the load conditions and internal stress of fatigue-fractured implants. Conclusions: These results demonstrate that fracture surface analysis of fractured implants has the potential to become a useful indicator for assessing implant fracture mechanisms. Keywords: dental implants, fatigue, finite element analysis, implant fractures, scanning electron micrography

Purpose: Donor morbidity is minimized when tissue engineering is applied to produce osteogenic grafts by growing osteoblasts on biomaterials. However, limiting factors are the origin, proliferation, and differentiation of osteoblasts. Therefore, the aim of this study was to evaluate the efficacy of growing osteoblasts from different types of bone samples and to assess the influence of the donor site. Materials and Methods: From 28 patients 37 bone specimens were obtained during removal of third molars in the maxilla and mandible. Seventeen specimens were bone chips and 20 were bone sludge. After subculturing primary cultures, histochemical and immunhistochemical tests (EZ4U test, BrdU labeling, ALP histochemistry, type I collagen immunohistochemistry, osteocalcin ELISA) were performed to determine cell proliferation, viability, and differentiation. Results: Both bone chips and bone sludge from the mandible and maxilla are suitable for culturing human osteoblastlike cells. However, bone chips were superior to bone sludge with respect to ability to grow cells, and maxillary bone was superior to mandibular bone in this regard. Harvesting technique had only little influence on the expression of cell differentiation markers (ALP, type I collagen, osteocalcin). Discussion and Conclusion: Chips from human membrane bone, especially from the maxilla, are suitable for culturing high numbers of differentiated osteoblastlike cells. These cells may be used to tissue engineer bone grafts, which may be used to enhance the implant placement site. Keywords: alveolar ridge augmentation, cell culture, cell proliferation and differentiation, implant placement, tissue engineering

Purpose: The aim of this study was to describe the revascularization process of autogenous bone block grafts placed with or without an expanded polytetrafluoroethylene (e-PTFE) membrane. Materials and Methods: Thirty Wistar male rats had their mandibles augmented by either an autogenous bone block graft (group A) or an autogenous bone block graft covered with an e-PTFE membrane (group B). The animals were sacrificed by perfusion at baseline, 3, 7, 14, and 21 days after surgery. Results: After 3 days, the presence of vascular sprouts derived from the recipient bed was observed in group A; more discrete sprouts were also observed in group B. After 7 days, revascularization continued, with vessels derived from both the recipient bed and the surrounding connective tissue in group A but only from the recipient bed in group B. At 14 days, group A showed penetration of vessels at the periphery of the graft; the vessels reached varying distances inside it. In group B, revascularization of the graft occurred mainly near its perforation, its borders, and at the recipient bed-graft interface. After 21 days, graft vascular penetration could be observed throughout the extent of the graft in group A but only approximately halfway through the graft in group B. Discussion: The results emphasized the importance of the vascular network and of the revascularization process of the autogenous bone graft in new bone formation. Early vascular penetration and nutrition of the graft are key factors in its integration with the recipient bed. Conclusions: Revascularization of the bone graft occurred in both A and B. However, vascular sprouts originated only from the recipient bed in group A, while in group B the graft was penetrated by vessels from both the recipient bed and the surrounding connective tissue. The revascularization took place more promptly and was more intense and extensive in group A than in group B for all periods. Keywords: animal models, autogenous bone grafting, bone augmentation, e-PTFE membrane, guided tissue regeneration, revascularization

Purpose: Microbial leakage and colonization between implants and their abutments may cause inflammatory reactions in the peri-implant tissues. This study evaluated microbial leakage at the implant-abutment interface with a new in vitro model. Materials and Methods: Bacterial leakage was tested during dynamic loading in a 2-axis chewing simulator. The authors theorized that dynamic loading would decrease the stability of the implant-abutment connections and thereby lead to bacterial penetration along the gap. Five different implant systems with 8 standard implant-abutment combinations for single molar crowns were tested. The internal aspects of the implants were inoculated with a bacterial suspension and connected to the superstructure with the recommended torque. The specimens were immersed in a nutrient solution and loaded with 1,200,000 cycles of 120 N in the chewing simulator. Results: Statistically significant differences (P = .05) between implant systems with respect to number of chewing cycles until bacterial penetration were found. Discussion: The degree of penetration in a specific implant system presumably is a multifactorial condition dependent on the precision of fit between the implant and the abutment, the degree of micromovement between the components, and the torque forces used to connect them. Conclusion: It was concluded that the newly developed test model is a sensitive tool for the detection of differences between current implant systems with respect to their ability to prevent bacterial penetration at the implant-abutment interface under dynamic loading conditions. Keywords: abutments, bacterial leakage, chewing simulation, dental implants

Purpose: Computer-aided technologies have been recently employed for use in extracorporeal bone tissue engineering strategies. In this pilot animal experimental study, the intention was to test whether autologous osteoblast-like cells cultured in vitro on individualized scaffolds can be used to support bone regeneration in a clinical environment. Materials and Methods: For this purpose, mandibular bone defects were surgically introduced into the mandibles of minipigs and the scaffold of the defect site was modeled by computer-aided design/computer-aided manufacturing technique. Autologous bone cells from porcine calvaria were harvested from minipigs and grown in culture. Cells were seeded on scaffolds generated by rapid prototyping of polylactic acid/polyglycolic acid copolymers. The defects were then reconstructed by implanting the tissue constructs. Results: The intraoperative sites as well as the postoperative computerized tomographic scans demonstrated an accurate fit in the defect sites. The implanted scaffold constructs enriched with osteoblast-like cells were well tolerated and appeared to support bone formation, as revealed by histologic and immunohistochemical analyses. Discussion: These results indicated that in vitro expanded osteoblast-like cells spread on a resorbable individualized scaffold can be capable of promoting the repair of bony defects in vivo. Conclusion: These results warrant further attempts to combine computer modeling and tissue engineering for use in bone reconstructive surgery. Keywords: animal model, bioengineering, bone, osteoblasts

Purpose: Sinus floor augmentation has become a routine procedure with predictable results. Flapless implant placement is recommended for a series of indications with sufficient bone volume. Flapless surgery in the atrophic maxilla is presented as a refinement of the endoscopic subantroscopic latero-basal sinus floor augmentation (SALSA) technique. Materials and Methods: Based on computerized tomography (CT) scans, the site of sinus trephination and implant positions are planned using a commercially available planning program, and surgical templates are fabricated according to the data of the treatment plan. Subantral space is augmented using the SALSA technique without raising a mucoperiosteal flap. Implants are placed transgingivally without raising a mucoperiosteal flap, with endoscopic control of the cover screw at the bone level. Results: In a case series of 6 patients, 21 implants were placed and augmented simultaneously. The mean augmentation height was 10.7 mm (range, 5.7 to 16.6 mm); the mean residual bone height was 5.1 mm (range, 1.9 to 12.1 mm). Complications such as insufficient primary stability and sinus membrane perforation were treated without changing to an open surgical approach. Discussion and Conclusion: Flapless sinus augmentation (FSA) can reduce the surgical trauma significantly. The procedure has high acceptance by the patient and less postoperative discomfort. FSA enlarges the spectrum of minimally invasive surgery and may offer better vascularization and less alveolar resorption. Keywords: endoscopy, minimally invasive surgery, sinus augmentation, 3-dimensional surgical templates

Purpose: The aim of this study was to evaluate how closely analysis of bone quality performed using the bone mineral density (BMD) values obtained by quantitative computerized tomography (QCT) reflected the histologic bone density. Materials and Methods: Eighteen patients requiring implant therapy underwent CT scanning. Their data were processed using Image Master software, and the BMD was calculated by measuring the Hounsfield units and relating those values to a phantom (Calibration Phantom, Quantitative Technologies). Each patient wore a radiographic-surgical template in which titanium cylinders were placed as a drilling guide for preparation of the implant site. The mouth regions where the titanium guides were placed (on the CT images and in the patient's mouth) corresponded to the implant sites where the BMD was measured and where tissue specimens for histomorphometric analysis retrieved. Forty specimens measuring 6 mm in length and 2 mm in diameter were obtained. Histomorphometric analysis was performed by digitizing the images, which were subsequently analyzed using the image analysis software IAS 2000. The bone volume (BV) was calculated as a percentage by dividing the area occupied by the mineralized bone over the entire microscopic field. Results: The results of the statistical analysis showed a Pearson correlation coefficient of 0.691 between the BV and BMD values, with a P value 0.01, which was considered significant. Discussion and Conclusion: The results of this study support the use of QCT to assess the bone quality before implant placement to improve the planning of implant treatment. Keywords: bone density, computerized tomography, histomorphometry

Purpose: In this multicenter study, the performance of Osseotite implants after a 1-stage surgery and abbreviated healing period of 2 months is reported. The implants were followed for up to 5 years. Materials and Methods: Partially or completely edentulous patients treated at 10 private practice centers were included in the study. Oral hygiene was assessed using the plaque index and the gingival index prior to surgery and at recall visits at 6 months, 1, 2, 3, 4, and 5 years after initial loading. Bone density and implant/bone fit were evaluated at the time of surgery. Implants were loaded after a healing period of about 2 months. Results: The mean age of the patients at time of enrollment was 60.4 ± 13.0 years; 44% (86) of the patients were men and 56% (109) were women. In all, 526 implants were placed, 65.4% in the mandible and 34.6% in the maxilla, with 23.0% placed in anterior locations and 77.0% in the posterior. The cumulative success rate of these 526 implants was 97.9% at 5 years. Eight of the 11 implant failures occurred during nonsubmerged healing prior to prosthetic loading. Provisional restorations were placed at 2.1 ± 0.5 months, at which time implants were evaluated for mobility, gingival health, symptomology, and radiolucency. The distribution of prosthesis types included 118 single-tooth restorations (118 implants), 134 short-span prostheses (327 implants), and 16 long-span restorations (81 implants). Discussion: The benefits of early loading cannot be fully appreciated if there is a substantive increase in implant failures. In this study, a cumulative success rate greater than 97% was maintained throughout 5 years of observation. Conclusion: These results suggest that success can be expected with Osseotite implants after a nonsubmerged reduced healing period of 2 months in this patient population. Keywords: cumulative success rate, dental implants, early loading protocol, osseointegration

Implant dentistry steadily evolves as more is learned about the unique biologic interrelationship of the dental implant restoration and the surrounding hard and soft tissues. Important factors include the impact of the surface microtopography on biochemically-mediated cell differentiation, the unavoidable bacterial colonization of the implant-abutment (or crown) microgap, the vertical and horizontal dimensions of biologic width, and the histology of surrounding structures. The recipient site, implant design, surgical technique, and location of the restorative platform significantly influence the optimal esthetics and biologic stability of implant restorations. There are differing opinions among clinicians regarding the appropriate positioning of the implant restorative platform in the vertical and sagittal planes relative to the alveolar crest. An apical and palatal orientation of the coronal platform relative to the alveolar crest in the esthetic zone is generally advocated for favorable facial and proximal emergence profiles of the definitive crown. Tissue-directed implant placement primarily considers the long-term consequences of the implant restoration upon the surrounding hard and soft tissues. The goal is to develop optimal gingival contours and a definitive restoration in the esthetic zone that coexist in stable biologic synergy. The rationale and the specific prosthodontic and surgical protocols inherent in the tissue-directed concept are discussed in this report. Keywords: biologic width, dental implants, gingival morphology, implant-supported dental prostheses, interdental papilla, osseous morphology, ovate pontics, single-stage implants

Purpose: The aim of this study was to evaluate the sagittal inclination of interforaminal implants, the clinical implant outcome, and the necessary extent of prosthodontic compensation modalities for implant overdentures (IODs). Materials and Methods: Lateral cephalometric radiographs of 62 patients, each with a mandibular IOD retained by 2 to 4 implants, were analyzed. The sagittal inclination of the longitudinal implant axis of the most anterior implant was analyzed relative to the mandibular and occlusal planes. The angle needed to compensate for the inclination of the mandibular implant to obtain Angle's class I for the prosthesis (the compensation angle) was measured and compared with respect to skeletal class. Peri-implant structures were measured using the Plaque Index and the Gingival Index. The compensation angle was correlated with the mandibular implant inclination, the degree of mandibular atrophy, and the anterior facial height. Results: The most anterior mandibular implants showed a mean retroinclination of 74.3 ± 9.3 degrees in relation to the mandibular plane; retroinclination was significantly more pronounced in skeletal class II than skeletal classes I and III (P .05). The compensation angle (26.9 ± 10.5 degrees) was more significant for skeletal class II than for skeletal classes I and III (P .01). Sagittal mandibular implant inclination correlated significantly to the compensation angle (r = -0.46; P .05), mandibular atrophy (r = 0.32; P .05) and mandibular facial height (r = -0.45; P .05). Implant survival rate and peri-implant parameters (bone loss, pocket-depth, Plaque and Gingival Indices) of the interforaminal implants were not shown to be influenced by implant retroinclination. Nine patients (2 skeletal class 1, 7 skeletal class II) reported phonetic problems with the IOD because of narrowing of the lingual space but described significant improvement after a median 4.7 months (range, 3 to 12 months). Discussion and Conclusion: Depending on skeletal class, prosthetic compensatory mechanisms will be operative in the presence of mandibular implant retroinclination for IOD. Knowledge of mandibular inclinations and the compensatory mechanisms may be an essential factor in successful prosthetic rehabilitation and may provide for a homogenous design of the bar construction and easier handling and may also reduce stress on the attachment mechanism. Keywords: interforaminal implants, mandibular overdentures, prosthodontic compensation

Survival Estimates and Risk Factors for Failure with 6 3 5.7-mm ImplantsMichael A. Gentile, DMD1/Sung-Kiang Chuang, DMD, MD2/Thomas B. Dodson, DMD, MPH3Purpose: Short dental implants facilitate prosthetic restoration in the setting of limited alveolar bone height. The study objectives were to (1) estimate the 1-year survival of Bicon 6 3 5.7-mm implants, (2) compare the 1-year survival of 6 3 5.7-mm implants with that of non-6 3 5.7-mm implants, and (3) identify risk factors associated with implant failure. Materials and Methods: A retrospective cohort study design was used. The sample was composed of patients who had received at least one 6 3 5.7-mm implant. Predictor variables were categorized as demographic, health status, anatomic, implant-specific, prosthetic, perioperative, and reconstructive. The outcome variable was implant failure, defined as explantation. Appropriate descriptive, bivariate, and multivariate survival statistics were computed. Results: The sample was composed of 35 patients in whom 172 implants had been placed (45 of which were 6 3 5.7-mm). The 1-year survival rates for 6 3 5.7-mm and non-6 3 5.7-mm implants were 92.2% and 95.2%, respectively (P = .76). After adjusting for covariates in a multivariate model, implant size was not associated with failure (P = .95). Discussion: The comparable survival estimates for 6 3 5.7-mm implants and non-6 3 5.7-mm implants in this study suggested that 6 3 5.7-mm implants can become osseointegrated and bear a functional load after placement. Conclusions: The survival of 6 3 5.7-mm implants was comparable to that of non-6 3 5.7-mm implants. Keywords: dental implants, implant survival, oral surgery, risk factors, short implants

Purpose: The aim of this study was to report the outcome of using a maxillary osteotomy with an interpositional bone graft and implants in the treatment of extremely resorbed maxillae. Materials and Methods: Twenty-two consecutive patients (mean age 65.7 years) were included in the study. Bone grafts from the iliac bone were used. The patients were followed in a standardized clinical and radiographic method for up to 5 years. Results: A total of 176 Astra Tioblast ST implants were placed. Six implant losses occurred. All patients had fixed prostheses. Only minor bone resorption (1.0 to 1.5 mm) occurred in the bone graft, as well as a certain amount of marginal bone remodeling around the implants (1.0 to 1.9 mm) during periods up to 5 years. Remodeling and resorption in the bone graft and around the implants occurred during the first postoperative year. The results represent cumulative sucess and survival rates of 97%, which is comparative to implant integration in conventional maxillary bone. Discussion and Conclusions: The orthognathic surgical technique using maxillary osteotomy with interpositional bone graft and implants in a 2-stage procedure has been shown to be a predictable and reliable method for rehabilitation of patients with extreme resorption of the maxilla when conventional implant surgical methods cannot be used. Although the procedures are trying for the patients, overall satisfaction with the end result can be rewarding. Keywords: bone grafting, dental implants, maxillary osteotomy

Purpose: The purpose of the article was to evaluate the survival rates of TiUnite implants and then compare them to a previous similar study of machined-surface implants. Materials and Methods: This report presents the results of 82 consecutive patients treated since the introduction of Nobel Biocare's TiUnite surface. The patients were treated with complete-arch restorations using bilateral pterygomaxillary implants in edentulous maxillae. A total of 840 implants were placed in immediate extraction or healed sites, with a mean of 10 implants placed per patient. Results: In all, 826 of the 840 implants osseointegrated, for a cumulative survival rate (CSR) of 98.3%. One hundred fifty-eight of 164 pterygomaxillary implants successfully osseointegrated, yielding a 96.3% survival rate. Discussion and Conclusion: The results of this complete-arch maxillary prospective study suggest that Brånemark System TiUnite implants are more predicable than implants with a machined surface. Compared to a similar 1999 study in which the survival rate for machined-surface implants was 92.1%, the present study had a significantly higher survival rate of 98.6% with the TiUnite surface (P .001). In the pterygomaxillary region, there was an increase of 8% with the TiUnite surface as opposed to the machined surface (P .001). In addition, 62% of the implants in the present study were immediately loaded, compared to 0% in the machined-surface implant study. The titanium oxide surface appears to assist the healing response of the bone-implant interface. Keywords: immediate loading, implant surfaces, osseointegration, pterygoid, zygomatic implants