Initial effects of low-level laser therapy on growth and differentiation of human osteoblast-like cells.

Low-level laser therapy is a clinically well established tool for enhancement of wound healing. In vitro studies have also shown that low level laser therapy has a biostimulatory effect on cells of different origin. The aim of this in vitro study was to investigate the initial effect of low-level laser therapy on growth and differentiation of human osteoblast-like cells. SaOS-2 cells were irradiated with laser doses of 1 J/cm2 and 2 J/cm2 using a diode laser with 670 nm wave length and an output power of 400 mW. Untreated cells were used as controls. At 24 h, 48 h and 72 h post irradiation, cells were collected and assayed for viability of attached cells and alkaline phosphatase specific activity. In addition, mRNA expression levels of osteopontin and collagen type I were assessed using semi-quantitative RT-PCR. Over the observation period, cell viability, alkaline phosphatase activity and the expression of osteopontin and collagen type I mRNA were slightly enhanced in cells irradiated with 1 J/cm2 compared with untreated control cells. Increasing the laser dose to 2 J/cm2 reduced cell viability during the first 48 h and resulted in persistently lower alkaline phosphatase activity compared with the other two groups. The expression of osteopontin and collagen type I mRNA slightly decreased with time in untreated controls and cells irradiated with 1 J/cm2, but their expression was increased by treatment with 2 J/cm2 after 72 h. These results indicate that low-level laser therapy has a biostimulatory effect on human osteoblast-like cells during the first 72 h after irradiation. Further studies are needed to determine the potential of low-level laser therapy as new treatment concept in bone regeneration.

Expression patterns of Ets2 protein correlate with bone-specific proteins in cell-seeded three-dimensional bone constructs.

The transcription factor Ets2 and its transcriptional targets osteopontin (OPN) and osteocalcin (OC) are expressed in tissue-engineered bone constructs in vitro. Up to now little is known about the role of Ets2 in tissue-engineering applications. This study was intended to investigate the hypothesis that protein expression of Ets2 is correlated with the expression of bone-specific proteinsin tissue-engineeredbone constructs. Cell-seeded three-dimensional bone constructs manufactured with osteoblastic cells and poly(lactic-co-glycolic acid) polymer fleeces over a period of 21 days were analyzed by SDS-PAGE and Western blotting. The protein expression of OPN, OC, osteonectin and collagen type I was analyzed. Cellularity, alkaline phosphatase-specific activity and histology confirmed the osteoblastic phenotype of the constructs. Correlations between Ets2 expression and OPN and Ets2 and collagen type I expression could be detected during the phase of late osteoblastic differentiation between days 9 and 21. The correlation between OC and collagen type I was significant in this late stage of osteoblastic differentiation. These results suggest that there is a strong interplay of Ets2 with bone-specific proteins in cell-seeded three-dimensional bone constructs. This study is a crucial step to elucidate the complex interplay of bone-related proteins in the application of bone tissue engineering.

Fast DRR splat rendering using common consumer graphics hardware.

Digitally rendered radiographs (DRR) are a vital part of various medical image processing applications such as 2D/3D registration for patient pose determination in image-guided radiotherapy procedures. This paper presents a technique to accelerate DRR creation by using conventional graphics hardware for the rendering process. DRR computation itself is done by an efficient volume rendering method named wobbled splatting. For programming the graphics hardware, NVIDIAs C for Graphics (Cg) is used. The description of an algorithm used for rendering DRRs on the graphics hardware is presented, together with a benchmark comparing this technique to a CPU-based wobbled splatting program. Results show a reduction of rendering time by about 70%-90% depending on the amount of data. For instance, rendering a volume of 2 x 10(6) voxels is feasible at an update rate of 38 Hz compared to 6 Hz on a common Intel-based PC using the graphics processing unit (GPU) of a conventional graphics adapter. In addition, wobbled splatting using graphics hardware for DRR computation provides higher resolution DRRs with comparable image quality due to special processing characteristics of the GPU. We conclude that DRR generation on common graphics hardware using the freely available Cg environment is a major step toward 2D/3D registration in clinical routine.

Comparison of laser surface scanning and fiducial marker-based registration in frameless stereotaxy. Technical note.

The authors compared the accuracy of laser surface scanning patient registration using the commercially available Fazer (Medtronic, Inc.) with the conventional registration procedure based on fiducial markers (FMs) in computer-assisted surgery. Four anatomical head specimens were prepared with 10 titanium microscrews placed at defined locations and scanned with a 16-slice spiral computed tomography unit. To compare the two registration methods, each method was applied five times for each cadaveric specimen; thus data were obtained from 40 registrations. Five microscrews (selected following a randomization protocol) were used for each FM-based registration; the other five FMs were selected for coordinate measurements by touching with a point measurement stylus. Coordinates of these points were also measured manually on the screen of the navigation computer. Coordinates were measured in the same manner after laser surface registration. The root mean square error as calculated by the navigation system ranged from 1.3 to 3.2 mm (mean 1.8 mm) with the Fazer and from 0.3 to 1.8 mm (mean 1.0 mm) with FM-based registration. The overall mean deviations (the arithmetic mean of the mean deviations of measurements on the four specimens) were 3.0 mm (standard deviation [SD] range 1.4-2.6 mm) with the Fazer and 1.4 mm (SD range 0.4-0.9 mm) with the FMs. The Fazer registration scans 300 surface points. Statistical tests showed the difference in the accuracy of these methods to be highly significant. In accordance with the findings of other groups, the authors concluded that the inclusion of a larger number of registration points might improve the accuracy of Fazer registration.

Measurement of volume changes after sinus floor augmentation with a phycogenic hydroxyapatite.

PURPOSE: The purpose of this study was the determination of time-dependent volumetric changes of particulate sinus inlay grafts. A mixture of phycogenic hydroxyapatite (Algipore/C-Graft) and autologous bone collected from the surgical access area was used as the grafting material. MATERIALS AND METHODS: Thirty-three sinus floor augmentations using phycogenic hydroxyapatite combined with autologous bone collected at the augmentation site and venous blood were performed on 18 patients aged 57.4 +/- 12.5 years (mean +/- SD) with severe atrophy of the posterior maxilla. Graft volume was measured 1 to 14 days postoperatively and before the placement of dental implants 6.1 +/- 2.1 months later (mean +/- SD; range, 4 to 11 months) to evaluate the amount of time-dependent resorption of the implanted material on computerized tomographic (CT) images of the augmented region. The images were put into Digital Imaging and Communications in Medicine (DICOM) format and evaluated using the software library Analyze. The implanted bone replacement material was plotted manually on each CT slice, and the volume of the implanted material was calculated. RESULTS: The average volume loss of the bone replacement material during the observation period was 13.9% +/- 1.9% (mean +/- SEM). All sinus floor augmentations healed without complications except for delayed membrane exposure in 2 cases. DISCUSSION: The results indicate that the graft material, a mixture of Algipore, bone chips from the access area, and venous blood, exhibited a small volume loss over a period of approximately 6 months, thus providing predictable height for second-stage implant surgery. CONCLUSION: Further investigations are needed to evaluate long-term stability and implant success.

A fully automated calibration method for an optical see-through head-mounted operating microscope with variable zoom and focus.

Ever since the development of the first applications in image-guided therapy (IGT), the use of head-mounted displays (HMDs) was considered an important extension of existing IGT technologies. Several approaches to utilizing HMDs and modified medical devices for augmented reality (AR) visualization were implemented. These approaches include video-see through systems, semitransparent mirrors, modified endoscopes, and modified operating microscopes. Common to all these devices is the fact that a precise calibration between the display and three-dimensional coordinates in the patient's frame of reference is compulsory. In optical see-through devices based on complex optical systems such as operating microscopes or operating binoculars-as in the case of the system presented in this paper-this procedure can become increasingly difficult since precise camera calibration for every focus and zoom position is required. We present a method for fully automatic calibration of the operating binocular Varioscope M5 AR for the full range of zoom and focus settings available. Our method uses a special calibration pattern, a linear guide driven by a stepping motor, and special calibration software. The overlay error in the calibration plane was found to be 0.14-0.91 mm, which is less than 1% of the field of view. Using the motorized calibration rig as presented in the paper, we were also able to assess the dynamic latency when viewing augmentation graphics on a mobile target; spatial displacement due to latency was found to be in the range of 1.1-2.8 mm maximum, the disparity between the true object and its computed overlay represented latency of 0.1 s. We conclude that the automatic calibration method presented in this paper is sufficient in terms of accuracy and time requirements for standard uses of optical see-through systems in a clinical environment.

HA/TCP compounding of a porous CaP biomaterial improves bone formation and scaffold degradation--a long-term histological study.

In the present study, two biphasic calcium phosphate biomaterials (BCP) with HA/TCP ratios of 50/50 and 30/70 were obtained from a pure HA biomaterial. The biomaterials which showed the same three-dimensional geometry were implanted into corticocancellous costal defects of sheep. In the specimens of all three biomaterials, abundant bone formation, mineral dissolution from the biomaterial scaffolds, and active cellular resorption of the scaffolds was present after 6 and 12 months. Backscattered electron microscopy showed bone invasion into the pores of the scaffolds and micromechanical interlocking at the bone/biomaterial interface without intervening soft tissue. The pattern of bone formation and scaffold resorption was different for cortical and cancellous bone. No time-based effect, however, was observed. Overall, the BCP biomaterials had formed significantly more bone than the HA biomaterial. Also, scaffold resorption, which was followed by a replacement with newly formed bone, was significantly higher in the BCP biomaterials. Although no significant differences were observed between both BCP biomaterials, the present study had confirmed the assumption that HA/TCP compounding was suitable to improve bone formation and scaffold resorption in the investigated biomaterials and at the same time maintain the osteoconductive properties of the scaffolds.

A head-mounted operating binocular for augmented reality visualization in medicine--design and initial evaluation.

Computer-aided surgery (CAS), the intraoperative application of biomedical visualization techniques, appears to be one of the most promising fields of application for augmented reality (AR), the display of additional computer-generated graphics over a real-world scene. Typically a device such as a head-mounted display (HMD) is used for AR. However, considerable technical problems connected with AR have limited the intraoperative application of HMDs up to now. One of the difficulties in using HMDs is the requirement for a common optical focal plane for both the realworld scene and the computer-generated image, and acceptance of the HMD by the user in a surgical environment. In order to increase the clinical acceptance of AR, we have adapted the Varioscope (Life Optics, Vienna), a miniature, cost-effective head-mounted operating binocular, for AR. In this paper, we present the basic design of the modified HMD, and the method and results of an extensive laboratory study for photogrammetric calibration of the Varioscope's computer displays to a real-world scene. In a series of 16 calibrations with varying zoom factors and object distances, mean calibration error was found to be 1.24 +/- 0.38 pixels or 0.12 +/- 0.05 mm for a 640 x 480 display. Maximum error accounted for 3.33 +/- 1.04 pixels or 0.33 +/- 0.12 mm. The location of a position measurement probe of an optical tracking system was transformed to the display with an error of less than 1 mm in the real world in 56% of all cases. For the remaining cases, error was below 2 mm. We conclude that the accuracy achieved in our experiments is sufficient for a wide range of CAS applications.

Computer-enhanced stereoscopic vision in a head-mounted operating binocular.

Based on the Varioscope, a commercially available head-mounted operating binocular, we have developed the Varioscope AR, a see through head-mounted display (HMD) for augmented reality visualization that seamlessly fits into the infrastructure of a surgical navigation system. We have assessed the extent to which stereoscopic visualization improves target localization in computer-aided surgery in a phantom study. In order to quantify the depth perception of a user aiming at a given target, we have designed a phantom simulating typical clinical situations in skull base surgery. Sixteen steel spheres were fixed at the base of a bony skull, and several typical craniotomies were applied. After having taken CT scans, the skull was filled with opaque jelly in order to simulate brain tissue. The positions of the spheres were registered using VISIT, a system for computer-aided surgical navigation. Then attempts were made to locate the steel spheres with a bayonet probe through the craniotomies using VISIT and the Varioscope AR as a stereoscopic display device. Localization of targets 4 mm in diameter using stereoscopic vision and additional visual cues indicating target proximity had a success rate (defined as a first-trial hit rate) of 87.5%. Using monoscopic vision and target proximity indication, the success rate was found to be 66.6%. Omission of visual hints on reaching a target yielded a success rate of 79.2% in the stereo case and 56.25% with monoscopic vision. Time requirements for localizing all 16 targets ranged from 7.5 min (stereo, with proximity cues) to 10 min (mono, without proximity cues). Navigation error is primarily governed by the accuracy of registration in the navigation system, whereas the HMD does not appear to influence localization significantly. We conclude that stereo vision is a valuable tool in augmented reality guided interventions.

Interactive stereotaxic teleassistance of remote experts during arthroscopic procedures.

This article describes the technical setup for stereotaxic telesurgical assistance for arthroscopic procedures. It also outlines the current state, limitations, and feasibility of this technical development. Teleassistance or teleconsultation implemented in endoscopic or arthroscopic procedures have not yet been reported. In this study, 7 computer-assisted arthroscopies of the temporomandibular joint were supported by extramural experts via interactive stereotaxic teleconsultation from distant locations. The external experts were supplied with close to real-time video, audio, and stereotaxic navigation data directly from the operation site. This setup allows the surgeons and external experts to interactively determine portals, target structures, and instrument positions relative to the patient's anatomy and to discuss any step of the procedures. Optoelectronic tracking interfaced to computer- based navigation technology allowed precise positioning of instruments for single or multiple temporomandibular joint punctures. The average error of digitizing probe measurements was 1.3 mm (range, 0.0 to 2.5 mm) and the average standard deviation was 0.7 mm (range, 0.4 to 0.9 mm). Evaluation of the reliability and accuracy of this technique suggests that it is sufficient for controlled navigation, even inside the small temporomandibular joint, a fact that encourages further applications for arthroscopy in general. The minimum requirement for high-quality video transmission for teleassisted procedures are integrated services digital network (ISDN) connections. Conventional ISDN-based videoconferencing can be combined with computer-aided intraoperative navigation. Transmission control protocol/internet protocol (TCP/IP)-based stereotaxic teleassistance data transmission via ATM or satellite seem to be promising techniques to considerably improve the field of arthroscopy.

Rehabilitation of the severely atrophied maxilla by horseshoe Le Fort I osteotomy (HLFO).

OBJECTIVE: The purpose of this study was to determine the long-term outcome of the horseshoe Le Fort I osteotomy (HLFO) as a preprosthetic operation technique for implant insertion in the extremely atrophied maxilla. STUDY DESIGN: 36 patients (8 male, 28 female, average age 57.6 years) underwent HLFO combined with iliac crest bone grafting. They were divided into 2 groups: group A with 12 patients who simultaneously received 100 implants; group B with 24 patients where 176 implants were inserted in 18 patients in a second-stage procedure. Clinical and radiographic outcome with regard to implant osseointegration, alveolar bone height in the canine and molar regions, peri-implant bone loss and satisfaction of patients (esthetics, masticatory function, overall treatment) were investigated in all cases. RESULTS: The overall 2-year failure-free fraction of implants was 95.5%; the 5-year failure-free fraction was 89.3%. In the 1-step group the 2-year and 5-year failure-free fractions were 95.9% and 86.9%, respectively, in the 2-step group 95.0% and 91.3% (log rank test P=.57). A total of 27 implants were lost during the entire follow-up: 14 in 6 patients of the 1-stage and 13 in 9 patients of the 2-stage group. The mean loss of alveolar bone after augmentation in the canine and molar regions was almost equal in both groups (overall means for the 2 regions 3.67 +/- 2.77 and 4.42 +/- 2.72 mm, respectively). The relationship between the jaws and thereby the esthetic profile could be improved in all cases. All patients were satisfied with the dental rehabilitation and the achieved new esthetic appearance. CONCLUSIONS: HLFO combined with iliac bone grafting is a feasible preprosthetic technique prior to implant insertion in cases of severe atrophy of the maxillary alveolar ridge, leading to satisfying implant survival and rehabilitation of function.

Fixation of mandibular fractures with biodegradable plates and screws.

OBJECTIVE: Little data exist regarding the use of biodegradable plates and screws for the internal fixation of human mandibular fractures. The purpose of this study was to evaluate the stability of biodegradable, self-reinforced poly-L-lactide plates and screws for the internal fixation of fractures of the human mandible. STUDY DESIGN: Twenty-two individuals (14 male, 8 female; average age, 26.3 years) with a variety of fracture patterns of the mandible underwent management with a biodegradable fixation system. After surgery, maxillomandibular fixation was applied in 3 cases. Images (panoramic radiograph, computed tomographic scan) were taken immediately after surgery and at the 4-week, 8-week, 12-week, and 24-week intervals. The follow-up period averaged 49.1 weeks (range, 22 to 78 weeks). RESULTS: Mucosal dehiscences over the resorbable devices were present in 2 patients. In 1 of these 2 cases, the material had to be replaced with titanium plates. Mucosal healing and consolidation of the fracture were normal in all other patients. CONCLUSION: Self-reinforced biodegradable osteosynthesis materials provide a reliable and sufficient alternative to conventional titanium plate systems.

Treatment results of bisphosphonate-related osteonecrosis of the jaws.

BACKGROUND: Osteonecrosis of the jaws occurs after the administration of bisphosphonates. An unequivocal treatment strategy is yet to be devised. We assess the treatment of patients with bisphosphonate-related osteonecrosis of the jaws (BRONJ). METHODS: The investigators studied a prospective cohort of 58 patients 6 months after surgical treatment of BRONJ. Outcome variables were the status of the mucosa, the visual analog score of pain, and prosthetic rehabilitation. Preoperative staging results were compared with the postoperative outcome and statistically evaluated. RESULTS: Of 58 patients, 41 surgically treated patients could be followed up after a mean period of 189 (+/-23) days. Twenty-four (58.5%) were free of pain and had an intact mucosa. A statistically significant improvement was registered between preoperative and postoperative staging (p <.01); 11 of 12 patients who had been treated with a flap procedure for soft tissue closure had an intact mucosa. CONCLUSIONS: This is the first prospective study to report the outcome of treatment in a cohort of patients with BRONJ. Minimal resection of necrotic bone and local soft tissue closure might be a feasible treatment strategy in patients with established BRONJ.

Exogenous recombinant human BMP-2 has little initial effects on human osteoblastic cells cultured on collagen type I coated/noncoated hydroxyapatite ceramic granules.

PURPOSE: Tissue engineering of bone entails the successful interplay between osteoinductive factors, osteogenic cells, their extracellular environment, and an osteoconductive biomaterial scaffold. Naturally produced ceramics, like hydroxyapatite (HA) calcified from red algae, are the most promising materials for use as scaffolds in this field. We hypothesized that extracellular matrix compartments and osteoinductive factors could further ameliorate the bioactivity of the scaffold. MATERIALS AND METHODS: Osteosarcoma cells with proven osteogenic phenotype (SaOS-2) were cultured onto type I collagen coated (Coll I/HA) and noncollagen coated HA granules (NC/HA) gained from red algae (C GRAFT/Algipore). Cells grown on tissue culture polystyrene dishes (TCPS) were used as controls. Second, SaOS-2 cells cultured on Coll I/HA, NC/HA, and TCPS were treated with recombinant human bone morphogenetic protein-2 (rhBMP-2) in different concentrations (10, 100, and 500 ng/mL). Non rhBMP-2-treated cultures were used as controls. Cultures of both experiments were grown under osteogenic differentiation conditions and after 24, 48, and 72 hours assays for cell viability, apoptosis, alkaline phosphatase activity (ALP), and osteocalcin (OC) secretion were done. RESULTS: Coating of HA granules with type I collagen showed higher cell viability in rhBMP-2-treated and nontreated cells. Supplementation of cultured cells with exogenous rhBMP-2 showed a dose-dependent effect only in the TCPS group. No alterations of the apoptotic rate within 1 investigation group were found. Addition of rhBMP-2 did not significantly alter the specific OC secretion of cells grown on Coll I/HA and TCPS. CONCLUSION: These in vitro findings show that in the initial period of cultivation and up to 72 hours, the coating of HA granules with collagen type I had positive effects on cell viability and osteoblastic characteristics of osteoblastic cells. In contrast, the supplementation with exogenous rhBMP-2 shows no dose-dependent effects. The combination of collagen type I and exogenous rhBMP-2 did not ameliorate the bioactivity of hydroxyapatite calcified from red algae in the initial period of cultivation.

Surface area analysis of dental implants using micro-computed tomography.

OBJECTIVES: In this study, we present and evaluate a micro-computed tomography (micro-CT)-based method for the calculation of the potential bone/implant contact area (p-BICA) on the surface of dental implants. MATERIAL AND METHODS: For seven commercially available implants (Ankylos implant, Brånemark System, Frialit CELLplus, Replace((R)) Select Tapered, Straumann Solid screw, XiVE S CELLplus, 3i Osseotite XP Threaded Miniplant, the p-BICA surface is determined by means of three-dimensional X-ray computed-tomography and computer-based data processing. Measurements were repeated two times, and the stability and repeatability of the measurement method were evaluated. RESULTS: Our analysis revealed a p-BICA of 118 mm(2) for the XiVE S CELLplus implant, 134 mm(2) for the Ankylos, 136 mm(2) for the Frialit CELLplus, 138 mm(2) for the Brånemark System, 139 mm(2) for the Replace((R)), 159 mm(2) for the 3i Osseotite XP and 199 mm(2) for the Straumann Solid screw implant. The measurement method proved to be stable and led to reproducible results. CONCLUSIONS: The micro- and macrostructure of dental implants define the surface and the p-BICA. Precise determination of this parameter can be achieved by means of the micro-CT-based method as presented in this study. The value of p-BICA lies in the predictability of industrial design before preclinical and clinical testing. Based on this method, dental implant properties become comparable even if geometrical details are not disclosed by the manufacturer.

Influence of three currently used bone replacing materials on the in vitro proliferation of human peripheral blood mononuclear cells.

OBJECTIVES: A cell culture system for biocompatibility testing of bone grafting materials is described. We investigated the in vitro viability and proliferative response of peripheral blood mononuclear cells (PBMC) from 10 healthy donors in the presence of three materials currently used for bone grafting: Algipore, Bio-Oss and Bone Source, for immunologic biocompatibility testing. MATERIAL AND METHODS: PBMC isolated from venous blood from 10 healthy donors were incubated for 4 days with each bone replacing material, in the presence and absence of interleukin-2 (IL-2). After 4 days, H3-thymidine was added for 18 h and the incorporated radioactivity was measured with a beta-plate counter. RESULTS: Basal PBMC counts were 152.9+/-66.2 counts per minute (c.p.m.) (mean+/-SD), in the presence of 0.4 U IL-2/well 206.5+/-83 c.p.m. were measured. With Algipore and Bio-Oss, which are deproteinized bone replacing materials, the proliferation rate of PBMC with IL-2 was not significantly modified: for Algipore 151+/-51 c.p.m./+IL-2 188.8+/-62 c.p.m., for Bio-Oss 144.5+/-64.9 c.p.m./+IL-2 176.3+/-71.23 c.p.m. For Bone Source 164.2+/-80.4/+IL-2 188.3+/-81 c.p.m. were measured. CONCLUSION: This in vitro experiment indicates, that the investigated bone replacing materials are not acting as specific antigens/haptens and are not generating increased proliferative responses of human PBMC from healthy donors. Even with IL-2, that induces proliferation of T lymphocytes, which encountered their specific antigen, the proliferation rate of PBMC from healthy donors was not increased after incubation with this bone grafting materials.

Computer-aided placement of endosseous oral implants in patients after ablative tumour surgery: assessment of accuracy.

The objective of this study was to evaluate the feasibility and accuracy of a novel surgical computer-aided navigation system for the placement of endosseous implants in patients after ablative tumour surgery. Pre-operative planning was performed by developing a prosthetic concept and modifying the implant position according to surgical requirements after high-resolution computed tomography (HRCT) scans with VISIT, a surgical planning and navigation software developed at the Vienna General Hospital. The pre-operative plan was transferred to the patients intraoperatively using surgical navigation software and optical tracking technology. The patients were HRCT-scanned again to compare the position of the implants with the pre-operative plan on reformatted CT-slices after matching of the pre- and post-operative data sets using the mutual information-technique. A total of 32 implants was evaluated. The mean deviation was 1.1 mm (range: 0-3.5 mm). The mean angular deviation of the implants was 6.4 degrees (range: 0.4 degrees - 17.4 degrees, variance: 13.3 degrees ). The results demonstrate, that adequate accuracy in placing endosseous oral implants can be delivered to patients with most difficult implantologic situations.

Long-term implant survival in the grafted maxilla: results of a 12-year retrospective study.

OBJECTIVE: The aim of this study was to determine the long-term outcome of implant insertion in the augmented severely atrophied maxilla. STUDY DESIGN: Three hundred and twenty-four implants were inserted in 35 patients (eight males, 27 females, average age 57.6 years) in extremely atrophied maxillae after osteotomy and interposition of iliac crest bone. One hundred implants were installed in 12 patients simultaneously with the osteotomy and grafting; 224 implants were placed in 23 patients in a second procedure 6-12 months later. Implant parameters like osseointegration and peri-implant bone loss; peri-implant tissue parameters like bleeding, gingival and plaque index; and patients' satisfaction were evaluated. RESULTS: Of 324 implants, 29 (8.9%) were lost during the entire follow-up: 14 in six patients of the one-step and 15 in 11 patients of the two-step group. The overall input-output survival in 141.1 months was 91.1%. The overall 2-year failure-free fraction of implants was 95.5%; the 5-year failure-free fraction was 89.3%. In the one-step group, the 2 (5)-year failure-free fraction was 95.9% (86.9%), and in the two-step group 95% (91.3%) (log-rank test P=0.57). Marginal peri-implant bone loss was 1.7+/-1.3 mm mesial and 1.8+/-1.3 mm distal. CONCLUSION: Implant insertion after osteotomy and iliac bone grafting is a reliable operation method for the dental rehabilitation of the severely atrophied maxilla showing good long-term results.

Evaluation of accuracy of computer-aided intraoperative positioning of endosseous oral implants in the edentulous mandible.

The overall accuracy of a novel surgical computer-aided navigation system for placement of endosseous implants was evaluated. Five dry cadaver mandibles were scanned using high resolution computed tomography (HRCT). The position of four interforaminal dental implants was planned on the computer screen and transferred to the cadaver mandibles using VISIT, a surgical navigation software developed at the Vienna General Hospital. The specimens were HRCT-scanned again to compare the position of the implants with the preoperative plan on reformatted slices after matching of the pre- and postoperative data sets using the mutual information technique. The overall accuracy was 0.96 +/- 0.72 mm (range 0.0-3.5 mm). No perforation of the mandibular cortex or damage to the mandibular canal occurred. We conclude that computer-aided implant surgery can reach a level of accuracy where further clinical developments are feasible.

Computer-enhanced stereoscopic vision in a head-mounted display for oral implant surgery.

We developed a head-mounted display (HMD) with integrated computer-generated stereoscopic projection of target structures and integrated it into visit, a specific oral implant planning and navigation software. The HMD is equipped with two miniature computer monitors that project computer-generated graphics stereoscopically into the optical path. Its position is tracked by the navigation system's optical tracker and target structures are displayed in their true position over the operation site. In order to test this system's accuracy and spatial perception of the viewer, five interforaminal implants in three dry human mandibles were planned with visit and executed using the stereoscopic projection through the HMD. The deviation between planned and achieved position of the implants was measured on corresponding computed tomography (CT) scan images recorded post-operatively. The deviation between planned and achieved implant position at the jaw crest was 0.57 +/- 0.49 mm measured from the lingual, and 0.58 +/- 0.4 mm measured from the buccal cortex. At the tip of the implants the deviation was 0.77 +/- 0.63 mm at the lingual and 0.79 +/- 0.71 mm at the buccal cortex. The mean angular deviation between planned and executed implant position was 3.55 +/- 2.07 degrees. The present in vitro experiment indicates that the concept of preoperative planning and transfer to the operative field by an HMD allows us to achieve an average precision within 1 mm (range up to 3 mm) of the implant position and within 3 degrees deviation for the implant inclination (range up to 10 degrees ). Control during the drilling procedure is significantly improved by stereoscopic vision through the HMD resulting in a more accurate inclination of the implants.