PubMed Health⌕ Search

Biomedical subjects

Arne Wagner

Publications and source records attributed to Arne Wagner.

At least 19 recordsLinked to original sources
PubMed2006

Point-to-point computer-assisted navigation for precise transfer of planned zygoma osteotomies from the stereolithographic model into reality.

PURPOSE: To evaluate the feasibility and accuracy of a new method for planning and realizing zygomatic osteotomies in cases of established post-traumatic deformities using stereolithographic (SL) models and computer assisted navigation. PATIENTS AND METHODS: In 5 patients, osteotomy and repositioning of the zygomatic complex was planned using SL models. The desired position of the zygoma in the patient was determined by fixing individualized osteosynthesis plates to predefined screw positions. The SL model and the patient were registered to the same 3-dimensional computed tomography data set via an occlusal reference frame on the patient and corresponding reference markers on the model. Prebent osteosynthesis plates from the surgical simulation on the model were fixed to corresponding screw positions on the patient, which were located by computer-assisted navigation. Evaluation of accuracy was performed by image fusion of postoperative computed tomography scans of the model and the patient. RESULTS: Clinical outcome was satisfactory in all cases. The evaluation by image fusion showed alignment of the patient's and the model's zygoma in 4 of 5 cases. Mean measured distance between screw positions in the models and the patients were 1.1 +/- 0.3 mm for 44 screws. In 1 patient the treatment plan was changed intraoperatively because of unforeseen soft tissue limitations. CONCLUSION: Point-to-point navigation is an accurate method to transfer the planning of a complex osteotomy from the SL model to the actual surgical procedure. Surgery is facilitated considerably because repositioning and osteosynthesis are achieved in 1 step.

Adult↗
PubMed2006

Accuracy of treatment planning based on stereolithography in computer assisted surgery.

Three-dimensional stereolithographic models (SL models), made of solid acrylic resin derived from computed-tomography (CT) data, are an established tool for preoperative treatment planning in numerous fields of medicine. An innovative approach, combining stereolithography with computer-assisted point-to-point navigation, can support the precise surgical realization of a plan that has been defined on an SL model preoperatively. The essential prerequisites for the application of such an approach are: (1) The accuracy of the SL models (including accuracy of the CT scan and correspondence of the model with the patient's anatomy) and (2) the registration method used for the transfer of the plan from the SL model to the patient (i.e., whether the applied registration markers can be added to the SL model corresponding to the markers at the patient with an accuracy that keeps the "cumulative error" at the end of the chain of errors, in the order of the accuracy of contemporary navigation systems). In this study, we focus on these two topics: By applying image-matching techniques, we fuse the original CT data of the patient with the corresponding CT data of the scanned SL model, and measure the deviations of defined parameter (e.g., distances between anatomical points). To evaluate the registration method used for the planning transfer, we apply a point-merge algorithm, using four marker points that should be located at exactly corresponding positions at the patient and at connective bars that are added to the surface of the SL model. Again, deviations at defined anatomical structures are measured and analyzed statistically. Our results prove sufficient correspondence of the two data sets and accuracy of the registration method for routine clinical application. The evaluation of the SL model accuracy revealed an arithmetic mean of the relative deviations from 0.8% to 5.4%, with an overall mean deviation of 2.2%. Mean deviations of the investigated anatomical structures ranged from 0.8 mm to 3.2 mm. An overall mean (comprising all structures) of 2.5 mm was found. The fiducial registration error of the point-merge algorithm ranged from 1.0 mm to 1.4 mm. The evaluated chain of errors showed a mean deviation of 2.5 mm. This study verifies that preoperative planning on SL models and intraoperative transfer of this plan with computer assisted navigation is a suitable and sufficiently reliable method for clinical applications.

Algorithms↗
PubMed2005

Stability of miniature electromagnetic tracking systems.

This study aims at a comparative evaluation of two recently introduced electromagnetic tracking systems under reproducible simulated operating-room (OR) conditions: the recently launched Medtronic StealthStation, Treon-EM and the NDI Aurora. We investigate if and to what extent these systems provide improved performance and stability in the presence of surgical instruments as possible sources of distortions compared with earlier reports on electromagnetic tracking technology. To investigate possible distortions under pseudo-realistic OR conditions, a large Langenbeck hook, a dental drill with its handle and an ultrasonic (US) scanhead are fixed on a special measurement rack at variable distances from the navigation sensor. The position measurements made by the Treon-EM were least affected by the presence of the instruments. The lengths of the mean deviation vectors were 0.21 mm for the Langenbeck hook, 0.23 mm for the drill with handle and 0.56 mm for the US scanhead. The Aurora was influenced by the three sources of distortion to a higher degree. A mean deviation vector of 1.44 mm length was observed in the vicinity of the Langenbeck hook, 0.53 mm length with the drill and 2.37 mm due to the US scanhead. The maximum of the root mean squared error (RMSE) for all coordinates in the presence of the Langenbeck hook was 0.3 mm for the Treon and 2.1 mm for the Aurora; the drill caused a maximum RMSE of 0.2 mm with the Treon and 1.2 mm with the Aurora. In the presence of the US scanhead, the maximum RMSE was 1.4 mm for the Treon and 5.1 mm for the Aurora. The new generation of electromagnetic tracking systems has significantly improved compared to common systems that were available in the middle of the 1990s and has reached a high level of technical development. We conclude that, in general, both systems are suitable for routine clinical application.

Artifacts↗
PubMed2005

Seven years of clinical experience with teleconsultation in craniomaxillofacial surgery.

PURPOSE: In this work the experiences from 50 telemedically supported treatments in craniomaxillofacial surgery are summarized and different setups for their technical realization are described. Furthermore, for the first time the innovative UMTS (universal mobile telecommunication system) is applied for the transmission of arthroscopic videos of the temporomandibular joint and other craniomaxillofacial structures. MATERIALS AND METHODS: The combination of computer-assisted navigation technology in augmented reality environments with telecommunication is used for execution of interactive stereotaxic teleconsultation. Furthermore, treatments without navigation are telemedically supported. This study is composed of 4 technical system configurations: 1) integrated services digital network (ISDN)-based videoconferencing without remote control of the navigation computer; 2) transmission control protocol/internet protocol (TCP/IP)-based interactive teleconsultation via bundled ISDN lines (including remote control of the navigation computer); 3) TCP/IP-based interactive teleconsultation via network; 4) combination of TCP/IP-connection and ISDN-based videoconferencing. The telemedically supported treatments are: orbitozygomatic osteotomies, positioning of the mandibular condyle in orthognathic surgery, insertion of implants, positioning of the maxilla in orthognathic surgery, distraction osteogenesis, arthroscopies of the temporomandibular joint, and operation simulations on stereolithographic models. The surgical interventions are evaluated on a 5-level system performance scale from the technical point of view. In a separate trial 20 videosequences of arthroscopies of the temporomandibular joint are transmitted via UMTS cellular phones and independently evaluated by 3 experts (ie, a total of 60 streamings) to investigate feasibility of this technology in the field of craniomaxillofacial surgery. RESULTS: In the years from 1996 to 2002 a total of 50 treatments were telemedically supported. All intraoperative applications were successfully finished; 48 of 60 UMTS transmissions were finished without any interruptions in constant quality, slight interruptions were observed in 8 tests, and a complete breakdown was observed during 4 streamings that required a restart of the transmission. Resolution was sufficient to diagnose even tiny anatomic structures inside the temporomandibular joint, but orientation was hardly recognizable. CONCLUSION: In many applications telecommunication technology can contribute to a quality improvement in cranio- and maxillofacial surgery because of the global availability of specialized knowledge. The required technical expenditure for teleconsultation crucially depends on the infrastructure that is already available at the clinic and the remote site. UMTS is a promising technology with the potential to be valuable in numerous craniomaxillofacial applications.

Arthroscopy↗
PubMed2005

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.

Adult↗
PubMed2004

Neoadjuvant radiochemotherapy of oral cavity and oropharyngeal cancer: evaluation of tumor response by CT differs from histopathologic response assessment in a significant fraction of patients.

BACKGROUND: Our aim was to compare and assess the predictive value of CT and histopathologic grading of tumor regression at primary tumor sites in patients with squamous cell carcinoma of the oral cavity and oropharynx after neoadjuvant (preoperative) radiochemotherapy (RCT). METHODS: We investigated 55 patients with carcinomas of the oral cavity and oropharynx who underwent RCT before curative surgery. Two blinded observers measured RCT-induced reduction of tumor volume in pretherapeutic and posttherapeutic CT scans. Volume changes were compared with histopathologic findings obtained at surgery. RESULTS: Histopathologic response evaluation revealed 31 complete remissions, 12 cases of partial response, and 12 nonresponders. We performed a logistic regression analysis to evaluate whether measured volume reduction could predict the likelihood of belonging to a certain response group. Taken together, we found 35 correct, 12 false-negative, and seven false-positive predictions. CONCLUSIONS: The extent of remission as assessed by CT scans 4 to 5 weeks after completion of neoadjuvant RCT leads to false predictions in a significant percentage of patients.

Adult↗
PubMed2004

SPECT-CT for topographic mapping of sentinel lymph nodes prior to gamma probe-guided biopsy in head and neck squamous cell carcinoma.

INTRODUCTION: Lymphoscintigraphic planar imaging is a common procedure for sentinel lymph node imaging prior to lymph node biopsy, but fails to elucidate the specific lymphatic drainage. Composite functional/anatomical imaging (SPECT-CT) has the potential to enhance topographic orientation and diagnostic sensitivity of sentinel lymph node imaging, but has not yet been applied in the head and neck region. STUDY DESIGN: A total of 30 patients were investigated. Planar imaging was 5 min, 265 x 265, right and left lateral; 500 kilocounts (Kcts) and SPECT (GE Millenium VG Hawk Eye 6 degrees/30s. step, 128 x 128, slice thickness 4.42 mm). Scans were performed 60 min after intra-mucodermal injection of 0.1 ml of 20 MBq 99mTc nanocolloid in patients with squamous cell cancer of the head and neck. SPECT studies were analysed by filtered back projection (FBP: Hann (0.7) prefiltering, Butterworth (0.5) postfiltering) and reconstruction (OSEM: Post Filter Hamming (0.85), 2 Iterations) and independently viewed with the co-registered CT image (eNTEGRA Functional Anatomical Fusion Vers 2.0216). The results were validated by comparing the results of each method employed in all 30 cases and intraoperative gamma probe-guided sentinel lymph node biopsy with histological examination in 13 of these patients. RESULTS: The majority of patients had more than one sentinel node (mean 1.63, min. 0, max. 4). Seven out of the 30 studies demonstrated lymphatic flow to the contralateral side of the neck. Forty-nine sentinel nodes were identified by iteratively reconstructed SPECT-CT. Thirty-eight out of these 49 could be located in lymphoscintigraphic planar imaging, whereas only 24/49 were detected in filtered back projection, respectively. In 11 of the 30 cases, a clinically unpredictable pattern of lymphatic drainage was observed. No correlation was found between T stage or tumour location and the number of sentinel nodes detected. In one out of the 13 cases, in whom imaging was followed by intraoperative gamma probe-guided biopsy, no sentinel node could be detected with the probe in the proximity of the primary tumour, although the node was clearly discernible in the reconstructed SPECT-CT. CONCLUSION: Composite functional/anatomical imaging (SPECT-CT) is feasible for sentinel lymph node detection. It enhances topographic orientation and diagnostic sensitivity with more sentinel nodes being detectable than by planar lymphoscintigraphy alone. Planar imaging should be accompanied by iterative reconstructed SPECT-CT to identify lymph nodes adjacent to the primary lesion. Such nodes are easily overlooked by planar lymphoscintigraphy and intraoperative gamma probes, as the high activity at the injection site can obscure their detection.

Adult↗
PubMed2004

Computer-aided navigation in dental implantology: 7 years of clinical experience.

PURPOSE: This long-term study gives a review over 7 years of research, development, and routine clinical application of computer-aided navigation technology in dental implantology. Benefits and disadvantages of up-to-date technologies are discussed. MATERIALS AND METHODS: In the course of the current advancement, various hardware and software configurations are used. In the initial phase, universally applicable navigation software is adapted for implantology. Since 2001, a special software module for dental implantology is available. Preoperative planning is performed on the basis of prosthetic aspects and requirements. In clinical routine use, patient and drill positions are intraoperatively registered by means of optoelectronic tracking systems; during preclinical tests, electromagnetic trackers are also used. RESULTS: In 7 years (1995 to 2002), 55 patients with 327 dental implants were successfully positioned with computer-aided navigation technology. The mean number of implants per patient was 6 (minimum, 1; maximum, 11). No complications were observed; the preoperative planning could be exactly realized. The average expenditure of time for the preparation of a surgical intervention with navigation decreased from 2 to 3 days in the initial phase to one-half day in clinical routine use with software that is optimized for dental implantology. CONCLUSIONS: The use of computer-aided navigation technology can contribute to considerable quality improvement. Preoperative planning is exactly realized and intraoperative safety is increased, because damage to nerves or neighboring teeth can be avoided.

Computer Systems↗
PubMed2004

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.

Adult↗
PubMed2004

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.

Atrophy↗
PubMed2003

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.

Depth Perception↗
PubMed2003

A comparative analysis of optical and conventional axiography for the analysis of temporomandibular joint movements.

STATEMENT OF PROBLEM: Currently available systems for pantographic tracing are heavy, bulky, and can interfere with jaw movements. PURPOSE: This study describes the development and clinical application of optoelectronic axiography designed to overcome system inherent problems of conventional bulky frame-based registration axiography. The purpose of this study is the comparison of the newly developed system and conventional axiography. MATERIAL AND METHODS: Three-dimensional recordings of condylar pathways were acquired by means of infrared digitizers interfaced to newly developed software. Ten distinct curves in each of 10 subjects were recorded by synchronous optoelectronic axiography (100 tracings) and by conventional axiography (100 tracings). Usually, two 3-dimensional (3D) light weight sensors are provisionally fixed to the facial surface of a maxillary and mandibular incisor by means of a single orthodontic bracket. To allow for direct comparison of all 100 pairs of curves in this study, the 3D sensors of the optoelectronic system were attached to the bulky double face-bow system of the axiograph. The conformity of tracings (protrusion, opening/closing, mediotrusion, and laterotrusion) was evaluated by means of correlation analysis. Resulting axiographic recordings from both systems were evaluated by 3 experts (dentists, experienced in axiographic investigations, who were blind to the source of the data), focusing on standardized qualitative criteria of the recordings (homogeneity/smoothness, pathway-characteristics, excursion, and left/right-symmetry). After testing for normal distribution of the ratio scaled data (length of pathway, horizontal condylar inclination [HCI], Bennett angle) with the Kolmogoroff-Smirnov test (alpha=.01), axiographic curves were quantitatively compared by means of an intraclass correlation coefficient ([ICC] alpha =.01). The Wilcoxon test (alpha=.01) was used to evaluate equivalence of ordinally scaled values (homogeneity of tracings) and Cohen's Kappa was used to compare excursion and left/right symmetry. RESULTS: High correspondence between curves recorded by conventional and optoelectronic axiography was observed. The mean differences of lengths between the protrusive, opening/closing, and mediotrusive pathways were 0.0 mm, 0.6 mm, and 0.1 mm, respectively. Pathways and values for HCI were found highly correlated (pathways: 95% CI of ICC 0.9776-0.9908; HCI: 95% CI of ICC 0.8641-0.9597). The 95% CIs for differences of pathways, HCI-value, and Bennett angle were -0.1mm/0.3mm, -3.4 degrees/1.9 degrees, and -2.8 degrees/4.8 degrees, respectively. Pathway characteristics also corresponded well (Cohen's Kappa: 0.73 for symmetric and 0.72 for asymmetric movements), 0.77 for left/right symmetry, whereas other characteristics showed less significant correlation (Cohen's Kappa of excursion: 0.21 for symmetric and 0.09 for asymmetric movements, homogeneity: 0.08 for symmetric and 0.15 for asymmetric movements). CONCLUSION: Within the limitations of this study, optoelectronic axiography proved to be an applicable, promising technique, leading to diagnostic interpretations equivalent (with respect to the CIs) to conventional axiography.

Dental Occlusion↗
PubMed2003

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.

Dental Implantation, Endosseous↗
PubMed2003

Quantification and clinical relevance of head motion during computed tomography.

OBJECTIVE: To quantify the 3-dimensional translation and rotation components of head motion during computed tomography and to analyze the influence of such motion on perceptible artifacts and distortion of volume image data sets. METHODS: Using high-precision optoelectronic motion-capture technology, changes in patient head position during axial CT scanning were registered in 20 cases and 2 phantoms with a spatial relative resolution better than 0.003 cm. Statistical analysis was performed on a base of 6-dimensional measurement-vectors, each with 3 translation and 3 rotation values. Because of the recording frequency of the tracking system, more than 80000 values were included in a statistical analysis. RESULTS: All 20 patients had head motion during the CT scanning, with only 4 of 20 patients showing perceptible motion artifacts. The frequency, the extent, and the direction of the movements did not correlate with either the observations made by the radiologic staff or with the patient's subjective estimation of comfort. Translation movements of the head during CT accounted for a maximum of 0.5 cm and rotations of more than 2 degrees without perceptible motion artifacts. The extent of positional changes of the head was found to correlate with the duration of scanning (Pearson's correlation coefficient: 0.647 for translation shifts, 0.453 for rotation shifts). The mean direction of head motion could be characterized predominantly as a rotation around the longitudinal axis of the body (xy plane) at a significance level of 0.01. CONCLUSION: Computed tomography evaluations of the head performed without rigid fixation suffer a spatial distortion of the volume image data sets, caused by interimage motion. The absence of motion artifacts is not correlated with the absence of motion.

Adolescent↗
PubMed2002

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.

Computer Graphics↗
PubMed2002

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.

Absorbable Implants↗
PubMed2002

A 3-dimensional finite-element analysis investigating the biomechanical behavior of the mandible and plate osteosynthesis in cases of fractures of the condylar process.

OBJECTIVE: The condylar region is one of the most frequent sites for mandibular fractures, with direct application of miniplates being the most commonly used open-fixation technique today. Yet, anatomic and biomechanical limitations continue to make this application technically challenging with a considerable complication rate. We sought to analyze such incongruencies with respect to the complex biomechanical behavior of the mandible. STUDY DESIGN: Individual human mandible geometry, the specific bone density distribution, and the position and orientation of the masticatory muscles were evaluated by performing computed tomography scans and a sequential dissection of the cadaver mandible. Three-dimensional finite-element analysis was performed for different fracture sites, osteosynthesis plates, and loading conditions. RESULTS: Osteosynthesis of fractures of the condylar neck with 1 or 2 miniplates of a diameter of 2.35 x 1.00 mm was found to be an insufficient fixation method. This also applies for plates (3.60 x 1.54 mm), according to Pape et al,(8) when used in singular fashion (high condylar neck fractures excepted). In cases of singular occlusal contacts in the molar region (particularly at the contralateral side of the fracture), the highest stress values inside the mandible and osteosynthetic devices could be observed. With even the static yield limit of titanium being exceeded in such cases, consecutive rapid failure of the miniplates becomes most likely when loading of the condylar region caused by bite forces cannot be prevented. CONCLUSION: We strongly recommend the use, whenever possible, of 2 plates in the manner described by Pape et al(8) for osteosynthesis of fractures of the condylar neck in combination with bicortically placed screws. The stiffness of a singular osteosynthesis plate made of titanium in a diametrical dimension of approximately 5.0 x 1.75 mm was found to be equivalent to the physiological bone stiffness in the investigated fracture sites. The actual stiffness of such a fixation plate is approximately 3 times higher than the stiffness of devices commonly in use.

Bite Force↗