Biomedical subjects
Ulrich Meyer
Publications and source records attributed to Ulrich Meyer.
On the three-dimensional physiological position of the temporomandibular joint.
Despite intensive research regarding the position of the temporomandibular joint, only few evidence-based facts are known about a three-dimensional physiological condyle-fossa relationship. The aim of this systematic literature review was therefore to summarize the existing literature regarding the condyle position and to draw conclusions about a standardized three-dimensional condyle position. An extended search profile based on the search strategy of the Cochrane Oral Health Group and applied to twelve medical databases was used to identify existing studies. Articles which were not electronically accessible (mainly those published before 1960) were identified from reference lists and bibliographies. These publications were assessed independently by two clinicians with reference to points based on specified criteria. The interexaminer agreement was assessed on the basis of the kappa coefficient.1903 articles published in the period 1899-2001 and relating to condyle position were identified. These studies showed a pronounced variability in their methodological approaches, with only 49 of them meeting the inclusion criteria. The interexaminer agreement yielded a kappa-value of 0.92. Although numerous studies used three-dimensional data, no physiological three-dimensional condyle position was determined. The most frequent analytic method was two-dimensional projection of the temporomandibular joint onto a subjectively selected sagittal plane. This evaluation method revealed a noticeable shift over time in condyle position from posterior to anterior, suggesting a clear-cut publication bias. Publications with the highest evidence level favored no specific position (p > 0.05). Simplification of the three-dimensional structure of the temporomandibular joint to a two-dimensional projection is questionable for therapeutic positioning of the condyle in relation to the fossa.
Sustained release of doxycycline for the treatment of peri-implantitis: randomised controlled trial.
UNLABELLED: With the increased use of osseointegrated implants and with many implants functioning for a long time, the treatment of peri-implantitis has become important. Animal studies and clinical case reports have shown that the principle of guided bone regeneration can be applied to the surgical treatment of moderate to profound loss of bone around the implant, but we have found no published clinical studies. PATIENTS AND METHODS: Twenty-eight patients whose ages ranged from 25 to 78 years and who had a total of 48 peri-implant defects were examined at baseline (week 0) and after 18 weeks. This included the recording of bleeding on probing, pocket probing depths, and probing attachment levels at six sites for each tooth. For 2-18 weeks before week 0 all patients had been treated for peri-implantitis, including motivation, instruction in oral hygiene, and implant scaling with a hand plastic instrument. They were then randomly allocated to continue with this treatment or to have in addition mechanical debridement and local application of Atridox trade mark which slowly release doxycycline. RESULTS: Patients treated with Atridox trade mark showed a significantly greater gain in mean (S.D.) probing attachment levels than those not treated with Atridox. Only subjects treated with Atridox had a significant gain in mean bleeding on probing (P = 0.001). Application of the biodegradable sustained release device after initial periodontal treatment resulted in a significant gain in mean probing attachment levels in the Atridox trade mark group and a significant reduction in pocket probing depths. There was also a significant difference in mean probing attachment levels (0.6mm).
Treatment of severe peri-implant bone loss using autogenous bone and a bioabsorbable polymer that delivered doxycycline (Atridox).
With an increase of the number of implants being inserted, it is inevitable that the number of cases of peri-implantitis with loss of bone will rise. We report a case in which an autogenous cancellous bone graft was placed into the peri-implant bone defect and given protection with a bioabsorbable polymer barrier (Atridox) that released doxycycline slowly.
Biomechanical and clinical implications of distraction osteogenesis in craniofacial surgery.
INTRODUCTION: Craniofacial distraction osteogenesis is an established surgical procedure to correct bony malformations. Force transduction through the osteotomized bone fragments elicits defined biological responses in the gap tissue, which determines the clinical success of the distraction treatment. OBJECTIVE: The purpose of this investigation was to evaluate clinically a new distraction protocol based on an analysis of the biological and biomechanical parameters executing direct effects on bone regeneration during distraction. STUDY DESIGN: A multistep distraction protocol was used in 39 patients and the clinical outcome was monitored postoperatively. RESULTS: All the distraction cases were successful with a single exception. Segmental displacements were stable clinically and radiologically. CONCLUSION: In order to improve the clinical success of distraction osteogenesis, individual treatment protocols are recommended.
Influence of titanium surfaces on attachment of osteoblast-like cells in vitro.
Implant surface topography influences osteoblastic proliferation, differentiation and extracellular matrix protein expressions. Studies on preliminary interactions of osteoblast-like cells on implant interface through in vitro systems, can give lucid insights to osseo-integrative efficacies of when in vivo implants. In the present investigation two titanium surfaces of dental implants, a sandblasted and acid-etched surface and an experimental grooved surface were compared through in vitro systems. The titanium implants were seeded with osteoblast-like primary cells and maintained for a period of 1-7 days. Expressions of fibronectin and osteonectin were assessed through immunogold labelling by scanning electron microscopy. The grooved surface, supported better osteoblastic cell adhesion and proliferation than the rough surfaces. Further, osteoblastic cells on the grooved surfaces also displayed a strong labelling for fibronectin at the cytoplasmic extensions coupled with intense osteonectin expression in comparison to the rough surfaced implants. In conclusion, grooved surfaces offered better cell attachment and proliferation than the other rough surfaces studied.
Treatment of fractures of the atrophic mandible in the elderly.
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[Pharmaceutical industry and "New German Medicine" ("Neue Deutsche Heilkunde")].
THe so-called "New German Medicine", initially propagated in the health policy of the National Socialist Party, promoted greater use of phytotherapeutic and homeopathic drugs by the medical community. In response, the "Reichsfachschaft der pharmazeutischen Industrie e. V." (Association of Pharmaceutical Industry of the Reich") was obliged to pursue a carefully chosen double strategy, given that the members of the Association were both manufacturers of natural remedies and manufacturers of allopathic drugs.However, the fact that I.G. Farben completely ignored the "New German Medicine" suggests that the large chemical-pharmaceutical manufacturers did not take this policy very seriously. The only documents pertaining to increased research in the area of natural remedies stem from the medium-sized manufacturers Knoll and Schering. In the case of both companies it is noteworthy that they worked towards obtaining a scientific foundation for the developed preparates, and that they employed conventional methods of chemical analysis and proof of activity. THe growth of the classical manufacturers of natural remedies, such as the company Willmar Schwabe was, as far as any growth at all could be observed, significantly smaller than had been theoretically postulated. There is no casual relationship between any commercial success during the period in which the Nazis were in power and today's commercial prosperity.Moreover, from the viewpoint of the pharmaceutical industry, the "New German Medicine" seems to have passed its zenith before 1936, when the 4-year plan for war preparation entered into force.
Bone tissue engineering by primary osteoblast-like cells in a monolayer system and 3-dimensional collagen gel.
PURPOSE: To engineer living bone tissue in vitro, bone cells must be multiplied and differentiated in cell culture. Osteoblasts are known to be the crucial cells responsible for the bone modeling process. Periosteal-derived osteoblasts were therefore cultured for up to 3 weeks in Petri dishes as well as in a 3-dimensional collagen gel. METHODS: Proliferation, migration, and differentiation of cells as well as the synthesis of extracellular matrix proteins were monitored during the culture period by histology, electron microscopy, and immunohistochemistry. Mineral formation was investigated by electron diffraction studies and element analysis. RESULTS: Osteoblasts proliferated and migrated in Petri dishes as well as in the collagen gel without loss of viability during the whole experimental period. They demonstrated a mature osteoblast phenotype as indicated by the synthesis of a bone-like extracellular matrix. They formed an extracellular matrix containing osteocalcin, osteonectin, and newly synthesized collagen type I in both environments. Mineral formation was seen in colocalization with the bone-like extracellular matrix proteins in Petri dishes. Microanalytical investigations revealed a matrix vesicle-mediated mineral formation at early stages of culture. CONCLUSIONS: Our cell culture confirmed the ability to multiplicate differentiated and viable osteoblast-like cells in 2- and 3-dimensional space. Additionally, bone-like mineralization can be induced by primary osteoblasts in monolayer culture. The data suggest that this approach can be used as a tool in bone tissue engineering.
New approach to control the methanogenic reactor of a two-phase anaerobic digestion system.
A new control strategy for the methanogenic reactor of a two-phase anaerobic digestion system has been developed and successfully tested on the laboratory scale. The control strategy serves the purpose to detect inhibitory effects and to achieve good conversion. The concept is based on the idea that volatile fatty acids (VFA) can be measured in the influent of the methanogenic reactor by means of titration. Thus, information on the output (methane production) and input of the methanogenic reactor is available, and a (carbon) mass balance can be obtained. The control algorithm comprises a proportional/integral structure with the ratio of (a) the methane production rate measured online and (b) a maximum methane production rate expected (derived from the stoichiometry) as a control variable. The manipulated variable is the volumetric feed rate. Results are shown for an experiment with VFA (feed) concentration ramps and for experiments with sodium chloride as inhibitor.
Validity of a three-dimensional public-domain system for contemporary endodontic research.
The purpose of this study was to evaluate the limits and benefits of a visualization system based on public-domain software for contemporary three-dimensional (3-D) endodontic research purposes. Three-dimensional bio-models of six human teeth and of one bone-implant specimen were generated using cross-sectional imaging. To evaluate the overall performance in processing large data sets and in reproducing accurate 3-D morphology, slices with a thickness varying from 100 microm to 10 microm were cut. Auto-outlining and segmenting techniques were tested. The 3-D bio-models represented in accurate detail the different morphological aspects of the specimen. Voxel volumes of 0.116 x 10(-5) mm3 could be realized and were only restricted by the computer hardware limitations. The system is not limited to dental hard tissues. Hypomineralized material and soft tissues as well as bone- and allogeneic-implant material could be visualized. The method presented is valid and meets current requirements applying to endodontic research. The broad-based use of high-quality, public-domain software and the resulting exchange of experience help to manage resources and may contribute to enhancing the in-process quality of research.
Long-term alterations of oral mucosa in radiotherapy patients.
PURPOSE: The aim of this investigation was to describe the alterations in oral mucosa after radiotherapy. METHODS AND MATERIALS: Biopsies were taken from patients before irradiation, at 60 Gy, and 6-12 months after radiotherapy. Histomorphological evaluation of the vessels was performed, and endothelial expression of ICAM-1, VCAM-1, and E-selectin was also evaluated, as well as distribution of LFA-1-, Mac-1-, VLA-4-, RM3/1-, 27E10-, and 25F9-bearing cells in the subepithelial tissue. RESULTS: The expression of ICAM-1 was downregulated after radiotherapy, whereas the percentage of LFA-1- and VLA-4-bearing cells increased. VCAM-1 remained at low levels. The subepithelial infiltration was still dominated by RM3/1-positive macrophages. The number of vessels decreased, while the lumina of the remaining vessels in the deeper connective layer increased. CONCLUSIONS: The late effects of radiotherapy are characterized by a decreased number of blood vessels and by significantly different expression patterns of the adhesion molecules studied, and of integrins and macrophage subpopulations compared to the conditions before irradiation and at 60 Gy.
[Chance and calculated development! The history of oral antidiabetics].
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Public domain computer-aided surgery (CAS) in orthodontic and maxillofacial surgery.
BACKGROUND: Computer-aided virtual three-dimensional (3D) surgical simulation assists the necessary visual understanding of complex pathological situations but has so far been dependent on expensive hardware and software. METHOD: For the first time a non-commercial, user-orientated application for orthognathic and craniofacial surgical simulation has been introduced, based on freeware NIH Image 1.62 provided by the National Institute of Mental Health (NIMH). Use and limitations are demonstrated here by the example of hypertelorism surgery. The osteotomy lines and the amount of resection for outward positioning of the orbits were determined by the surgeon on a workstation using CT data. Possible movement patterns of the osteotomy fragments were rotations, sagittal and transversal movements or combinations of these. The program then allows the calculation of anatomical distances on the screen in a 1:1 relation. Normative values according to age and pathological anatomy determine the degree of displacement. The program calculates the new position of the osteotomy fragments and transfers the data of the segment movement to the original CT data. RESULTS: 3D visualization of bone and soft tissue contours have been produced with an acceptable quality on a workstation for the demonstration and visual understanding of the surgical plan. Evaluation of a postoperative CT showed that the amount of movement and size of bone resection in the simulation was slightly overestimated rather than underestimated. This was also dependent on the complexity of the pathological anatomy and on how experienced the surgeon was. CONCLUSION: The use of 3D simulation programs allows a better understanding of the pathological anatomy in all dimensions, and in many cases enables limitations to be recognized in advance. The public domain program makes a major contribution to the quality of orthognathic and craniofacial surgical planning through cost-free usability, and supports continuous development and exchange of experience.
On-line titration of volatile fatty acids for the process control of anaerobic digestion plants.
The on-line titration of volatile fatty acids (VFA) was found to be a reliable method to measure the substrate (metabolite) concentration without the use of expensive analytical devices. A measurement cell was designed that ensures stable long-term operation, high throughputs and copes with both very low and very high VFA concentrations. Using synthetic textile wastewater, a recalibration of the pH probe was necessary only twice a week. A good reproducibility of the VFA concentrations was determined and standard deviations were below +/- 1% of the measured concentration. Changing salt concentrations of the wastewater in the range of 2.5-150 gl(-1) NaCl did not influence the determined VFA concentration significantly. The method was suitable to control the hydraulic retention time in an acidic phase reactor and to determine the acidification rates of wastewater compounds in batch experiments.
TCP is hardly resorbed and not osteoconductive in a non-loading calvarial model.
Tricalciumphosphate (TCP) has been used as a ceramic bone substitute material in the orthopedic field as well as in craniofacial surgery. Some controversies exist concerning the osteoconductive potential of this material in different implantation sites. This study was designed to evaluate the biological response of calvarial bone towards TCP granules under non-loading conditions to assess the potential of TCP as a biodegredable and osteoconductive bone substitue material for the cranial vault. Full-thickness non-critical size defects were made bilaterally in the calvaria of 21 adult Wistar rats. One side was filled by TCP granules, the contralateral side was left empty and used as a control. Animals were sacrified in defined time intervals up to 6 months. Bone regeneration was analyzed with special respect toward the micromorphological and microanalytical features of the material-bone interaction by electron microscopy and electron diffraction analysis. Histologic examination revealed no TCP degradation even after 6 months of implantation. In contrast, a nearly complete bone regeneration of control defects was found after 6 months. At all times TCP was surrounded by a thin fibrous layer without presence of osteoblasts and features of regular mineralization. As far as degradation and substitution are concerned, TCP is a less favourable material tinder conditions of non-loading.
Bone loading pattern around implants in average and atrophic edentulous maxillae: a finite-element analysis.
Introduction: Oral implants placed in the maxilla, especially the posterior region, have a lower success rate than those placed in the mandible. Poor bone quantity and quality have been suggested as a reason for this differential success rate. Objective: The purpose of this study was, therefore, to evaluate stress and strain distributions around loaded implants in the normal and atrophic maxilla by finite-element (FE) analyses. Material: FE models of a solitary implant were generated to determine stresses and strains in the bone adjacent to the implant surface under loading conditions. Study design: Different bony situations and implant lengths were used in a FE model. Static loads were applied axially and the resulting stresses and strains calculated. Results: Bone quality and quantity play a major role in decreasing bone strains adjacent to the implant surface under loading. It was found that stresses were more homogeneously distributed when more spongy bone was present. Decreased bone height was found to have less pronounced effects on strain and stress alterations than poor bone quality. Atrophic bony dimensions in combination with poor bone quality were associated with surface strains exceeding physiological levels (>6000 microstrains). Conclusion: Our investigation indicates that supraphysiological bone strains adjacent to the implant surface should be expected under mechanical loading in the atrophic maxilla. Copyright 2001 European Association for Cranio-Maxillofacial Surgery.
Optical data acquisition for computer-assisted design of facial prostheses.
PURPOSE: The conventional impression technique for manufacturing facial prostheses has the disadvantage of deforming the soft tissues because of the tension caused by the impression material, as well as causing discomfort to the patient. The purpose of this study was to establish a system that allows contact-free reproduction of the facial surface combined with computer-assisted design and fabrication of facial prostheses. MATERIALS AND METHODS: Three-dimensional data of the facial surface were obtained using an optical acquisition system based on the method of phase-measuring profilometry. A sensor head with a fringe projector and two CCD cameras for photogrammetric triangulation were used in connection with a PC for measurement control and data evaluation. Software for computer-assisted design of the facial surface to be reconstructed was developed. A prototype facial prosthesis was fabricated using stereolithography. The system was tested using a modified puppet head. First clinical tests were performed with a patient who had undergone maxillofacial surgery including the resection of one eye. RESULTS: Three-dimensional data acquisition and imaging allow visualization of a whole face without causing tension or neuromuscular reaction. As surface brightness is also part of the digital model, it is even more realistic than a plaster cast. The stereolithographic object showed good marginal fit and satisfactory shape. CONCLUSION: The presented technique allows three-dimensional data reproduction of the facial surface, computer-assisted design of a facial prosthesis, and transfer to a rapid prototyping unit. The system has obvious advantages over conventional impression techniques. Further clinical trials are planned to evaluate the clinical success of the technique.