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Biomedical subjects

U Meyer

Publications and source records attributed to U Meyer.

At least 73 records · Page 4Linked to original sources
PubMed2001

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.

Journal Article↗
PubMed2001

The GPI transamidase complex of Saccharomyces cerevisiae contains Gaa1p, Gpi8p, and Gpi16p.

Gpi8p and Gaa1p are essential components of the GPI transamidase that adds glycosylphosphatidylinositols (GPIs) to newly synthesized proteins. After solubilization in 1.5% digitonin and separation by blue native PAGE, Gpi8p is found in 430-650-kDa protein complexes. These complexes can be affinity purified and are shown to consist of Gaa1p, Gpi8p, and Gpi16p (YHR188c). Gpi16p is an essential N-glycosylated transmembrane glycoprotein. Its bulk resides on the lumenal side of the ER, and it has a single C-terminal transmembrane domain and a small C-terminal, cytosolic extension with an ER retrieval motif. Depletion of Gpi16p results in the accumulation of the complete GPI lipid CP2 and of unprocessed GPI precursor proteins. Gpi8p and Gpi16p are unstable if either of them is removed by depletion. Similarly, when Gpi8p is overexpressed, it largely remains outside the 430-650-kDa transamidase complex and is unstable. Overexpression of Gpi8p cannot compensate for the lack of Gpi16p. Homologues of Gpi16p are found in all eucaryotes. The transamidase complex is not associated with the Sec61p complex and oligosaccharyltransferase complex required for ER insertion and N-glycosylation of GPI proteins, respectively. When GPI precursor proteins or GPI lipids are depleted, the transamidase complex remains intact.

Acyltransferases↗
PubMed2000

Interaction of the Neurospora crassa heat shock factor with the heat shock element during heat shock and different developmental stages.

The interaction of the heat shock factor (HSF) with the heat shock element (HSE) was determined by a non-radioactive electrophoretic mobility shift assay, in order to analyze HSF regulation in Neurospora crassa. HSF binds to HSE under normal, non-stress conditions and is thus constitutively trimerized. Upon heat shock, the HSF-HSE complex shows a retarded mobility. This was also observed in Saccharomyces cerevisiae, where this mobility shift was shown to be due to HSF phosphorylation [Sorger and Pelham (1988) Cell 54, 855-864]. In N. crassa, HSE-dependent electrophoretic mobility shift is temperature- and time-dependent. Under normal growth conditions, the HSF is located in the cytoplasm as well as in the nucleus. In germinating conidia the HSF shows a retarded mobility typical for heat shock even at normal growth temperatures. No HSF-dependent mobility shift was detectable in aerial hyphae.

DNA-Binding Proteins↗
PubMed2000

Active site determination of Gpi8p, a caspase-related enzyme required for glycosylphosphatidylinositol anchor addition to proteins.

Glycosylphosphatidylinositol (GPI) anchors are attached to newly synthesized proteins in the ER by a transamidation reaction during which a C-terminal GPI attachment signal is replaced by a preformed GPI precursor lipid. This reaction depends on GAA1 and GPI8, the latter belonging to a novel cysteine protease family. Homologies between this family and other Cys proteinases, such as caspases, pointed to Cys199 and His157 as potential active site residues. Indeed, gpi8 alleles mutated at Cys199 or His157 are nonfunctional, i.e., they are unable to suppress the lethality of Deltagpi8 mutants. The overexpression of these nonfunctional alleles in wild-type cells leads to the accumulation of the free GPI precursor lipid CP2, delays the maturation of the GPI protein Gas1p, and arrests cell growth. The dominant negative effect of the Cys199 mutant cannot be overcome by the simultaneous overexpression of Gaa1p. Most GPI8 alleles mutated in other conserved regions of the protein can complement the growth defect of Deltagpi8, but nevertheless accumulate CP2. CP2 accumulation, a delay in Gas1p maturation and a slowing of cell growth can also be observed when Gpi8p is depleted to 50% of its normal level in wild-type cells. The dominant negative effect of nonfunctional and partially functional mutant alleles can best be explained by assuming that Gpi8p works as part of a homo- or heteropolymeric complex.

Alleles↗
PubMed2000

[Experimental and finite-element models for the assessment of mandibular deformation under mechanical loading].

Biomechanical investigations of the mandible are difficult to perform due to a variety of conditions involved. For the appropriate reconstruction of biomechanical properties, a geometrically correct body model has to be established which fits to complex in vivo conditions. The aim of our study was to evaluate the use of finite-element models (FEM) for the assessment of mandibular deformation under mechanical loading. Explanted human mandibles (n = 5) were investigated by strain gauges to determine the individual strain distribution under mechanical loading. FEM analysis based on a computed tomograph (CT) was performed and the results were matched with the test data. Our study demonstrates only minor interindividual differences in the strain distribution for each load studied. The mechanical response in terms of deformation was found to depend mainly on gross geometrical properties and to a minor extent on the various other variables. At all positions the maximum principal strain was tensile, the minimum principal strain was compressive, and the absolute strain values were correlated with the magnitude of the applied force. CT-based FEM analysis revealed the utility of mathematical models to approximate simulated data our experimental results. Hence, FEM analysis is a non-invasive tool in the prediction of biomechanical behaviour of individual mandibles and therefore may help in trauma reconstruction and treatment planning.

Biomechanical Phenomena↗
PubMed2000

Clinical anatomy and palpability of the inferior lateral pterygoid muscle.

STATEMENT OF PROBLEM: The intraoral palpation technique of the inferior belly of the inferior lateral pterygoid (ILP) muscle is a standard diagnostic examination method for temporomandibular joint dysfunction syndrome, although different studies have revealed inconsistent results. PURPOSE: This study assessed the feasibility of the ILP muscle palpation by a simulated clinical setting. MATERIAL AND METHODS: Three dentists performed a bilateral palpation of the ILP muscle in 53 fresh and unfixed human cadavers and decided whether the muscle was palpable or unpalpable. In a second step, it was observed through the dissected infratemporal fossa, whether the examiner's finger did or did not touch the ILP muscle by simulating the performed palpation. Palpatory findings were supplemented by 1-dimensional measurements for determination of topographic relations of the ILP muscle within the infratemporal fossa. For statistical analysis, sensitivity, specificity, and negative and positive predictive values of the palpation technique were calculated. Interexaminer agreement was estimated with the kappa value. RESULTS: In 86 of 106 dissected specimens, a superficial fascicle of the medial pterygoid muscle was found in direct proximity to the ILP muscle. In these cases, a residual distance of 7.8 +/- 3.2 mm remained between the ILP muscle and buccinator fascia indented by the tip of the examiner's finger. In 10 of 20 specimens with an absent superficial fascicle, the finger was able to reach the ILP muscle. CONCLUSION: It is recommended that the ILP muscle palpation technique should no longer be considered as a standard clinical procedure because it is nearly impossible to palpate the ILP muscle anatomically and because the risk of false-positive findings (by palpation of the medial pterygoid muscle) is high.

Facial Pain↗
PubMed2000

Oral findings in three different groups of immunocompromised patients.

The objective of this study was to determine the frequency of oral, dental and periodontal findings in three different groups of immunocompromised patients and in a healthy control group, to evaluate whether there is a correlation between manifestations of disease and immunologic parameters. The survey included 46 patients with a diagnosis of systemic lupus erythematosus, 48 heart transplant recipients, and 53 adult patients suffering from acute leukemias. Fifty matched healthy subjects were used as a control group. Each patient had to answer questions on medical and dental health and underwent a thorough oral, dental and serological investigation. Oral mucosal lesions were found in nearly half of all immunocompromised patients (49.6%), but in only 26% of control patients. No significant associations were found between different types of oral lesions and the underlying cause of immunosuppression. Leukemia patients showed age-unrelated higher scores in periodontal indices (P<0.05). Laboratory parameters failed to be significant in the assessment of oral health.

Adult↗
PubMed2000

Experimental and finite element study of a human mandible.

Knowledge of the complex biomechanical behaviour of the human mandible is of great importance in various clinical situations. Various approaches can be used to evaluate the physical behaviour of bony specimens. In the course of this study, we investigated mandibular deformation under mechanical loads in an experimental setting and compared them with results derived from finite element analysis (FEA). A special apparatus was developed to apply various forces under defined conditions on an explanted human mandible in vitro. Strains on the surface of the mandible were measured with strain gauges and subsequently a voxel based finite element mesh was generated. Strain patterns of the mandible were calculated in the FE analysis and matched with the experimental data. Comparing the numerical with the experimental data, we found a good correlation between in vitro measurements and mathematical modelling (correlation coefficient = 0.992). Then the FE model was used to evaluate mandibular biomechanics relative to aspects of load transfer, stress distribution and displacements. It is concluded that the applied procedure of generating the FE model is a valid and accurate, non-invasive method to predict different parameters of the complex biomechanical behaviour of human mandibles.

Biomechanical Phenomena↗
PubMed2000

Phosphatidylethanolamine is the donor of the phosphorylethanolamine linked to the alpha1,4-linked mannose of yeast GPI structures.

Glycosylphosphatidylinositol (GPI) anchors of all species contain the core structure protein-CO-NH-(CH(2))(2)-PO(4)-Manalpha1-2Manalpha1-6Manalpha1-4GlcNalpha1-6inositol-PO(4)-lipid. In recent studies in yeast it was found that gpi10-1 mutants accumulate M2, an abnormal intermediate having the structure Manalpha1-6[NH(2)-(CH(2))(2)-PO(4)-->]Manalpha1-4GlcNalpha1-6(acyl-->)inositol-PO(4)-lipid. It thus was realized that yeast GPI lipids, as their mammalian counterparts, contain an additional phosphorylethanolamine side chain on the alpha1,4-linked mannose. The biosynthetic origin of this phosphorylethanolamine group was investigated using gpi10-1 Deltaept1 Deltacpt1, a strain which is unable to synthesize phosphatidylethanolamine by transferring phosphorylethanolamine from CDP-ethanolamine onto diacylglycerol, but which still can make phosphatidylethanolamine by decarboxylation of phosphatidylserine. Gpi10-1 Deltaept1 Deltacpt1 triple mutants are unable to incorporate [(3)H]ethanolamine into M2 although metabolic labeling with [(3)H]inositol demonstrates that they make as much M2 as gpi10-1. In contrast, when labeled with [(3)H]serine, the triple mutant incorporates more label into M2 than gpi10-1. This result establishes that the phosphorylethanolamine group on the alpha1,4-linked mannose is derived from phosphatidylethanolamine and not from CDP-ethanolamine.

Carbohydrate Sequence↗
PubMed2000

Identification of two genes encoding putative new members of the ECF subfamily of eubacterial RNA polymerase sigma factors in Clostridium acetobutylicum.

Two genes from Clostridium acetobutylicum DSM 792 were identified which are predicted to encode new members of the ECF subfamily of eubacterial RNA polymerase sigma factors. The sigX gene has the potential to encode a 184-amino acid protein with a molecular mass of 21,870 Da and with the highest overall similarity to Fecl of Escherichia coli (27 % identical residues). The second gene, which is predicted to encode an alternative sigma factor of the ECF subfamily, is the previously described orf2 gene (Gerischer and Dürre, 1990) located in the adc gene region of C. acetobutylicum. The deduced protein of orf2 has significant similarity to SigX of C. acetobutylicum (22 % identical residues) and shares structural features with other alternative sigma factors. Therefore, it is proposed to rename orf2 as sigY. Analysis of the phylogenetic relationship revealed that SigX from C. acetobutylicum, together with sigmaE from Streptomyces coelicolor and SigX from Bacillus subtilis, form a gram-positive cluster within the ECF subfamily and that SigY from C. acetobutylicum together with UviA from Clostridium perfringens, form a separate cluster located between the gram-positive cluster and the sporulation sigma factor sigmaH from B. subtilis.

Amino Acid Sequence↗
PubMed2000

A subgroup-specific evaluation of the efficacy of intraarticular triamcinolone hexacetonide in juvenile chronic arthritis.

OBJECTIVE: To determine the subgroup-specific differences of intraarticular triamcinolone hexacetonide (TH) in the treatment of joint inflammation in patients with juvenile chronic arthritis (JCA). METHODS: A retrospective review of 194 children of all subgroups of JCA, treated by a single or repeated TH injection between 1989 to 1994. Efficacy and duration of benefit were evaluated after a mean duration of 3, 15, 30, and 64 weeks. RESULTS: In all, 1439 TH injections were given to 194 patients; 368 of these were reinjections. The median duration of improvement of all injections was 74 weeks. Responses were significantly different among subgroups (p = 0.0001): there were 121 weeks of efficacy in early-onset pauciarticular JCA type I (223 injections), 47 weeks in late-onset pauciarticular JCA type II (190 injections), 105 weeks in rheumatoid factor negative polyarticular JCA (445 injections), 63 weeks in rheumatoid factor positive polyarticular JCA (127 injections), and 36 weeks in systemic JCA (413 injections). Forty-one injections were done in other rheumatic diseases. In relation to this result there were also differences with regard to joint groups, antinuclear antibody (ANA) and HLA-B27 status, and sex. Side effects were rare: infections of skin or joints were not noted; skin and lipoatrophy were seen after 15 injections, necrosis of the hip in one case, luxation of 2 shoulders of one patient, and periarticular calcification in 3 patients. CONCLUSION: Intraarticular TH is an effective therapy for inflammatory joint disease in all subgroups of JCA. The risk of major complications is low. The median duration of improvement depends on the subgroup of the disease.

Administration, Topical↗
PubMed2000

["My contribution to humanity". The work of the Prussian lay physician Arthur Lutze (1813-1870)].

The aim of this paper is to describe the life and work of the homeopathic lay physician Arthur Lutze (1813-1870), particularly his work in Prussia. The paper also helps explain the extraordinary popularity of non-medical practitioners during this period. Lutze's years in Prussia were fundamental for his homeopathic ambitions, since they afforded him access to many of the renowned homeopaths of the period. Lutze gained popularity by focusing his practice on the common people. Even though he was not licensed and he collaborated with unknown non-medical practitioners, Lutze gained legitimacy through the work of properly certified doctors.

Germany↗
PubMed1999

Irradiation induces increase of adhesion molecules and accumulation of beta2-integrin-expressing cells in humans.

PURPOSE: The purpose of our investigation was to describe the dose- and time-dependent histomorphologic alterations of the irradiated tissue, the composition of the infiltrate, and the expression patterns of various adhesion molecules. METHODS AND MATERIALS: We analyzed immunohistochemically alterations in oral mucosa in 13 head and neck cancer patients before radiotherapy and with 30 Gy and 60 Gy. All had oral mucosa irradiation, with a final dose of 60 Gy using conventional fractionation. Snap-frozen specimens were stained using the indirect immunperoxidase technique. Histomorphology was studied in paraffin-embedded sections. In addition, we determined the clinical degree of oral mucositis. RESULTS: Histomorphologic evaluation showed no vascular damage. Irradiation caused a steep increase of beta2-integrin-bearing cells (p < 0.01), whereas the percentage of beta1-integrin-positive cells remained at low levels. Additionally we found an increase in the expression of endothelial intercellular adhesion molecule-1 (ICAM-1) (p < 0.01) and E-selectin (p < 0.05), while endothelial vascular cell adhesion molecule-1 (VCAM-1) expression remained at very low levels. CONCLUSION: Our findings indicate that in radiation-induced oral mucositis there is no marked vascular damage until the end of radiotherapy. For recruitment of leukocytes, beta2 is more involved than beta1. Pharmaceuticals that block leukocyte adhesion to E-selectin or ICAM-1 may prevent radiation-mediated inflammation in oral mucosa.

Aged↗
PubMed1999

Identification of apoptotic cell death in distraction osteogenesis.

The purpose of this experimental work was to investigate whether apoptosis contributes to tissue remodelling during distraction bone healing. In a rabbit model of mandibular distraction osteogenesis, we quantitatively analysed the extent of apoptotic cell death in relation to differently applied mechanical loadings. Apoptotic cells were identified by means of an in situ detection assay for nuclear DNA fragmentation using a modified TUNEL procedure and by electron microscopical examination for typical morphological features of programmed cell death. TUNEL-positive cells were frequently detected in samples distracted at higher strain magnitudes. Ultrastructurally, these apoptotic cells displayed a condensed chromatin and fragmented nuclei, while the continuity of their plasma membranes remained intact. Our results clearly indicated that the discontinuous traction of osteotomized mandibles induced enhanced apoptosis. In contrast to non-distracted samples and mandibles distracted at low strain magnitudes, in which only minimal evidence of apoptotic cell death was detected, the application of hyperphysiological strain magnitudes resulted in an increased apoptosis rate. Thus, mechanical loading seems to be a triggering factor for apoptotic changes in osteoblastic cells. These findings suggest a pathophysiological role of apoptotic cell death in the control of tissue integrity during distraction osteogenesis.

Animals↗
PubMed1999

Heart transplants--assessment of dental procedures.

The object of this study was to evaluate the effects of dental foci on survival rates and rejection episodes in heart transplant recipients. Therefore, in a retrospective longitudinal study we studied 74 heart transplant recipients at the Department of Maxillofacial Surgery and Department of Thoracic and Cardiovascular Surgery, University of Münster. Study patients were divided into groups: those in which dental foci had been verified (n = 31) and those without dental foci (n = 43). Statistical analysis was performed using the chi-square test, Kaplan-Meier life table analysis, and the log-rank test. Before heart transplantation, patients were screened clinically and radiographically to determine the extent of dental foci. Postoperatively, patients were evaluated dentally and medically to identify the impact of dental foci on the incidence of systemic and oral infections, frequency and severity of rejection episodes, mortality, and complications arising during dental treatment. By comparing the mortality, infection and rejection rates in the various groups no statistically significant differences (P > 0.05) were found between patients. Despite immunosuppression, extended inflammatory processes such as abscess formation or viral stomatitis were not found in the oral cavity. We therefore suggest that patients suffering from the symptoms of severe heart failure need not be subjected to rigorous preoperative dental treatment.

Bacteremia↗
PubMed1999

[Regeneration of mouth mucosa in the buccal plane following graft procurement for reconstruction of bulbar urethral stenoses].

The use of free buccal mucosal grafts in the treatment of urethral strictures has become very popular. In 1996 and 1997 we harvested free buccal mucosal grafts up to 7 cm long and 4 cm wide from 12 patients who underwent urologic surgery for urethral strictures. In 2 patients the donor site was closed primarily by sutures. Four patients received Lyodura and another 4 patients received Syspurderm as temporary wound coverage. In 2 patients Ethisorp patches were used. Donor site pain was judged by the patients on a visual analogue scale during the first postoperative week. The 2 patients who received the Ethisorp patches complained of more intense pain, probably caused by the rigidity of the material. In all patients regeneration of the donor site mucosa was good. During the follow-up period of 4-18 months scar formation at the lower vestibulum was noticed as the only complication. Permanent limitation of mouth opening, stenosis of the parotid duct or hypesthesia did not occur.

Adolescent↗
PubMed1999

[Examining patients with facial skull fractures from an etiological and legal perspective].

Maxillofacial traumas are common and often associated with other injuries. From a forensic point of view, it is often necessary to relate the traumatic event to the subsequent injuries. The aim of this study was to explore the etiology of maxillofacial injuries due to objective signs and the anamnestic history of patients. In a prospective study over a 1-year period, all patients presenting with mandibular and midface fractures seeking treatment at the University Medical Center in Münster. Germany, were investigated. Demographic data, patient history, and pattern and etiology of injury were recorded, along with evaluations of the patients' descriptions. Thorough clinical and radiological investigation was performed and photographic records were taken. In our study, 122 patients, with a male to female ratio of 2:1 were included. The mean age was 30.7 +/- 13.4 years. Assault was the most common etiology (40%), followed by traffic accidents (29%) and falls (17%). Alcohol was reported to play a role in 40% of all injuries. There was no difference in the number of patients with mandibular or midface fractures. In 75%, maxillofacial fractures were associated with other injuries. The patients' descriptions of the orofacial traumas seemed to be highly. For age, anatomical location, concomitant injuries, and other signs of trauma, we found no statistical association with the underlying etiology.

Adolescent↗