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Biomedical subjects

M Behr

Publications and source records attributed to M Behr.

At least 55 records · Page 3Linked to original sources
PubMed1998

Intraoral repair of fiber-reinforced composite fixed partial dentures.

STATEMENT OF THE PROBLEM: Fractured composite facings may result in replacement of a fixed partial denture unless a reliable intraoral repair method can be provided. PURPOSE: This in vitro study tested the quality of an intraoral repair method for fractured facings of fixed partial dentures made of a fiber-reinforced composite system. MATERIAL AND METHODS: Shear bond strengths of a light-curing composite to a fiber-reinforced composite material were determined after different mechanical surface treatments. Aluminum oxide air abrading provided the most reliable bond strength values and therefore was used as a pretreatment for the facing repair of three-unit posterior fixed partial dentures. Facing repair was performed with the tested light-curing hybrid composite. Facing fracture strengths of repaired and original fixed partial dentures were determined after thermocycling and mechanical loading. RESULTS: Median facing fracture strength of the original fixed partial dentures was 1450 N after a simulated clinical service of 5 years. Facing fracture strengths of the repaired fixed partial dentures were significantly lower compared with the control group after an additional simulated 2-year interval. However, the median fracture force was still 1000 N. CONCLUSIONS: The facing repair of a fiber-reinforced fixed partial denture with a hybrid composite in combination with aluminum oxide air-abrading pretreatment and silanization provided sufficient fracture strength. Therefore the replacement of the complete restoration may be avoided.

Acrylates↗
PubMed1998

Complication rate with prosthodontic reconstructions on ITI and IMZ dental implants. Internationales Team für Implantologie.

The aim of this study was to compare the complication rate of two implant systems with different prosthodontic concepts: rigid conical or resilient support of the suprastructure. In 66 patients, 138 ITI implants were inserted whereas 31 patients received a total of 50 IMZ implants. Over an average observation period of 3.5 years (range from 0.5 to 8 years), not only was implant survival recorded, but also prosthodontic complications such as screw loosening, fractures of screws, inserts (intramobile elements, intramobile connectors) and abutments, as well as fractures of metal framework and veneers. With the ITI system, 28.8% of all devices placed exhibited such problems during the observation period. With the IMZ system, this rate was significantly higher (P < 0.05), in that 77.4% of all reconstructions required a repair at some point. The various complications were divided into those occurrences which affected only the suprastructure, i.e., failures of frameworks, veneers, bar devices or other retentive elements, and those which involved implant components per se, such as screws and abutment components. In the first category, adverse effects occurred more frequently with ITI-supported prostheses (15.1%) versus IMZ suprastructures (6.4%). Regarding complications with implant components, the rate with IMZ components was considerably higher (71%) compared with ITI (13.5%). This was mainly due to the presence of intramobile elements (IME) and connectors (IMC) in the IMZ system. In this retrospective study, precise fitting, non-resilient abutment components leading to rigid connections of suprastructures, proved to be clinically more successful than resilient anchoring components.

Adolescent↗
PubMed1998

Tissue distribution of hantavirus antigen in naturally infected humans and deer mice.

The Sin Nombre virus (SNV) is the etiologic agent of hantavirus pulmonary syndrome in humans but does not cause disease in chronically infected deer mice (Peromyscus maniculatus), the natural host. In this study, murine antiserum raised against recombinant SNV nucleocapsid protein was utilized to localize viral antigen immunohistochemically in tissues from both humans (n = 20; 11 positive, 9 negative) and deer mice (n = 6; 4 positive, 2 negative). Viral infection status was confirmed by Western blot or reverse transcriptase-polymerase chain reaction. SNV antigen was detected in pulmonary and cardiac endothelium in both species, but positive cells in deer mice were rare. Other deer mouse tissues, including kidney, were negative; in contrast, vascular elements of several tissues from infected humans were positive, with strong staining of renal endothelium. The paucity of positive cells in chronically infected mice suggests a low virus burden compared with that of acutely infected humans.

Animals↗
PubMed1998

In vivo color stability of resin composite veneers and acrylic resin teeth in removable partial dentures.

OBJECTIVE: The color stability of laboratory-made composite veneers was compared to that of artificial resin teeth under in vivo conditions. METHOD AND MATERIALS: Veneers and resin teeth of removable partial dentures were measured colorimetrically with reflection spectrophotometry; the color changes were characterized in the Commission Internationale d'Eclairage L*a*b* color space. The color was first determined 24 hours after manufacture and again after 6, 12, and 18 months at incisal, cervical, and centrofacial tooth positions. The denture teeth and veneers were measured, cleaned to eliminate the influence of surface discoloration, and measured again at every recall. The food consumption and tooth cleaning habits of the patients were taken into account. RESULTS: In all groups the maximum color changes from the baseline measurement were delta L* = 2.1, delta a* = 0.4, and delta b* = 1.8. The changes in the delta E* values were between 1.0 and 2.5 units. Despite polishing, the delta E* values increased by approximately 0.2 to 0.3 units in relation to the previous measurement with increased wearing time. External discolorations were eliminated by polishing, depending on the type of material; the maximum color change because of polishing was between 0.8 and 2.0 units for delta E*. The resin teeth showed no significant changes in the delta E* values. CONCLUSION: After a wearing period of 18 months, the discolorations of the tested materials were clinically acceptable. The artificial resin teeth showed statistically smaller color changes than did the veneering materials.

Color↗
PubMed1998

In vitro study of fracture strength and marginal adaptation of fibre-reinforced-composite versus all ceramic fixed partial dentures.

In this in vitro study fracture strength and marginal adaptation of adhesive-fixed three-unit posterior fixed partial dentures made with two different fabrication modifications--with and without the retainer material "Single"--of the new fibreglass system Vectris/Targis and from the metal-free Al2O3-ceramic In-Ceram were examined. The quality of the marginal adaptation was characterised using SEM evaluation and dye penetration techniques. In-Ceram and Vectris/Targis with "Single" showed good marginal adaptation, both statistically significantly better than the modification without "Single". After thermal cycling and mechanical loading the fibreglass reinforced systems showed a significantly higher fracture strength than the In-Ceram.

Aluminum Oxide↗
PubMed1997

Expression of a functional tagged human thyrotropin receptor in HeLa cells using recombinant vaccinia virus.

We report a new effective system for expression of FLAG and six histidine tagged TSH receptor in mammalian cells using recombinant vaccinia virus. HeLa cells infected with recombinant virus produced large amounts of human TSH receptor of approximately 150,000 functional molecules per cell. This value is one to two orders of magnitude higher than those in thyroid cells and is comparable with receptor number of the best stably transfected mammalian cell clones previously described. Vaccinia virus produced TSH receptor was able to bind TSH (Kd of 2.1 +/- 0.1 x 10(-10) M) and Graves'disease autoantibodies. TSH caused an increase of the intracellular cAMP level in infected HeLa cells in a concentration-dependent manner, demonstrating the coupling of expressed recombinant TSH receptor to the cAMP second messenger system of the cells. 6His-tagged recombinant TSH receptor was immobilized on Ni2+ nitrilotriacetic acid-agarose. Bound receptor was fully functional, interacting with both TSH and Graves' disease autoantibodies in patient sera. The solid phase bound TSH receptor technique provides a new and simple method for the diagnosis of autoimmune diseases.

Autoantibodies↗
PubMed1997

[Artifacts in MR imaging of the temporomandibular joint caused by dental alloys: a phantom model study at T1.5].

PURPOSE: The influence of dental alloys on MRI of the temporomandibular joint was studied using a phantom model for this joint. METHODS: At 1,5 T, 15 dental alloys and 14 of their most important components were investigated acquiring sagittal (FOV: 150 mm) and transverse (FOV: 250 mm) T1-weighted SE images. In 11 cases, T1- and T2*-weighted FLASH images were measured additionally. The artifacts were assessed qualitatively as well as quantitatively, and the samples were subdivided into four artifact categories. RESULTS: Ag, Cu, Ga, In, Tl, Sn, Zn, amalgam, the precious alloys, the Au-Pd and Ag-Pd alloys showed no artifacts (category I). Minimal artifacts below 10 mm on transverse images (category II) were found for Cr, Pd, Pt and for the Ni-Cr alloy. Mn and the remaining non-precious alloys induced artifacts up to 30 mm (category III). Significant artifacts-more than 30 mm-(category IV) were caused by Ni-Cr and 18/8 wires and by Co, Fe, and Ni. T2*-weighted FLASH proved to be more susceptible for artifacts than T1-weighted SE and FLASH techniques. CONCLUSIONS: In contrast to dental alloys for fixed prosthodontics, Ni-Cr- or 18/8 wires used for orthodontic bands can influence not only the image quality, but also the diagnostic reliability of MRI of the temporomandibular joint.

Artifacts↗
PubMed1997

Deoxyribonucleic acid binding and transcriptional silencing by a truncated c-erbA beta 1 thyroid hormone receptor identified in a severely retarded patient with resistance to thyroid hormone.

We describe the analysis of a thyroid hormone receptor (TR) beta causing resistance to thyroid hormone, the patient exhibiting hypothyroid symptoms (severe mental retardation, hypoactivity, obesity) and hyperthyroid symptoms (tachycardia, low serum cholesterol) and, additionally, relative early puberty, advanced bone age, and short stature. The patient was heterozygous, with a point mutation producing a premature stop-codon in TR beta-gene exon 10, resulting in a 28-amino acid carboxy-terminal deletion in the cognate TR beta (TR beta-EZ). T3 binding was abolished. Homodimer binding of TR beta-EZ to DR4- and F2-T3 response elements (TREs) was weaker, and to a palindromic TRE (PAL) was stronger than that of wild-type TR beta (TR beta-WT) in the absence of T3. T3 dissociated TR beta-WT, but not TR beta-EZ homodimer, from DR4, F2, and Pal. Heterodimerization of TR beta-EZ with retinoid x receptor beta was seen. TR beta-EZ repressed basal thymidine kinase-promotor activity, coupled to DR4, F2, or PAL. Silencing of basal gene transcription via PAL was weaker, and via DR4 and F2 was more pronounced, compared with TR beta-WT. TR beta-EZ had a strong dominant negative effect on TR beta-WT, attenuated in a TRE- and cell-specific manner by high T3 concentrations. Finally, the degree of TR beta-EZ homodimer-binding affinity to DNA did not correlate with the degree of transcriptional dominant negative activity.

Adolescent↗
PubMed1997

Colour stability of visible light-curing hybrid composites.

The colour stability of six visible light-curing fine hybrid composites was evaluated after 24 and 120 hours of irradiation using a xenon lamp. Discoloration of four shades of each material (A1, A2, A3.5 and B2- Vita shade guide) was measured using a reflection spectrophotometer with the CIE-L*a*b* system. The discoloration after 24 hours of irradiation had values of between 0.7 and 3.8 DE*, and was therefore, with the exception of Z 100 (colours A1 and B2), clinically acceptable. The results showed that the differences in colour of all shades of Pekafill NF and Tetric tested were significantly less than those of the other products. All samples, with the exception of Pekafill NF (A3.5 and B2), showed increased discoloration to values of 3.7 to 7.8 DE* after 120 hours of exposure to UV light. In general, all the composites tended to become more yellow (b*), darker (L*) and slightly greener (a*).

Analysis of Variance↗
PubMed1996

Diagnostic potential of pseudo-dynamic MRI (CINE mode) for evaluation of internal derangement of the TMJ.

In addition to the patient's history and a thorough clinical investigation, magnetic resonance imaging (MRI) of the temporomandibular joint (TMJ) has been introduced to complete the findings for the diagnosis of internal derangement of the TMJ. However, 'dynamic information' is desirable to help us to understand the mechanism of internal derangement. This information is given for example by electronic axiography recording systems. The lack of any ability to assess joint function dynamically in MRI is a point of criticism. Using a computer-driven pseudodynamic MRI system (CINE mode) 'dynamic information' should be now available. In this investigation 21 patients with TMJ disorders were examined using both conventional static MRI and CINE mode. For the diagnosis of an anterior displaced disc with or without reduction in 18 cases (86%) it was only necessary to consider two static MRIs: a closed mouth position and a maximal open mouth position. Comparison showed there was no advantage in using CINE mode. Contrast and resolution of the static MRIs were shown to be better and so additional findings such as joint effusion and disc deformation could be diagnosed on static MRIs with greater certainty. Only in three (14%) cases was the dynamic information from CINE mode useful for the diagnosis of the displacement of the disc.

Adult↗
PubMed1996

Periodically hyperthyroid phenotype in thyroid hormone resistance is associated with mutation D322N in the thyroid hormone receptor beta gene: transcriptional properties of the mutant and the role of retinoid X receptor.

We report a point mutation in the ligand-binding domain of the TR beta 1 gene in an affected patient and his daughter. The phenotype was borderline hyperthyroid with periodic aggravation of symptoms. In the cognate variant TR beta (TR beta-CN) amino acid codon 322 was exchanged from aspartic acid to asparagine. TR beta-CN revealed strongly decreased T3-binding activity. At low T3 levels TR beta-CN transactivated a palindromic thyroid hormone response element (TRE-PAL) only to a limited extend, whereas full activity was retained at a high T3 concentration. At low T3 levels, TR beta-CN exerted a dominant negative effect on wild-type TR beta, whereas this effect was diminished in the presence of high T3 concentrations. TR beta-CN could not be activated by retinoid X receptor (RXR) beta in the presence of T3, whereas addition of 9cis-retinoic acid (9c-RA) resulted in the transactivation of TRE-PAL through RXR beta independently of the presence of TR beta-CN. In conclusion, the time dependent variable THR phenotype of patient CN might be influenced by the differential expression of RXRs and the T3 and 9c-RA hormonal status.

Adult↗
PubMed1996

MR-imaging of the TMJ: artefacts caused by dental alloys.

The aim of the study was to investigate the influence of dental alloys and their components on magnetic resonance imaging of the temporomandibular joint. A plaster and a water- filled acrylic resin phantom - representing the disc and the condyle of the TMJ - were used. Cylindrical crow-type samples of 13 alloys and 14 pure substances were investigated. All alloys were examined with regard to their magnetic susceptibility, using a vibrating sample magnetometer. Metallic artefacts appeared on spin-echo technique as distortions, and on gradient-echo technique signal loss could be observed. Precious alloys were shown to be diamagnetic. The non precious alloys we investigated were paramagnetic. Paramagnetic alloys with a magnetic molar-susceptibility Cmol > 2000 x10(-6) cm3/mol can produce clinically relevant artefacts.

Artifacts↗
PubMed1995

Comparative study of results of electronic axiography with results of magnetic resonance imaging including MRI-assisted splint therapy.

The most common temporomandibular joint disturbance is the internal derangement. Its prevalence has been shown to be as high as 28%. The purpose of this study was on one hand to compare the diagnostic efficiency of an electronic axiographic system with magnetic resonance imaging, and, on the other hand to evaluate the results of MRI-assisted treatment monitoring of occlusal splint therapy. The results of this survey clearly show that in evaluation of temporomandibular joint disorders, electronic axiography and magnetic resonance imaging should be used in conjunction with one another to increase the accuracy of positive and differentiated diagnoses. The medical concept of disc recapture involving the use of occlusal splints seems to be merely a clinical term which is not necessarily hinged on anatomical intraarticular changes.

Adult↗
PubMed1993

A heritable point mutation in an extracellular domain of the TSH receptor involved in the interaction with Graves' immunoglobulins.

The TSH receptor (TSHR) is the central antigen in Graves' disease. Variant receptor proteins, arising from mutations in the TSHR gene, may play a role in the pathogenesis of the disease. Therefore, we analysed the TSHR from a 38-year-old patient affected with autoimmune hyperthyroidism, diffuse goitre and ophthalmopathy. Reverse transcription PCR and DNA amplification followed by DNA sequencing revealed a point mutation (C-->A) at cDNA position 253 in one of two alleles. This leads to the replacement of a proline (CCC) by threonine (ACC) at amino acid position 52 of the predicted receptor protein. Secondary structure predictions indicated a major change of protein structure as a result of the mutation. By using allele-specific PCR, we were able to show that this mutation is heritable. Screening of 50 random individuals revealed that four of them also carried this mutation in the heterozygous state. This study shows the presence of different forms of the TSHR gene in the population. The mutation, which is in a portion of the receptor apparently involved in binding of Graves' immunoglobulins, is discussed as to its possible pathophysiological role in autoimmune hyperthyroidism.

Adult↗
PubMed1992

A point mutation (Ala229 to Thr) in the hinge domain of the c-erbA beta thyroid hormone receptor gene in a family with generalized thyroid hormone resistance.

Various point mutations in the c-erbA thyroid hormone receptor (TR) beta gene of unrelated kindreds have been reported to be responsible for different phenotypes of generalized thyroid hormone resistance. We now report a new point mutation, Td, in one of two TR beta alleles of three affected members of one family, designated family T. In contrast to the previously described point mutations, all located in the T3-binding domain of the TR beta gene, mutation Td was identified in the carboxy-terminal part of the hinge domain. Direct sequencing of the polymerase chain reaction-amplified whole coding region of the patients' fibroblast TR beta genes displayed a single guanine to adenine transition at cDNA nucleotide position 985. This altered alanine (GCC) to threonine (ACC) in codon 229. Garnier prediction of the consequence of the mutation indicated an altered secondary structure. The G----A nucleotide substitution was not present in 80 random TR beta alleles, suggesting that this point mutation is responsible for generalized thyroid hormone resistance in family T. The in vitro expressed mutant TR beta was shown to bind with high affinity to various thyroid hormone response elements. However, the affinity of the TR beta to bind to T3 was reduced 3-fold, indicating that the hinge domain of the TR beta is important for full ligand-binding activity. Moreover, it seems that multiple subdomains of the TR beta interact cooperatively to achieve optimal T3 activity.

Alleles↗
PubMed1991

Analysis and nucleotide sequence of the genes encoding the surface-layer glycoproteins of the hyperthermophilic methanogens Methanothermus fervidus and Methanothermus sociabilis.

The genes (slgA) encoding the surface-layer glycoproteins of the hyperthermophilic methanogens Methano-thermus pervidus and Methanothermus sociabilis were cloned and sequenced. The nucleotide sequences of these genes differ at only nine positions, resulting in three amino acid differences. In both organisms, the transcription start site was localized by primer extension analyses. The DNA sequence at this site conforms to the promotor box B motif for promotors of archaea. 24 nucleotides upstream of the transcription start is an A + T-rich region, which closely resembles the consensus box A motif of promoters of methanogens. Ribosome binding sites are exactly complementary to the 3' end of the 16S rRNA of these methanogens. Both slgA genes encode for a precursor of the mature surface-layer protein containing 593 amino acid residues with a putative N-terminal signal sequence of 22 amino acid residues. The deduced protein sequences contain 20 sequon structures representing possible carbohydrate-binding sites. In comparison with other surface-layer proteins, these obtained from the two hyperthermophilic methanogens contain unusually high amounts of isoleucine, asparagine and cysteine residues. Predicted secondary structures have a high content of beta-sheet structure (44%) and only 7% alpha-helix structures.

Amino Acid Sequence↗