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Biomedical subjects

W Bähr

Publications and source records attributed to W Bähr.

At least 37 records · Page 2Linked to original sources
PubMed1990

[The use of osteosynthesis screws in child mandibles. Anatomical and mechanical considerations].

Thirty seven child mandibular skeletons were analysed radiographically and computer tomographically to establish if there is enough room for osteosynthesis screws. The study demonstrated that in the primary and early mixed dentition there is not enough room in the canine or post-canine region to allow the installation of an osteosynthesis screw without damaging the inferior dental nerve or teeth buds. However, in the later stage of permanent tooth eruption the entire caudal portion of the mandibular body seems to provide sufficient room for osteosynthesis screws. SEM examinations of implant beds of 100 2 mm AO miniscrews inserted into the mandibles of eight fresh cadavers aged eight to twelve years showed cracks, as well as signs of squashing, crushing and shearing stress, regardless of whether the screws were pretapped or not. When, during screw insertion, the axis of the screw deviated by at least 10 degrees from the axis of the tap, two crossing thread courses resulted.

Bone Screws↗
PubMed1989

The effects of pre-tapping on the miniscrew-bone interface in the midface.

The effects of pre-tapping on the AO miniscrew-midface bone interface were investigated in 140 methacrylate-fixed human cadaver specimens. An adequate contact was found in all 40 self-tapped and in 68 out of 100 pre-tapped samples. Since inadequate contact was found in the remaining 32 specimens from the pre-tapped group, it was concluded that the pre-tapping was responsible for the inadequate bone screw interface.

Bone Screws↗
PubMed1989

[Bone contact of miniscrews with and without a pretapped thread].

Better contact between screw and bone when using 2 mm AO-Miniscrews in the human midface is achieved if the thread is not pre-tapped. This could be demonstrated on metacrylate sections. In most implants with pre-tapped threads the bone does not fill out the space between the threaded core and the pretapped hole. The average measured distance between screw and bone is 110 microns. The contact surface between bone and screw is considerably greater than with pre-tapped threads.

Biomechanical Phenomena↗
PubMed1989

[Morphology of bone threads following implantation of 2 mm AO miniscrews in the midfacial area].

How well an osteosynthesis screw holds depends on the amount of friction between the thread flank of the screw and the bone thread. Factors undermining the mechanical integrity of the bone thread, such as cracks, can lead to reduced friction and consequently less ability to hold. To investigate the micromorphology of the bone thread in the thin bone of the midface, 131 bony implant beds of 2-mm AO miniscrews and 10 drill holes which had been pretapped but received no screws were studied by incident light and scanning electron microscopy. The angle of insertion of the screws was varied to assess the effect this has on the implant bed surface. In 30 of the 131 implant beds the insertion axis of the screws corresponded to the axis of the threaded or unthreaded drill holes. Sixty-six of the screws had been inserted at an inclination of greater than or equal to 10 degrees to the axis of the pretapped hole. Twenty pretapped implant beds had an inclination between 0 degrees and 10 degrees to the drill hole. Finally, 15 bone threads formed by inclining the screws upon insertion into untapped drill holes were also studied. Both pretapped and untapped implant bed surfaces were damaged with cracks, as well as signs of squashing, crushing and shearing stress. The extent of the damage often varied in the different implant beds as well as at different locations in the same implant bed. The pretapped implant beds seemed to have a relatively smoother surface when the drill or threader and the screws had the same axis.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone Plates↗
PubMed1977

The functional and fluorescence properties of Escherichia coli RNA polymerase reacted with fluorescamine.

1. Fluorescamine (4-phenylspiro[furan-2,(3)1'-phthalan]-3,3'-dione) reacts rapidly with Escherichia coli RNA polymerase and produces a fluorescent derivative which is inactivated to an extent dependent upon reagent concentration. Excess fluorescamine is rapidly hydrolysed. Reaction is with xi-amino gruops of lysine residues in all subunits as revealed by gel electrophoresis and fluorescence scanning. 2. The extent of inactivation and fluorescence yield are diminished in the presence of added template, a finding which provides evidence for the existence of reactive and essential amino groups which can be at least partially shielded by DNA in the binary complexes. The relative decrease of fluorescence is greatest in the betabeta' subunits. Holoenzyme and core enzyme show essentially the same behavior. 3. The inactivation of activity by fluorescamine is primarily at the level of initiation. Template binding and chain propagation are less affected. 4. The enzyme derivatized by fluorescamine shows an intense fluorescence with a peak at 490 nm and an excitation maximum at 390 nm. The fluorescence lifetime is in the range of 3-8 ns and the emission is highly polarized. In reactions carried out at high ionic strength the fluorescence yield is approximately double that at low ionic strength and insensitive to the presence of template. 5. Energy transfer is observed between the derivatized enzyme as donor and ethidium bromide as acceptor in the presence of template to which both the enzyme and intercalating dye are bound. The transfer efficiency is a function of the relative concentrations and of the conditions of reaction with fluorescamine. An average transfer distance of approx. 4-5 nm has been calculated suggesting a close proximity between bound polymerase and helical regions of the template.

Binding Sites↗
PubMed1975

Covalent attachment of DNA to agarose. Improved synthesis and use in affinity chromatography.

DNA has been covalently linked to insoluble matrices of agarose (Sepharose) in high yield using cyanogen bromide activation. Both double-stranded and single-stranded DNA have been coupled with yields up to 225 nmol/mg dry weight Sepharose or 3-8 mumol nucleotide phosphate/ml bed volume. The DNA-Sepharose has been used for (a) the affinity chromatography of various enzymes (Escherichia coli DNA polymerase I and RNA polymerase) from crude extracts or after initial purification steps, resulting in high yields and degrees of purification, and for (b) nucleic acid hybridization. The DNA-Sepharose is stable to high temperature, prolonged storage, and in the case of single-stranded DNA, can be washed with NaOH to destroy nuclease activity and to release any digested oligonucleotides or mononucleotides.

Animals↗