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Biomedical subjects

J Hahn

Publications and source records attributed to J Hahn.

At least 73 records · Page 4Linked to original sources
PubMed1995

Enantioselective determination of chiral 2,2',3,3',4,6'-hexachlorobiphenyl (PCB 132) in human milk samples by multidimensional gas chromatography/electron capture detection and by mass spectrometry.

The enantiomeric ratio (ER) of the chiral polychlorinated biphenyl (PCB) 132 (2,2',3,3',4,6'-hexachlorobiphenyl) was determined in human milk samples. The enantiomers were separated by multidimensional gas chromatography (MDGC), using different achiral columns for pre-separation and a Chirasil-Dex column for enantiomer separation, and quantified by electron-capture detection (ECD) and by mass spectrometry (MS/SIM). The determined enantiomeric ratios varied between 0.45-0.85 (enantiomeric excess: 38-8%).

Chromatography, Gas↗
PubMed1995

A simple fail-safe method for the harvesting of cranial bone.

The technique of cranial bone graft harvesting with the sagittal saw is described. With this technique regular bone grafts of any size can be obtained. Bone-graft size dictates the technique to be used. Small grafts (less than 3.0 cm in shortest dimension) are harvested in situ, while larger grafts are harvested by formal craniectomy.

Bone Transplantation↗
PubMed1995

Efficacy of threaded hydroxyapatite-coated implants placed in the anterior mandible.

A data subset from an ongoing prospective multicenter clinical study of threaded hydroxyapatite-coated implants was evaluated to assess safety and efficacy of the implants in anterior maxillary regions when used to support fixed prostheses. Observations were recorded before surgery, at first-stage surgery, at second-stage surgery, at loading, and at quarterly post-restoration prophylactic exams and annual comprehensive patient visits. Of 2,062 implants restored in 720 patients in the parent study, a total of 95 implants in 54 patients met the criteria for inclusion into this portion. Implant failure criteria included mobility, radiographic evidence of bone loss greater than one-third the length of the implant or peri-implant radiolucency, fracture, exfoliation, removal for any reason, and patient reported pain upon palpation. Soft tissue indices were monitored as part of the study. Post-restoration implant performance was analyzed using life-table methodology. No failures were observed before prosthodontic rehabilitation. Three implants failed during an observation period of up to 5 years after completion of prosthodontic treatment. The Cutler-Ederer life table success rate after 5 years was 93.4 percent. Results of this investigation suggest that threaded hydroxyapatite-coated implants are safe and effective when placed in anterior maxillary regions to support fixed prostheses.

Adult↗
PubMed1995

Inactivation of mecA prevents recovery from the competent state and interferes with cell division and the partitioning of nucleoids in Bacillus subtilis.

The development of genetic competence in Bacillus subtilis requires the synthesis of ComK, a transcription factor, which is normally produced as a culture enters the stationary phase. This synthesis is known to be regulated in part by the protein MecA. Loss-of-function mutations in mecA result in overexpression of ComK and its appearance early during exponential growth. We show here that mecA inactivation also causes a loss of colony-forming ability, especially during stationary phase. This loss is accompanied by the appearance of cells in which normal nucleoid separation has failed to occur. Renografin gradient fractionation of mecA cultures grown to competence reveals that nearly 100% of the cells band at the low buoyant density characteristic of competent cells, and that this low density is competence-related. The loss of viability, the low buoyant density and the nucleoid separation defect, are all comK-dependent. The loss of viability can be reversed by even the transient introduction of mecA+. It is proposed that these effects of ComK overexpression are related to the DNA replication arrest normally exhibited by the competent cell fraction and that MecA is needed to reverse this arrest and to permit escape from the competent state. The shift of nearly 100% of the cells to light buoyant density in a mecA mutant culture strongly suggests that the MecA protein is a regulator of the cell-type-specific expression of competence.

Bacillus subtilis↗
PubMed1995

Interim clinical study report: a threaded, hydroxylapatite-coated implant--five-year post-restoration safety and efficacy.

An ongoing prospective clinical trial is being conducted at three study sites to evaluate the safety and efficacy of a threaded, hydroxylapatite-coated implant (Steri-Oss Inc., Yorba Linda, CA) in a patient population reflective of the investigators' overall population of implant candidates. The 2062 implants placed and restored among 720 patients over the five-year period up to the study interim analysis cut-off date (November, 1994) include over 600 implants and 200 patients at each study site. Mean age and sex distribution of patients were comparable among the study sites. Study design attributes included well-defined patient selection criteria, standardized study procedures, standardized measurement and observation methodology, complete data accountability, and rigorously applied implant success/failure criteria. Thirty-five implants were considered failures at exposure, and the surgical success rate was 98.3%. Of 65 implants that failed post-restoration, three were removed, while 62 remained functional and in service. The five-year post-restoration follow-up success rate, determined by means of life table methodology, was 96.0%. By region, the five-year life table success rates post-restoration were 94.3% in the anterior maxilla, 96.6% in the posterior maxilla, 97.2% in the anterior mandible, and 95.6% in the posterior mandible. Adverse events occurred in association with less than 1% of the implants placed.

Adolescent↗
PubMed1994

Enantioselective degradation of alpha-hexachlorocyclohexane and cyclodiene insecticides in roe-deer liver samples from different regions of Germany.

Remarkably high concentrations of alpha-hexachlorocyclohexane (alpha-HCH), cis-heptachlorepoxide and oxychlordane were found in roe-deer liver samples both from the northern and southern German states Schleswig-Holstein and Baden-Württemberg, respectively. The data revealed no significant regional differences, but they showed some common characteristics: a preferential degradation of (+)-alpha-HCH, and a preferential enrichment of (+)-oxychlordane and of (+)-cis-heptachlorepoxide as determined by chiral capillary gas chromatography using modified cyclodextrin phases. Calculation of the spearman rank correlation coefficients rS supported the assumption that higher concentrations of alpha-HCH may result in a stronger decomposition of the (+)-enantiomer, while higher levels of cis-heptachlorepoxide and oxychlordane appear to lead to a faster decomposition of the respective (-)-enantiomer or a preferential formation of the respective (+)-enantiomer.

Animals↗
PubMed1994

The regulation of competence transcription factor synthesis constitutes a critical control point in the regulation of competence in Bacillus subtilis.

comK, which encodes the competence transcription factor, is itself transcriptionally activated at the transition from exponential growth to stationary phase in Bacillus subtilis. MecA, a negative regulator of competence, also inhibits comK transcription when overexpressed, and a mecA null mutation results in comK overexpression. Although null mutations in mecA, as well as in another gene, mecB, are known to bypass the requirements for nearly all of the competence regulatory genes, the comK requirement is not suppressed by mecA inactivation. Various competence regulatory genes (comA, srfA, degU, abrB, sin, and spo0A) are shown to be required for the expression of comK. srfA transcription is shown to occur equally in cells destined for competence and those destined not to become competent. In contrast, comK transcription is restricted to the presumptive competent cells. These and other results are combined to describe a regulatory pathway for competence.

Bacillus subtilis↗
PubMed1994

[Refuse incinerators in industrial areas (pro and contra)].

Update refuse incineration plant is meanwhile available as complete residue utilisation and recycling plant at reasonable waste disposal cost. Residual refuse of unknown composition is transformed into defined raw materials. The resulting "products" of such high-temperature treatment plant are energy, glass slake, gypsum, hydrochloric acid and metal fractions that can be re-introduced, i.e. recycled, into the cyclic process applicable to raw and engineering materials.

Equipment Reuse↗
PubMed1994

Implant and prosthetic principles according to the desired prosthesis.

In restoring our patients to comfort, form, function, and aesthetics, it is often necessary to place one or more implants to provide support to the desired prosthesis. This presentation and paper discuss the principles of implants and prostheses, based on the author's 25 years of clinical experience in implant dentistry. Occlusal scheme, treatment of overdenture, use of abutments and attachments, single tooth replacements, quality and quantity of bone, and the selection of implants are considered.

Dental Implants↗
PubMed1993

Spontaneous direct carotid-cavernous fistula in childhood.

We report the occurrence, surgical treatment and long-term follow-up of a spontaneous, direct carotid-cavernous fistula in a child. It is the third angiographically documented, spontaneously occurring fistula to be reported in this age group and the first to arise directly from the internal carotid artery based on our review of the literature. Although our patient required fistula closure, other reported fistulae were nonprogressive and did not require treatment. The communication between the internal carotid artery and the cavernous sinus was left sided while the contralateral eye was proptotic. The clinical features, selected hemodynamic characteristics, and treatment of carotid-cavernous fistulas are reviewed.

Arteriovenous Fistula↗
PubMed1993

Characterization of comE, a late competence operon of Bacillus subtilis required for the binding and uptake of transforming DNA.

The binding and transport of DNA by competent Bacillus subtilis requires the assembly of a specialized apparatus. We present here the characterization of comE, an operon under competence control that is required for both DNA binding to the competent cell surface, and for uptake. comE contains three open reading frames (ORF1-3) read in the forward direction, preceded by a long untranslated leader sequence and an apparent E sigma A promoter. A minor promoter also is responsible for transcription of ORF2 and -3. A transcript containing a single ORF is produced in the reverse direction. The reverse ORF overlaps ORF1 and the untranslated comE leader. The comE transcript is present at a very low level during growth and at an elevated level in stationary-phase cells. Conversely, the reverse transcript is present during exponential growth and disappears during stationary phase. The reverse ORF resembles prokaryotic and eukaryotic pyrroline-5'-carboxylate reductases, while ORF2 is similar to several dCMP deaminases. ORF1 and ORF3 are predicted to be integral membrane proteins. The latter is specifically required for DNA uptake but not for binding.

Amino Acid Sequence↗
PubMed1993

A five year clinical evaluation showing optimum results in dental implants.

Implant dentistry has made great advances since its inception several decades ago. As a result, predictability and success have reached high levels. Nonetheless, efforts continue to further refine implant design, materials, and techniques to reduce even the small percentage of failures that still occur. As part of this effort, the authors for the past six years have conducted clinical trials of Steri-Oss threaded titanium implants and HA-coated implants. The results have been consistent with the body of implant research reported since the 1970s. Optimum implant performance is realized when a well-designed system such as those tested is utilized in association with astute clinical judgment.

Clinical Trials as Topic↗
PubMed1992

Attempts to explain and reduce variability of superovulation.

The variability in response to superovulation treatment is a major disadvantage for economical use of embryo transfer and clearly limits use of embryo transfer in animal breeding. Despite considerable efforts, it has not yet been possible to reduce this variability drastically. Less than 40% of the causes for variability has been explained to date. The high proportion of unexplained variability leads to the hypothesis that variability is a special biological function that supports natural selection over the long term. Corresponding data from laboratory animal studies support this hypothesis.

Journal Article↗