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Biomedical subjects

D Kozak

Publications and source records attributed to D Kozak.

14 recordsLinked to original sources
PubMed2000

Effect of repeated closures on opening torque values in seven abutment-implant systems.

STATEMENT OF PROBLEM: Implant abutment screw joints tend to loosen under clinical conditions. During impression and prosthesis fabrication, repeated clinical closing and opening of abutment screws may cause component wear and decrease frictional fit of the mating parts, resulting in altered resistance to opening and potential for loss of preload in function. PURPOSE: This study recorded changes in opening torque values due to multiple consecutive closures at a constant torque within and between different abutment/implant (A/I) systems. MATERIAL AND METHODS: Repeated opening-closing cycles were used to simulate in vitro embedment relaxation and component wear of 7 A/I systems from 5 manufacturers. Screw opening torque values were recorded up to 200 consecutive closures at 20 N/cm. RESULTS: A progressive decrease in opening torque values was measured in all implant systems. Significant differences were found between A/I systems. Systems with morse tapered and spline connections consistently maintained a higher resistance to opening force. Percentage torque loss ranged from 3% to 20% on immediate opening, and from 4.5% to 36% for average of first 30 opening/closing cycles. CONCLUSION: Repeated opening and closing of implant abutment screws caused progressive loss of torque retention with variations between systems. This was probably due to a decrease in the coefficient of friction between the mating components.

Analysis of Variance↗
PubMed1999

Manual closing torque in five implant abutment systems: an in vitro comparative study.

STATEMENT OF PURPOSE: A significant percentage of abutment/implant (A/I) assemblies tend to unscrew on functional loading. PURPOSE: This in vitro study evaluated the maximum closing torque generated manually for comparison with recommended closing torque values in 5 implant systems. METHODS: Closing torque generated by 9 operators with 5 manual torque drivers was measured and compared by using a mannequin and torque gauge assembly. RESULTS: Closing torque values were found to be significantly different between operators and between implant systems (P <.0001). Mean closing torque values of 9 operators performing 5 closures for 5 systems ranged from 7 to 14.6 N/cm for habitual closures and from 9.4 to 19.9 N/cm for maximum closures. CONCLUSIONS: The results demonstrated that maximum manual closure did not approach recommended closing torque in any of the system measured. Significant interoperator and intraoperator variability was found in the closing torque with manual drivers, and the driver diameter and grip were probably an important feature in the generation of high closing torque.

Analysis of Variance↗
PubMed1999

VEGI, a novel cytokine of the tumor necrosis factor family, is an angiogenesis inhibitor that suppresses the growth of colon carcinomas in vivo.

A novel member of the tumor necrosis factor (TNF) family has been identified from the human umbilical vein endothelial cell cDNA library, named vascular endothelial growth inhibitor (VEGI). The VEGI gene was mapped to human chromosome 9q32. The cDNA for VEGI encodes a protein of 174 amino acid residues with the characteristics of a type II transmembrane protein. Its amino acid sequence is 20-30% identical to other members of the TNF family. Unlike other members of the TNF family, VEGI is expressed predominantly in endothelial cells. Local production of a secreted form of VEGI via gene transfer caused complete suppression of the growth of MC-38 murine colon cancers in syngeneic C57BL/6 mice. Histological examination showed marked reduction of vascularization in MC-38 tumors that expressed soluble but not membrane-bound VEGI or were transfected with control vector. The conditioned media from soluble VEGI-expressing cells showed marked inhibitory effect on in vitro proliferation of adult bovine aortic endothelial cells. Our data suggest that VEGI is a novel angiogenesis inhibitor of the TNF family and functions in part by directly inhibiting endothelial cell proliferation. The results further suggest that VEGI maybe highly valuable toward angiogenesis-based cancer therapy.

Amino Acid Sequence↗
PubMed1998

Randomized clinical trial of lifestyle interventions in Pima Indians: a pilot study.

A pilot trial was conducted to test adherence to specific lifestyle interventions among Pima Indians of Arizona, and to compare them for changes in risk factors for diabetes mellitus. Ninety-five obese, normoglycaemic men and women, aged 25-54 years, were randomized to treatments named 'Pima Action' (Action) and 'Pima Pride' (Pride), which were tested for 12 months. Action involved structured activity and nutrition interventions, and Pride included unstructured activities emphasizing Pima history and culture. Adherence to interventions, changes in self-reported activity and diet, and changes in weight, glucose concentrations, and other risk factors were assessed regularly. Thirty-five eligible subjects who had declined randomization were also followed as an 'observational' group and 22 members of this group were examined once at a median of 25 months for changes in weight and glucose concentration. After 12 months of intervention, members of both intervention groups reported increased levels of physical activity (median: Action 7.3 h month(-1), Pride 6.3 h month(-1), p < 0.001 for each), and Pride members reported decreased starch intake (28 g, p = 0.008). Body mass index, systolic and diastolic blood pressures, weight, 2-h glucose and 2-h insulin had all increased in Action members (p < 0.003 for each), and waist circumference had decreased in Pride members (p = 0.05). Action members gained more weight than Pride members (2.5 kg vs 0.8 kg, p = 0.06), and had a greater increase in 2-h glucose than Pride members (1.33 mM vs 0.03 mM, p = 0.007). Members of the observational group gained an average of 1.9 kg year(-1) in weight and had an increase of 0.36 mM year(-1) in 2-h glucose. Sustaining adherence in behavioural interventions over a long term was challenging. Pimas may find a less direct, less structured, and more participative intervention more acceptable than a direct and highly structured approach.

Adult↗
PubMed1997

Bone regeneration in extraction sites. Part 2: The staged approach.

The use of guided tissue regeneration in conjunction with implants is a routine procedure in oral implant reconstruction. Three patient reports of the staged approach are presented and discussed. Implants were placed in regenerated bone 9 months after augmentation. Barrier membranes, with and without supporting screws, were used in different types of extraction site defects and followed for 2 years postoperatively.

Adult↗
PubMed1991

Functional expression of cloned human splicing factor SF2: homology to RNA-binding proteins, U1 70K, and Drosophila splicing regulators.

SF2 is a protein factor essential for constitutive pre-mRNA splicing in HeLa cell extracts and also activates proximal alternative 5' splice sites in a concentration-dependent manner. This latter property suggests a role for SF2 in preventing exon skipping, ensuring the accuracy of splicing, and regulating alternative splicing. Human SF2 cDNAs have been isolated and overexpressed in bacteria. Recombinant SF2 is active in splicing and stimulates proximal 5' splice sites. SF2 has a C-terminal region rich in arginine-serine dipeptides, similar to the RS domains of the U1 snRNP 70K polypeptide and the Drosophila alternative splicing regulators transformer, transformer-2, and suppressor-of-white-apricot. Like transformer-2 and 70K, SF2 contains an RNP-type RNA recognition motif.

Amino Acid Sequence↗
PubMed1990

The essential pre-mRNA splicing factor SF2 influences 5' splice site selection by activating proximal sites.

SF2 is a 33 kd protein factor required for 5' splice site cleavage and lariat formation during pre-mRNA splicing in HeLa cell extracts. In addition to its essential role in constitutive splicing, SF2 can strongly influence 5' splice site selection. When pre-mRNAs containing multiple cis-competing 5' splice sites are spliced in vitro, high concentrations of purified SF2 promote the use of the 5' splice site closest to the 3' splice site. However, SF2 discriminates properly between authentic and cryptic splice sites. These effects of SF2 on splice site selection may reflect the cellular mechanisms that prevent exon skipping and ensure the accuracy of splicing. In addition, alterations in the concentration or activity of SF2, and of other general splicing factors, may serve to regulate alternative splicing in vivo.

Base Sequence↗
PubMed1990

Purification and characterization of pre-mRNA splicing factor SF2 from HeLa cells.

SF2, an activity necessary for 5' splice site cleavage and lariat formation during pre-mRNA splicing in vitro, has been purified to near homogeneity from HeLa cells. The purest fraction contains only two related polypeptides of 33 kD. This fraction is sufficient to complement an S100 fraction, which contains the remaining splicing factors, to splice several pre-mRNAs. The optimal amount of SF2 required for efficient splicing depends on the pre-mRNA substrate. SF2 is distinct from the hnRNP A1 and U1 snRNP a polypeptides, which are similar in size. Endogenous hnRNA copurifies with SF2, but this activity does not appear to have an essential RNA component. SF2 appear to be necessary for the assembly or stabilization of the earliest specific prespliceosome complex, although in the absence of other components, it can bind RNA in a nonspecific manner. SF2 copurifies with an activity that promotes the annealing of complementary RNAs. Thus, SF2 may promote specific RNA-RNA interactions between snRNAs and pre-mRNA, between complementary snRNA regions, and/or involving intramolecular pre-mRNA helices. Other purified proteins with RNA annealing activity cannot substitute for SF2 in the splicing reaction.

HeLa Cells↗
PubMed1979

Environmental assessment helps in planning process.

The AHA's planning document, which identifies factors that affect the hospital industry on a nationwide basis, can be a useful reference for individual hospitals in identifying similar factors that affect them on the local level.

American Hospital Association↗
PubMed1979

Logical thought process key to corporate plan.

Corporate planning allows an organization to determine where it is going and how it will get there. There are two major phases that make up this planning process.

American Hospital Association↗
PubMed1979

Effects of systemically administered bleomycin or adriamycin with local hyperthermia on primary tumor and lung metastases.

Exposure of cells in tissue culture to bleomycin or Adriamycin during 43 degrees C hyperthermia increased cytotoxicity dramatically compared to exposure at 37 degrees C. This study was designed to test whether this interaction was useful in tumor-bearing animals. C3H mice bearing the KHT tumor were treated with bleomycin (7 or 15 mg/kg) or with Adriamycin (2.5 or 5 mg/kg) with or without local heating of the tumor to 43 degrees C for 30 minutes by 13.56 MHz radiofrequency fields. The effects were assessed by growth delay (mean tumor diameter doubling time) and cure rate. In separate experiments, BALB/c mice bearing EMT6 tumors were treated identically, but tumors were excised 2 hours after treatment and tumor cell survival was assayed by colony formation. Antitumor effects of systemic bleomycin were potentiated by local hyperthermia. The two modalities had to be administered close together in time to observe the potentiation, suggesting a true interaction. There was a "threshold" for bleomycin potentiation in vivo between 42 degrees C and 43 degrees C, just as observed in tissue culture experiments. The antitumor activity of Adriamycin was not potentiated in vivo in these tumor systems except in cell survival experiments at doses higher than those compatible with survival of the host. The toxicity of drug combined with heat was greater than that of either modality alone. Hyperthermia did not adversely affect the incidence or severity of spontaneous lung metastases from KHT tumors. In fact, groups treated with heat and bleomycin had less severe lung metastases than groups treated with bleomycin alone. We conclude that local heating of tumors may be a useful adjunct to systemic bleomycin therapy. In vivo potentiation of Adriamycin by heat, however, could not be demonstrated in these tumor systems.

Animals↗
PubMed1976

Thermodynamic properties of polyelectrolyte solutions containing mixtures of monovalent and trivalent counterions.

The osmotic coefficients, heats of dilution, and volume changes on dilution of aqueous solutions containing mixtures of polystyrenesulfonic acid and its lanthanum salt have been determined at 25 degrees C. The curve representing the osmotic coefficient as a function of the equivalent fraction of the acid has a maximum; the corresponding curves for the enthalpy and volume changes on dilution have a sigmoidal shape. Experimental results have been compared with predictions of the theory based on the cell model with cylindrical symmetry. A semiquantitative agreement between theory and experiment has been found.

Electrolytes↗