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Biomedical subjects

R W Anderson

Publications and source records attributed to R W Anderson.

At least 55 records · Page 3Linked to original sources
PubMed1995

Longitudinal evaluation of the microleakage of dentin bonding agents used to seal resected root apices.

A material that bonds to dentin and seals both the root canal and exposed dentinal tubules would be desirable following root resection. The purpose of this study was to measure the sealing ability of four dentin bonding agents on the resected root end. The bonding systems evaluated were Amalgambond (AMB), Scotchbond Multi-Purpose (SMP), Prisma Universal Bond 3 (PUB 3), and All-Bond 2 (AB2). All materials were applied directly to the resected root end without a class I preparation. One-half of the roots in each group were contaminated with human blood before bonding. Microleakage was measured using fluid filtration at various time intervals from 1 to 24 wk. Results indicated that all dentin bonding agents significantly reduced apical microleakage compared with prebonded controls at all time intervals. Blood contamination did not adversely affect the sealing ability of AMB, PUB 3, or SMP. The blood-contaminated AB2 group displayed significantly greater microleakage after 12 and 24 wk than the uncontaminated roots.

Analysis of Variance↗
PubMed1995

Characterization of npf mutants identifying developmental genes in Physarum.

In Physarum polycephalum, uninucleate haploid amoebae develop into macroscopic multinucleate plasmodia. Wild-type, sexual development is triggered when two amoebae carrying different alleles of matA fuse to form a zygote which develops into a diploid plasmodium. Mutations in the matA genetic region give rise to apogamic strains in which a single haploid amoeba can develop into a haploid plasmodium. An essential stage in both sexual and apogamic plasmodium formation is an extended cell cycle in uninucleate cells, which ends with the formation of a binucleate cell by mitosis without cytokinesis. Using a 'brute force' screening method, we have isolated mutants blocked in apogamic plasmodium development. Genetic analysis showed that the mutations we have identified were unlinked to matA, unlike mutations previously identified following an enrichment step. Most of the loci revealed by our screen were represented by only one allele, indicating that further screening should lead to the identification of additional genes required for plasmodium development. Phenotypic analysis showed that different mutants were blocked at different stages of plasmodium formation. Some of the mutations blocking apogamic development at an early stage, close to the start of the long cell cycle, failed to block sexual development in zygotes homozygous for the mutation. Since the two modes of plasmodium formation differ only in the initiation of development, these mutations presumably interfere with the initiation process. In the remaining mutants, in which both sexual and apogamic development were blocked, development first became abnormal towards the end of the long cell cycle. This suggested that the wild-type gene products were required by this time and was consistent with previous evidence that many changes in cellular organization and gene expression occur during the long cell cycle. Each of these mutants showed a different terminal phenotype and some aspects of plasmodium development occurred normally although others were blocked, suggesting that development involves multiple pathways rather than a dependent sequence of events. Phenotypic analysis of double mutants supported this conclusion and also revealed epistatic interactions, presumably due to blocks in the same pathway. In several of the mutants, terminally differentiated cells died by an apoptosis-like mechanism; since this was never observed in vegetative cells, it was presumably triggered by the failure of development. Phenotypic analyses of additional mutants will extend our understanding of the pathways involved in plasmodium development.

Animals↗
PubMed1995

The relationship between hospital charges and a modified Parsonnet risk score.

Health care now consumes approximately 14 percent of the U.S. Gross National Product (GNP). The amount of money spent on health care in America per capita and as a percentage of GNP far exceeds that of any other industrialized country. Currently, the financial burden of health care is being shouldered by government and business. The expenditure of billions of dollars of corporate profits on health care progressively undermines the global competitiveness of American business. These economic realities have emerged as the dominant driving force in health care reform. Cost control efforts to date have focused on strategies to limit inpatient hospital expenditures. The DRG prospective payment system is designed to reimburse a fixed sum based on the diagnostic category of the patient. The DRG payment is essentially independent of underlying patient characteristics that can potentially drive up expenditures. The work reported in this article was done to develop a descriptive formula that could be used to predict resource consumption in the care of patients. The financial viability of a hospital depends on its ability to predict expenditures, allocate resources, and choose its service areas correctly. Errors in financial forecasting in the era of prospective payment will result in financial failures of entire institutions.

Age Factors↗
PubMed1994

Evaluation of the bond strength of dentin bonding agents used to seal resected root apices.

A number of improved dentin bonding agents have recently become available, but have not been evaluated on apical radicular dentin. The purpose of this study was to compare the tensile bond strengths of four adhesive resins on resected root ends before and after blood contamination. Forty single-rooted human incisors were cleaned and shaped and obturated. The apical 3 mm was then resected at a 45-degree angle, bonded, and tested for tensile bond strengths using an Instron machine. The bonding systems evaluated included Prisma Universal Bond 3, Scotchbond MultiPurpose Dental Adhesive, Amalgambond, and All Bond 2. All bonding systems were then covered with Prisma APH light-cure composite resin. Results indicated that the bond strengths of the blood contaminated groups were significantly less than those of the control groups, except in the case of Amalgambond where no significant difference was noted. When the surface was contaminated with blood, Prisma Universal Bond 3 had significantly lower bond strengths, whereas Amalgambond had significantly higher bond strengths than the other subgroups.

Analysis of Variance↗
PubMed1994

Longitudinal evaluation of the seal of IRM root end fillings.

IRM has been recommended for root end filling during endodontic surgery. This study evaluated the seal of IRM root end fillings prepared with various powder to liquid ratios (P:L) at extended time intervals using a fluid filtration method. The P:L of IRM evaluated included 2, 3, 4, 5, and 6 g/ml and the P:L which resulted from the manufacturer's recommended scoop and dropper. Ten teeth were evaluated for microleakage for each group at 1, 2, 3, 4, 8, and 12 wk after insertion. There were no significant differences in the microleakage of any of the various P:L groups at weeks 3, 8, and 12. These results suggest that higher P:L of IRM than those previously recommended for temporary restorations and for endodontic access preparations may be acceptable for root end fillings. IRM of higher P:L has other advantages such as ease of placement and decreased setting time, toxicity, and solubility.

Analysis of Variance↗
PubMed1994

Computer-assisted design of an implantable, intrathoracic artificial lung.

A semiempirical mathematical model of convective oxygen transport is used to design a new, low pressure loss, implantable artificial lung that could be used as a bridge to lung transplantation in patients with advanced respiratory failure. The mass transfer and flow friction relations pertinent to the design of a cross-flow hollow fiber membrane lung are described. The artificial lung is designed to transfer over 200 ml/min of oxygen at blood flow rates up to 5 L/min. A compact design and a blood-side pressure loss of < 15 mm Hg allows the device to be implanted in the left chest without the need for a prosthetic blood pump. Surgical implantation of the artificial lung would require the creation of inflow and outflow anastomoses. Oxygen would be supplied via an external source. Blood properties, operating conditions, and empirically determined mass transfer and flow properties are all specified and input into a computer program that numerically solves the design equations. Computer-generated values for the device frontal area, blood path length, and fiber surface area are thereby obtained. The use of this computer-assisted design minimizes the need for extensive trial-and-error testing of prototype devices. Results from in vitro tests of a prototype implantable lung indicate that the mathematical model we describe is an accurate and useful tool in the design of hollow fiber artificial lungs.

Algorithms↗
PubMed1993

A Cayley tree immune network model with antibody dynamics.

A Cayley tree model of idiotypic networks that includes both B cell and antibody dynamics is formulated and analysed. As in models with B cells only, localized states exist in the network with limited numbers of activated clones surrounded by virgin or near-virgin clones. The existence and stability of these localized network states are explored as a function of model parameters. As in previous models that have included antibody, the stability of immune and tolerant localized states are shown to depend on the ratio of antibody to B cell lifetimes as well as the rate of antibody complex removal. As model parameters are varied, localized steady-states can break down via two routes: dynamically, into chaotic attractors, or structurally into percolation attractors. For a given set of parameters percolation and chaotic attractors can coexist with localized attractors, and thus there do not exist clear cut boundaries in parameter space that separate regions of localized attractors from regions of percolation and chaotic attractors. Stable limit cycles, which are frequent in the two-clone antibody B cell (AB) model, are only observed in highly connected networks. Also found in highly connected networks are localized chaotic attractors. As in experiments by Lundkvist et al. (1989. Proc. natn. Acad. Sci. U.S.A. 86, 5074-5078), injection of Ab1 antibodies into a system operating in the chaotic regime can cause a cessation of fluctuations of Ab1 and Ab2 antibodies, a phenomenon already observed in the two-clone AB model. Interestingly, chaotic fluctuations continue at higher levels of the tree, a phenomenon observed by Lundkvist et al. but not accounted for previously.

Animals↗
PubMed1993

Reliability of electric pulp testing after pulpal testing with dichlorodifluoromethane.

The purpose of this study was to determine if the sequence and interval between electric pulp testing and cold vitality testing with dichlorodifluoromethane affects the reliability of pulpal diagnostic testing. Sixty vital teeth in 15 volunteers were tested. Ten endodontically treated teeth were used as negative controls. After isolation and asepsis techniques, baseline threshold responses from a digital electric pulp tester were recorded from the maxillary incisors. A dichlorodifluoromethane-saturated cotton pellet was applied to teeth 8, 9, and 10. Electric pulp testing was repeated at 30-s, 1-min, and 2-min intervals on all test teeth after the cold test. The level of responses were recorded and statistically analyzed. The results of this study indicate that electric pulp testing is not adversely affected by the use of dichlorodifluoromethane.

Analysis of Variance↗
PubMed1993

An evaluation of the effect of methylene blue dye pH on apical leakage.

The effect of varying the pH of 2% methylene blue dye on apical leakage was evaluated. Eighty-four roots of extracted human teeth were used in this study. The roots were endodontically cleaned and shaped, obturated, apically resected, and amalgam or Temporary Endodontic Restorative Material retro-fillings were placed. The roots were immersed for 7 days in dye solutions of controlled pH of 1, 2, 3, 5 or 7, or in a 2% unbuffered deionized water solution of methylene blue. The results demonstrated significantly less leakage in the pH 1 and 2 amalgam groups. All other amalgam groups and the Temporary Endodontic Restorative Material groups showed no significant differences attributable to pH. Temporary Endodontic Restorative Material retrofilling groups demonstrated statistically significantly less apical leakage at each pH evaluated than the amalgam-retrofilled groups. Additionally, a significant buffering effect of the root structure on the dye solutions was measured.

Composite Resins↗
PubMed1993

An evaluation of three materials as barriers to coronal microleakage in endodontically treated teeth.

Barrier Dentin Sealant, glass ionomer cement, and TERM were evaluated as possible barriers to coronal microleakage. The root canals of 70 extracted teeth were accessed, cleaned and shaped, and then obturated with gutta-percha and sealer. The teeth were divided into four groups, one for each barrier material evaluated and one control group. Subgroups were stored in a humidor or immersed in artificial saliva for 7 days and then placed in methylene blue dye. Barrier Dentin Sealant and TERM groups demonstrated the lowest dye penetration measurements. The difference between them was not statistically different. Glass ionomer cement demonstrated the greatest dye penetration and was statistically different from the other two barrier materials.

Composite Resins↗
PubMed1993

The woodchuck hepatitis virus X gene is important for establishment of virus infection in woodchucks.

All mammalian hepadnaviruses possess a gene, termed X, that encodes a protein capable of transactivating virus gene expression. The X gene overlaps the polymerase and precore genes as well as two newly identified open reading frames (ORFs) termed ORF5 and ORF6. In this investigation, we examined whether ORF5, ORF6, and the X gene were important for the replication of woodchuck hepatitis virus (WHV) in susceptible woodchucks. First, we investigated whether proteins were produced from ORF5 and ORF6 by in vitro translation of appropriate viral transcripts, searched for antibodies against the putative proteins in the sera of animals infected with wild-type virus, and looked for an antisense WHV transcript, necessary for expression of a protein from ORF6, in the livers of acutely or chronically infected woodchucks. All such experiments yielded negative results. Next, we used oligonucleotide-directed mutagenesis to introduce termination codons into ORF5 and ORF6 at two locations within each ORF. Adult woodchucks in groups of three were transfected with one of the four mutant genomes. All of these woodchucks developed WHV infections that were indistinguishable from those of animals transfected with the wild-type WHV recombinant. Polymerase chain reaction amplification and direct DNA sequencing confirmed that reversion of the mutants to a wild-type genotype did not occur. Taken together, these data indicate that ORF5 and ORF6 are not essential for virus replication and are unlikely to represent authentic genes. Finally, we generated five WHV X-gene mutants that either removed the initiation codon for protein synthesis or truncated the carboxyl terminus of the protein by 3, 16, 31, or 52 amino acids. Groups of three adult woodchucks were transfected with one of the five X-gene mutants. Only the mutant that possessed an X gene lacking 3 amino acids from the carboxyl terminus was capable of replication within the 6-month time frame of the experiment. In contrast, all seven woodchucks transfected with wild-type WHV DNA developed markers consistent with viral infection. Thus, it is likely (P < 0.01) that the WHV X gene is important for virus replication in the natural host.

Amino Acid Sequence↗
PubMed1993

Free beta-chorionic gonadotropin: a cross-reactivity study of two immunometric assays used in prenatal maternal serum screening for Down's syndrome.

We have evaluated the cross-reactivity characteristics of two distinct immunometric assays for the measurement of free beta-human chorionic gonadotropin (free beta). These maternal serum assays have been used in the initial studies which evaluated free beta as a marker in the prenatal detection of Down's syndrome. It has been suggested that free beta assays are subject to substantial potential for cross-reactivity. To confirm that free beta was the analyte responsible for enhanced detection efficiency both non-competitive and competitive cross-reactivity evaluations were undertaken. These studies demonstrated acceptably small cross-reactivity to other glycoprotein hormones or their beta components. We conclude that properly designed free beta assays will provide specific analyte measurement and improved detection efficiency in Down's syndrome screening.

Antibodies, Monoclonal↗
PubMed1993

Dual analyte immunoassay in neural tube defect and Down's syndrome screening: results of a multicentre clinical trial.

We report a multicentre clinical field trial of a novel dual analyte enzyme immunoassay method for the simultaneous measurement of alpha-fetoprotein (AFP) and free beta-human choriogonadotropin (hCG) in the same microtitre well. The assay was shown to have good technical performance in the hands of all trial centres, with between assay coefficients of variation better than 10% for both analyte across the whole of the assay ranges. The method compared well with single analyte measuring procedures and produced acceptable performance as judged by external quality assurance criteria. Recovery of added analyte and analyte dilution curves also showed acceptable performance. In clinical evaluation of a large set of neural tube defect cases, good clinical discrimination from unaffected cases was observed using AFP. With over 150 Down's syndrome cases, the combination of AFP and free beta hCG confirmed the high detection rates achievable using this marker combination, with detection rates in excess of 70% in early gestation. We conclude that the combination of clinically superior markers coupled with technologically innovative assay design will lead to more efficient Down's screening programmes.

Adolescent↗
PubMed1993

Evaluation of air quality in a sterile-drug preparation area with an electronic particle counter.

The air quality in a sterile-drug preparation area was assessed with an electronic particle counter. The numbers of airborne particles of > or = 0.5 and > 5 microns in a hospital i.v. room were determined. Initially, a total of seven sampling sites were designated; the four locations and four times with the highest concentrations of particles were analyzed. To determine the classification of the cleanroom, as described in Federal Standard 209E (FS209E), four equally spaced locations in the room were examined on one day. According to FS209E, the average concentration of particles in samples obtained at each of four locations uniformly spaced in a room must be < or = 100,000 per cubic foot of sampled air for particles of > or = 0.5 micron in order for a room to qualify as a Class 100,000 cleanroom. Throughout the seven-day initial study, all measurements of particles of > or = 0.5 micron except one yielded counts of < 100,000/cu ft. The four highest average particle concentrations were recorded at 1000, 1100, 1400, and 1500. Although measurement of particles of > 5 microns was not necessary, the measurements of these particles showed that their concentrations were highly dependent on staff activity. The average particle concentration at the four equally spaced locations was < 36,000/cu ft. At the four locations, the mean of the average concentrations was 29,664 particles per cubic foot. The upper limit of the 95% confidence interval for particle concentration at the four locations was 35,896/cu ft.(ABSTRACT TRUNCATED AT 250 WORDS)

Air Pollution, Indoor↗
PubMed1992

Influenza basic polymerase 2 peptides are recognized by influenza nucleoprotein-specific cytotoxic T lymphocytes.

Cytotoxic T lymphocytes (CTL) play an important role in limiting viral infections and in eradicating virus from host tissues. Recent progress in understanding the processing and presentation of viral antigens to CTL indicates that the CTL antigen receptor recognizes peptides derived from viral proteins that are bound to an antigen binding groove present in class I major histocompatibility complex (MHC) molecules. In understanding CTL anti-viral responses and in creating vaccines designed to elicit CTL responses, it is critical to identify the portions of viral proteins that bind class I molecules and are recognized by T cell receptors. Previous findings have indicated that a significant portion of the CTL response of H-2d mice to influenza virus is specific for one of the viral polymerases (PB2). To identify the region of PB2 naturally processed and presented by influenza virus-infected mouse cells to CTL, 31 PB2 peptides of 9-16 residues in length were chosen and chemically synthesized. Two peptides, PB2, residues 146-159 and 187-195, were found to sensitize histocompatible target cells for recognition by influenza virus-specific CTL. When CTL were generated to individual viral proteins using influenza-vaccinia recombinant viruses, we found, to our surprise, that PB2-specific CTL failed to recognize cells sensitized with PB2 peptides 146-159 and 187-195. Further analysis showed that these PB2 peptides were, in fact, recognized by nucleoprotein (NP)-specific CTL generated by NP-vac virus priming and influenza A virus stimulation, or NP peptide stimulation in vitro of NP-vac or influenza A-primed CTL. These results demonstrate that while screening peptide libraries one cannot assume that positive peptides necessarily identify the viral protein to which the CTL response is directed.

Algorithms↗
PubMed1992

Use of dental instruments for bridging during electric pulp testing.

It has been suggested that dental instruments can be used as bridging instruments to facilitate electric pulp testing of teeth with extensive restorations. This study reports a clinical investigation to evaluate the effectiveness of this procedure. One hundred seventeen vital teeth in 20 volunteers were tested. Ten endodontically treated teeth functioned as controls. Following appropriate isolation and asepsis technique, baseline recordings of the threshold response with the electric pulp tester were taken. With the use of dental explorers and endodontic files to bridge between the probe tip and the tooth surface, recordings were made of the threshold responses. Findings indicate that electrically conductive dental instruments can be reliably used as bridging instruments with the electric pulp tester.

Dental Instruments↗