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Biomedical subjects

R Storer

Publications and source records attributed to R Storer.

At least 19 recordsLinked to original sources
PubMed2001

Effect of an internal rotating current on low-frequency inductively coupled plasmas.

The effect of an internal low-frequency rotating current on inductively coupled plasmas in cylindrical chambers is studied. The electromagnetic field structure, power density distribution, the plasma density, and the operating regimes of the discharge are investigated using electrodynamic, power, and particle balance equations. It is shown that the rotating current sheet can dramatically improve the uniformity of the electromagnetic fields and the power transferred to the plasma electrons from that of conventional low-frequency inductively coupled plasma sources with external flat spiral inductive coils.

Journal Article↗
PubMed1994

The clinical serviceability of two permanent denture soft linings.

Forty-four patients, most of whom had previous experience of soft linings, had a total of 62 soft linings placed in their lower complete dentures:32 of the silicone-based Molloplast-band 30 of the heat-cured plasticised acrylic Palasiv 62. Linings were evaluated at insertion and then at 3-monthly intervals. Surface changes and the reasons for lining replacement were used to assess the clinical serviceability of the linings. The median survival time of Molloplast-b linings was significantly greater than that of Palasiv 62, whose performance was inadequate with frequent failure due to surface deterioration, with and without a failure of bonding. Denture fracture was the most common cause of lining failure for Molloplast-b and occurred more frequently than with Palasiv 62. Fading and lining discolouration was commonly observed for both materials.

Acrylic Resins↗
PubMed1993

Enzymatic production of optically pure (2'R-cis)-2'-deoxy-3'-thiacytidine (3TC, lamivudine): a potent anti-HIV agent.

Although equipotent in terms of antiviral activity, the two enantiomers of 2'-deoxy-3'-thiacytidine (BCH 189) differ markedly in their cytotoxicity. (2'R-cis)-2'-deoxy-3'-thiacytidine (3TC) is substantially less toxic than its optical antipode, and is undergoing development for the therapy of HIV infection. Cytidine deaminase from Escherichia coli is shown here to deaminate 2'-deoxy-3'-thiacytidine enantioselectively to leave 3TC essentially optically pure. This reaction has been used to develop a process for production of 3TC in multikilogram amounts. The production of cytidine deaminase was enhanced by strain improvement, fermentation development, and finally by cloning and overexpression of the gene. The enzyme was immobilized on Eupergit-C, which allowed it to be reused many times. The biotransformation conditions were optimized so that the best use could be made of the catalyst. A robust scaleable product isolation process was developed to yield the crystalline product. Overall, yields through the resolution process of 76% were obtained. All aspects of this process are capable of substantial further scaleup with only minor modifications.

Antiviral Agents↗
PubMed1993

Evaluation of the viscoelastic properties of denture soft lining materials.

Denture soft lining materials are widely used in prosthetic dentistry. Their success has been attributed to their softness and resilience, properties described by their viscoelasticity. Though these properties have been extensively investigated in laboratory studies, clinical studies have been limited. The viscoelastic properties of the temporary soft lining material Coe Soft and the permanent soft lining materials Palasiv 62 and Molloplast-B have been studied using a force/distance probe whereby penetration was measured against time under constant stress. Derived values of an initial and time-dependent compliance has allowed a quantitative in vivo and in vitro assessment of freshly prepared samples of each test material and comparison between materials. The baseline behaviour of each test material in response to the test regimen was similar for both clinical and laboratory specimens. Three types of behaviour could be identified: (i) constant strain in which penetration was clearly less than specimen thickness--elastic behaviour (Molloplast-B); (ii) constant strain in which the penetration was equal or nearly equal to specimen thickness--apparent elastic behaviour (Coe Soft); (iii) strain which increased with time of load application--viscoelastic behaviour (Palasiv 62). The mean and range of baseline clinical thickness for Coe Soft was approximately half that seen for the permanent soft lining materials. There was a much smaller range in the baseline compliance of all materials than might have been anticipated from a knowledge of their relative softness.

Acrylic Resins↗
PubMed1993

Age changes in the viscoelasticity of permanent soft lining materials.

Age-related changes in the viscoelasticity of an acrylic-based (Palasiv 62) and silicone (Molloplast-B) permanent soft lining material were evaluated in parallel clinical and laboratory longitudinal studies using a force/distance probe. Changes in the viscoelastic properties of Palasiv 62 in clinical use were characterized by a significant and continued reduction in both initial and delayed compliance. That is, the material became harder whilst still retaining the underlying pattern of viscoelasticity seen at baseline. Laboratory immersion in distilled water resulted in significant reductions in compliance values. These reductions were cumulatively similar to those seen clinically but did not occur as rapidly. There was evidence of small, continued reductions in the measured thickness of clinical linings of Palasiv 62. The clinical and laboratory compliance of Molloplast-B remained stable over time. Ageing did not affect the essential elasticity of this material.

Acrylic Resins↗
PubMed1993

Age changes in the viscoelasticity of a temporary soft lining material.

The viscoelastic properties of a widely used temporary soft lining material have been monitored in vivo and in vitro using a force distance probe. Over a period of 8 weeks' clinical use, Coe Soft demonstrated a significant and continued reduction in compliance with time, the reduction being particularly rapid over the first week. These changes were not associated with a reduction in measured lining thickness for which significant changes were not found. In vitro immersion in water, saline or artificial saliva was characterized by a rapid and significant reduction in compliance values over the first week. Further continued reductions in compliance values were only observed in artificial saliva over 8 weeks, and on prolonged immersion in distilled water over 96 weeks. All reductions in compliance were significantly less than those seen clinically.

Acrylic Resins↗
PubMed1992

The separated enantiomers of 2'-deoxy-3'-thiacytidine (BCH 189) both inhibit human immunodeficiency virus replication in vitro.

Racemic 2'-deoxy-3'-thiacytidine (BCH 189) is a dideoxycytidine analog having a sulfur atom in place of the 3' carbon. The enantiomers of BCH 189 have been resolved and found to be equipotent in antiviral activity against human immunodeficiency virus types 1 and 2. However, the (-)-enantiomer (3TC) is considerably less cytotoxic than the (+)-enantiomer.

Antiviral Agents↗
PubMed1992

Haemodynamic effects and uptake of enflurane in patients undergoing cardiac surgery: good versus poor myocardial function.

We measured haemodynamic effects and uptake of enflurane in patients undergoing cardiac surgery utilizing a standard anaesthetic technique of fentanyl 15 mcg/kg nitrous oxide 50%/enflurane 1%. We divided 22 patients preoperatively into two groups according to standard criteria: good and poor myocardial function. Regression lines could be drawn illustrating the relationship of cardiac output and uptake (at 1 minute: r = -0.56, P less than 0.01; at 5 minutes: r = -0.43, P less than 0.05; at 30 minutes: r = -0.31, P = 0.08). Although patients with poor myocardial function had decreased uptake of enflurance (approximately 10-20%), this did not reach statistical significance. Fentanyl/nitrous oxide/enflurane anaesthesia provided stable haemodynamics, even in patients with poor myocardial function. Both groups had a shunt fraction of approximately 10% and an arterial: end-tidal carbon dioxide difference of approximately 3-4 mmHg.

Anesthesia, Inhalation↗
PubMed1991

Carbovir: the (-) enantiomer is a potent and selective antiviral agent against human immunodeficiency virus in vitro.

In this paper we describe the in vitro antiviral activity of the (-) enantiomer of carbocyclic 2',3'-deoxydidehydroguanosine, (-) carbovir, a nucleoside analogue that has selective and potent anti-HIV activity in a series of lymphocyte culture systems. The cellular cytotoxicity of this compound has also been evaluated in a number of systems and compared to the saturated dideoxynucleoside analogues AZT and ddC.

CD4-Positive T-Lymphocytes↗
PubMed1991

Comparison of a novel photogrammetric technique and modified USPHS criteria to monitor the wear of restorations.

This paper describes monitoring the wear of restorations borne by partial dentures over a 12 months period using a novel photogrammetric technique and modified United States Public Health Service (USPHS) criteria. The performance of Class II restorations of Dispersalloy was compared with that of similar restorations of either KetacFil or Occlusin. The photogrammetric technique highlighted differences in performance not detected by the modified USPHS criteria. It is concluded that the photogrammetric technique should prove valuable in the in vivo assessment of the performance of restorative materials but that further refinement of the method is required particularly with regard to the orientation of replicas for sequential measurements.

Composite Resins↗
PubMed1990

The effect of storage media upon the surface microhardness and abrasion resistance of three composites.

The effects of various storage media [distilled water, lactate (pH 4.0), and citrate (pH 6.0) buffers] upon the hardness and wear factor values of three composites [Occlusin (O), P-30 (P), and Fulfil (F)] were studied. Over the one-year storage period, the hardness of all three materials stored in citrate buffer was unchanged. In the case of P in water and all materials stored in lactate buffer, a reduction was observed. There was no significant difference (P greater than 0.05) between the wear factors of specimens after one year or one week of water storage. Specimens of F stored in citrate buffer had a wear factor (P less than 0.01) higher than that of those stored in water. The other materials were not affected by storage in the lactate or citrate buffers. A reduction in surface hardness for some materials did not result in an increase in wear rate. This indicates that the softening effect was limited to a thin surface layer. Although not significant in vitro, this effect would probably increase the rate of in vivo wear, since the softened material would be lost, exposing a fresh surface to further attack. This would adversely prejudice the material's long-term clinical durability by impairing its resistance to abrasion.

Buffers↗
PubMed1989

The effect of placement technique upon the compressive strength and porosity of a composite resin.

This paper examines the effect of two placement techniques upon the compressive strength and level of porosity of specimens of a composite resin. Those specimens prepared by a condensation technique had a significantly lower mean compressive strength (P less than 0.05) and value of Weibull modulus (P less than 0.05) than specimens prepared using a smearing technique. No significant differences in the overall mean percentage area occupied by porosity and mean number of pores were demonstrated (P greater than 0.05) between the two placement techniques. Specimens prepared using the smearing technique, however, had significantly smaller mean maximum pore diameters (P less than 0.05) than those prepared using the condensation technique. It is therefore desirable when placing composite resins to reduce to a minimum handling procedures that are likely to influence the levels of porosity within the material.

Composite Resins↗