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Biomedical subjects

G E Evans

Publications and source records attributed to G E Evans.

13 recordsLinked to original sources
PubMed2001

The influence of preparation technique and sodium hypochlorite on removal of pulp and predentine from root canals of posterior teeth.

AIM: To test the null hypothesis that removal of pulp tissue and predentine from root canals of multirooted teeth is not significantly different when performed by one of two mechanical preparation techniques in conjunction with either water or 3% sodium hypochlorite (NaOCl) irrigation. METHODOLOGY: Forty-six freshly extracted premolar or molar teeth, with pulps vital at the time of extraction, were assigned to four groups balanced by anatomy (group 1, step-back filing/NaOCl; group 2, step-back filing/water; group 3, automated rotary/NaOCl; group 4, automated rotary/water). Preparation was undertaken by a single operator and the volumes of irrigant recorded for each tooth. One root from each tooth was prepared for transverse histological assessment at eight levels, including one at and two apical to the working length. A validated index was used to measure the presence and location of residual pulp tissue and predentine. RESULTS: No statistically significant differences were found in the frequency with which residual pulp tissue or predentine were observed amongst the groups. Coronal parts were more frequently devoid of pulp tissue and predentine than the apical. Canals were frequently occluded with residual pulp tissue apical to the working length. There was a trend for better pulp and predentine removal in accessible parts of the canal as a function of rotary preparation and NaOCl irrigation. The isthmus had residual pulp tissue less frequently in the NaOCl groups. Accessory anatomy was unaffected regardless of technique or irrigant. CONCLUSIONS: Pulp tissue and predentine removal were not significantly different between a step-back filing and an automated rotary preparation technique in conjunction with water or NaOCl.

Bicuspid↗
PubMed1990

The calcium ion dependence of scallop myosin ATPase activity.

The ATPase activity of scallop (Pecten maximus) striated adductor myosin and heavy meromyosin (HMM) have been investigated as a function of [Ca2+] using formycin triphosphate (FTP) as a fluorescent ATP analogue. The FTPase activity of the regulated fraction of these preparations was activated steeply over the range of 0.1 to 1 microM [Ca2+], implying the existence of a form of cooperativity that is intrinsic to the myosin heads. In addition to the previously characterised heterogeneity with respect to an unregulated fraction, the regulated fraction of HMM was resolved into two populations whose activities showed a slightly different dependency on [Ca2+]. This was revealed unambiguously at intermediate levels of activation where, in some experiments, the product release rate constants differed for the two populations by more than fivefold. At maximum relaxation or maximum activation, these rate constants differed by two- to three-fold and were not clearly resolved by the multiexponential fitting procedure. The populations might arise as a consequence of isoenzymes, modification during preparation or slowly interconverting conformers; Ca2+ binding itself being a rapid equilibrium process in both populations. FTP turnover by myosin could not be analysed in such detail because of the technical problems of measuring the fluorescence of a suspension of filaments, but the rates of the elementary steps appeared similar to those of HMM. The fraction of unregulated molecules in myosin preparations was comparable to that of HMM indicating that if it is a consequence of preparative damage, the modification must occur prior to tryptic digestion.

Animals↗
PubMed1990

Antitrust's recent attack on the peer review practitioner: is the Health Care Quality Improvement Act a viable remedy?

Peer review, an increasingly important function in the hospital setting, is unique in that physicians are granted the task of evaluating and supervising the actions of their counterparts. Regardless of the consequences resulting from the peer-review system now operating within the hospitals, it will continue to be a mainstay until a more workable alternative is proved successful.

Hospital Administration↗
PubMed1989

Independent status for hospital medical staffs: no cause for antitrust alarm.

In recent years, there has been a growing controversy surrounding the issue of so-called "independent status" for hospital physician staffs. During the late 1970s and early 1980s, some articles advanced the theory that any conduct creating the appearance of an independent status for the hospital staff separate from that of the hospital could generate the environment for an antitrust action. These early theories, however, failed to fully appreciate the basic nature of antitrust law and the changing role of the hospital medical staff. Indeed, the changing nature of the hospital medical staff and the current application of antitrust law strongly indicate the early theories are misplaced and the "independent status" of the hospital medical staff does not create cause for antitrust alarm.

Medical Staff, Hospital↗
PubMed1989

Triplicate prescription: an idea whose time has yet to come.

A coalition of Maryland state officials and agencies is considering the introduction of legislation that would enact a triplication prescription program, a concept that dates back almost a half century. To date, only eight states have adopted such legislation, and since 1964, at least sixteen other states have thoroughly examined the concept and rejected it.

Drug Prescriptions↗
PubMed1987

Morphometric analyses of changes in cell shape in the neuroepithelium of mammalian embryos.

During neurulation the elevation of the neural folds is accompanied by, and thought to be partly driven by, changes in the shapes of the neuroepithelial cells. This paper explores the use of form factors for the measurement of changes in cell shape during normal and perturbed neural fold elevation in rat embryos; it is the first attempt to quantify changes in the shapes of cells during neurulation in mammalian embryos. Rat embryos at 9.9 days of gestation, when the neural epithelium is a biconvex plate, and at 10.4 days of gestation, when the cervical neural epithelium has formed the neural tube and when the cephalic neural folds have elevated but not fused, were used. In addition, embryos in which the cephalic neural folds had been caused to re-open by culture in saline with low calcium were examined. Embryos were fixed and then fractured across the neural axis. A montage of the fractured edge of the neuroepithelium was prepared from a series of scanning electron micrographs. Cells of the neuroepithelium were classified according to the shapes of their profiles as rectangular, round, apically tapered, basally tapered or spindle-shaped, the last three categories being considered as 'tapered'. The outlines of the cells were digitised using a computer-linked graphics tablet to provide estimations of the perimeters (p) and areas (a) of the cell profiles, and the form factors, f. of the cell profiles were calculated by f = 4 pi a/p2. This factor is a unitless ratio which is unity for a circle and less than unity for any other shape. It provides a measure of the efficiency with which a perimeter encloses an area, and thus indicates the degree of deformation of a shape from circular. From 9.9 to 10.4 days the cervical neuroepithelium shows a decrease in the percentage of rectangular cells and an increase in the percentage of spindle-shaped cells. The mean form factors of cells in the apically tapered and spindle-shaped categories decrease, showing that these cells are more elongated and tapered in later embryos. When embryos at 10.4 days are cultured in saline with low calcium the elevated cephalic neural folds collapse. Concomitantly the percentage of round cells in the cephalic neural folds increases and the percentage of apically tapered and spindle-shaped cells decrease.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1978

Biomimetic syntheses of phenols from polyketones.

As a result of speculation that many enzymes control polyketone cyclization in vivo by converting a key carbonyl group to a cis-enol ether derivative, we describe two novel biomimetic cyclizations. The first involves condensation of two C6 units derived from triacetic lactone to form an arylpyrone related to aloenin. In the second a naphthapyrone of the rubrofusarin type is formed by condensation of an orsellinic acid derivative with the ether of triacetic lactone.

Anthracenes↗
PubMed1967

Hydrazine-air fuel cells. Hydrazine-air fuel cells emerge from the laboratory.

A fuel cell is an electrochemical device that continues to generate electrical power as long as reactants are supplied and products are removed at properly controlled rates. An assembly of cells is required within which the conversion of chemical to electrical energy occurs; also required is a set of auxiliary components to supply the reactants and remove the products (including waste heat) under controlled steady-state conditions. In addition to the desired energy-conversion reactions, there are deleterious side reactions that can impair fuel economy. From knowledge of these factors influencing the possible reactions, and guided by principles of elementary chemical thermodynamics, the electrochemist can select optimum conditions for cell performance. It is then the job of the engineer to design auxiliary components and controlling devices to provide the electrochemical cells with the best possible approach to these optimum conditions.

Air↗