PubMed Health⌕ Search

Biomedical subjects

W D Bowman

Publications and source records attributed to W D Bowman.

At least 19 recordsLinked to original sources
PubMed1995

De/remineralization from sodium fluoride dentifrices.

PURPOSE: To test the demineralization/remineralization effects of sodium fluoride dentifrices using an in situ single-section crown model system. MATERIALS AND METHODS: A fluoride dose response was evaluated using 0, 1100 and 2800 ppm F-, along with the effects of an enhanced fluoride delivery system (polyampholyte-NaF). The single-section crown model was employed with supervised toothbrushing twice a day. At the end of each 1-month study leg, sections were removed and replaced with new sections for the next leg. Both before and after the double-blind, crossover portion of the study, sections were evaluated by polarized light microscopy and microradiography. The change in mineral content of the enamel and root lesions was analyzed by ANOVA with a Waller-Duncan K-Ratio Test post hoc. RESULTS: The placebo dentifrice group showed a loss of mineral and was statistically different from all groups. The fluoride dentifrices showed increasing amounts of enamel mineral gain, with increasing fluoride concentration. The polyampholyte-NaF delivery system with 1100 ppm F- was equivalent to the 2800 ppm F- dentifrice. Root lesions gave similar rank-order results although all treatments showed demineralization or mineral loss.

Adult↗
PubMed1992

Demineralization and remineralization evaluation techniques--added considerations.

Methods used for the analysis of tooth de- and remineralization include techniques with various degrees of sophistication and quantitative capabilities, ranging from direct measures of mineral gain/loss (e.g., microradiography) to indirect measures (e.g., iodide permeability) of changes in tooth mineral properties. In all instances, the capabilities of methods for accurate determination of changes in tooth mineral properties are affected by procedures used in the preparation of specimens for analysis, the magnitude of change taking place in the test (vs. the detection limits of the techniques), and protocols for specimen analysis. In specific instances, such as in the case of dentin, unique specimen-handling and analysis procedures must be used to prevent artifacts. The choice of techniques for the assessment of de- and remineralization depends strongly upon study protocols and laboratory capabilities; however, 'quantitative' measures of mineral gain and loss are possible only if direct chemical or radiographic techniques are used. Either radiographic, cross-sectioned microhardness or polarized light can be used for the determination of lesion depth. Porosity, light-scattering, and surface microhardness are indirect techniques which complement direct measures of mineral gain and loss. Whatever methods are used in the analysis of de- and remineralization, researchers must take care to differentiate accurately among the quantitative capabilities of techniques used in analysis.

Dental Enamel↗
PubMed1991

Delayed Onset of Isoprene Emission in Developing Velvet Bean (Mucuna sp.) Leaves.

Isoprene (2-methyl-1,3-butadiene) is one of the major volatile hydrocarbons emitted by plants, but its biosynthetic pathway and role in plant metabolism are unknown. Mucuna sp. (velvet bean) is an isoprene emitter, and leaf isoprene emission rate increased as much as 125-fold as leaves developed, and declined in older leaves. Net CO(2) assimilation and stomatal conductance, under different growth and environmental conditions, increased 3 to 5 days prior to an increase in isoprene emission rate, indicating that photosynthetic competence develops before significant isoprene emission occurs.

Journal Article↗
PubMed1989

Short-term changes in leaf carbon isotope discrimination in salt- and water-stressed c(4) grasses.

Online carbon isotope discrimination (Delta) and leaf gas exchange measurements were made with control and salt-stressed Zea mays and Andropogon glomeratus, two NADP-ME type C(4) grasses. Linear relationships between Delta and p(i)/p(a) (the ratio of intercellular to atmospheric CO(2) partial pressure) were found for control plants which agreed well with theoretical models describing carbon isotope discrimination in C(4) plants. These data provided estimates of phi, the proportion of CO(2) fixed by phosphoenolpyruvate carboxylase which leaks out of the bundle sheath and the component of fractionation due to diffusion in air. Salt-stressed plants had wider variation in Delta for the same or less range in p(i)/p(a). Additional work indicated Delta changed independently of p(i)/p(a) in both water- and salt-stressed plants, suggesting a possible diurnal change in phi as plant water status changed linked to a decrease in the activity of the C(3) photosynthetic pathway relative to C(4) pathway activity. The possible effect of stress-induced changes in phi on organic matter delta(13) C of C(4) plants is apt to be most apparent in chronically stressed environments.

Journal Article↗
PubMed1988

19F MAS-NMR and solution chemical characterization of the reactions of fluoride with hydroxyapatite and powdered enamel.

Solution chemical and 19F magic angle spinning-nuclear magnetic resonance (MAS-NMR) methods have been utilized to study the effects of fluoride dose, fluoridating pH, and mineral surface area on the dynamics of fluoride reactivity with hydroxyapatite and powdered human dental enamel in vitro. Both solution chemical fluoride uptake and NMR measurements demonstrated that the reaction products of ionic fluoride with apatite include mixtures of FAP, FHAP, and CaF2, with increased amounts of CaF2 promoted by increased F concentration or decreased pH. NMR analysis showed FAP or FHAP as a reaction product of fluoride uptake under all conditions, regardless of whether CaF2 was formed, unambiguously demonstrating fluorite as an additive rather than substitute form of F reactivity. pH stat measurements demonstrated the release of OH- during F reactivity with apatites corresponding to ion exchange formation of FAP/FHAP or dissolution/reprecipitation formation of CaF2. Phosphate release into solution accompanied fluoride uptake under all conditions, including regions where ion exchange predominated. Whereas powdered dental enamel demonstrated fluoride uptake behavior similar to that of synthetic apatite, the resulting reaction products differed as analyzed by 19F MAS-NMR.

Adsorption↗
PubMed1987

Effect of salinity on leaf gas exchange in two populations of a c(4) nonhalophyte.

Gas exchange measurements were made on plants from two natural populations differing in salt tolerance of Andropogon glomeratus, a C(4) nonhalophyte, to examine the effect of salinity on components responsible for differences in photosynthetic capacity. Net CO(2) uptake and stomatal conductance decreased with increasing salinity in both populations, but to a greater extent in the inland (nontolerant) population. The intercellular CO(2) concentrations increased with increasing salinity in the inland population, but decreased in the marsh (tolerant) population. Water use efficiency decreased as salinity increased in the inland population, and remained unchanged in the marsh population. Carboxylation efficiency decreased and CO(2) compensation points increased with increasing salinity in both populations, but to a lesser extent in the marsh population. Carboxylation efficiencies were higher with 2% relative to 21% atmospheric O(2) in salt stressed plants, suggesting that a decrease in the carboxylation:oxygenation ratio of ribulose 1,5-bisphosphate carboxylase/oxygenase was partly responsible for the decrease in photosynthetic capacity. Populational differences in photosynthetic capacity were the result of greater salinity-induced changes in carboxylation efficiency in the inland population, and not due to differences in the stomatal limitation to CO(2) diffusion.

Journal Article↗
PubMed1985

Randomized clinical trial of cyclophosphamide, 5-FU, and prednisone with or without tamoxifen in postmenopausal women with advanced breast cancer.

The purpose of this study was to determine if tamoxifen added to the efficacy of a CFP (cyclophosphamide, 5-FU, and prednisone) regimen. One hundred thirty-one postmenopausal women with advanced breast cancer without prior chemotherapy exposure were randomized to receive CFP alone or combined with tamoxifen; six were disqualified because of ineligibility. Objective responses were seen in 68% of the eligible patients receiving CFP and in 61% of those receiving CFP plus tamoxifen. Median times to progression were 287 days for CFP and 158 days for CFP plus tamoxifen (two-sided log-rank test of equality of progression distributions, P = 0.07). Median survival times were 544 days for CFP and 394 days for CFP plus tamoxifen (two-sided log-rank test of equality of survival distributions, P = 0.14). The addition of tamoxifen to CFP was not associated with longer time to progression or survival in any Cox covariate model. On the basis of our data, it can be concluded that the addition of tamoxifen to CFP does not substantially improve either the time to disease progression or survival in women with metastatic breast cancer.

Adult↗
PubMed1981

Normal mode analysis of lumiflavin and interpretation of resonance Raman spectra of flavoproteins.

The normal modes of lumiflavin (10-methyliso-alloxazine) are analyzed with a valence force field constructed with bond length-stretching force constant correlations and bending and interaction force constants transferred from small ring molecules. Observed resonance Raman (RR) bands of flavin are assigned to calculate modes on the basis of frequency and isotope shift matching. The normal mode patterns confirm previous inferences, based on selective effective of chemical substitutions, of localization to certain regions of the molecule. These results are used to interpret the observed variability of the prominent RR bands among different flavoproteins on the basis of protein-isoalloxazine interactions.

Flavins↗
PubMed1977

Quality control of small-volume sterile products.

A method for bacterial surveillance of small-volume sterile products in hospitals was developed and tested. The criteria for the method of quality control were to: (1) assure detection of contamination associated with touch, which could occur during the filling process; (2) be economically feasible; (3) be simple and easy to implement; and (4) be versatile in adapting to small-volume sterile packages with and without needles. Ten percent of each lot of prepackaged unit dose syringes is tested by filtration through a sterile micropore filter. The filter unit is incubated after fluid thioglycollate medium has been added. If turbidity or color change is found, further testing with blood agar and gram staining is performed to identify the organism. The effectiveness of the method was tested by adding E. coli to one lot within each of several lots tested of six products. The inoculated samples were stored under refrigeration for three days before testing. With one exception, the E. coli was detected in the samples. Growth did not occur in any of the noninoculated units. The apparent false negative result was believed to be caused by the bacteriostatic agent killing the organism during the three-day storage period.

Drug Contamination↗