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Biomedical subjects

C Mercer

Publications and source records attributed to C Mercer.

At least 19 recordsLinked to original sources
PubMed2007

Contact damage in an yttria stabilized zirconia: implications.

This paper presents the results of a combined experimental and computational study of contact damage in a 3 mole% yttria partially stabilized zirconia (3-YSZ) that is relevant to hip implants and dental restorations. Contact-induced loading in real applications is idealized using Hertzian contact model to explain plasticity phenomena and failure mechanisms observed under monotonic and cyclic loading. Under monotonic loading, the elastic moduli increase with increasing loading levels. Under cyclic loading, the ceramic specimens fail with progressive cone cracking. X-ray analyses reveal that stress-induced phase transformation (from tetragonal to monoclinic phases) occurs under cyclic contact loading above the critical load levels (approximately 8.5 kN). Furthermore, when the cyclic loading level (5.0 kN) is less than a critical load levels (7.5 kN) that is required to induce surface cone cracks, significant plastic damage is observed in the subsurface zone underneath the contact area. These suggest that the cyclic contact loading induce both plastic damage and tetragonalto-monoclinic phase transformation in the 3-YSZ, leading to significant degradation in long-term strength. The implications of the results are discussed for the design of zirconia femoral heads in total hip replacements and zirconia crowns in dental restoration.

Biocompatible Materials↗
PubMed2005

Mechanisms governing the inelastic deformation of cortical bone and application to trabecular bone.

To understand the inelastic response of bone, a three-part investigation has been conducted. In the first, unload/reload tests have been used to characterize the hysteresis and provide insight into the mechanisms causing the strain. The second part devises a model for the stress/strain response, based on understanding developed from the measurements. The model rationalizes the inelastic deformation in tension, as well as the permanent strain and hysteresis. In the third part, a constitutive law representative of the deformation is selected and used to illustrate the coupled buckling and bending of ligaments that arise when trabecular bone is loaded in compression.

Animals↗
PubMed2005

Factors associated with HIV testing among black Africans in Britain.

OBJECTIVE: To describe the factors associated with HIV testing among heterosexual black Africans aged 16-44 years living in Britain. DESIGN: We analysed data from the second British National Survey of Sexual Attitudes and Lifestyles (Natsal 2000)-a stratified national probability sample survey conducted between 1999-2001. Data from Natsal's main and ethnic minority boost (EMB) samples were analysed. Multivariate analysis was performed using complex survey functions to account for the clustered, stratified, and differential selection probabilities inherent within the survey. RESULTS: A total of 385 (216 women and 169 men) black African respondents were included in the study. 44.0% women and 36.4% men reported ever having had an HIV test. In univariate analysis, HIV testing was associated with being born abroad (OR 3.63), having a new partner(s) from abroad in past 5 years (OR 2.88), and attending a GUM clinic (OR 3.27) among men; and educational attainment (OR 3.50), perception of "not very much" personal risk of HIV (OR 2.75), and attending a GUM clinic (OR 2.91) among women. After adjusting for potential confounders, an increased likelihood of HIV testing was associated with being in the United Kingdom less than 5 years relative to being UK born (adjusted OR 9.49), and ever attending a GUM clinic (adj OR 5.53), for men; and educational attainment (adj OR 4.13), and low perception of HIV risk (adj OR 2.77) for women. CONCLUSIONS: Black Africans appear to have relatively high rates of HIV testing reflecting, at least partially, awareness of risk behaviours and potential exposure to HIV. Nevertheless, there remains substantial potential for health gain and innovative approaches are required to further increase timely HIV testing.

Adolescent↗
PubMed2004

A microsatellite map of white clover.

The white clover ( Trifolium repens) nuclear genome (n = 2x = 16) is an important yet under-characterised genetic environment. We have developed simple sequence repeat (SSR) genetic markers for the white clover genome by mining an expressed sequence tag (EST) database and by isolation from enriched genomic libraries. A total of 2,086 EST-derived SSRs (EST-SSRs) were identified among 26,480 database accessions. Evaluation of 792 EST-SSR primer pairs resulted in 566 usable EST-SSRs. Of these, 335 polymorphic EST-SSRs, used in concert with 30 genomic SSRs, detected 493 loci in the white clover genome using 92 F1 progeny from a pair cross between two highly heterozygous genotypes--364/7 and 6525/5. Map length, as estimated using the joinmap algorithm, was 1,144 cM and spanned all 16 homologues. The R (red leaf) locus was mapped to linkage group B1 and is tightly linked to the microsatellite locus prs318c. The eight homoeologous pairs of linkage groups within the white clover genome were identified using 96 homoeologous loci. Segregation distortion was detected in four areas (groups A1, D1, D2 and H2). Marker locus density varied among and within linkage groups. This is the first time EST-SSRs have been used to build a whole-genome functional map and to describe subgenome organisation in an allopolyploid species, and T. repens is the only Trifolieae species to date to be mapped exclusively with SSRs. This gene-based microsatellite map will enable the resolution of quantitative traits into Mendelian characters, the characterisation of syntenic relationships with other genomes and acceleration of white clover improvement programmes.

Chromosome Mapping↗
PubMed2003

Is use of antiretroviral therapy among homosexual men associated with increased risk of transmission of HIV infection?

BACKGROUND/OBJECTIVE: There is concern that use of highly active antiretroviral therapy (HAART) may be linked to increased sexual risk behaviour among homosexual men. We investigated sexual risk behaviour in HIV positive homosexual men and the relation between use of HAART and risk of HIV transmission. METHODS: A cross sectional study of 420 HIV positive homosexual men attending a London outpatient clinic. Individual data were collected from computer assisted self interview, STI screening, and clinical and laboratory databases. RESULTS: Among all men, sexual behaviour associated with a high risk of HIV transmission was commonly reported. The most frequently reported type of partnership was casual partners only, and 22% reported unprotected anal intercourse with one or more new partners in the past month. Analysis of crude data showed that men on HAART had fewer sexual partners (median 9 versus 20, p=0.28), less unprotected anal intercourse (for example, 36% versus 27% had insertive unprotected anal intercourse with a new partner in the past year, p=0.03) and fewer acute sexually transmitted infections (33% versus 19%, p=0.004 in the past 12 months) than men not on HAART. Self assessed health status was similar between the two groups: 72% on HAART and 75% not on HAART rated their health as very or fairly good, (p=0.55). In multivariate analysis, differences in sexual risk behaviour between men on HAART and men not on HAART were attenuated by adjustment for age, time since HIV infection. CD4 count and self assessed health status. CONCLUSION: HIV positive homosexual men attending a London outpatient clinic commonly reported sexual behaviour with a high risk of HIV transmission. However, behavioural and clinical risk factors for HIV transmission were consistently lower in men on HAART than men not on HAART. Although use of HAART by homosexual men with generally good health is not associated with higher risk behaviours, effective risk reduction interventions targeting known HIV positive homosexual men are still urgently needed.

Adult↗
PubMed2002

Interactions between MC3T3-E1 cells and textured Ti6Al4V surfaces.

This paper presents the results of an experimental study of the interactions between MC3T3-E1 (mouse calvarian) cells and textured Ti6Al4V surfaces, including surfaces produced by laser microgrooving; blasting with alumina particles; and polishing. The multiscale interactions between MC3T3-E1 cells and these textured surfaces are studied using a combination of optical scanning transmission electron microscopy and atomic force microscopy. The potential cytotoxic effects of microchemistry on cell-surface interactions also are considered in studies of cell spreading and orientation over 9-day periods. These studies show that cells on microgrooved Ti6Al4V geometries that are 8 or 12 microm deep undergo contact guidance and limited cell spreading. Similar contact guidance is observed on the surfaces of diamond-polished surfaces on which nanoscale grooves are formed due to the scratching that occurs during polishing. In contrast, random cell orientations are observed on alumina-blasted Ti6Al4V surfaces. The possible effects of surface topography are discussed for scar-tissue formation and improved cell-surface integration.

Alloys↗
PubMed2002

Phase specific strategies for the prevention, control, and elimination of sexually transmitted diseases: background country profile, England and Wales.

The development of non-invasive tests for evidence of current or past infection offers new prospects for carrying out population studies of sexually transmitted infection (STI) epidemiology, and for improved understanding of the behavioural and biological determinants of STI transmission. In turn this may guide screening, treatment, and behavioural interventions. The evidence base for many interventions is sparse and randomised trials of interventions are in their early days. Increasingly, linked behavioural and biological outcomes will be required to measure effectiveness. Integrated efforts are needed at a national level to achieve greater coordination between STD, HIV, and contraception services, school education, and broader public education and programmes.

Adolescent↗
PubMed2001

The Hood Mysticism Scale: does the presence of a neutral response-item affect response style.

The widely used Hood Mysticism Scale (1975) was administered to one of two groups of college students in its original version and a modified version without the option of responding with "?" to an item. Scoring of the scale assigns an intermediate value to the "?" response, suggesting this response implies a meaning on the item somewhere between "probably true" and "probably not true." Omitting this response option requires respondents to make a forced-choice answer, either to agree or to disagree with a statement and eliminates the middle ground. It was hypothesized that, if the response reflects a neutral attitude, then randomly selected groups administered the scale with or without the option should show no difference in overall means. An intact group of 23 advanced psychology students achieved a mean of 114.4 (SD = 20.4) on the original mysticism scale, while 25 advanced psychology students in a second intact group had a mean of 113.3 (SD = 17.1) on the modified version. This difference was not significant and supported the hypothesis that the scales were equivalent. Advantages of the modification and implications for interpretation of the "?" response are discussed.

Adult↗
PubMed2000

Very low density lipoprotein subfractions in Type II diabetes mellitus: alterations in composition and susceptibility to oxidation.

AIMS/HYPOTHESIS: Type II (non-insulin-dependent) diabetes mellitus is associated with raised triglycerides and increased very low density lipoprotein cholesterol. The aim of this study was to assess if very low density lipoprotein subfraction composition and potential to oxidise were altered in this condition. METHODS: Very low density lipoprotein was separated into four subfractions (A-->D) by a novel, rapid ultracentrifugation procedure. Analysis of each subfraction included lipid and fatty acid composition. Preformed peroxides were measured spectrophotometrically and conjugated dienes were used as an indicator of in vitro lipid oxidation. RESULTS: In all results we compared patient and control subfractions. Mean fasting plasma glucose was 8.9 +/- 2.0 mmol/l in patients vs 5.1 +/- 0.4 mmol/l in control subjects (p < 0.001); patient HbA1c was 7.6 +/- 1.4%. Patient total lipid standardised for apo B was higher than controls in subfractions A, B and C; A, 201 vs 60; B, 191 vs 40; C, 63 vs 21; D, 29 vs 34 micromol lipid per mg apo B (p < 0.05). Preformed peroxides were higher in all patient subfractions compared with controls: A, 340 vs 48; B, 346 vs 42; C, 262 vs 28; D, 54 vs 16 nmol per mg apo B (p < 0.001). Patient subfractions A and D were more susceptible to in vitro oxidation. Monounsaturated fatty acids were lower in patients subfractions, 35.2 vs 36.7; B, 35.1 vs 38.7; C, 34.4 vs 36.5; D, 33.0 vs 35.5 as per cent total (p < 0.05). CONCLUSIONS/INTERPRETATION: These results indicate abnormalities in very low density lipoprotein subfraction composition and oxidation profile in Type II diabetic subjects, which are characteristic of more atherogenic particles and that may contribute to the development of cardiovascular disease in these patients.

Apolipoproteins B↗
PubMed2000

The ferroxidase activity of caeruloplasmin is reduced in haemodialysis patients.

Increased free-radical production leading to oxidative stress may contribute to the development of cardiovascular complications in haemodialysis patients. The ferroxidase activity of caeruloplasmin forms an important component of antioxidant defences in body fluids. The aim of this study was to assess ferroxidase activity in haemodialysis patients. Venous blood was collected from 83 haemodialysis patients immediately prior to and after dialysis and from 52 healthy controls. Immunoreactive caeruloplasmin was measured by rate nephelometry, and ferroxidase activity determined by measuring loading of ferrous iron onto iron-free transferrin. A significant reduction in ferroxidase activity was observed in dialysis patients when compared with controls (37 +/- 1.20 and 46 +/- 1.14 mU/l, respectively; p < 0.001). Following dialysis, ferroxidase activity rose significantly to 41 +/- 1.16 mU/l, with a significant difference still remaining between control and patient ferroxidase activity (p < 0.005). Immunoreactive caeruloplasmin was found to be similar in all groups (before dialysis 0.40 +/- 0.07 g/l, after dialysis 0.39 +/- 0.07 g/l, control 0.42 +/- 0.09 g/l: p = NS). A significant difference in caeruloplasmin-specific activity was therefore observed between predialysis, postdialysis and control samples (97 +/- 2.31, 105 +/- 1.74 and 112 +/- 1.51 mU/g; p < 0.001, p < 0.01, respectively). Ferroxidase activity of caeruloplasmin is impaired in renal failure. Inhibition of caeruloplasmin ferroxidase activity in dialysis patients may contribute to increased oxidative stress in these patients.

Adult↗
PubMed1999

Elemental composition of human milk from mothers of premature and full-term infants during the first 3 months of lactation.

To examine longitudinal and gestational effects of mineral content in human milk, we analyzed human milk from lactating mothers of premature (PRT, n = 24, < 2000 g birth weight, < 37 wk gestation) and full-term (FT, n = 19, > 2500 g, 39-41 wk gestation), living in Newfoundland, Canada. Samples were collected once a week for 8 wk with one final sample collected at 3 mo. Milk samples collected in acid-washed containers were wet ashed with concentrated HNO3, and barium, cadmium, calcium, cesium, cobalt, copper, cerium, lanthanum, magnesium, manganese, molybdenum, nickel, lead, rubidium, tin, strontium, and zinc were measured using inductively coupled plasma-mass spectrometry. Data were analyzed using standard multiple-regression procedures with correlated data analyses to take account of the relationship between successive weeks. Results indicated lower Ca and Pb in PRT milk. Calcium was the only nutritionally significant element to differ between groups. Molybdenum in both PRT and FT milk showed a definite decrease with time, suggesting that the Mo content in milk is homeostatically regulated. However, Ce, La, Ba, and Sn did not display any pattern indicative of biological regulation and potential human requirement.

Female↗
PubMed1999

Plasma glutathione peroxidase activity is reduced in haemodialysis patients.

Cardiovascular disease is the major cause of morbidity and mortality in patients with end-stage renal failure. Increased free radical production and antioxidant depletion may contribute to the greatly increased risk of atherosclerosis in these patients. Glutathione peroxidase (GPX) is an important antioxidant, the plasma form of which is synthesized mainly in the kidney (eGPX). The aim of this study was to assess the activity of eGPX in patients with end-stage renal failure on haemodialysis. Venous blood was collected from 87 haemodialysis patients immediately prior to and after dialysis and from 70 healthy controls. Serum eGPX activity was measured using hydrogen peroxide as substrate and immunoreactivity determined by ELISA. eGPX activity was significantly reduced in dialysis patients when compared to controls (106 +/- 2.7 and 281 +/- 3.6 U/l respectively, p < 0.001). Following haemodialysis, eGPX activity rose significantly to 146 +/- 3.8 U/l, p < 0.001, although remaining below control values (p < 0.005). Immunoreactive eGPX, however, was similar in all groups (pre-dialysis 14.10 +/- 1.26 microg/ml, post-dialysis 14.58 +/- 1.35 microg/ml, controls 15.20 +/- 1.62 microg/ml, p = NS). A decrease was observed in the specific activity of eGPX in patients when compared to controls (8.81 +/- 1.14, 10.71 +/- 1.54 and 21.97 +/- 1.68 U/mg respectively, p < 0.0001). eGPX activity is impaired in patients undergoing haemodialysis and so may contribute to atherogenesis in renal failure.

Adolescent↗
PubMed1997

Gepirone and diazepam in generalized anxiety disorder: a placebo-controlled trial.

This randomized, double-blind clinical trial involving 198 generalized anxiety disorder (GAD) patients was conducted to more clearly define gepirone's role for the treatment of anxiety in daily dosages of 10 to 45 mg compared with diazepam and placebo. A secondary goal was to test for possible discontinuation symptoms after abrupt discontinuation of therapy. After a 1-week washout period, patients were treated for 8 weeks and then abruptly shifted under single-blind conditions for 2 weeks on placebo. The highest attrition rate occurred with patients on gepirone (58%) and the lowest on diazepam (34%). Medication intake for week 4 was 19.5 +/- 12.5 mg/day diazepam and 19.0 +/- 11.5 mg/day gepirone and was similar at week 8. The major adverse events were light-headedness, nausea, and insomnia for gepirone and drowsiness and fatigue for diazepam. Clinical improvement data showed gepirone's anxiolytic response to be delayed, being significant from placebo beginning at week 6, whereas diazepam caused significantly more relief than placebo from week 1 onward. Taper results showed that only diazepam, but not gepirone, caused a temporary worsening of anxiety symptoms or rebound.

Adult↗
PubMed1997

Evaluation of full-term infants fed an evaporated milk formula.

The objective of this prospective, cohort study was to compare the nutritional status of full-term infants who were fed human milk (BF, n = 29), formula (FF, n = 30) or evaporated milk formulae (EM, n = 30) for at least 3 months. Infants were seen at enrollment, 3 and 6 months, at which times a blood sample, diet record and anthropometric data were collected. Infants in the EM group received solids earlier (12 +/- 5 weeks) than did FF infants (15 +/- 4 weeks), and both were earlier than BF infants (19 +/- 4 weeks). Only 26% of the EM fed group received iron supplements as ferrous sulphate drops. Seven BF, 12 FF and 20 EM had abnormal ferritin values (< 10 ng ml-1) at 6 months. Copper intake was lower in the EM infants at 3 and 6 months. However, plasma copper and erythrocyte copper zinc superoxide dismutase (ZnCuSOD) levels did not differ between groups. Selenium intake was lower in the EM group (5 +/- 1 and 10 +/- 5 micrograms d-1; 3 and 6 months) than in the FF infants (13 +/- 4 and 19 +/- 7 micrograms d-1; 3 and 6 months). Erythrocyte SeGHSPx levels in EM infants were lower at 6 months (EM, 33.2 +/- 3.4; FF. 35.2 +/- 3.9: BF, 36.1 +/- 3.8 mU mg Hb-1). Thiamin intake (0.99 +/- 0.08 and 1.24 +/- 0.32; 3 and 6 months, mg 1000 kcal-1) was higher in the FF group than in EM infants (0.38 +/- 0.39 and 0.66 +/- 0.38; 3 and 6 months). There were more (13%) abnormal thiamin assays in the EM group at 6 months than in the BF and FF infants (0%). In conclusion, infants fed evaporated milk formula receive adequate copper but may not receive enough thiamin or selenium. Unless supplemented from birth with medicinal iron, intakes of iron will be inadequate.

Animals↗
PubMed1996

Laboratory gloves as a source of trace element contamination.

Contamination in a trace element laboratory can come from a variety of sources, including laboratory gloves. Therefore, vinyl and latex gloves were obtained from as many manufacturers as would supply gloves. These gloves were either prepared for acid-washing and subsequent soaking in an acid solution, or immersed in an acid solution for a duration of either 1 min or 1 h. Incubation washes were analyzed for a variety of trace elements by flame atomic absorption spectroscopy (AAS) or inductively coupled mass spectrometry (ICP-MS). Results indicated that only three brands of vinyl gloves were acceptable for use in a trace element laboratory, whereas others had contamination of different elements. Latex gloves contained such high levels of biologically important elements that they were not considered suitable for routine trace element work. Vinyl gloves of choice should be routinely acid-washed before use in a trace element laboratory.

Air Pollution, Indoor↗
PubMed1996

Lasers in dentistry: a review. Part 1.

Papers describing the dental applications of lasers have appeared in the dental literature for more than 30 years but there have been few comprehensive reviews. In this, the first of a two-part series, the author describes the earliest dental uses of lasers, the heightened interest which followed the appearance of the Nd:YAG laser in 1987 and the use of lasers in dentistry on hard and soft tissue. Part 2 will deal with the use of lasers in diagnosis, treatment and dental research.

Dental Equipment↗