Biomedical subjects
Publications and source records attributed to M C Downer.
Using femtosecond microscopy, we observe subpicosecond transport of thermal energy radially outward from a micrometer-sized spot of an aluminum target following P-polarized excitation at >10(18) W/cm2 with a 24 fs pulse. The rapid expansion coincides with the onset of nonlocal energy transport dominated by radiation and hot electrons.
OBJECTIVE: To examine the provision of dental services by salaried personnel in the countries of Western Europe, together with Australia, Canada and New Zealand, and to weigh the merits of this method against alternatives, namely, capitation and fee for item of service. In light of the findings, to consider the future role of salaried dental services in the National Health Service (NHS) in England. METHOD: Information was gathered from published reports, the World Wide Web and by mailed questionnaire to national chief dental officers or equivalents. RESULTS: Narrative descriptions of service provision in the countries with salaried primary dental care services were compiled. Demographic, macro-economic, workforce, and oral health data for the broader spectrum of Western industrialised countries were tabulated. Examination of the quantitative data showed no strong associations between variables. CONCLUSIONS: Dental services delivered by a salaried workforce can be costly in relation to the volume of clinical activity produced. However, deployment of clinical auxiliary personnel can keep costs down. Salaried services foster a preventive approach to care and are particularly suitable where care is directed towards vulnerable groups within the community. Salaried staff generally receive a lower level of remuneration than private practitioners but usually work in an environment less subject to undue pressures of time.
OBJECTIVES: To use a decision-analytic model to determine the incremental costs and outcomes of alternative oral cancer screening programmes conducted in a primary care environment. DESIGN: The cost-effectiveness of oral cancer screening programmes in a number of primary care environments was simulated using a decision analysis model. Primary data on actual resource use and costs were collected by case note review in two hospitals. Additional data needed to inform the model were obtained from published costs, from systematic reviews and by expert opinion using the Trial Roulette approach. The value of future research was determined using expected value of perfect information (EVPI) for the decision to screen and for each of the model inputs. SETTING: Hypothetical screening programmes conducted in a number of primary care settings. Eight strategies were compared: (A) no screen; (B) invitational screen--general medical practice; (C) invitational screen--general dental practice; (D) opportunistic screen--general medical practice; (E) opportunistic screen--general dental practice; (F) opportunistic high-risk screen--general medical practice; (G) opportunistic high-risk screen--general dental practice; and (H) invitational screen--specialist. PARTICIPANTS: A hypothetical population over the age of 40 years was studied. MAIN OUTCOME MEASURES: The main measures were mean lifetime costs and quality-adjusted life-years (QALYs) of each alternative screening scenario and incremental cost-effectiveness ratios (ICERs) to determine the additional costs and benefits of each strategy over another. RESULTS: No screening (strategy A) was always the cheapest option. Strategies B, C, E and H were never cost-effective and were ruled out by dominance or extended dominance. Of the remaining strategies, the ICER for the whole population (age 49-79 years) ranged from pound 15,790 to pound 25,961 per QALY. Modelling a 20% reduction in disease progression always gave the lowest ICERs. Cost-effectiveness acceptability curves showed that there is considerable uncertainty in the optimal decision identified by the ICER, depending on both the maximum amount that the NHS may be prepared to pay and the impact that treatment has on the annual malignancy transformation rate. Overall, however, high-risk opportunistic screening by a general dental or medical practitioner (strategies F and G) may be cost-effective. EVPIs were high for all parameters with population values ranging from pound 8 million to pound 462 million. However, the values were significantly higher in males than females but also varied depending on malignant transformation rate, effects of treatment and willingness to pay. Partial EVPIs showed the highest values for malignant transformation rate, disease progression, self-referral and costs of cancer treatment. CONCLUSIONS: Opportunistic high-risk screening, particularly in general dental practice, may be cost-effective. This screening may more effectively be targeted to younger age groups, particularly 40-60 year olds. However, there is considerable uncertainty in the parameters used in the model, particularly malignant transformation rate, disease progression, patterns of self-referral and costs. Further study is needed on malignant transformation rates of oral potentially malignant lesions and to determine the outcome of treatment of oral potentially malignant lesions. Evidence has been published to suggest that intervention has no greater benefit than 'watch and wait'. Hence a properly planned randomised controlled trial may be justified. Research is also needed into the rates of progression of oral cancer and on referral pathways from primary to secondary care and their effects on delay and stage of presentation.
We demonstrate an experimental technique for isolating and enhancing quadrupolar second-harmonic generation in isotropic materials by using two orthogonally polarized laser beams that create wavelength-scale, forward-radiating gradients in the second-harmonic polarization.
Optical second-harmonic generation (SHG) is used as a noninvasive probe of the interfaces of Si nanocrystals (NCs) embedded uniformly in an SiO2 matrix. Measurements of the generated SH mode verify that the second-harmonic polarization has a nonlocal dipole form proportional to (E x Delta inverted) E that depends on inhomogeneities in the incident field E, as proposed in recent models based on a locally noncentrosymmetric dipolar response averaged over the spherical NC interfaces. A two-beam SHG geometry is found to enhance this polarization greatly compared to single-beam SHG, yielding strong signals useful for scanning, spectroscopy, and real-time monitoring. This configuration provides a general strategy for enhancing the second-order nonlinear response of centrosymmetric samples, as demonstrated here for both Si nanocomposites and their glass substrates.
OBJECTIVES: To document data on current and past levels of dental decay in British children and compare trends with those in other countries, in Europe in particular. METHOD: Data were abstracted from multiple sources and collated and tabulated. RESULTS: The dental health of the majority of British children has improved dramatically since the early 1970s. Twelve-year-old children now have on average less than one decayed, missing (extracted) or filled tooth. Levels of dental decay in UK children at 5 and 12 years are among the lowest in the world. There are still marked inequalities in the dental decay experience of children between the territorial regions of the UK, high and low socio-economic groups, and regular and symptomatic dental attenders. Many children in areas of deprivation are either not motivated to seek dental treatment or experience barriers in obtaining it. In parallel with improvements in the dental health of the majority of children, the proportion of UK adults who have no natural teeth has fallen from 37% to 12% over the past four decades. Total tooth loss is now confined almost entirely to individuals over 45 years of age. Most of the improvements in children's dental health are attributable to environmental factors, in particular the widespread availability of fluoride containing toothpastes since the 1970s. There are clear benefits from fluoridation of public water supplies over and above those attributable to other factors. CONCLUSIONS: The findings suggest initiatives should be directed to bringing children from deprived backgrounds under the umbrella of dental care. To help alleviate the inequalities in dental health, water fluoridation should be implemented, in urban industrial areas in particular, where levels of dental decay are still unacceptably high.
OBJECTIVES: To demonstrate the feasibility of opportunistic oral cancer and precancer screening in general dental practice and to determine the prevalence of relevant lesions and risk habits in a population of general dental practice attenders. DESIGN: A prospective demonstration study, recruiting patients opportunistically. SETTING: General dental practices. METHODS: Eighteen general dental practitioners took part in this study. Each attended training sessions to be advised of the study protocol and the criteria of a positive and negative screen. Patients over the age of 35 years were prospectively and opportunistically recruited. Each patient was asked to complete a health questionnaire concerning age, gender, ethnicity, smoking and drinking habits. The dentist then examined the soft tissues and recorded the presence or absence of lesions independently on a second form. The forms were collated and data were analysed to determine prevalence of lesions and associations with risk habits. RESULTS: Data on 2,265 patients were available for analysis. Oral lesions were detected in 319 patients (14.1%). Ninety-four patients (4.2%) had lesions considered to be either malignant or potentially malignant. There was a significant association between positive lesions and male gender(IRR 1.86, 95% CI 1.22-2.82), heavy smoking (males: IRR 3.68, 95% Cl2.10-6.43: female; IRR 3.58, 954b CI 1.35-9.50) and heavy alcohol use in males (IRR 2.98, 95%q CI 1.06-3.47). CONCLUSIONS: The results suggest that patients attending general dental practices are representative of the general population both in terms of lesion prevalence and high risk habits such as smoking and drinking. This supports the view that opportunistic screening in a general dental practice setting may be a realistic alternative to population screening. Further research is needed to determine the cost effectiveness of this approach and to investigate the value of targeting high risk groups within this population. General dental practice is ideal for the evaluation of such systems prior to extending these studies to other healthcare settings.
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OBJECTIVE: To elicit a range of values for sensitivity, specificity and other measures of performance in screening for oral cancer and precancer. METHOD: A literature search which included three databases was conducted. Strict inclusion criteria were applied. Values for sensitivity (Sn) and specificity (Sp), from seven investigations, were expressed as a receiver operator characteristic (ROC) curve. Meta-analysis of the combined results was used to produce a summary operator characteristic (SROC) curve. RESULTS: The pooled weighted value of Sn from the seven studies was 0.796. From the SROC, the corresponding value of Sp at this level of Sn was 0.977 (95% CI 0.941, 0.991). When Sp was held at 0.977, the corresponding value of Sn from the SROC was 0.796 (95% CI 0.594, 0.912). CONCLUSIONS: The reports selected for eventual inclusion revealed a high level of heterogeneity with respect to the location of investigations, prevalence of lesions, the personnel used and other factors. The meta-analysis indicated that overall the studies had high discriminatory ability. The estimates of Sn and Sp, and values obtained for other measures of screening performance, were considered suitable for input to a simulation model in assessing the likely cost-utility of a variety of screening scenarios in further planned research.
The role of the major risk factors, tobacco smoking and alcohol consumption, on trends in intra-oral cancer mortality in England and Wales between 1911 and 1990 was investigated, using lung cancer and liver cirrhosis as surrogate markers for smoking and drinking. Standardised mortality data on lung cancer and liver cirrhosis from the Office of Population Censuses and Surveys, aggregated into 5-year time periods for ages 35-64 and 65+ years, were regressed on corresponding data for intra-oral cancer. The strongest associations were in males aged 35-64 with a high negative correlation between lung and intra-oral cancer (rho=-0.98, 95% CI -0.99 to -0.96, P<0. 01) and, conversely, a positive correlation between liver cirrhosis and intra-oral cancer (rho=0.71, 95% CI 0.34 to 0.89, P<0.01). The findings suggest that rising alcohol consumption since the 1950s is more closely related to increasing intra-oral cancer incidence and mortality than smoking, most notably among younger males since the early 1970s.
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OBJECTIVE: To assess the effect of altering bitewing examination recall intervals on health gain from dental restorative treatment and to determine optimum recall intervals under varying clinical conditions. DESIGN: A computer simulation of the caries process in posterior approximal tooth surfaces. The effect of superimposing restorative treatment, based on diagnoses from bitewing radiological examinations carried out at differing time intervals, was incorporated. Input data included caries attack rates, median survival times of restorations, and sensitivity (Sn) and specificity (Sp) of treatment decision making by a high (A) and a low (B) performing dentist. PARTICIPANTS: A hypothetical population, initially 14-15 years old. INTERVENTIONS: Class II amalgam restorations. OUTCOME: Health gain in utility based units (UBUs) was assessed relative to interim end point UBUs pertaining under 'do nothing scenarios'. RESULTS: One thousand approximal surfaces, designated initially as 920 sound, 51 carious and 29 filled were followed in the model over 10 years. The greatest health gain (39.33 UBUs) was from dentist A (Sn = 0.23, Sp = 0.99, restoration median survival time = 20 years, caries rate = 4.4% per annum, optimal recall interval between bitewing radiological examinations = 7 months). The least was from dentist B (Sn = 0.52, Sp = 0.88, median survival time = 5 years. caries rate = 0.0% per annum, optimal recall interval between bitewing radiological examinations > 120 months) representing a loss of 16.79 UBUs compared with 'do nothing'. CONCLUSIONS: In the best interests of their patients, it would seem that dentists need to exercise considerable caution in making positive decisions to restore approximal tooth surfaces on the basis of bitewing radiographic evidence and that for some dentists current guidelines for bitewing examination intervals would appear to be too permissive.
OBJECTIVE: To examine trends in lip cancer mortality and incidence during the 20th century, and its geographical distribution, in England and Wales as a prerequisite to establishing any essential differences in the aetiology of lip and intra-oral cancer. METHOD: Age-standardised rates for lip cancer mortality by gender from 1901 to 1991 were derived from archived OPCS data. Standardised incidence rates from 1962 to 1986 were also calculated. Registrations of lip cancer between 1979 and 1983 in the 15 RHAs covering England and Wales were obtained from the same source and standardised incidence ratios (SIR) computed. RESULTS: Progressive and sustained falls in lip cancer mortality and incidence were recorded in the period covered. In males, these related particularly to cohorts born after 1856. In addition, the incidence of lip cancer in both genders was found to be raised in a band stretching from East Anglia to the South West and also in the Trent and Wales RHAs. CONCLUSIONS: The findings support an hypothesis that employment in the agriculture, forestry and fishing industries, and also pipe smoking, were the major risk factors for lip cancer in the 20th century. Further research is required to differentiate between the aetiological risk factors for lip and intra-oral cancer.
OBJECTIVES: 1) To describe the relationships between intra-oral cancer incidence, in England and Wales and the corresponding incidence of lung cancer (a surrogate for cigarette smoking), and liver cirrhosis mortality (a surrogate for alcohol consumption). 2) To elucidate the role and relative importance of cigarette smoking and alcohol consumption in the aetiology of intra-oral cancer. METHOD: Registration data for intra-oral cancer in males and females aged 35 years and over for the 15 regional health authorities (RHAs) in England and Wales in 1979-1983 were obtained from the Office of Population Censuses and Surveys and aggregated for the five-year period. Census-based population data enabled standardised incidence ratios (SIR) to be calculated for each RHA. Using the identical method. SIRs were also computed for lung cancer and standardised mortality ratios (SMR) for liver cirrhosis, the latter for the period 1974-1978 to reflect the shorter induction time for liver disease than for cancer. Correlation coefficients (Spearman's rho) were calculated between the surrogate measures and intra-oral cancer incidence. RESULTS: For all three diseases a north-south gradient, favouring the more southerly RHAs was generally apparent. For males, the correlation between liver cirrhosis mortality and intra-oral cancer incidence was greater and statistically more significant (rho=0.75, P<0.01) than that between lung and intra-oral cancer incidence (rho = 0.63, P<0.05). For females, the corresponding correlation coefficients were positive but not significant. CONCLUSION: For males at least, the association between a surrogate marker for alcohol consumption and intra-oral cancer was greater than that observed for cigarette smoking. This adds further evidence to the current view that alcohol consumption may be more important in the aetiology of intra-oral cancer than cigarette smoking.
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OBJECTIVE: To conduct a systematic review of the literature on the longevity of routine dental restorations in permanent posterior teeth, and to identify and examine factors influencing its variability. METHOD: Accepted guidelines were followed. An advisory group oversaw the project. Simple Class I and Class II amalgam, composite resin, glass ionomer and cast gold restorations were covered. Comprehensive searching of electronic databases, hand-searching, and location of 'grey' literature, generated 124 research reports. Those considered relevant were assessed for validity and quality according to agreed criteria. The analysis was descriptive. RESULTS: Eight of 58 relevant research reports were categorised, according to agreed criteria, as being of satisfactory validity and quality. They suggested that 50% of all restorations last 10 to 20 years, although both higher and lower median survival times were reported. The findings were supported by the totality of studies reviewed. However, variability was substantial. Restoration type, materials, the patient, the operator, the practice environment and type of care system appeared to influence longevity. CONCLUSIONS: Many studies were imperfect in design. Those considered to be the most appropriate for analysis were too limited to undertake a formal statistical exploration. Therefore there remains a need for definitive randomised controlled trials of restoration longevity, of sound design and adequate power, employing standardised assessments and appropriate methods of analysis.
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OBJECTIVE: A previous study suggested that the most likely explanation for the rise and subsequent fall in caries in children in England and Wales during the last 50 years was the concurrent increase and then reduction in the sugar challenge to the population, mitigated after the early 1970s by the preventive effect of fluoride toothpaste. The current objective was to quantify the relationship between sucrose available for consumption annually since 1948 and caries experience at 5 and 12 years. METHOD: In a retrospective, longitudinal ecological study, cross-sectional mean dmft values at 5 years and DMFT values at 12 years in England from 1948 to 1968 and England and Wales from 1973 to 1996/97, from three series of standardised surveys, were regressed on data for the relevant years on sucrose available for consumption in the UK. RESULTS: For sucrose consumption and 5-year-old dmft, Spearman's rho was +0.62 (P < 0.05) while for 12-year-old DMFT the value was +0.84 (P < 0.001). For the 12 year age group, Pearson's coefficient could also be calculated (r = +0.87; P < 0.001). CONCLUSION: For several reasons caution should be used in interpreting these findings. Nevertheless they do suggest a strong positive correlation over time between dmft/DMFT and sucrose availability nationally.