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Biomedical subjects

T C Aw

Publications and source records attributed to T C Aw.

At least 37 records · Page 2Linked to original sources
PubMed1998

Effect of mixing technique on surface characteristics of impression materials.

STATEMENT OF PROBLEM: Previous studies have shown a relationship between the disinfection process, wettability, and mass change of impression materials. Hand-mixed high viscosity impression materials usually result in a material with numerous voids, which contribute to surface roughness and affect the surface characteristics of the material. PURPOSE: This study evaluated the effect of mixing technique on advancing contact angle, receding contact angle, imbibition, and mass loss of various high and low viscosity polyether and polyvinyl siloxane materials. The null hypothesis tested was no differences exist between the different mixing systems. MATERIAL AND METHODS: The Wilhelmy technique was used for deriving wetting properties of the materials used (Impregum F and Penta, Permadyne Syringe, Garant and Penta, Dimension Penta and Garant L, Aquasil). Conditions included no disinfection (0 hours) and 1, 5, and 18 hours of immersion disinfection in a full-strength solution of 2% acid glutaraldehyde disinfectant (Banicide). Weight changes before and after disinfection were measured to detect weight loss or mass increase over time. Weight loss in air was also measured to detect mass loss. Data were analyzed with a one-way analysis of variance at alpha = 0.05. RESULTS: All materials displayed some degree of imbibition of the disinfectant and experienced mass loss with polymerization, except the light viscosity polyvinyl that gained 0.18% at 5 hours. No significant differences were found in wettability among the polyether materials after 1 hour of disinfection. Less imbibition was observed for high viscosity mechanically mixed materials compared with the hand-mixed materials for both polyether and polyvinyl siloxane at 1-hour disinfection time. CONCLUSIONS: Polyether materials were more wettable than polyvinyl. Imbibition of high viscosity polyether and polyvinyl materials after 1 and 18 hours of disinfection were affected by the mixing system used.

Analysis of Variance↗
PubMed1997

Clinical and epidemiological data on lung cancer at a chromate plant.

The workforce of the only chromite ore processing plant in the United Kingdom at Eaglescliffe has been the subject of several epidemiological studies. There are also medical data available through a health surveillance program conducted by the plant's medical center. The clinical information has in part been collected to fulfill the requirements of health and safety legislation. Through this system, 18 cases of lung cancer among the workforce have been identified. The mean age at diagnosis was 57 years, with all but two cases occurring in smokers. There were no obvious histological or clinical features that could allow differentiation between the occupational and nonoccupational cancers. The epidemiological studies indicated an excess lung cancer risk among the workers beginning employment on the site before 1960. The risk appeared to have diminished after a major process change in 1960 which removed the addition of calcium carbonate to the process. Further studies including case-control analyses and construction of a job exposure matrix through use of recall by long-term workers and pensioners are in progress. The feasibility of an updated cohort mortality study at Eaglescliffe and possibly using the same protocol for other similar cohorts in U.S. and European plants should be considered.

Case-Control Studies↗
PubMed1997

Polymerization shrinkage of restorative resins using laser and visible light curing.

OBJECTIVE: This in vitro investigation compared the amount of linear shrinkage that occurs when a light-cured composite resin is cured with a visible light source, and also with an argon laser. SUMMARY BACKGROUND DATA: When composite resins are light-cured, they undergo a certain degree of polymerization shrinkage, which can be clinically significant and affect the efficacy of the restoration. A new protocol utilizes laser curing instead of conventional visible light. METHODS: Two hybrid composite resins were used, Z100 and TPH-Spectrum. Dimensional change was measured in a linear direction, using a calibrated light-microscope. A total of 40 samples of composite resin was tested using two curing lights, and two hybrid composite resins, resulting in four groups of 10 samples (n = 10) each. According to manufacturer instructions, curing time for the laser was 10 sec, and for visible light was 40 sec. RESULTS: With TPH-Spectrum, the mean shrinkage with visible light was 0.583% compared to that with laser light which was 0.591%. With Z100, the mean shrinkage with visible light was 0.565%, compared to that with laser light which was 0.551%. CONCLUSIONS: There was no significant difference in amount of shrinkage of hybrid composite resins between using visible light or laser light. There was also no significant difference in shrinkage between the two hybrid composites for either light source.

Analysis of Variance↗
PubMed1997

Ethical issues in occupational medicine practice: knowledge and attitudes of occupational physicians.

Views on ethical conduct in occupational medicine practice can vary from country to country and even between occupational health practitioners. However, there are many areas of common agreement, and this is apparent on comparing guidance documents on ethics produced by several different organizations. The usefulness of these documents will depend in part on how aware practitioners are of their existence. A standardized questionnaire administered to 70 occupational physicians in the Netherlands, UK, and Singapore showed that there was a lack of awareness of guidance documents on ethics, even for publications from their own countries. Only five of the 70 respondents consulted an ethics document in the past year. In addition to publications, other avenues were used for advice on ethical issues. There was a difference in opinion between the physicians from Singapore and those from the two European countries on whether specific occupational health activities were ethical. These findings reinforce the need for international guidance on ethics to take into account differences in attitudes and practice between countries. On many issues there was no unanimity of opinion, even between occupational physicians from the same country. This may be an indication of the complexity of ethical matters, and provides a rationale for publishing guidance on ethics in occupational medicine.

Adult↗
PubMed1997

Occupational infection in an offal porter: a case of Q fever.

This case report describes the job activities of an offal porter who developed Q fever while processing livers from sheep. The diagnosis was confirmed by an increase in specific serial antibody titre. The main clinical features were anorexia, nausea, headache, pyrexia and elevated gamma-glutamyl transferase. Twenty-four cases of occupationally-acquired Q fever were noted by the Communicable Diseases Surveillance Centre (CDSC) between 1984 and 1994. This case report has an important feature in that a workplace visit was performed to evaluate the system of work and the circumstances of exposure to the infectious agent. Relevant preventive measures for this zoonotic infection are discussed.

Abattoirs↗
PubMed1997

Central obesity, insulin resistance, syndrome X, lipoprotein(a), and cardiovascular risk in Indians, Malays, and Chinese in Singapore.

STUDY OBJECTIVE: To examine the hypothesis that the higher rates of coronary heart disease (CHD) in Indians (South Asians) compared with Malays and Chinese is at least partly explained by central obesity, insulin resistance, and syndrome X (including possible components). DESIGN: Cross sectional study of the general population. SETTING: Singapore. PARTICIPANTS: Random sample of 961 men and women (Indians, Malays, and Chinese) aged 30 to 69 years. MAIN RESULTS: Fasting serum insulin concentration was correlated directly and strongly with body mass index (BMI), waist-hip ratio (WHR), and abdominal diameter. The fasting insulin concentration was correlated inversely with HDL cholesterol and directly with the fasting triglyceride concentration, blood pressures, plasminogen activator inhibitor 1 (PAI-1), and tissue plasminogen activator (tPA), but it was not correlated with LDL cholesterol, apolipoproteins B and A1, lipoprotein(a), (Lp(a)), fibrinogen, factor VIIc, or prothrombin fragment (F)1 + 2. This indicates that the former but not the latter are part of syndrome X. While Malays had the highest BMI, Indians had a higher WHR (men 0.93 and women 0.84) than Malays (men 0.91 and women 0.82) and Chinese (men 0.91 and women 0.82). In addition, Indians had higher fasting insulin values and more glucose intolerance than Malays and Chinese. Indians had lower HDL cholesterol, and higher PAI-1, tPA, and Lp(a), but not higher LDL cholesterol, fasting triglyceride, blood pressures, fibrinogen, factor VIIc, or prothrombin F1 + 2. CONCLUSIONS: Indians are more prone than Malays or Chinese to central obesity with insulin resistance and glucose intolerance and there are no apparent environmental reasons for this in Singapore. As a consequence, Indians develop some but not all of the features of syndrome X. They also have higher Lp(a) values. All this puts Indians at increased risk of atherosclerosis and thrombosis and must be at least part of the explanation for their higher rates of CHD.

Adult↗
PubMed1997

Hypercholesterolaemia and its treatment in Singapore with implications for screening.

The National University of Singapore Heart Study is a cross-sectional survey of the whole of Singapore from 1993 to 1995 with a random sample of 961 persons aged 30 to 69 years (response rate 71.2%). Serum lipids were measured enzymatically on an autoanalyser (Ektachem, kodak). Hypercholesterolaemia was diagnosed if the person was on lipid lowering drugs or had a serum cholesterol > or = 6.5 mmol/L (250 mg/dL). Results for the 40 to 64 age group are presented. The proportion and number in Singapore with hypercholesterolaemia were high, 23.7% and 186,544 persons respectively. However, they declined with the additional requirement of coronary heart disease (CHD) or risk factors (i.e. cigarette smoking, hypertension or diabetes mellitus), and were small if only hypercholesterolaemic persons with CHD were included, 1.6% and 13,126 persons respectively. For both genders, the proportions on drugs increased with the added options of CHD or risk factors, so that for persons with hypercholesterolaemia and CHD the proportion on drugs was very high i.e. 84.0%. However, 11.2% of persons with only hypercholesterolaemia (i.e. without CHD or other risk factors) had been prescribed drugs. The main conclusions were:1) The use of different criteria for the screening and treatment of hypercholesterolaemia would involve large differences in the number of Singaporeans on lipid lowering drugs and this should be considered when deciding policy and 2) Medical practitioners currently to some extent do consider the presence of CHD or other risk factors when prescribing lipid lowering drugs for hypercholesterolaemia.

Adult↗
PubMed1996

The incidence of viremia and the heterogeneity of hepatitis C virus genotypes among blood donors, hemophiliacs and patients with chronic liver disease.

Hepatitis C Virus (HCV) is the major cause of parentally transmitted non-A, non-B hepatitis. We studied the incidence of HCV Viremia in blood donors, hemophiliacs and patients with chronic liver disease who are positive for antibodies to HCV, and then correlated the HCV genotypes among the three groups. 23 blood donors, 10 hemophiliacs and 97 patients with chronic liver disease were found to be positive for anti-HCV during this study period from June 1993 to December 1993. Only 3 (13%) blood donors, 6 (60%) hemophiliacs and 71 (73%) patients with chronic liver disease were found to be viremic when tested for HCV RNA by reverse transcriptase-polymerase chain reaction (RT-PCR). The low incidence of viremia among blood donors may be due to any one of the following three reasons. 1, the level of viremia was below the level of detection. 2, the viremia was intermittent with persistent infection. 3, the majority of cases represented resolved infection. The HCV genotypes were heterogeneous among the three groups. All the blood donors with viremia and 35 (50%) of patients with chronic liver disease, belonged to type II (1b). However only one (17%) of the hemophiliacs belonged to type II (1b). Studies have shown that the genotype I(1a) is the predominant type in the USA and Europe, whereas type II(1b) is more frequent in the Far East. It is also suggested that type II (1b) is associated with non-responsiveness to interferon therapy. Our hemophiliacs were treated with imported coagulation factors, thus they were probably exposed to the genotypes in the west. There was significant difference in the incidence of HCV type II (1b) among local blood donors and hemophiliacs (P = 0.005). However the difference between the hemophiliacs and the patients with chronic liver disease was not statistically significant. The number of patients in this study was too small to draw any firm conclusions. However the findings highlight the importance of studying the genotypes of patients with Hepatitis C infection due to their relevance in the management of these cases with interferon therapy.

Adolescent↗
PubMed1996

Effect of phototherapy on thyroid stimulatory hormone and free thyroxine levels.

OBJECTIVE: To study the effect of phototherapy for neonatal hyperbilirubinaemia on thyroid function as neonatal thyroid screening is sometimes performed during exposure to phototherapy. METHODOLOGY: Infants with non-haemolytic hyperbilirubinaemia were sequentially allocated to fibre-optic phototherapy, conventional daylight phototherapy, or a combination of both. Bilirubin concentration was monitored 12 hourly by capillary blood sampling; venous blood was sampled for thyroid stimulating hormone (TSH) and free thyroxine (fT4) determinations, at start of exposure, at 24 h, end of exposure and 1 day later. Comparable unexposed infants served as controls. RESULTS: All 123 study infants and 25 controls remained well during the study. Bilirubin levels declined during phototherapy, being most rapid in the combination group. The TSH and fT4 values at start of exposure were 3.86 +/- 0.41 mU/L (mean +/- SEM) and 33.20 +/- 1.16 pmol/L, respectively, in the fibre-optic group, 3.62 +/- 0.38 mU/L and 37.22 +/- 1.76 pmol/L in the daylight group, and 4.40 +/- 0.48 mU/L and 29.91 +/- 1.13 pmol/L in the combined group, compared with 5.77 +/- 0.40 mU/L and 34.46 +/- 1.68 pmol/L in the control group. The TSH and fT4 values declined with increasing age in the phototherapy and control groups with end of exposure values of 2.90 +/- 0.28 mU/L and 27.71 +/- 0.71 pmol/L, 2.77 +/- 0.31 mU/L and 33.52 +/- 1.22 pmol/L, and 3.44 +/- 0.30 mU/L and 27.54 +/- 0.88 pmol/L, respectively, compared with 4.21 +/- 0.61 mU/L and 27.19 +/- 2.33 pmol/L (at 72 h) in the control group. The pattern of TSH and fT4 decline in the exposed and control groups was similar, being related to increasing age. CONCLUSIONS: The validity of neonatal thyroid screening is not affected by fibre-optic or conventional phototherapy or by both combined.

Humans↗
PubMed1996

Serum lipid & lipoprotein profiles of obese Chinese children.

The serum lipid and lipoprotein levels of 59 obese Chinese children with a mean age of 13.0 years and mean relative weight of 164.2% were analysed. Between 40% to 54% of these children had elevated lipid and lipoprotein levels and about 78% had reduced high density lipoprotein (HDL) level when compared to healthy American and Japanese children. The obese children also had higher mean levels of total cholesterol (TC) and lower HDL compared to male adults in the local population. Those with elevated TC had higher mean relative weight (170% vs 159%, p < 0.05). In view of the close association between hyperlipidaemia and atherosclerosis, obese children should be carefully screened and managed to prevent long term morbidity and mortality of coronary artery disease.

Adolescent↗