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Biomedical subjects

J W van Dijk

Publications and source records attributed to J W van Dijk.

At least 19 recordsLinked to original sources
PubMed2001

A review of the properties of the dosimetric systems and the quality assurance programmes of 48 dosimetric services in the European Union and Switzerland.

This paper summarises the evaluation of the 1997 EURADOS questionnaire on dosimetric systems able to assess personal dose equivalent. In total, 56 approved dosimetric services in the European Union and Switzerland responded, together monitoring approximately 615,000 occupationally exposed persons. Of these services, 48 stated they were able to assess the external doses in terms of personal dose equivalent. The general aspects of the dosimetric systems and the quality assurance programmes of these services are discussed.

European Union↗
PubMed2001

Harmonisation and dosimetric quality assurance in individual monitoring for external radiation.

The current situation amongst Member States is that there are widely differing national requirements for dosimetric services and for dosemeter performance. It is clear that with the free movement of workers within the European Union (EU) and the requirements for individual dosimetry given in Council Directive 96/29 EURATOM, a degree of harmonisation of requirements and procedures of EU Member States would be desirable. A EURADOS action group, made up of members from each of the EU Member States plus Switzerland, was set up with the overall objectives of consolidating within the EU the quality of individual monitoring using personal dosemeters and assisting movement towards harmonised procedures. An outline of the work of the action group is given and the term 'harmonisation' is discussed.

Europe↗
PubMed1993

Relationships between birefringence and mineral content in artificial caries lesions of enamel.

The microradiographic mineral content and birefringence in water and Thoulet's solution were measured at selected points in sections of caries-like lesions. Birefringence was not related to mineral content in sound superficial enamel immersed in Thoulet's solution or in the lesion body immersed in water. For the surface layer of the lesion, birefringence in water could be used to obtain qualitative information about mineral content. For the lesion body, birefringence in Thoulet's solution was linearly related to mineral content and can be used to estimate the latter with a standard error of about 7 vol%. The intrinsic birefringence for the lesion body was estimated as -34.5 (+/- 2.3) x 10(-4); This value may also be valid for other parts of the lesion. From consideration of ionic sizes, it is argued that Thoulet's solution cannot necessarily penetrate all enamel pores accessible to water. It appeared that there is a progressive fall in the content of pores inaccessible to Thoulet's solution in the surface layer of the lesion as demineralisation increases.

Birefringence↗
PubMed1990

Caries experience in the deciduous dentition as predictor for caries in the permanent dentition.

The present study aims at determining a reliable screening test for the prediction of caries. In order to identify children at risk of caries, individual classifications were recorded for 268 children at the age of 7 years, according to different screening criteria of the caries experience in the deciduous dentition and according to caries increment as validation criterion. In order to determine the best screening criterion, ratios of sensitivity, specificity and false-positive and false-negative ratios were computed and plotted in receiver operating characteristic curves. The best screening criterion at less than or equal to 4 dmft resulted in a sensitivity ratio of 0.69, specificity of 0.72 and diagnostic power of 0.78 for caries increment in the permanent dentition at the age of 7-11 years. The potential of the screening is elucidated with an example, showing that 48% of the expenses needed for a preventive treatment for all children could be saved by selecting children at risk with the aid of a screening test. The disadvantage of this decision making is that 19% of the children who develop caries would not benefit from the preventive treatment.

Child↗
PubMed1989

Plasma calcium difference between man and vertebrates.

1. Literature data about the plasma content of total calcium, ionized calcium and inorganic phosphate in healthy animals and man of different age and sex were collected. 2. It was established that under normal conditions ionized calcium is about 45% of total calcium. 3. The degree of saturation of these blood samples with respect to octocalcium phosphate OCP was calculated. 4. In young animals and man the blood plasma has a higher degree of saturation than in adult animals and man. 5. The blood plasma of healthy animals is supersaturated with respect to OCP during their whole life. 6. However, the blood plasma of healthy human adults is slightly undersaturated with respect to OCP.

Age Factors↗
PubMed1989

Caries in fissures of permanent first molars as a predictor for caries increment.

A group of 268 children were checked for caries experience at the age of 7.2 yr later at the age of 9 and 4 yr later at the age of 11 yr. Caries experience of fissures in permanent first molars at the age of 7 yr served as a screening criterion for caries increment between the ages of 7 and 11 yr. This screening resulted in a sensitivity of 0.62, a specificity of 0.82, and a diagnostic power of 0.83 for total caries increment in the permanent dentition and in a sensitivity of 0.68, a specificity of 0.80, and a diagnostic power of 0.78 for caries increment in fissures of permanent first molars. It was concluded that this screening offered the best method available for identifying children at risk from fissure caries in their permanent first molars. Cost effectiveness of preventive treatment directed towards individuals, for instance the application of fissure sealants, can be improved by using this screening method.

Child↗
PubMed1989

A systemic approach to the oral problem of mandibular resorption.

It is argued that mandibular resorption can be considered as osteoporotic in nature. This calls for a systemic approach in its treatment. One aspect mostly neglected is the tendency of bone to bind calcium and phosphate ions. A direct measure for this tendency is the difference in pH between the bone extracellular fluid and blood plasma. This pH difference is directly reflected by the degree of saturation of blood plasma with octocalcium phosphate. Calculation of these degrees of saturation of about 2000 data of blood plasma compositions given in the literature indicates that calcitonin injection, estrogen replacement and magnesium supplementation increase the tendency of bone to bind calcium and phosphate ions and hence should be used in the therapy of mandibular resorption and of bone resorption in general.

Animals↗
PubMed1986

Dissolution and precipitation reactions in human tooth enamel under weak acid conditions.

Slices of enamel were demineralized in weak acid solutions at pH 5. The solutions were analysed for Ca, P, Na and Mg. A substantial increase of the Ca/P ratio in the solution after about 6 h of demineralization was ascribed to brushite formation. The ratios of liberated Ca/Na, P/Na, Ca/Mg and P/Mg were always lower than the correspondent ratios in sound enamel. It was concluded that precipitation of brushite, and a preferential dissolution of Na and Mg compounds from the enamel both play a role in the dissolution-precipitation reactions in dental enamel during acid attack.

Acids↗
PubMed1985

Effect of time, degree of saturation, pH and acid concentration of buffer solutions on the rate of in-vitro demineralization of human enamel.

The rate of demineralization of the artificial caries-like process was measured using two methods. The rate calculated from microradiography of the demineralized enamel appeared to be equal to the one calculated from calcium and phosphate analysis of the demineralizing buffer. In small volumes of demineralizing solution, the rate of demineralization decreased with time, due to the increase in saturation of the solution during the demineralization of the enamel. With increasing saturation, with respect to hydroxyapatite, and with increasing pH the rate of demineralization decreased. Increasing acid concentration had a marked influence only at the lower concentrations; a further increase had no effect on the rate of demineralization.

Buffers↗
PubMed1984

The effect of undissociated acetic-acid concentration of buffer solutions on artificial caries-like lesion formation in human tooth enamel.

A chemical system for lesion production was used. The influence on lesion characteristics of the concentration of undissociated acetic acid in a calcium and phosphate-containing buffer solution was investigated. Artificial lesions obtained after demineralization in buffers with a pH of 4.0, 4.5, 5.0 or 6.0 at 5 or 6 different acid concentrations for different demineralization times were investigated micro-radiographically. The lesion characteristics studied were: the mineral content of the surface layer; the mineral content of the body of the lesion; and the depth at which these mineral levels were reached; the depth of the lesion. The concentration of undissociated acetic acid had little effect on the lesion characteristics at low pH. When lower concentration buffers at pH 6.0 were used, the effect was more pronounced. At this level, the buffer capacity of the acetic acid/acetate buffer is small.

Acetates↗