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Biomedical subjects

H M Theuns

Publications and source records attributed to H M Theuns.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1984

Effect of annual application of polyurethane lacquer containing silane-fluoride.

The effect of an annual application of a F- -lacquer on dental caries was investigated in a 3-yr study. Two groups of children 10 and 12 yr of age at baseline were examined. At the end of the study no significant difference in DMFS could be detected between test and control group. The following factors might have affected this negative result: firstly, the use of other forms of F- supplementation, secondly, the relatively low caries experience in both groups and thirdly, the frequency and mode of application of the F- -lacquer.

Acrylic Resins↗
PubMed1983

The mineral content of human enamel studied by polarizing microscopy, microradiography and scanning electron microscopy.

The total observed birefringence and mineral content of the outer 300 micron of longitudinal sections of sound buccal premolar enamel were measured and three-dimensional contour maps were made. Using similar contour maps of calcium, carbonate and magnesium content from the literature, it seemed possible to explain the differences between the contour maps of total observed birefringence and mineral content. Scanning electron micrographs provided information about the orientation of the prisms. The cervical part of the enamel had a high intrinsic birefringence which may explain the difference between mineral content and total observed birefringence. This high intrinsic birefringence may be caused by a high carbonate content in cervical enamel.

Bicuspid↗
PubMed1982

Birefringence and mineral content of the first stage of artificial carious lesion formation (a combined polarizing microscopic, microradiographic and scanning electron microscopic investigation).

Artificial carious lesions were made using acetic buffer solutions of pH 6.0 containing calcium and phosphate. The solutions were highly undersaturated with respect to hydroxyapatite. Out of 72 lesions 51 showed subsurface demineralization, whereas in 21 only a superficial demineralization occurred. These superficial lesions were examined using polarized light microscopy, microradiography and scanning electron microscopy. This superficial breakdown of enamel material, considered as the initial demineralization of the enamel, appeared to occur at the prism junctions. This was indicated by the polarizing microscope technique and was made clearly visible using scanning electron microscopy. Quantitative polarizing microscopy and microradiography revealed results which correlated very well. From this it is probable that the initial superficial demineralization of the enamel is--under the described conditions--a simple dissolution reaction.

Birefringence↗
PubMed1980

Polarizing microscopy and microradiography of sound enamel.

Plano-parallel longitudinal sections from 19 sound human premolars were imbibed in water and in air. The total birefringence of the occlusal, the midcoronal and the cervical region of the buccal sound enamel cap was then determined. The volume percentage mineral was measured in the same areas using semi-quantitative microradiography. The results show that when the mean values of both water and air imbibed occlusal and midcoronal enamel are considered, there is a positive correlation between the observed total birefringence and the mineral content. The cervical, fissure and cuspal regions showed a poor correlation between mineral content and total birefringence. In longitudinal sections, the influence of the structural organization and the organic matrix is not marked in the occlusal and midcoronal regions although the cervical, fissure and cuspal regions are probably influenced to the greatest extent by these factors.

Air↗