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Biomedical subjects

M J Larsen

Publications and source records attributed to M J Larsen.

At least 91 records · Page 5Linked to original sources
PubMed1978

Effects of a single dose of fluoride on calcium metabolism.

Fluoride 27 mg was given perorally to 14 subjects. It was found that the serum fluoride concentration increased followed by a decrease to normal levels during 24 h. Serum concentrations of calcium and phosphate decreased initially whereas those of serum immunoreactive parathyroid hormone increased. After 24 h the measured quantities were within normal limits. The results are discussed with reference to mineralization of hard tissues and to fluoride treatment of osteoporotic patients.

Adult↗
PubMed1978

Structural studies on calcium fluoride formation and uptake of fluoride in surface enamel in vitro.

The structural changes in human enamel during exposure to an acetate buffer, pH 4, containing 150 parts/10(6) fluoride have been studied using scanning electron microscopy and polarized light microscopy. After exposure for 2 h the enamel surface was covered by a fine-granular layer of calcium fluoride. The underlying enamel was highly eroded with an increased pore volume in the outer layer. Following an equilibration period of 3 months the uptake of fluoride in the apatite lattice had resulted in a highly mineralized, 100-micrometer-thick surface layer rich in fluoride covering a subsurface porous zone with an unchanged fluoride content. The deeply located, caries-like porous zone may have provided calcium and phosphate for saturation of the liquid.

Acetates↗
PubMed1977

Surface etching and subsurface demineralization of dental enamel induced by a strong acid.

Intact enamel surfaces were exposed to 20 ml of 0.1% HCl for various periods. When the acid was unsaturated with respect to both hydroxyapatite and fluorapatite the surface enamel was etched away. With time the liquid close to the enamel became supersaturated with respect to fluorapatite but remained unsaturated with respect to hydroxyapatite. Under this condition subsurface lesions developed. These observations are discussed with reference to the use of diffusion-restricting agents in laboratory caries experiments.

Acid Etching, Dental↗
PubMed1977

Calcium fluoride formation on enamel and its influence on uptake of fluoride in the apatitic lattice.

Human dental enamel was exposed to a pH 4 buffer containing 150 parts/10(6) fluoride. It was found that due to the arising degrees of saturation with respect to calcium fluoride and apatites, surface enamel dissolved coincident with a formation of calcium fluoride. The calcium fluoride redissolved while it kept the liquid saturated with respect to this salt. During this second period, fluorapatite was formed while hydroxyapatite dissolved. Finally, all calcium fluoride was dissolved and the unreacted fluoride was taken up in the apatitic lattice. The results are discussed with reference to the conditions of the oral cavity and enamel solubility experiments.

Apatites↗
PubMed1976

Anti-caries effect of a 2% Na2PO3F-dentifrice in a Danish fluoride area.

A 3-year experimental toothbrushing study was conducted in a natural fluoride area in Denmark to evaluate the anti-caries effect of a 2% sodium monofluorophosphate dentifrice. In a previous report the results for the total population of 1,407 schoolchildren, representing a broad age-span (7-12 years), at the commencement of the study in 1970 were given. In the present report results are presented for two subpopulations of "8-year-olds" and "11-year-olds" at the commencement of the study. Differential analysis of the effect of the test dentifrice on defined types of surfaces for the two subpopulations is given. The evaluation was performed using both the conventional DMF-indices and the recently published ECSI-Index6. The evaluation showed that the test dentifrice had a valuable anti-caries effect in both age groups, above and beyond the effect of the waterborne fluoride. Proximal surfaces were affected most baneficially by the active agent both in relative and absolute terms. However, an appreciable caries-preventive effect was also found on the "pit and fissure" surfaces.

Child↗
PubMed1976

Polarized light microscopy of enamel structure in incisors from newborn infants.

Enamel structure in human primary incisors was histologically examined in order to compare the observations with those from recent studies on incipient carious and fluorosed enamel. Ground sections from mandibular incisors of five full-term human infants were examined in polarized light using aqueous media (water, Thoulet's media), alcohols with different refractive indices, and quinoline. Imbibition graphs were made along traverses from the amelodentinal junction (ADJ) to the enamel surface. Quantitative assessments of the birefringence in different media along the traverses indicated a change in the relative volumes of crystallites and surrounding medium with a continuous growth of crystallites toward the ADJ. The influence of organic material is discussed in relation to the differences in calculated form birefringence observed within the specimens. When examined in quinoline, a 30-40-mum-thick surface zone appeared distinct positively birefringent, indicating that the outermost enamel reacted as a molecular sieve. Because of the lower content of minerals the interpretation of this zone differed from that of similar "dark zones" observed in carious and fluorosed enamel.

Dental Enamel↗
PubMed1975

Degrees of saturation with respect to apatites in parotid saliva at various ph values.

The purpose of the present work was to investigate the degrees of saturation with respect to hydroxyapatite and fluorapatite in saliva at various pH's. The data of ionic activities in parotid saliva were collected from the literature and the degrees of saturation with respect to hydroxyapatite and fluorapatite were calculated. It was found that parotid saliva was supersaturated with respect to both apatites above pH 5.5, unsaturated with respect to hydroxyapatite and concurrently supersaturated with respect to fluorapatite in the pH range 5.5-4.5, while it was unsaturated with respect to both apatities below pH 4.5. In the laboratory it has been found that when enamel is exposed to a liquid unsaturated with respect to hydroxyapatite and supersaturated with respect to fluorapatite, a caries-like lesion is developed. A liquid unsaturated with respect to both apatites leads to an erosion-like injury. It is concluded that the two chemical conditions leading to the two types of enamel lesions may both occur in the oral cavity.

Apatites↗
PubMed1975

Degrees of saturation with respect to apatites in fruit juices and acidic drinks.

Some fruit juices and carbonated acidic drinks, recognized as agents causing dental erosions, were analyzed for calcium, phosphate, fluoride and pH. Ionic activity/concentration products for hydroxyapatite and fluorapatite were calculated. It was found that all liquids analyzed were unsaturated with respect to both apatites, which explains their erosive effect.

Apatites↗