Leon Singer

A comparison of methods used in root canal sealability studies

The purpose of the study was to compare several methods that have been used to assess marginal leakage of root canal fillings. Sixty-three extracted, single-rooted teeth were instrumented and filled in a standardized manner. Teeth were randomly divided into groups of twenty and exposed to solutions containing methylene blue dye, calcium-45, carbon-14-labeled urea, and iodine-125-labeled albumin for 48 hours to compare the degree of leakage indicated by each technique. Methylene blue dye was found to penetrate farther up the canal than any of the isotope tracers. Carbon-14-labeled urea penetrated farther than the calcium-45- or iodine-125-labeled albumin. The mean volume of solution penetrating the teeth was exceedingly small (0.0011 ml) and probably unimportant physiologically.

The Sex-Related Difference in Perfluorooctanoate Excretion in the Rat

Abstract The urinary excretion of perfluorooctanoic acid (PFO) by male and female rats was investigated. Female rats excreted 76 ± 2.7 (SEM)% of a 2-mg dose of nonionic fluorine (as PFO) in the urine in 24-hr whereas male rats excreted only 9.2 ± 3.5% of the dose. The PFO clearance, inulin clearance, net excretion rate of PFO, and the glomerular filtration rate of PFO were measured. The effect of probenecid, an inhibitor of the organic acid transport system, on these measurements was also determined. In female rats the PFO clearance was severalfold greater than the inulin clearance and the clearance of PFO was markedly reduced by probenecid. Conversely, in male rats the PFO clearance was only a fraction of the inulin clearance and was virtually unaffected by probenecid. The data indicate that female rats are able to rapidly eliminate PFO in the urine by an active secretory mechanism which is inhibited by probenecid. In male rats this secretory mechanism is either absent or relatively inactive. This difference in PFO excretion by the male and female may explain the sex-related difference in PFO toxicity in which male rats are more susceptible to high doses than females.

DISTRIBUTION AND EXCRETION OF RADIOFLUORIDE IN THE HUMAN

Summary One mg fluoride labeled with radiofluoride was ingested by each of 2 adult humans. Observations of renal clearance of fluoride, chloride and creatinine were made. Fluoride clearance always exceeded chloride clearance by many fold and increased with urine flow, but fluoride clearance was always less than creatinine clearance. Renal tubules in 2 individuals, reabsorbed respectively 51 and 63% of fluoride in the glomerular filtrate which indicates a net process of glomerular filtration with a variable amount of tubular reabsorption. Plasma contained 72% of whole blood radiofluoride and radiofluoride concentration of plasma exceeded that of parotid gland saliva. Measurement of uptake and release of the radioisotope by soft tissues and by the skeleton showed characteristic differences of radiofluoride retention in these tissues. Skeletal tissues retained the isotope but soft tissues lost nearly all their activity within 4 hours after ingestion.

Determination of fluoride: Procedure based upon diffusion of hydrogen fluoride☆

Abstract The principle of fluoride determination by diffusion of hydrogen fluoride in Conway-type cells made of polypropylene has been applied to the determination of fluoride in plasma, liver, muscle, calcified tissues, urine, and saliva. Methods for preparation of the low fluoride containing biological specimens by precipitation of proteins with perchloric acid and analysis of the supernatant liquid are described. The results of fluoride analyses by diffusion compare well with those obtained by microdistillation. The diffusion method for fluoride analysis is more simple than distillation procedures.

Metabolic Handling of Perfluorooctanoic Acid in Rats

Summary The metabolic fate of perfluorooctanoic acid administered by stomach intubation to female rats was investigated. The nonionic fluorine level in the serum was increased 200-fold after administration of the dose but returned to baseline levels by 52.5 hr. Although perfluorooctanoic acid is rapidly absorbed and bound to nonultrafilterable components in the serum, the entire dose of nonionic fluorine was recovered in the urine and feces after 96 hr. Neither the ionic fluoride level in the serum nor the rate of ionic fluoride excretion in the urine was significantly altered by the administration of perfluorooctanoic acid. Although perfluorooctanoic acid has not been identified in the urine, the available data suggest that it has been excreted intact or in possibly conjugated form.

The effects of high and low fluoride diets on the frequencies of sister chromatid exchanges

A recent report suggests that fluoride has mutagenic activity in mice. To examine the potential clastogenic effect of ingested fluoride, we examined the frequencies of baseline SCE and mitomycin C induced SCE as well as baseline chromsomal aberrations and cell-cycle kinetics in mice raised on high and low fluoride diets. The lack of significant differences in any of these parameters between the two groups of animals indicates that dietary fluoride is not clastogenic and supports the continued use of water fluoridation.

Lack of cytogenetic effects in mice or mutations in Salmonella receiving sodium fluoride

We have examined the possible effect of fluoride intake on chromosome damage. There was no evidence of increased frequency of chromosomal aberration in bone marrow or testis cells of mice with either 50 ppm fluoride intake over several generations or 100 ppm intake for 6 weeks compared to animals drinking distilled water. Fluoride was not found to be mutagenic in a widely used bacterial mutagenesis assay over a range of 0.1 to as high as 2000 microgram fluoride per plate.

Placental transfer of fluoride and calcium.

Abstract Maternal (uterine) artery, maternal (uterine) vein, umbilical artery, and umbilical vein blood were obtained simultaneously at the time of 16 cesarean sections. Calcium determinations of these blood plasma samples and those from women in their ninth month of pregnancy suggest either that a calcium “pump” operates in the placenta supplying a higher concentration of calcium to the fetal blood supply than is found in the maternal circulation or that the calcium homeostatic mechanisms operate at different levels in the maternal and fetal organisms. The fluoride concentrations found in the blood plasmas suggest that the placental barrier to the transport of fluoride ion does not operate so as to maintain a difference in concentration of fluoride between the maternal and fetal body fluids.

Total fluoride content of human serum.

Abstract The analysis of six human sera for its fluoride content by (a) fluoride ion-electrode determination in diffusates of unashed samples, (b) colorimetric determination in diffusates from unashed samples ( Singer and Armstrong , 1965), (c) colorimetric and electrode methods applied to diffusates of ashed samples and (d) colorimetric assay of steam distilled ashed samples ( Singer and Armstrong , 1959) are reported. Concordant results were obtained with ashed sera by all methods. Consistently higher results were obtained with ashed than with unashed samples when the fluoride ion-electrode was used. Evidence is presented that part of the fluoride evolved by diffusion from unashed samples is unavailable for measurement with the electrode. The determinations of total fluoride in serum requires ashing of the sample prior to diffusion or rigid adherence to 20–26 hr diffusion under prescribed conditions. Analyses of plasma of rats raised on different fluoride intakes are used to demonstrate the responsiveness of the direct diffusion method to variations of total serum fluoride contents.

Metabolic aspects of bone resorption in calcium-deficient lactating rats.

SummaryLactating female rats were fed diets containing 1.0, 0.1, or 0.04% Ca for 21 days. Fat-free dry weight, ash weight, calcium and phosphorus content of the humerus, plasma calcium levels, and bone acid and alkaline phosphatase activites were compared to those of nonlactating rats fed the same diets. Bone, plasma, and urinary cAMP levels were also studied.Dietary calcium deficiency and/or lactation caused significant loss of bone mass from experimental animals. Urinary cAMP levels reflecting increased parathyroid activity were elevated by the stresses of lactation and calcium deficiency over those of control animals. Plasma and bone levels of cAMP were not different. Bone alkaline and acid phosphatase activities were affected only by the most extreme stress. The results demonstrated that the calcium-deficient lactating rat is an excellent model for bone resorption studies.