Frank A. Smith

INORGANIC AND ORGANIC COMPONENTS OF TOOTH STRUCTURE

There have been three phases of the study of tooth composition. Early work was concerned with the chemistry of the entire tooth. With the development of procedures for separating dental tissues it became possible to determine the composition of enamel, dentin, and cementum. The next logical step, the study of the chemistry of successive layers of enamel, dentin, and cementum, is the subject of this paper. In its connection the following yuestions may be raised. In what respect does the composition of surface enamel, dentin, and cementum differ significantly from that of the same subsurface tissues? To what extent do chemical changes in the surface layer take place with age? What is tooth maturation? How are the various surfaces affected by fluoride and other trace elements in food and drinking water? What are the components of surface enamel that strengthen i t , and what is its optimal composition? These are basic questions to which we must seek the answers if we are to comprehend the many complex phenomena taking place in the tooth structure. We have worked in this field for some years; this paper summarizes our published1-12 and unpublished findings on the composition of successive layers of enamel, dentin, and cementum. Isotope studies have shown that surface reactions in both bone and teeth are pr~nounced?~ Because of its relatively simple metabolism, the tooth is better suited for observations of surface changes than bone, which undergoes rapid alterations due to remodeling and growth. The highly calcified, nonvital enamel provides a more clear-cut picture of surface changes than does the rest of the tooth. Crown dentin, like enamel, is exposed to fluids on one side but, unlike enamel, the surface is continuously renewed because of appositional dentin formation. On the other hand, the enamel surface, which is morphologically stable, is more static and thus exposed to more prolonged exchange reactions. In the root of the tooth conditions are still more complex than in crown dentin and in many ways they may bc compared to those of bone. As in long bones, we are concerned with two surfaces, the external and the internal, or pulpal and, as in bone, there is appositional growth, but without the remodeling process of bone. In the present study, pooled layer samples were obtained from the enamel, the crown dentin, and the root of a large number of teeth, and were subjected to chemical analyses. The external layers of the root were composed of cementum; the innermost layers, of dentin. Because the root was considered a metabolic entity, no attempt was made to separate cementum and dentin in the intervening layers. * The studies reported in this aper were supported in part by Grants D-214 and D-798 from the Institute of Dental Heath , Public Health Service, Rethesda, Md.

Solubility Rate and Natural Fluoride Content of Surface and Subsurface Enamel

THE surface enamel is more resistant to acid than is subsurface enamel, the rate of dissolution of phosphate from the surface being less than that from the subsurface enamel.1-3 With ordinary and polarized light microscopy, as well as with soft x-rays, it has also been shown that it is possible for demineralization of the subsurface enamel to occur without any apparent change in the enamel surface,4 5and when ground sections of teeth were exposed to EDTA the outer portion of enamel was the last to be demineralized.6 The reason for this difference between surface and subsurface enamel has not been established. That fluoride may play a role, at least at the level of 2 ppm in the water supply, is suggested by the work of Jenkins, Armstrong, and Speirs,2 who found that the solubility rate of surface enamel of teeth from areas with 2 ppm fluoride in the water supply was less than that from areas with 0.25 ppm, although there was no difference in the solubility rate of the bulk of the enamel. Since fluoride accumulates in the surface enamel, even in teeth from areas low in fluoride,7 it was considered that fluoride acquisition might generally be responsible for the decreased solubility rate of surface compared to subsurface enamel. Therefore, in the present study an attempt was made to correlate the solubility rate and fluoride concentration of successive layers of enamel from areas with different levels of fluoride in the drinking water.

Occupational fluoride exposure.

Effects of airborne fluoride on industrial health are discussed with regard to acute and chronic effects. Injuries to lungs and skin from acute exposures are described. Chronic effects are discussed with regard to industrial sources of fluoride and air concentrations vs. urinary concentrations of fluoride. An extensive literature review is presented in the form of a table showing responses in man exposed to industrial airborne fluorides. Osteosclerosis is discussed with regard to the fluoride air standard, bone fluoride, and air fluoride concentrations. Occupational exposures to fluoride are also discussed with regard to arthritis, shortness of breath, asthma, upper respiratory infections, chronic respiratory disease, effects on kidneys, effects on pregnancy, and indices of fluoride intoxication. A table is presented showing references to studies on responses in neighborhood residents exposed to fluoride emissions. (HLW)

Health Information during a Week of Television

Abstract A commercial-network television channel in Detroit was monitored during a typical 130-hour broadcast week. Health-related content used 7.2 per cent of the time. Only 30 per cent of this health time offered useful information, and 70 per cent of the health material was inaccurate or misleading or both. Television programming did not use the educational capacity of the health professions to any notable extent. There were 10 times as many television messages that urged the use of pills or other remedies as there were against drug use or abuse. Although some useful health information was offered, the major health problems such as heart disease, cancer, stroke, accidents, hepatitis, maternal death, hunger, venereal disease, mental health, sex education, child care, lead poisoning and family planning were virtually ignored during the television week.

Regional deposition and absorption of inhaled hydrogen fluoride in the rat

The regional deposition of inhaled hydrogen fluoride (HF) was investigated by drawing known amounts of this irritant gas through the surgically isolated upper respiratory tract of anesthetized rats, while each animal respired HF-free room air through an endotracheal tube. At HF concentrations ranging from 30 to 176 mg F/m3, greater than 99.7% of the HF drawn into the upper respiratory tract was removed from the airstream during passage through that site. Plasma fluoride concentrations were significantly elevated by this upper respiratory tract exposure to HF and were highly correlated with airborne HF concentrations (r (8) = 0.98, p < 0.01). For comparative purposes, intact anesthetized rats were subjected to nose-only exposure to 63 mg F/m3 HF for 1 hr. Both pulmonary and plasma fluoride concentrations were significantly elevated over control levels by nose-only exposure; however, pulmonary fluoride concentrations in these rats were no higher than plasma fluoride concentrations, providing little evidence that airborne HF penetrates to the lungs of rats respiring normally. These results indicate that in the anesthetized rat virtually all inhaled HF deposits in the upper respiratory tract from which it may be absorbed and/or translocated to other sites, e.g., the gastrointestinal tract, where systemic absorption may occur.

Renal Clearance of Fluoride.

Summary Fluoride in dog plasma was completely ultrafilterable through visking membranes when tested using the centrifuge type apparatus. In dogs with a normal water load, the average normal renal fluoride clearance was 2.7 ml/min.; the fluoride : chloride clearance ratio, 19; and the fluoride : creatin-ine clearance ratio, 0.077. Fluoride clearance was more rapid than that of simultaneously measured sodium or chloride clearances or urine flow. During mannitol diuresis, fluoride was cleared at a rate higher than that of sodium, chloride, or phosphate. Fluoride clearance, although greater than urinary flow, varied directly with the flow under mannitol osmotic diuresis. Intravenous infusion of hy-pertonic NaNO3 or Na2SO4 solutions, creating a salt diuresis, did not affect fluoride excretion. Hypertonic NaCl infusion did increase the fluoride clearance. Although fluoride : creatinine clearance ratios were raised greatly by intravenous fluoride, the highest ratios were attained during fluoride infusion plus osmotic diuresis with hypertonic mannitol or NaCl. No evidence for a tubular secretion of fluoride was obtained.

TOXIC EFFECTS OF FLUORIDE ON THE RAT KIDNEY. I. ACUTE INJURY FROM SINGLE LARGE DOSES

Abstract 1. 1. The 30-day LD 50 of sodium fluoride administered intravenously as a 2% aqueous solution in the young rat (75 days old) was 26 mg/kg. The lethal action of sodium fluoride appeared to involve two mechanisms: one causing death in a few hours and the other in 3–10 days. 2. 2. Renal injury did not appear to be the cause of the delayed deaths. Single doses of sodium fluoride (20 and 30 mg/kg, intravenously) produced a mild necrosis of the tubular epithelium in the inner third of the cortex. The necrosis was evident on the first and third days after treatment. Regeneration began by the fifth day and was nearly complete by the ninth day. The renal lesion was relatively limited. A few rats receiving a single dose of sodium fluoride showed a dilatation of the tubules at the junction of the cortex and medulla. 3. 3. Renal functions were deranged temporarily by near lethal doses. A single dose of sodium fluoride of 20 or 30 mg/kg, intravenously, increased urine volume and decreased specific gravity. Sugar excretion was markedly increased the first day after treatment and then decreased below normal for several days. Protein excretion was slightly increased.

Toxic effects of fluoride on the rat kidney. II. Chronic effects.

Abstract 1. 1. The 30-day LC50 of sodium fluoride administered in the drinking water was 205 ppm fluoride in the weanling rat. Death generally occurred between the third and fifth day after administration was begun. When levels of 150–250 ppm fluoride were administered in the water, 30–40% of the surviving rats showed a renal lesion consisting of dilatation of the tubules at the corticomedullary junction. 2. 2. Levels of 0, 1, 5, 10, 25, 50, and 100 ppm fluoride were administered in the drinking water to rats for 6 months. No growth depression was seen, even at 100 ppm, but mortality was slightly increased in males and females ingesting 50 ppm and males ingesting 100 ppm. The only pathologic changes were seen in the kidney and the bone. Two of the 12 rats receiving 100 ppm for 6 months showed a marked dilatation of the tubules in the corticomedullary region of the kidneys. The lesion was accompanied by a high water consumption and urine output. Radiographically, an increase in the deposition of trabecular bone was seen in the rats ingesting 100 ppm fluoride. A slight increase was also seen in the males ingesting 50 ppm fluoride. 3. 3. Balance studies showed that rats retained about 50% of the ingested fluoride after 3 months on fluoridated water. Seventy-five to 80% of the ingested fluoride was absorbed, and 65–70% of the absorbed fluoride was retained. After 6 months, the male rats retained 45% of the ingested fluoride, the females about 60%. Both males and females absorbed 80% of the ingested fluoride. The males retained 60% of the absorbed fluoride; the females, 80%. The percentage fluoride retained was independent of the fluoride level in the water. The increased age of the rats did not alter fluoride retention, except that the females retained a higher percentage of the ingested fluoride than the males after 6 months. 4. 4. The fluoride concentration in the femur ash of the rats ingesting fluoridated water for 3 months was directly proportional to the fluoride level in the water, even with a level of 100 ppm. After 6 months, the fluoride concentration was directly proportional to the fluoride level in the water at levels of 50 ppm and less. The rats ingesting 100 ppm fluoride in the water had a lower concentration than would be expected from this proportionality. 5. 5. The natural fluoride present in a stock animal ration such as Purina Fox Chow Meal was of limited availability. Only 10–15% of this fluoride was metabolized by the rat.

Airborne fluorides and man: Part II

Fluorine is the 13th element in order of abundance and occurs throughout mans environment. Airborne fluorides in very low concentrations may be introduced into pristine atmospheres from sources such as volcanic actions, dusts picked up by winds blowing over surface soils and weathered rocks, and from sea spray. Urban and surburban atmospheres may contain higher concentrations derived from burning fossil fuels and from miscellaneous effluents disseminated from a variety of industrial point sources. A number of states now have standards regulating the concentrations of fluoride which may be present in the air or released to the ambient air. Higher concentrations may be encountered in the work place, but again, limits selected to protect the worker from significant effects are in force. The principal effect of industrial fluoride‐containing dust to be protected against is the excessive deposition of fluoride in the skeleton. This condition, skeletal fluorosis, was recognized in Danish cryolite workers in th...

Air Quality Criteria for the Effects of Fluorides On Man

Minute traces of fluoride are found in the air of rural communities and of cities, having been contributed perhaps from volcanic effluvia, perhaps from burning coal, and perhaps from industrial sources. Atmospheres of urban areas of the U. S. have been found to contain from less than 0.2 μg F/m3 to as much as 1.9/μg F/m3. Fluorides released from industrial processes may release elemental fluorine, soluble gaseous fluorides, and soluble or insoluble fluoride dusts. At least in some instances inhaled fluoride from fluoride containing dusts has proven to be as biologically available as that from similar concentrations of inhaled HF. Measurement of the amount of fluoride excreted in the urine has proven to be a valuable index of exposure and a means of preventing cumulative injury. Average urinary F concentrations not exceeding 5 mg/liter, which corresponds approximately to a daily intake of 5 mg, are not associated with osteosclerosis in such workmen, and such changes are unlikely at daily intakes of 5 – 8 m...