F. Brudevold

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 We have worked in this field for some years; this paper summarizes our published1-12 and unpublished findings on the composition of successive layers of enamel, dentin, and cementum.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.

A study of zinc in human teeth

Abstract Zinc accumulates in the surface structures of teeth and occurs in low concentrations in subsurface material, thus exhibiting a distributive pattern similar to that of fluoride and lead. Concentrations of zinc in surface enamel of teeth from different areas range from 430 to 2100 p.p.m. In terms of molar concentrations the concentrations are frequently of the same order as those of fluoride. In enamel the major deposition of zinc takes place before tooth eruption. In contrast to fluoride, posteruptive deposition of zinc appears to be irregular. Zinc is readily acquired by synthetic hydroxyapatite, competing with calcium for positions on the surface of the apatite crystal. Zinc pretreatment of hydroxyapatite produces a resistance to acid dissolution similar in magnitude to that produced by equivalent molar concentrations of fluoride.

An enamel biopsy method for determination of fluoride in human teeth.

Abstract An enamel biopsy method has been developed which involves polishing off about 0.2 mg enamel from accessible surfaces of single teeth. This is accomplished with a rotating midget felt cone impregnated with silicon carbide. The cone is coated with glycerine which traps and forms a slurry with the ground enamel particles. The slurry and the felt cone are transferred to a plastic test tube and subjected to F and Ca analysis, employing an F electrode and atomic absorption spectrophotometry. Findings showed that the levels of F in intact anterior teeth from the same individual usually were similar, and that mean concentrations varied from 400 to 2500 ppm in the anterior teeth of the different persons studied. A second biopsy taken from the same tooth surface showed lower concentrations of F than the first biopsy, confirming previous findings in extracted teeth of F gradient in enamel. It was calculated that a layer of enamel between 1 and 2μ in thickness usually was removed by the biopsy procedure. Patients have no objection because the treatment is similar to a pumice prophylaxis and produces a highly polished surface. The biopsy procedure is harmless to the patient, takes little chair time and is simple to perform.

The direct determination of fluoride in human saliva by a fluoride electrode: Fluoride levels in parotid saliva after ingestion of single doses of sodium fluoride

Abstract The concentration of F in human parotid saliva has been determined by means of a specific F ion electrode. Best results were obtained when the pH of the saliva was adjusted to pH 4.7–4.8 prior to measurements. Known amounts of F added to saliva were accurately assessed by this approach and there was good agreement between electrode determinations of F taken directly on saliva and chemical analyses of ashed salivary samples. The findings indicate that F levels in stimulated duct saliva range from less than 0.01–0.05 ppm. Ingestion of single doses of F resulted in an increase in salivary F starting after 5–15 min, and reaching a maximum in 30–60 min. Thereafter concentrations decreased slowly, approaching the original concentration in 2–6 hr depending on the amount of fluoride ingested. Representative maximal values for parotid salivary F after ingestion of 10, 5 and 1 mg were 0.3 ppm, 0.2 ppm and 0.06 ppm respectively. It was noted that the maxima tended to increase after repeated ingestions.

The effective concentrations of calcium and inorganic orthophosphate in salivary secretions

Abstract The pH, ionic strength and the concentrations of ionic calcium and monohydrogen phosphate were determined on parotid and submandibular salivary secretions at varying rates of flow. The activity product, αCa 2+ × αHPO ) 4 2− , was compared with the presently known solubility of enamel in saliva. With the exception of a number of unstimulated parotid secretions, all samples studied were supersaturated with respect to hydroxyapatite. The submandibular secretions were more saturated than the parotid, and all secretions became more saturated with increase in flow rate. The results are discussed in relation to calcification processes occurring in the oral cavity.

A Microradiographic and Polarizing Microscopic Study of Sound Enamel

TN POLARIZING microscopy studies of developing enamel, Schmidt1 and 1 others found that retardation depended not only on the negative (intrinsic) birefringence of the apatite crystals, but also on the positive (form) birefringence produced by the minute spaces between the crystals, except when they were filled with a liquid having the same refractive index as that of enamel. The birefringence of the organic matrix was so small that it could be ignored. Cinnamon oil, quinoline, and other oily liquids commonly used in polarized light studies readily imbibed developing enamel but failed to penetrate into fully calcified enamel. Therefore, it was assumed that in mature enamel intercrystalline spaces had been eliminated by mineral deposition. From a polarized light and radiographic study, Thewlis2 concluded that the outer portion of fully developed enamel was more calcified than the inner portion, presumably because of higher content of water and/or organic matter in the inner portion. In this work, retardation was assessed front the colors of birefringence without employing imbibition liquids. Recently, Darling3 found that sound enamel adjacent to various lesions could be imbibed if solutions of iodide in water were used rather than the hydrophobic media employed by previous workers. This suggested that intercrystalline spaces may be present in fully calcified enamel and that previous failures to detect them might be due to the physical properties of the imbibition liquids which were used. This possibility was investigated in the present study. Retardation was measured in outer and inner portions of intact, mature enamel, using different imbibition liquids with the same refractive index as that of enamel, and the measurements were compared with densitometric tracings of microradiographs of the same specimens.

Density fractions in human enamel

Abstract A micromethod for determining the density of small amounts of powdered enamel has been developed. Fractionation by density of successive layers of enamel from single teeth showed predominance of high density fractions in the outer enamel and low density fractions in the inner enamel. The overall effect was a gradual decrease in density from the surface toward the dentine. A small portion of the enamel, probably representing prism sheaths, had a density below 2.70. This fraction contained from 47 to 79% ash. The Ca/P ratio, ranging from 2.06 to 2.24 was similar to that reported for enamel mineral. Exposure of intact enamel to fluoride followed by immersion in a metastable calcium phosphate solution increased the density of the most superficial enamel layer.

The distribution and composition of density fractions from human crown dentine

Abstract Density fractionation of finely powdered layer samples of coronal dentine from single teeth from a low fluoride area showed predominance of low density fractions adjacent to the enamel and to the pulp and predominance of higher density fractions in the middle portion. There was an increase in the proportion of high density fractions with increase in age. Two teeth from an area with 5 ppm of fluoride in the water supply showed densities in the outer half of the crown increasing from the enamel then plateauing towards the pulp. It was concluded that the high density fractions found in many layer samples contained a large proportion of highly mineralized peritubular dentine. The carbonate concentration varied directly with the density of fractions, the nitrogen content varied inversely. The concentrations of fluoride and zinc differed markedly in fractions from individual layer samples. These findings suggested two gradients of these elements in coronal dentine, one of decreasing concentrations going from peritubular to intertubular dentine and an overall increasing gradient going from the enamel toward the pulp.