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Detailed knowledge about the constitution and the solubility behaviour of the mineral in calcified tissues is still lacking. This knowledge is important for the understanding of the behaviour of the mineral under physiological and pathological conditions. In this study literature data on the composition and particle size of the mineral are reviewed. Their predominantly apatitic nature goes back to hydroxyapatite as their prototype. However, other calcium phosphates, like whitlockite, are also important. The various analytical data on the content of Ca, P, Na, Mg and CO3 as the main components were analyzed for their consistency with a model of variable phase composition of the mineral. This analysis revealed that the probable phase composition of the mineral in dentin and bone is the same, but different from that in tooth enamel. Studies on the solubility behaviour indicate that near the physiological pH (7.4) all phases are solubility controlling simultaneously. This supports a physiological model according to which the body fluids are close to physicochemical equilibrium with bone mineral. Hence, changes in the chemical and phase composition of the mineral which occur under pathological conditions are related to changes in the activities of the relevant components in the surrounding body fluid. The latter depend mainly on cellular activity and organic transport activity. Attention is also paid to the anticariogenic effect of fluoride and the incorporation of that component in the mineral of fluorotic bone. This study is closed with some remarks about the use of synthetic analogues of biominerals as implants in dentistry and surgery.

Evidence accumulates that mineralization in the body, whether physiological or pathological, takes place only, when and where body fluids become supersaturated with respect to the formation product of fast nucleators like brushite, octocalcium phosphate, calcite and calcium oxalates. In the pH ranges above 8.0, between 8.0 and 7.0 and below 7.0 the most frequently occurring nucleating phases are calcite, octocalcium phosphate and brushite, respectively. After nucleation of brushite this phase is transformed spontaneously into a mixture of a sodium- and carbonate containing apatite, of dolomite and of calcium deficient hydroxyapatite. After nucleation of octocalcium phosphate that phase is transformed spontaneously into a mixture of a sodium- and carbonate containing apatite, of magnesium whitlockite and of heavily carbonated calcium deficient hydroxyapatite. In addition, other phases can be formed in the presence of enough fluoride, zinc, etc.

A reevaluation of the chemical, physical and physicochemical properties of the mineral in tooth enamel and dentine shows that the current models can not adequately account for the observed characteristics. On the basis of thermodynamical and solid state chemical principles an alternative model for the mineral in tooth enamel and dentine is proposed. According to the model the tooth enamel mineral consists of a magnesium whitlockite, a sodium- and carbonate containing apatite and a slightly carbonated hydroxyapatite approximately in the ratio 1: 1: 3. The latter phase also contains the chloride and fluoride ions of the mineral. The consistency of this three-phase model is discussed. Dentine mineral appears to have qualitatively the same phase composition as bone mineral, although the relative amounts of the three constituting mineral phases differ considerably.

The ESR spectrum near g=2 of several carbonated calciumapatites synthesized at high temperatures, is studied as a function of incident microwave power. It is shown that the ESR signal observed is the composition of several powder spectrum contributions, arising from different paramagnetic centres. At low microwave power, the spectrum essentially reduces to be superposition of two very related spectra, probably to be ascribed to two CO33− radicals. The major component is assigned to CO33− at a phosphate site, while the other can be due either to a CO33− at a hydroxyl site or a surface CO33−.

Fluorhydroxyapatites were synthesized by solid state reaction at 1000°C. The solubility was determined in diluted phosphoric acid. At pH 4 and 5 a degree of substitution x of OH− by F− ions of only a few percent was sufficient to reduce the solubility by 50%, At pH 6 and 7 very high degrees of substitution were necessary to reach this effect. Addition of F ions to the diluted phosphoric acid had no effect on the solubility in the ranee x > 0.3, but it caused a reduction in solubility with up to 88% for hydroxyapatite at pH 7. Addition of Ca2+ ions to the diluted phosphoric acid had no effect on the solubility of hydroxyapatite (OHA). However, it increased the solubility of fluorapatite (FA) and of OHA - FA solid solutions considerably.

On the basis of the composition of the mineral in bone and the saturation level of blood plasma with respect to the slightly soluble calcium phosphates it is shown that normal tissue fluids are not supersaturated with whole bone but with the minerals of dead bone. The solubility controlling phase in living bone is octocalcium phosphate and the presence of this phase regulates the calcium and phosphate concentrations of the body fluids by simple physicochemical equilibrium.

Struvite or magnesium ammonium phosphate MgNH4PO4 has been proposed as active component in setting surgical cements. The usual formulation is one in which the magnesium component in the powder is either magnesium hydrogen phosphate trihydrate or trimagnesium phosphate or a mixture of these two compounds. As the cement liquid a concentrated solution of diammonium phosphate is taken. To make the cement attractive as a bone substitute material a calcium phosphate filler is generally incorporated. Thus such materials are a type of pseudo calcium phosphate cements. This study was intended to find out which calcium phosphate and which magnesium compound are the most suitable. In the first series of experiments a mixture of 12 g Mg3(PO4)2 and 4 g MgHPO4.3H2O was used as the magnesium component in the powder. To that powder 30 g of either precipitated hydroxyapatite PHA or CaHPO4 or CaHPO4.H2O or b-TCP or a-TCP was added. The cement liquid was a 3.5 M solution of (NH4)2HPO4. At specific liquid/powder ratios L/P suitable setting times were obtained for the different formulations. However, the compressive strengths after immersion of the cements in 0.9% saline solution at 37°C varied over a large range. The best formulation was that with a-TCP which reached a compressive strength of 57 MPa after 18 h of immersion. In the second series of experiments 20 g of Mg3(PO4)2 was used as the magnesium component in the powder. Again 30 g of either of the above mentioned calcium phosphates was used as filler and again a 3.5 M solution of (NH4)2HPO4 was used as the cement liquid. At the appropriate L/P ratios the respective setting times were longer than in the first series of experiments but all five formulations appeared to result in good compressive strengths varying from 41 MPa for the formulation with b-TCP to 67 MPa for the formulation with PHA. In the third series of experiments 30 g a-TCP was taken as the calcium phosphate in the powder. As magnesium components mixtures of Mg3(PO4)2.8H2O and MgHPO4.3H2O and Mg3(PO4)2 were used. Again the cement liquid consisted of a 3.5 M solution of (NH4)2HPO4. The formulations with Mg3(PO4)2.8H2O had the shortest setting times and the lowest compressive strengths, whereas those with Mg3(PO4)2 had the longest setting times and the highest compressive strengths. Therefore, it is advantageous to use Mg3(PO4)2 as the magnesium component.

Nanoapatites are apatites consisting of nanometer size crystals. The commercial calcium phosphate cements set by the precipitation of nanoapatitic calcium phosphates in the range 1.5or = Ca/P1.8. In this study it is shown that a continuum of nanoapatites can precipitate in the range 0.8Ca/Por = 1.5. In order to be formed these nanoapatites need to incorporate K+ ions. In addition they can incorporate some Na+ ions. Upon immersion in aqueous solutions these nanoapatites loose phosphate, K+ and Na+ so that in an open system they are transformed into calcium deficient hydroxyapatite Ca9(HPO4)(PO4)5OH within about 2 months.

In this study, a series of potassium- and carbonate-containing apatites is prepared by solid state reactions at high temperature in a nearly dry CO2 atmosphere. Chemical and physical analyses showed that the samples are single-phase and contain 4-12 wt % carbonate. Their stoichiometry conforms to Ca10-xKx[(PO4)(6-x)(CO3)(x)][(OH)(2-2y)(CO3)(y)] with 0 K+ + CO32-] and [2OH(-) CO32- + V-OH], where V-OH stands for a vacancy in the OH- sublattice. Although these mechanisms appear to occur independently of each other, they have a marked effect on the IR characteristics of the solid.

Living beings can maintain their metastable state, e.g. can escape from the first law of thermodynamics by being open systems, by taking up high energy molecules and by dissipating waste products, heat and work. According to the present theory thay can stay alive as long as they can escape from the external chaos which is due to the second law of thermodynamics. It is argued that aging is caused by penetration of this chaos into our body in the form of excess trace elements and as xenobiotic elements which either stop the functioning of our living cells or bring it out of neural or hormonal control. Aging might be delayed by the fact that sulfur metabolism maintains an H 2 S tension in the human body able to precipitate the xenobiotic elements from our tissues. For our defense we depend further on phagocytes to transport the precipitates to organs where they can be dissolved and excreted. It is suggested that the regular passing of kaoline, a nalural cation exchanger, through the intestinal tract will help to extract the xenobiotic elements from the body. As far as cardiovascular diseases are concerned, they start with the inevitable tendency of triglycerides to form crystalline precipitates at the surface of the intima in the arteries and capillary vessels. It is hypothesized here that cholesterol serves as a complex former, together with yet unknown plasma protein factors to the triglycerides enabling the solubilization of the precipitates. It is supposed to act as a sort of hormone. Cardiovascular diseases are thought to become fatal either by decreased functioning of the heart muscle, by atherosclerosis and/or by calcification of the atheromatous plaques. The present data indicate that these processes can all be prevented by magnesium supplementation. As shown elsewhere, this is also helpful to prevent osteoporosis, arterial wall calcification and chondrocalcinosis. Tobacco smoking accelerates aging in two ways '(1) it introduces xenobiotic elements directly into the lung cells' (2) it accelerates the precipitation of triglycerides onto the intima of arteries and capillary vessels.

After de- and subsequent remineralization at 0.03 and 1.0 ppm fluoride and either 0, 1, 10, 20 or 25 mM carbonate, artificial lesions in bovine enamel were demineralized again. The amount of secondary demineralization was determined after 15, 30 and 70 h of demineralization by means of quantitative microradiography. The results showed that fluoride incorporated during the remineralization period retards lesion formation during secondary demineralization. Carbonate incorporated during the remineralization period enhances secondary demineralization. An interaction between both ions was observed.

The influence of fluoride, carbonate, and fluoride in combination with carbonate on the in vitro remineralization of bovine enamel was investigated with the use of a sandwich technique. After demineralization, enamel slices were subjected for 610 h to remineralizing solutions with 0.03 or 1.0 ppm fluoride. At each fluoride level, either 0, 1, 10, 20, or 25 mmol/L carbonate was tested. After 0, 22, 62, 126, 192, 329, and 610 h of remineralization, contact microradiographs were made by Cu Kα-radiation. At 0.03 ppm fluoride, carbonate had an inhibiting influence on remineralization. At 1.0 ppm fluoride, the inhibiting influence of carbonate changed into a stimulation of remineralization at 20 and 25 mmol/L carbonate. At 0, 1, and 10 mmol/L carbonate, fluoride had an inhibiting influence on remineralization. The differences in remineralization between the groups were explained by events concerning crystal growth, i. e., different types of minerals might have precipitated with differences in precipitation rates, and retardation of a precipitation step might have occurred under the various remineralization conditions. There was a mutual influence of fluoride and carbonate on the remineralization process. We conclude that the composition of the remineralizing solution with respect to fluoride and carbonate concentrations is important for the remineralization process.

Previous studies have shown that rat incisor dentin contains a considerable amount of magnesium that is distributed heterogeneously. The cementum-related dentin, especially its incisal portion, is richest in magnesium. It was the purpose of the present study to investigate the changes that occur in the magnesium content during dentin maturation. Cross-sections were prepared from rat incisors at the apical, middle, and incisal levels. By means of an electron microprobe, tracings were made of the Ca-, Mg-, and P- signal frequencies. Comparison of corresponding dentin layers within and between the cross-sections showed that the Mg/P molar ratio was always higher in the cementum-related dentin (CRD) than in the enamel-related dentin (ERD) and increased from the apex toward the incisal edge. Especially in the incisal cross-section, an increase in Mg/P was found from the older (peripheral) toward the younger (central) dentin layers. As the Mg/P ratio varied from 0.07 to 0.33, the Ca/P ratio was found to fluctuate from 1.48 to 1.15. The two ratios appeared to be highly correlated (r = -0.97; p

Subsurface lesions in bovine enamel slices were remineralized. The remineralization solutions contained either 0.03, 0.3, or 1.0 ppm fluoride at either pH 5.5 or 6.8. The amount of remineralization was determined after periods of up to 610 h, using quantitative microradiography. The results showed that after 126 h of remineralization in the presence of 0.03 ppm fluoride significantly (p less than 0.05) more remineralization occurred at pH 6.8 than at pH 5.5. At 0.3 and 1.0 ppm fluoride no significant differences between pH 5.5 and pH 6.8 were observed. An interaction between fluoride and pH was observed. The observed differences in the rates of remineralization are explained by the formation and subsequent transformation of the precursors octacalcium phosphate (pH 6.8) and brushite (pH 5.5) into (fluor)apatites.

Intact human enamel was demineralized in vitro to obtain artificial caries lesions. Part of the lesions was then treated with different surface-active compounds and remineralized with a remineralizing solution. The other part of the lesions was de- and remineralized in the same way, but was not treated with a surface-active compound. The results indicate that none of the surface-active compounds do affect the remineralization of the caries lesions. Possible applications of the tested compounds in combination with fluoride, for the prevention of dental caries, are discussed.

The lipids and ultrastructure of the forming, maturing and erupted parts of incisors were compared in rats fed a zinc-deficient diet for 28 days, pair-fed rats and control rats. The lipid levels in the forming portions of zinc-deficient incisors were 30-50% below control levels and were associated with longer Tomes' processes in the secretory ameloblasts, porosities in the forming enamel and fewer malachite green-aldehyde-phospholipid aggregates in the predentine. No marked structural changes were seen in the erupted portions of the teeth, although variations in lipid composition were detected both in the maturing and erupted parts. No differences were found between teeth from the 3 groups of animals for Na, Mg, Cl, Ca and P signals with the electron microprobe.

Remineralization experiments of bovine enamel with subsurface lesions were carried out with the use of a sandwich technique. The remineralizing solutions contained no or 2 ppm fluoride added to the solution. The amount of remineralization was determined after remineralization periods up to 324 by means of quantitative microradiography. After 84 h the group with fluoride showed significantly (p less than 0.05) less remineralization than the nonfluoride group. This inhibition of fluoride on the remineralization may be explained by the inhibiting effect that fluoride at certain concentrations has on the crystal growth of apatites.

This paper deals with the influence of (1) the pH, (2) the degree of saturation with respect to hydroxylapatite (OHA) and (3) the fluoride concentration of demineralizing buffer solutions on the development of surface layers of artificial carious lesions. The pH did not affect the surface layer during demineralization. With increasing saturation with respect to OHA, the mineral content of the surface layer increased and the gradient of mineral content at the inside of the surface layer became less negative. The effect of the fluoride concentration depended on the degree of saturation of the solution with respect to OHA. At the highest undersaturation used in this study (pIoha126) an increase of the fluoride concentration caused an increase of the mineral content of the surface layer, an unchanged gradient in mineral content at the inside of the surface layer, and an increased intercept of this gradient. At low undersaturation with respect to OHA (pIoha122) an increasing fluoride concentration caused a less negative gradient. An explanation for the results is given on the basis of the driving forces for dissolution of enamel mineral and reprecipitation of less soluble mineral. It is concluded that the degree of saturation with respect to fluorapatite and the fluoride concentration are factors determining the development of the surface layer.

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.

The morphology of dentinal cavity walls, wetting by poly (methyl methacrylate), and resistance to tensile forces was studied with a scanning electron microscope, before and after etching or fixation, or both, with glutaraldehyde. Results indicated that the surface layer of dentinal cavity walls after etching is of an aqueous-organic nature, that glutaraldehyde fixation improves the mechanical properties of the surface layer of the cavity wall, and that wetting by poly (methyl methacrylate) is effective.

Fluorhydroxyapatites were synthesized by solid state reaction at 1000°C. They contain vacancies in the OH sublattice and are, in this respect, a good model for tooth enamel mineral. The presence of fluoride at the 0.1 to 1 ppm level reduced the solubility of these defective apatites with a factor 8 in the caries relevant range 4 < pH < 5. The simultaneous presence of Ca2+ ions, till a level similar to that in saliva, together with the F− ions in the physiological range 6.5 < pH < 7.5 suppressed the eventual decrease in solubility of these defective apatites caused by the presence of F− ions alone. Thus, the combined effect of Ca2+ and F− ions on the solubility behaviour of defective apatites is supposed to be relevant to the caries process and the caries reducing capacity of extra F− additions. Durch eine Festkorperreaktion bei 1000°C wurden Fluorhydroxyapatite synthetisiert. Sie enthalten Leerstellen im OH-Untergitter und sind in dieser Hinsicht eine gute Modellsubstanz fur das Zahnschmelzmineral. Die Anwesenheit von Fluoriden im Bereich von 0,1 bis 1 ppm erniedrigte die Loslichkeit solcher gestorter Apatite um den Faktor 8 in dem fur Karies relevanten pH-Bereich 4 < pH < 5. Die gleichzeitige Anwesenheit von Ca2+-Ionen bis zu einem Grad ahnlich dem in Speichel unterdruckte in dem physiologischen Bereich 6,5 < pH < 7.5 die eventuelle Abnahme der Loslichkeit dieser gestorten Apatite, wie sie durch F−Ionen allein hervorgerufen wird. Deshalb wird angenommen, das der gemeinsame Einflus von Ca2+- und F−-lonen auf die Loslichkeit von gestorten Apatiten relevant ist fur die Kariesbildung und fur die Moglichkeit, durch zusatzliche F−lonen die Kariesbildung zu hemmen.

One of the mechanisms proposed for the caries-reducing effect of fluoride is diffusion inhibition of OH–– groups through the 63 columns of the apatite structure thereby increasing the resistance of the crystal against acidic attack. The validity of this hypothesis was checked by investigation of the reactivity of solid solutions of hydroxyapatite and oxyapatite for oxydation during storage for 3 years in air. These solid solutions provide the same number of vacancies in the OH positions as occur in the apatite of tooth enamel, whereas the mobility of the OH–– ions is the critical quantity for its reactivity in analogy with fluorhydroxyapatite solid solutions. It was found that the solid solutions were not oxydized as their lattice parameters did not change during the storage period although the experimental period was far within the limits of the theoretical estimate. This invalidates the proposed mechanism for the caries-reducing effect of fluoride, as it proves the solid state diffusion is not important in apatites at normal temperatures.

The effect of orthophosphate, pyrophosphate, trimetaphosphate, hexametaphosphate, phytate and 1,1-hydroxyethyldiphosphonate on the ion-selective properties of bovine tooth enamel was investigated using electrochemical methods. All phosphates increased the ion-selectivity of enamel, an effect that increased with increasing number of phosphate groups. The effects of phytate and the diphosphonate were more pronounced than those of the corresponding phosphates.

The stability of Na- and CO3-containing apatites was investigated at 870°C in a nearly dry CO2 atmosphere. In a P/Ca versus Na/Ca plot the single-phase apatite field has a triangular form of which one extreme composition corresponds to Ca10(PO4)6(CO3) and another to Ca8·5Na1·5(PO4)4·5(CO3)2·5. Chemical and physical analyses show that the stoichiometry of apatites with a composition varying between these two extremes can be accounted for by the substitution mechanism Ca + PO4 ↔ Na + CO3. Although 40% of the carbonate ions of the sodium containing extreme component are on OH− lattice sites, the IR spectrum is very similar to that of an apatite containing carbonate on phosphate sites only.

Variations in the composition of bone and tooth mineral are consistent with the model that the constituents are a mixed microcrystalline apatite (AP)-octocalcium phosphate (OCP) like phase and an amorphous or submicrocrystalline calcium phosphate (ACP) like phase whereby these phases can occur in different proportions. An appropriate model for a description of the variable composition and the solubility behavior of the apatite phase is given by the formula (formula: see text) in which the compositional parameters x, y, z, and u each account for one type of defect mechanism. Other point defects are formed as well by incorporation of minority amounts of ions such as Cl-, K+, and F-; a number of trace elements can substitute for Ca2+ ions under in vivo conditions. It is suggested that the incorporation of ions in or loss from the crystals in contact with aqueous solutions is reversible. Literature data are used to show the direction in which the solubility product of the apatite phase shifts by incorporation of the different physiologically relevant ions. A quantitative evaluation of the available literature data revealed that Na+ and CO3= incorporation is the main cause for shifts in the solubility product of biological apatites.

Slices of bovine enamel and intact human enamel were treated with (a) a two-step treatment consisting of phytate followed by hexadecyl amine, or (b) 2-O-stearoylglycerol-1,3-diphosphate (Glydip), or (c) phosphatidic acid. The effect of these agents on the rate of caries lesion formation and on the permeability of dental enamel was quantitatively determined. Glydip had the most pronounced effect on lesion formation and showed a strong inhibiting effect on the rate of demineralization, combined with a reduction of the permeability. The results indicate that at least a part of the effect of Glydip on the demineralization was caused by a reduction of the rate of dissolution of the enamel mineral. The reduction in permeability may have had an additional effect.

In this study a buffer system containing calcium and phosphate was used to produce caries-like lesions. The influence of the pH on the lesion characteristics was investigated. The degree of saturation with respect to hydroxylapatite and the concentration of the undissociated acid were kept constant. The pH was either 4.0, 4.5, 5.0 or 6.0. The lesions were examined microradiographically. The lesion characteristics studied were: the mineral content of the surface layer; the mineral content of the body of the lesion; the depths at which these mineral levels were reached, and the depth of the lesion. The most important influence of the pH was that on the rate of demineralization. A striking phenomenon was the sudden change in the rate at which the different levels of demineralization were reached. In solutions with a pH lower than or equal to 4.5, the time needed to reach a certain demineralization was considerably shorter than for solutions with a pH higher than or equal to 5.0.

The enamel of human premolars of two post-eruptive ages was demineralized in hydroxyethylcellulose gel adjusted to pH 4 with lactic acid. Calcium and phosphate were determined in the enamel as a function of depth and in the gel during consecutive periods of demineralization. Significant differences with post-eruptive age were found between a depth of 25 and 60 μm where the younger teeth demineralized much faster. This agreed with the results from analyses of the gel. The molar ratio of Ca:P release was initially very high in younger teeth, whereas it was nearly constant for older teeth during consecutive periods of demineralization. The data are interpreted in terms of four different calcium phosphate phases presumed to occur in enamel mineral having a certain order of dissolution rates, related to their respective solubility. The hypothesis explains also the preferred reported losses of carbonate and magnesium from carious enamel.

Diffusion coefficients of 86 Rb + , 36 Cl − , [ 3 H]-sorbitol and [ 14 C]-glycerol through enamel were determined both in the absence and the presence of urea or t -butanol which are known for their structure-breaking and structure-promoting properties respectively in aqueous solutions. Their effect on the diffusion coefficients could be explained solely on the basis of the respective shifts in the relative viscosities of the aqueous solutions, indicating that the water of the transport phase is probably free water, in accord with explanation for the extra increase of diffusion coefficients with temperature (Burke and Moreno, Archs oral Biol. 17 , 433–437 (1975)) by the hypothesis that the amount of free water increases with temperature at the expense of bound water.

A critical evaluation of the literature reveals that during equilibration of well crystallized hydroxyapatite in aqueous solutions metastable states can occur. They are characterized by a persistent supersaturation with respect to hydroxyapatite and a systematical dependence of the ion activity product of this compound on the solution composition. For products synthesized by thermal treatment it is known that they are transformed into oxyhydroxyapatite so that the theoretical solubility behaviour could be predicted from the extrapolated value of the free energy of oxyapatite at room temperature: the negative logarithm of the ionic product for hydroxyapatite should become close to that of oxyapatite during equilibration. The discrepancy with experimental data is probably due to the formation of thin layers seeming dicalcium phosphate dihydrate, octocalcium phosphate or defective hydroxyapatite as coatings on the apatite crystals. This is derived from the apparent Ca/P ratio of the solubility controlling phase. According to chemical potential plots this apparent Ca/P ratio can have values close to 1, 1.33, 1.50 or 1.67. The aqueous solutions are clearly undersaturated with respect to the more acidic calcium phosphates so that the coatings must deviate from the compositions of these compounds in their pure state. The formation of these metastable states during equilibration of oxyhydroxyapatites is compared with others occuring during precipitation and crystal growth of calcium phosphates. A model is proposed which explains the observations qualitatively.

Intact roots of human molars, which had not been exposed to the oral environment, were exposed to buffer solutions of pH 5.5, which contained, besides calcium and phosphate, various concentrations offluoride. Densitometric measurements on contact-microradiograms of transverse sections of these roots produced data which were used to calculate the rate of demineralization ( Vdem). Vdem appeared to be reduced with increasing fluoride concentration and with decreasing pIOHA (i.e., the negative logarithm of the ionic product of hydroxyapatite) of the buffer solution. In addition, it was observed that, after some days of exposure, remineralization started to occur within the surface layer at some μm from the outer surface and that the region within which remineralization took place was extended inward with increasing time of exposure. These data suggest that fluoride is effective in the prevention of root surface caries. The mechanism of the interaction of fluoride with the root mineral is discussed.

A high-temperature X-ray diffractometer has been used to investigate the transition of Mn3O4 from the tetragonal hausmannite to the cubic spinel structure. In air the transition was found to take place at 1,130±10°C and in CO2 at 1,110±10°C[log Po2 (atm) = −4] The degree of distortion below the temperature of transition and the dependence of the transition temperature on the oxygen partial pressure are discussed in connection with the defect structure of Mn3O4. The cation arrangements in the structure of CuxMn3-xO4 (0⩽χ⩽1.03) and ZnxMn3-xO4(0⩽χ⩽1.5) have been determined with X-rays after the method of Bertaut (1951). Cu and Zn have a preference for tetrahedral sites and the degree of inversion found in quenched samples of CuMn2O4 and ZnMn2O4 is only about 10% in either compound. Oxygen-deficient samples CuxMn3-xO4 + γ(0⩽χ⩽0.5 and -0.08⩽γ⩽0.00) probably contain copper ions between two oxygen ions as in the structure of Cu2O. The investigated cation distributions are discussed in connection with the valencies of the cations and with their interaction.

The classical theory on the solubility of ionic compounds has been extended to solid solutions and deviations from stoichiometry by combination of thermodynamical and solid state chemical principles.

In previous papers it has been shown that octocalcium phospate OCP occurs in bone mineral of vertebrates. Although this compound is not stable, there is a continuous new-formation of OCP due to bone turnover. Literature data of the calcium and phosphate concentrations in the blood plasma of vertebrates were collected and the degree of saturation with OCP was calculated. The results show that blood plasma of vertebrates is almost saturated with OCP. This fact indicates that OCP is the solubility controlling phase in the mineral of vertebrates. Further it verifies the expectation based on physicochemical theory that the interaction between body fluids and bone mineral is important in the calcium and phosphate homeostasis

A radiochemical method was developed to determine quantitatively and simultaneously the transport of up to four different compounds through dental enamel. The compounds chosen were [3H]-sorbitol, [14C]-glycerol, 36Cl− and 86Rb+. Effective diffusion coefficients of these compounds determined at 4 °C were considerably different for different specimens of enamel. Thus values for [3H]-sorbitol varied from 0.04 × 10−8 to 2.5 × 10−8cm2s−1. Most enamel membranes showed an ion selective behaviour by which the cations were more mobile than the anions. A molecular sieve effect was observed for glycerol and sorbitol.

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 microradiographically. The lesion characteristics studied were: (a) the mineral content of the surface layer; (b) the mineral content of the body of the lesion; (c) and (d) the depth at which these mineral levels were reached; (e) 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.

The effect of fluoride and monofluorophosphate on the ion selective properties of bovine tooth enamel was investigated using electrochemical methods. The effect of monofluorophosphate was fundamentally different from that of fluoride. The anti-cariogenic properties of fluoride or monofluorophosphate cannot be deduced from their effect on the ion selectivity of enamel.

Roots of extracted human molars were treated for both 10 and 30 min with a saturated solution of dicalcium phosphate dihydrate (DCPD) of pH 2.4 and subsequently with a 5.3 mmol.L -1 solution of sodium fluoride of pH 7.0. The objective of these combined treatments was to convert the highly-soluble root mineral into the less-soluble fluoridated hydroxylapatite, with DCPD as an intermediate, to improve caries resistance. The mineral content of the surface layer was not affected in a significant way. Roots treated in this way were subjected to 50 mmol.L-1 acetate buffer solutions of pH 5.5 and with pIOHA-values of 112, 116, and 122. The proportional reduction of the rate of demineralization (Vdem) of similarly treated roots subjected to buffer solutions of pIOHA 112 and 116 appeared to be equal initially. Since fluoridated hydroxylapatite is insoluble under these conditions, these findings are in agreement with expectations. The reduction of Vdem amounted to about 45 and 70% for roots treated for 10 and 30 min, respectively. When roots were treated for 10 and 30 min and then exposed to buffer solutions with a pIOHA 122, reductions of Vdem of about 30 and 55%, respectively, were found. Conversion of the root mineral into fluoridated hydroxylapatite can eliminate, in principle, the existing difference in caries susceptibility of the root and of the dental enamel.

Fluoride specifically adsorbed to hydroxyapatite reduces the rate of dissolution of hydroxyapatite. Since specific adsorption is a property which anions of all weak acids have in common, it is expected that the anions of lactic and acetic acid will be specifically adsorbed to hydroxyapatite too and in this way will cause a reduction in the rate of dissolution of hydroxyapatite. In order to investigate this, we used the experimental results from Featherstone and Rodgers (1981). Calculations of the rate of increase of the lesion depth in dental enamel per mmol. L -1 of the un-ionized acid revealed that lesion progress was pH-dependent and was lowest at that pH which corresponds with the pK-value of the relevant acid. It is concluded that the anions of lactic and acetic acid are specifically adsorbed to the enamel mineral and in this way reduce the rate of dissolution of the mineral. This suggests that a description of the development of an artificial caries lesion in mathematical terms should include the effect on the rate of dissolution of the mineral of specific adsorption of the relevant acid anions to the mineral.

1. 1. Literature data about the plasma content of total calcium, ionized calcium and inorganic phosphate in healthy animals and man of different age and sex were collected. 2. 2. It was established that under normal conditions ionized calcium is about 45% of total calcium. 3. 3. The degree of saturation of these blood samples with respect to octocalcium phosphate OCP was calculated. 4. 4. In young animals and man the blood plasma has a higher degree of saturation than in adult animals and man. 5. 5. The blood plasma of healthy animals is supersaturated with respect to OCP during their whole life. 6. 6. However, the blood plasma of healthy human adults is slightly undersaturated with respect to OCP.

Sound buccal surfaces of human premolars were exposed to buffer solutions which were slightly under- or supersaturated with respect to hydroxyapatite as well as fluorapatite (FA). It appeared to be possible to create subsurface lesions under these conditions, and fluoride appeared not to be necessary for the formation of a surface layer. The mineral content of the surface layer was dependent on the degree of saturation with respect to FA. A comparison is made with literature data, and the differences found are discussed.