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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.

Phase diagrams were constructed from phase equilibrium calculations for the quaternary system Ca(OH)2-Sr (OH)2-H3PO4-H2O and for the system Ca(OH)2-Sr(OH)2-H3PO4-HX(BOH)-H20 at 25°. On the basis of these diagrams the stability field of solid solutions of calcium and strontium hydroxyapatite was derived. The calculations show the borderlines of the apatite field to be determined by the activity isotherms of the sparingly soluble phosphates CaHPO4.2H2O, Ca8H2(PO4)6.5H2O, β-SrHPO4 or Sr6H3(PO4)5.2H2O depending on the pH and the molar cSr:cCa and cCa: cP ratios in the solution. The biological implications of these results are discussed.

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.

The solubilities of synthetic β-Ca3 (PO4)2 [TCP] and Mg-containing β-Ca3 (PO4)2 [TCMP] were determined in the system Ca(OH)2-Mg(OH)2-H3PO4-KCl-H2O at 25° C. The thermodynamic solubility product of TCP is found to be (1,14 ± 0.10) x 10−30 mol5. l−5. The incorporation of Mg2+ results in a remarkable stabilization of the β-TCP structure as reflected by a drastic decrease in the amount of solid dissolved for TCMP compared to that for TCP and by the fact that the solutions are undersaturated with respect to calciumhydroxyapatite. On the basis of solid state chemical and thermodynamical principles the solubility behaviour of TCMP solid solutions is discussed. Indications are found that magnesium whitlockite possibly precipitates during the equilibrations of TCMP.

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.

It is shown that the distribution of ions over the solid phase and an aqueous solution can be interpreted in terms of Roozeboom's classification in the case of ideal ionic solid solutions and regular ionic solid solutions with and without ordering or substitutional disorder. A general relation is derived between the distribution coefficient D of the system and the solubility products of the components of the solid phase. In this way D can be determined experimentally in an independent way. It appears that in practice type II and type III systems are indistinguishable from type I systems, when the distribution coefficient D differs about one order of magnitude or more from unity even in the case of good recryatallization. In those cases distribution diagrams are not suitable to derive the nature of the series of solid solutions involved.

In order to investigate possible diffrences in the mineral composition of rat incisors, Wistar rats received either a zinc-deficient or a normal diet (the latter were pair fed or ad libitum). Three incisors from each group were subjected to microanalysis by me electron microprobe. No differences were found in mineraI composition between the three groups. The average molar Ca/P ratio in the enamel and the dentin were (1.62+/- 0.05) and ( 1.50 +/- 0.05), respectively. The distribution of sodium and magnesium over the dentin was homogeneous and inhomogeneous , respectively. Dentin did not contain detectable amounts of chlorine. The gradients for sodium, magnesium and chlorine as a function of depth in enamel were similar to those reported for these elements in human and rhesus monkey enamel : sodium and magnesium had a low concentration at the enamel surface, wnereas chlorine had a high concentration there.

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.

Some newly designed surface-active phosphates were investigated with respect to their capacity to inhibit caries lesion formation in vitro. On the labial or buccal surfaces of sound human third molars, windows were prepared for investigation. One half of each window was treated with the test compound at pH values of 7.5, 5.5, or 3.5. The other half served as a control. Both halves were demineralized and the generated caries lesions in both parts were compared by means of quantitative microradiography. Mono-, bis- and trisphosphates differed only marginally in their effect on the demineralization. The compounds diminished the demineralization down to 30% of that of untreated enamel. Per molecule at least one long alkyl chain (more than 12 C atoms) was required for achieving decreased demineralization, indicating the importance of a low surface tension. The results suggest that some of the tested compounds have promising properties for their use as anticaries agents, especially when applied in combination with fluoride.

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

To estimate permeability properties of bovine dental enamel, complex impedance measurements and radioisotope diffusion experiments were carried out before and after X-ray irradiation (single dose, 72 Gy) of enamel specimens. Neither impedance measurements nor diffusion experiments showed significant changes in permeability.

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 literature on how Mg is present in tooth enamel and on the incorporation of Mg in synthetic apatites is reviewed. Then a theoretical consideration is given on the basis of ionic radii about the incorporation of Mg in F-, Cl- and OH-apatite. Finally, the results are given of experiments on the incorporation of Mg in fluor, chlor, hydroxy, and carbonate apatite. It appears that the extent of incorporation of Mg in the apatite lattice, if at all, is very limited and that Mg in tooth enamel is to a very limited extent incorporated in the apatite lattice, the main portion being surface bound or present in a separate phase.

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.

Literature data on equilibria between solid calcium phosphates having the apatite structure and aqueous solutions containing Na+ and CO3 2- ions were reexamined in view of the present data about the complexation of ions in such systems. Recalculations showed that all solutions were undersaturated or just saturated with respect to either brushite or octocalciumphosphate or more or less finely dispersed calcite and supersaturated with respect to pure hydroxylapatite. Sections through the quasi-sextary phase diagram were constructed which are representative for the system under simulated in vivo conditions.

A solid-state chemical model is derived to estimate the solubility of dolomites having different degrees of cation ordering. It is shown that the solubility of dolomites formed by precipitation at ordinary temperatures is such that it allows for the formation of dolomite in tooth enamel during in vivo mineralization.

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.

Third molars just erupting and premolars (before eruption or half a year or 3.5 years after eruption) were extracted and sawn vertically through the buccolingual plane. Tracings of the Ca, P, Na and Mg contents of the outer 100-µm layer of the enamel were made with an electron microprobe. Care was taken to limit the diameter of the excited volume to about 1 µm and to suppress the evaporation of Na. On the unerupted and freshly erupted surfaces the Na and Mg content varied from 50 to 80% of the content at 100 µm depth. However, half a year or 3.5 years after eruption the Na and Mg contents were negligibly small at the tooth surface and they remained smaller than in unerupted or freshly erupted teeth up to a depth of 10–30 µm. These data suggest that posteruptive maturation occurs in the mineral of the outer layer of tooth enamel whereby it builds up a higher resistance to carious breakdown. This interpretation is corroborated by clinical findings reported in the literature. The consequences of wear and abrasion on these phenomena are not known yet. The above-mentioned depth of 10–30 µm agrees with the penetration depth of pH changes estimated to result from the consumption of foods and drinks with varying pH.

Point count analyses were made with the electron microprobe for Ca, Na and Mg in a vertical cross-section through the enamel of a freshly erupted human pre-molar in the approximal area. A low excitation energy was chosen to limit the size of the excited volume and to suppress the evaporation of Na. The Na content showed variations with a wavelength of 6 ± 1 µm, which equals the distance of cross-striations. The Mg content showed variations with a wavelength of 25 ± 4 µm which equals the distance of striae of Retzius, whereby these striae probably contain a higher Mg content. On the assumption that higher Na and/or Mg contents represent mineral with a higher solubility, the observed variations in mineral composition help to explain the fine structure of carious lesions as observed frequently by microscopy and microradiography.