On the Mechanisms of Calcification: the Remineralization of Dentin

Factors Influencing the Remineralization of Dental Calculus

SYNOPSIS IN INTERLINGUA

FACTORES DE INFLUENTIA IN LE REMINERALISATION DE CALCULO DENTAL.-Esseva studiate le signification de Ca, P, K, Na, μ, CO2, pH, temperatura (4,25 e 37,5 C) e pressura (760 e 190 mm de Hg) como factores de influentia in le remineralisation del matrice organic de calculo dental e in le formation possible de un "placa" precursori. Matrices dividite in medietates in un solution o sub conditiones de cognoscite reactivitate serviva como controlos.

Le studios indicava que supra un Ca X P (mg %)2 de 35 remineralisation occurreva si o non CO2 esseva presente. Infra un Ca X P (mg %)2 de 35, le induction del remineralisation requireva le presentia de CO2. Na a un alte μ promoveva le remineralisation. Quando le pH esseva reducite, un temperatura de 37,5 esseva plus efficace que un temperatura de 25 C. A un pression de 756 mm de Hg, le remineralisation esseva nodular intra e super le matrice (Ca:P de 2,0). A 190 mm, remineralisation occurreva in omne partes del matrice.

An Evaluative History of Bisphosphonate Drugs: Dual Physiologic Effects of Pyrophosphate as Inspiration for a Novel Pharmaceutical Class

The documented history of the development of the bisphosphonate drugs is reviewed in sufficient detail to permit independent evaluation of the consistency of the conclusions reached from the available data. The evidence developed during the early interval of these studies 1960-1975 was sufficient to establish that pyrophosphate shares the subsequently established dual bisphosphonate characteristics of bone resorption inhibition and prevention of tissue mineralization.

Thorough analysis of silicon substitution in biphasic calcium phosphate bioceramics: a multi-technique study

Four samples of composition Ca(10)(PO(4))(6-x)(SiO(4))(x)(OH)(2-x), with x=0.0, 0.1, 0.2 and 0.5, were prepared and characterized using powder X-ray and neutron powder diffraction, and (1)H, (31)P and (29)Si nuclear magnetic resonance (NMR) spectroscopy. The composition of the Si-substituted HAp phases was determined by joint Rietveld refinements from powder X-ray and powder neutron diffraction data. Taking into account electroneutrality, a chemical formula for the Si-substituted HAp phases with indication of the incorporated silicate amount is proposed. Solid-state (29)Si NMR confirms the presence of only Q(0) species, in good agreement with the presence of substituted HAp and beta-TCP phases only. Thanks to NMR spectroscopy, two types of protons in the Si-substituted HAp phase were identified, the new site corresponding to species engaged in hydrogen bonding with silicate anions. This allowed further refinement of the formulae for these phases with very good quantitative agreement for populations derived from the refinement and integration of NMR data.

Histological evaluation of the osteoinduction capability of human dentine

Aim To assess whether human dentine has the potential to promote the development of calcified tissues when implanted in the muscle tissue of mice. Methodology Root canals in extracted human teeth were instrumented to produce dentine fragments. The dentine fragments produced were divided into two. In group 1, fragments were demineralized and sterilized. In group 2, the fragments were not submitted to any additional treatment. The dentine fragments were then implanted in the muscle of mice. In group 3, the muscles were implanted with rehydrated lyophilized human bone powder. Animals were killed following test periods of 7, 15, 30, 60, 120 and 180 days, the fragments were removed together with adjacent muscle and examined under light microscopy to assess calcification. Results Areas of calcification were observed in groups 1 and 3 after a period of 180 days. In group 2, the surrounding tissues displayed only chronic inflammatory infiltration. Conclusions On the basis of the experimental model adopted in this study, fibroblast-rich connective tissue formed in groups 1 and 3, which could reflect an osteoinductive process. Further studies are suggested to identify which dentinal factors are capable of inducing the formation of a calcified matrix.

Apatite induction by insoluble dentin collagen

Phosphoproteins are thought to play a role in mineral formation in dentin. A portion of this phosphoprotein is bound to collagen. We have investigated the requirement for bound phosphate in mineral induction by isolated dentin collagen. Insoluble bovine dentin collagen obtained by ethylene-diamino-tetra-acetic acid (EDTA) demineralization had 19.5 mol of P/mol of collagen that could not be extracted with 0.5 M EDTA in 4 M guanidine HCl. When this collagen was incubated in supersaturated solutions that did not spontaneously precipitate, apatite was induced. With progressive enzymatic dephosphorylation, induction times for mineral formation became progressively longer. The dentin did not induce mineral formation when 90% of the ester phosphate was removed. Insoluble bone collagen, which had even less phosphate, also did not induce mineral formation. Mineral induction times by dentin collagen increased with decreasing solution saturations. Using these data, the interfacial tension for mineral induction was determined to be 90 ergs/cm2. This value approximated that of phosphatidic acid liposomes and of phosvitin cross-linked to agarose beads, and it might reflect the energetics of heterogeneous nucleation on a highly phosphorylated surface. Sequestering of calcium-phosphate clusters on the phosphoprotein probably accounts for the observed calcium binding by dentin collagen in excess of that required to neutralize the phosphate esters of the collagen. Because the phosphoprotein is immobilized at a low density on the collagen, it cannot self-associate in calcium-phosphate solutions as it does when it is free in solution. This immobilized phosphoprotein allows the mineral clusters formed on its surface to grow into a crystalline order.

Oriented and lengthwise growth of octacalcium phosphate on collagenous matrix in vitro

A correlation among the oriented growth of octacalcium phosphate (OCP), the arrangement of the collagen fibrils in a collagenous matrix and direction of ionic flow was studied in vitro at pH7.0 and at 37 degrees, using two types of collagen disks made from sliced bovine Achilles tendon. Disk A and disk B were made from slices cut perpendicular and parallel to the collagen fibrils, respectively. The products on the collagen fibrils were a mixture of OCP and apatite in the both disks, but the relative amounts of apatite and OCP could not be determined. Short plate-like or flake-like OCP crystals grew parallel to the collagen fibrils and ionic flow on the Ca-side of the disk A. On the contrary, ribbon-like or rectangular OCP crystals grew along the collagen fibrils lying on the disk B. Apatite also grew with the same orientation as OCP in the both cases. The oriented and length-wise growth of OCP crystals on the disk B was ascribed to the arrangement of the collagen fibrils in the disk.

Promotion of calcification on carboxymethylchitin discs

A series of water-insoluble carboxymethylchitin (CM-chitin) discs of varying degrees of substitution (d.s.) has been investigated for their interaction with calcium phosphate. Discs of d.s. 0.03, 0.11, 0.14 and 0.23 were prepared by casting from solutions of CM-chitin in 90% formic acid. Calcium uptake and calcium phosphate nucleation were found to increase with the degree of substitution of the CM-chitin discs. The results suggest that water-insoluble CM-chitin may be useful as a platform for in vivo calcification.

Oriented growth of octacalcium phosphate on and inside the collagenous matrix in vitro

To investigate the factors which regulate the growth of apatite in a collagenous matrix, a calcification experiment was carried out in a model system, where Ca2+ and PO43- ions diffused into a slice of Achilles tendon from mutually opposite grew on the Ca-side of the collagenous matrix, while small plate-like OCP crystals (< 1 micron) grew inside the matrix. The major part of crystals grew with the c-axis parallel to the collagen fibers. Others grew with the c-axis parallel to the collagen bands or perpendicular to the fibrils. Crystals grew with orientation on collagen fibrils from the beginning. It was concluded that collagen fibrils and property of the collagenous matrix played a regulatory role in the deposition and growth of OCP in the collagenous matrix.

Patterns of mineralization in vitro

Various patterns of mineralization are found in the organism during fetal and postnatal development. Different findings and theories have been published in the literature with regard to the mechanisms of mineralization, many of which are controversely discussed. In the present study the different patterns of mineralization observed in the organoid culture system of fetal rat calvarial cells were investigated by electron microscopy. In organoid culture, calvarial cells grow and differentiate at high density, and deposition of osteoid and mineralization of the matrix occur to a very high extent. Different types of mineralization could be observed more or less simultaneously. It was found that hydroxyapatite crystals were formed at collagen fibrils as well as in the interfibrillar space. Mineralization was frequently seen in necrotic cells and cellular remnants as well as in extra- and intracellular vesicles. Addition of bone or dentin matrices or the artificial hydroxyapatite Interpore 200 to the cells caused an increased mineralization in the vicinity and on the surface of the matrices with and without participation of collagen. On previously formed mineralized nodules, an apposition of mineralizing material appeared due to matrix secretion by osteoblasts. It is concluded that initiation of mineralization occurs--at least in vitro--at every nucleation point under appropriate conditions. These mineralization foci enlarge by further apposition as well as by cellular secretion of a mineralizing matrix. Furthermore, cell necroses may liberate mineralizable vesicles. All these patterns of mineralization are the result of different activities of one cell type.

Osteonectin inhibiting de novo formation of apatite in the presence of collagen

The effect of bone matrix protein of osteonectin on de novo formation of apatite was studied in a wide range of calcium phosphate solutions in the presence of collagen. In every solution, from which amorphous calcium phosphate, octacalcium phosphate, or apatite precipitated as a possible initial phase, osteonectin at concentrations less than 1 microM retarded the precipitation, subsequent transformation to apatite, and ripening crystal growth of apatite. Collagen present as either reconstituted or denatured form had no effect on the osteonectin-associated reactions as well as osteonectin-free reactions, and no structural correlation was observed between collagen fibrils and any of the calcium phosphates that appeared in our system. Direct measurement of free calcium levels in the solutions suggested that the reduction in calcium activity due to complexing with osteonectin hardly explained the inhibitory activity of osteonectin in retarding the formation of apatite. Instead, our transmission electron microscopic (TEM) observation strongly suggested that the primary mechanism for osteonectin to inhibit the formation of apatite is to block growth sites of calcium phosphates nucleated. The apatite thus formed in the presence of osteonectin showed less resolved X-ray diffraction patterns, partly because of smaller crystallites as suggested by TEM.

Calcification of dentinal collagen by cultured rabbit periosteum: the role of alkaline phosphatase

Periostea were dissected from 1-2 weeks old rabbit calvaria and folded around decalcified and extracted bovine dentin matrix slices (DMS). The cocultures were grown in serum-containing medium supplemented with beta-glycerophosphate or other organic phosphate esters. [45Ca]-uptake measurements indicated that the DMS calcified. Initiation of the calcification process was associated with alkaline phosphatase activity and could be prevented by adding the inhibitor L-levamisole to the culture medium. Using [32P]-adenosine-monophosphate as a substrate for phosphatase activity it was demonstrated that very little, if any, phosphate was utilized for the phosphorylation of higher molecular weight substances. The results suggest that over 99% of the phosphate produced was laid down in inorganic form. Further, it was noted that mineral deposition in the DMS was accompanied by the simultaneous inclusion of methylene blue and PAS-positive substances whose nature, origin and function remain to be determined. The results lend support to the theory that alkaline phosphatase is involved in the initiation of calcification processes by raising the local concentration of phosphate ions.

Induction and inhibition of hydroxyapatite formation by rat dentine phosphoprotein in vitro

Highly phosphorylated rat incisor phosphoprotein (PP-H) was purified and covalently attached to agarose beads. The beads were incubated for 24 h in solutions having an ionic strength of 0.165, a molar Ca/P ratio of 1.67, and a pH of 7.4. The calcium-phosphate concentration products [( Ca][P]) in the stable incubation solutions ranged from 1.0 to 1.8 mM2, from which no spontaneous precipitation occurred. In a timed series mineral formation was monitored by SEM and X-ray diffraction. The inhibitory capacity of PP-H, free solution, was also studied. The first mineral appeared after 10 min at a [Ca][P] product as low as 1.2 mM2; X-ray diffraction showed that the mineral was (hydroxy)apatite. Thus small amounts of PP-H attached to a surface are capable of inducing mineral formation in vitro at comparatively low supersaturation, whereas PP-H is a mineral inhibitor when free in solution.

Diffuse hepatic calcification as a sequela to shock liver

A 31-yr-old Japanese woman who was on chronic hemodialysis for 3 yr died of intractable congestive heart failure. Three years before death, the patient was in a state of shock for 48 h due to ventricular tachycardia and gastrointestinal bleeding, which was followed by marked elevation of serum transaminase. Four months later, abdominal plain radiography demonstrated diffuse hepatic calcification. At autopsy, microscopic examination of the liver revealed parenchymal necrosis and tiny calcifications in the central to midzonal area of the lobule. Calcification in the degenerative area of the hepatic lobule occurred subsequent to parenchymal ischemia after overt shock that lasted for 2 days. Although a definitive explanation for the calcification was not obtained, it may be related to the disturbances of intracellular Ca2+ homeostasis as a result of ischemic liver injury or it may be related to an elevated calcium-phosphorus product in the uremic state.

Calcification inhibitors in rat and human serum and plasma

Rat and human serum and plasma were shown to contain considerable amounts of calcium phosphate precipitation inhibitors. Two general classes of inhibiting molecules were observed for both species: high molecular weight (approx. 30 000-200 000) and low molecular weight (less than 1000). The high molecular weight components eluted from a Bio-Gel P-200 column in two peaks, one at approx. 158 000 and a broader peak at approx. 43 000. The identity of these inhibitors is unknown at present. Low molecular weight inhibitors include magnesium, pyrophosphate, and citrate ions and at least one unidentified component that coelutes with pyrophosphate and citrate on a Bio-Gel P-4 column. Quantitatively, most of the inhibitor activity resides in the high molecular weight components and it is possible that it is this activity which is responsible for maintaining the metastability of the circulating fluids. The role of the low molecular weight components may be to regulate calcification at sites inaccessible to high molecular weight molecules.

The histology of sclerotic human root dentine

Studies by optical microscopy, microradiography and SEM suggested that sclerosis is the result of occlusion of the dentinal tubules by a mineral substance with a refractive index similar to that of the rest of the dentine. Translucence appeared before the majority of the tubules were completely occluded. The deposition of the occluding mineral took place initially in individual tubules or in groups of tubules. The occluding material and the peritubular dentine were almost indistinguishable under SEM. Both were smooth and densely mineralized. The process of deposition of occluding mineral appeared to be more like that of in-vitro mineralization and thus different from that of peritubular dentine.

The kinetics of mineralization of human dentin in vitro

The prospect of restoration of damaged dental tissues has recently attracted great interest. An understanding of the remineralization of human dentin in vitro was attempted by using super-saturated calcium phosphate solutions at sustained supersaturation by means of a constant solution composition method. The direct growth of HAP from solutions of low supersaturation on powdered whole human dentin was confirmed. Moreover, it was found that the kinetics were similar to those of the seeded growth at synthetic HAP. A high apparent activation energy pointed to a surface-controlled mechanism.

Precipitation of calcium phosphates under conditions of double diffusion in collagen and gels of gelatin and agar

One-dimensional double diffusion was applied to determine critical concentrations at which the precipitation of calcium phosphates occurs in reconstituted connective tissue collagen and agar gels at 37 degrees C and in gelatin gels at 25 degrees C. Experiments were performed in the presence of unbuffered 0.15 mol dm-3 NaCl, or 0.15 mol dm-3 NaCl-veronal adjusted to pH 7.4. It was found that critical concentrations of precipitation of both precipitating components, CaCl2 and phosphate buffer (pH 7.4), were equimolar and independent of the ratios of initial concentrations of the components. Critical concentrations of precipitation were not affected by the concentrations and kinds of gels used. The first-formed precipitates showed amorphous structure by X-ray diffraction analyses. Infrared (IR) spectra of the precipitates indicated CaHPO4 . H2O to be their predominant species. The molar Ca/P ratio obtained by chemical analyses was 1.08. This precipitate transformed in time into octacalcium phosphate. In all experiments, two very thin membranes of precipitate were formed in the gel column at the onset of precipitation simultaneously on both sides of the actual disc of precipitate. IR spectra and chemical analyses showed that both membranes were identical to the actual precipitation discs.

Remineralization of dentin in vitro

The remineralization of completely demineralized bovine dentin was studied in vitro by monitoring the velocities of fall of small particles through calcifying solutions. The density of a particle of dentin may be found from its velocity of fall through a fluid using Stokes' law. The minimum concentration product of calcium and acid phosphate ions of the solution in which remineralization would take place was 3.6 (mM)2 in the presence of 22 mM bicarbonate, pH 7.35, and ionic strength 0.1. This just above the solubility product of brushite (CaHPO4-2H2O). Incubation of decalcified dentin in a phosphoprotein removed from dentin during demineralization, or in phosvitin, had no effect on remineralization. The rates of remineralization and of the fraction remineralized were inversely proportional to particle size. This inverse correlation may be due to deposition of mineral in a surface layer of constant depth irrespective of particle size. The fraction of a particle remineralized was greatly increased by the use of highly supersaturated calcifying solutions or by the incorporation of fluoride into the solutions. The empirical reaction order of remineralization for both calcium and phosphate ions was found to be unity, which is, within the error limits, equal to the order of growth of seed crystals of hydroxyapatite in calcifying solutions of the same composition.

Nucleation of monosodium urate crystals

(1) Calcium greatly increased crystallization of monosodium urate in otherwise pure water, by enhancing both nucleation and growth. (2) Acid accelerated urate nucleation, both by its direct action and indirectly by increasing the free calcium in physiological fluids. (3) Synovial fluid from one gouty patient accelerated urate nucleation, while that from one rheumatoid patient inhibited nucleation. (4) X-rays, collagen, ethyl alcohol, cupric ion, and potassium ion all had negligible influence on urate nucleation. (5) Mechanical shock greatly increased urate nucleation.

Urolithiasis induced with DL-3,a-dimethyltyrosine methylester HCl. I. A scanning electron microscopic investigation

Scanning electron microscopic investigations on rats subjected to DL-3,a-dimethyltyrosine methylester HCl treatment, indicated that the drug in reference induces renal lesions substantiated by proximal tubular epithelial cell regression and eventual exfoliation, coupled by formation of 3,a-dimethyltyrosine calculi both in the upper and lower segments of the urinary tract. The development of calculi was found to be preceded by a moderate to massive precipitation of a fibrin-like substance intermixed with blood cells, and with an occasionally concomitant deposition of exfoliated cells of epithelial origin, to be succeeded by precipitation of crystals.

Recalcification of artificially decalcified dentin in vivo

Cavity floor dentin of dog teeth was artificially decalcified in vivo by acid to investigate recalcification. The first decalcified layer was soft with low calcium content and could be recalcified only slightly by external deposition from saliva or capping. The second layer was decalcified intermediately and could be recalcified to a considerable degree by vital reaction.

Remineralization of carious dentin

Based on radiographic and microradiographic evidence, a 10% stannous fluoride solution produced remineralization of the carious dentin more rapidly than, and was superior to, other remineralizing solutions and calcifying solutions. Permeability to dye penetration was reduced. Electron photomicrographs showed an electron-dense material deposited in the dentinal matrix.