Growth Of Apatite Crystals Research Articles

Inhibition of apatite crystal growth by the amino-terminal segment of human salivary acidic proline-rich proteins.

Inhibition of seeded apatitic crystal growth by human salivary acidic proline-rich phosphoproteins (PRP) has been related to their adsorption onto the apatite seeds. The amino-terminal 30-residue segment of the PRP makes an important contribution to this adsorption. This peptide (PRP1(T1] and its dephosphorylated analogue from PRP3 (PRP3(T1)DP) were prepared. They have identical sequences, except the phosphates at residues 8 and 22 in PRP1(T1) are absent from PRP3(T1)DP. Adsorption of these peptides onto hydroxyapatite and their effect on crystal growth from a defined supersaturated solution was studied. Adsorption behavior was adequately described by the Langmuir adsorption isotherm. The adsorption affinity constant of PRP1(T1) (K = 20,200 ml/mumol) was more than 10 times the corresponding value for PRP3(T1)DP (1,800 ml/mumol), and similar to that of the parent protein, PRP1 (26,200 ml/mumol). Inhibition of crystal growth by the peptides was interpreted in terms of the fractional coverage of the maximum number of adsorption sites (as derived from the adsorption isotherms), suggesting that the molecules block, by adsorption, specific growth sites on these surfaces. Comparison of precipitation kinetics showed that PRP1(T1) is a more effective inhibitor than PRP3(T1)DP at the same initial concentration (10(-6)-10(-7)M). However, on the basis of per mol adsorbed, PRP3(T1)DP displays a greater inhibitory activity; such a behavior is consistent with a more open molecular structure which blocks more growth sites per mol adsorbed than PRP1(T1).(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of seeded growth of enamel apatite crystals by amelogenin and enamelin proteins in vitro.

The effect of enamel matrix proteins on the seeded growth of enamel apatite crystals was studied in stable supersaturated solutions at pH 7.4 and 37 degrees C. Of the two major protein classes in the enamel matrix, the enamelins were considerably more effective than the amelogenins in retarding seeded growth. However, the amelogenin species that did show significant inhibitory activity are those known to be lost first from the enamel matrix during the rapid mineralization stage of enamel maturation.

Phosphoprotein modulation of apatite crystallization.

Several phosphoprotein preparations (phosvitin, rat incisor and fetal calf molar dentin phosphoproteins) all inhibit apatite growth/replication from pre-existing crystal seeds in metastable solutions. Two stages of the crystal growth process were inhibited by these phosphoproteins. First an initial lag period was induced, probably associated with seed surface phenomena. This period was prolonged indefinitely when a combination of phosphoprotein precoated seeds was used together with soluble phosphoproteins in the crystal growth reaction. Second, the phosphoproteins prolonged that stage of the reaction where octacalcium phosphate is the predominant mineral phase present prior to its conversion to the final apatite product. Pre-treatment of the phosphoproteins with calcium diminished their inhibitory activity to seeded crystal growth as well as towards de novo apatite formation in synthetic extracellular fluids. The presence of collagen diminished the inhibitory activity of the phosphoproteins towards de novo precipitation but had no effect on phosphoprotein-modulated apatite crystal growth in the seeded systems. These results suggest a potential regulatory role for phosphoproteins in dentin mineralization.

Crystal growth of mineral phases in skeletal tissues

The study of crystal growth mechanisms in skeletal tissues is complicated by the fact that important physicochemical factors governing the nucleation and growth of apatite crystals, the principal component of bone mineral, are often obscured by cellular and biochemical processes. Fortunately, many kinetic and thermodynamic features of apatite growth in vivo can be inferred from solution investigations of synthetic analogues possessing biological-like properties. This paper reviews these synthetic studies and considers their applicability to the biological situation. As a preface, a brief description of some of the salient features of the biomineralization process as it pertains to skeletal tissues is included. Two points of great significance which have emerged from these comparative studies to date are that: (1) apatite formation is not simple and straightforward, but is a complex process involving one or more precursor phases, and (2) both the cells of mineralized tissue and the extracellular organic matrices play important roles in initiating and controlling in vivo mineral deposition.

Electron microscopy of enamel surface after reactions of apatite accretion.

Abstract. Images were obtained from intact and acid etched enamel surfaces (both before and alter growth of surface apatite) with electron diffraction, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Labial surfaces (intact) of bovine incisor teeth were slightly abraded and pumiced. They were then etched by a 14‐hour immersion in 2mM sodium acetate‐acetic acid buffer at pH 5.0; an average of 31 μ.Mol/cm2 calcium and 24 μMol/cm2 phosphate was dissolved from the surfaces. The SEM. and TEM showed loss of minerals to a depth of 10 μm. Dissolution was largely in central areas of enamel prisms, and prismatic structure in the etched surfaces was retained. Electron diffraction, SEM, and TEM showed the growth of crystalline apatites at the etched surfaces after 24 to 96 hours immersion in neutral pH solution (metastable) which contained 1.5 mM Ca+2, 0.9 mM H2PO4/HPO4−2, 0.05 mM F−, and 150 mM NaCl. Indirect analysis, at the loss of calcium and phosphate concentrations in the metastable solution after immersion periods, indicated deposition of approximately 24μMol/Cm2 calcium and 14μMol/cm2 phosphate on the etched surfaces. Results show induction of apatite crystal growth and recrystallization at enamel surfaces in otherwise stable solutions containing 0.05 mM F−.

The mechanism by which tetracycline hydrochloride inhibits mineralization in vitro.

Abstract 1. 1. The inhibitory action of tetracycline hydrochloride on mineralization was demonstrated in vitro . Low concentrations of the drug interfered with teh precipitation of apatites from supersaturated mineralization buffers at 37° and pH 7.4. In the presence of 20 μM tetracycline, the ionic produce of calcium and phosphate required for spontaneous precipitation rose from 2.5 to 4.0 (mM) 2 . The amount of mineral in the precipitate was not altered, which suggests that tetracycline affects the primary nucleation of mineralization. 2. 2. In metastable mineralization buffers tetracycline also depressed the uptake of minerals by extracted fibers of collagen X-ray diffraction studies showed that the crystalline structure of the apatites formed in the collagen was not disturbed by the drug. The binding of radio-labeled tetracycline to the collagen was closely associated with the mineralization of the collagen. 3. 3. Finally, in a kinetic model of the mineralization induced by collagen, the two phases of apatite formation, nucleation and crystal growth, could be dissociated. In the experimental conditions used, 20 μM tetracycline depressed nucleation to about half and crystal growth to about one-third of the control values. 4. 4. It is concluded that inhibition of mineralization by antibiotics of the tetracycline group during osteogenesis and tooth formation may be due to mechanisms similar to those operating during the experimental mineralization demonstrated in the present study.

The effect of some inhibitors on the nucleation and crystal growth of apatite.

Mg, Sr and F ions acted as inhibitors of apatite formation when added to a calcification buffer separately or in combinations.

Elliptical tubules as unit structure of forming enamel matrix in the rat

The mechanism of the lengthwise and oriented growth of enamel apatite crystals was studied on the basis of a hypothesis that (1) enamel crystals grow initially as octacalcium phosphate (OCP) as a precursor of apatite and (2) a one-directional Ca2+ ion supply from the ameloblasts promotes the lengthwise and oriented growth of the crystals. To test this, OCP crystals were grown in a model system of enamel formation, where a cation selective membrane was used to control the Ca2+ ion diffusion, at 37°C and at pH 6.3–7.4. The lengthwise and oriented growth of OCP was enhanced by the Ca influx from the membrane. H+ ion enhanced while F−, Mg2+ and CO32− ions decreased the growth in the c-axis direction. F− induced an epitaxial overgrowth of apatite on the (1 0 0) of OCP, embedding an OCP lamella in the center of a crystal. When 5% polyacrylamide gel was attached to the membrane, OCP grew in long plate-like or ribbon-like crystals at pHs between 6.5 and 7.4. The length of these crystals was greater than that of those grown on the membrane without gel. The crystal size decreased with an increase in gel concentration from 5 to 20%. When a thin slice of tendon was used in place of the membrane, long OCP crystals grew along the collagen fibrils; these crystals were oriented with their axis of elongation perpendicular to the direction of ionic inflow. The size of crystals grown inside the collagenous matrix was much smaller than the size of crystals formed outside of the matrix and on the membrane. Thus, crystal growth was regulated by ionic diffusion and the matrix. When there were no constituents which regulated the growth direction, OCP crystals tended to grow along the direction of ionic inflow.

Electron microscopy of matrix formation and calcification in rat enamel

Enamel from incisors and molars of 4-day, 10-day and 1-year old rats has been cut with a diamond knife, as non-decalcified ultra-thin sections, and examined by electron microscopy and diffraction, with the following findings: 1. (1) Enamel matrix elaboration starts in the ameloblastic cytoplasm, next to the amelo-dentinal junction membrane. Fibrogenesis occurs in two steps: first by an elaboration of diffusely scattered fibrillar protein bundles, embedded in ground substance; secondly, by the appearance of elongated ovoid or frequently cord-like structures, which by coalescence form the enamel matrix. When completed, the fibrillar matrix assumes a three-dimensional reticular appearance. 2. (2) The apatite crystal growth starts selectively within and on the longitudinal fibrils of the reticulum, in the form of small crystallization centres, which later fuse together, giving rise to strips of calcifying fibrils. Grouping of adjacent calcifying fibrils is followed by partial and then complete fusion, ultimately forming adult apatite crystals, which contain in their core calcified protein fibrils. These crystals take the shape of elongated hexagonal prisms. 3. (3) In the rat incisor, matrix differentiation and calcification of enamel proceeds progressively from the enamel-dentine junction toward the enamel surface. Three distinct layers can be recognized: inner, middle and outer enamel. The narrow inner and outer enamel contain aggregates of parallel oriented apatite crystals, without any distinct rod structure, whereas the wider middle enamel exhibits a complicated rod interrelationship characterized by alternating layers of rods running in different directions. 4. (4) In adult rat teeth, a difference in apatite crystallization has been noted both in incisor and molar enamel which is characterized by zones of well-formed apatite crystals intermixed with zones of unfused calcified fibrils.

An Appinitic Facies Associated with Certain Granites in Jersey, Channel Islands

Summary The rocks here referred to as appinites form part of the essentially dioritic facies marginal to both the north-western and south-eastern complexes in Jersey. Mineralogically they are characterized by abundant long prismatic amphiboles, rich in titanium. Many of these contain cores of mica or felsic material, the nature and origin of which are discussed. The country rock commonly occurring in association with the appinitic rocks is dioritic in both complexes; and at Ronez in the north of the island it contains relicts which prove it to be, at least in part, metasomatized gabbro. The diorites and appinites both consist of essentially the same mineral assemblage and, whilst the latter are not metasomatic in the generally accepted sense of the word, there is no doubt that a large proportion of their substance has been derived from gabbro by way of a series of changes initiated by the nearby granites. The changes by which gabbroic material was converted into dioritic have been continued and accentuated, presumably by emanations from the granite, with the local building up of strong flux concentrations, which led to the formation of " pockets " consisting of crystal mush with interstitial liquid. It was from this " magma " that the appinitic rocks crystallized, under essentially pegmatitic conditions. It was demonstrably mobile, and a turbulent fluxional structure is highly characteristic. Textural interpretation receives critical attention in the paper, particularly in so far as it concerns replacement phenomena. The observed changes in mineral contents are consistent with crystallization from a magma, and follow the lines of Bowen's discontinuous reaction series, which must be extended at the low temperature end to include phases usually regarded as secondary, but here unquestionably primary. An unusual feature, occasioned by the special environmental conditions, has been the growth of amphibole and apatite crystals of a hollow-shell type, in which crystallization starts on the outside and progresses towards the centre. In the sequence of paramorphic changes, the inheritance by a later phase of the internal structure of the earlier one which it is replacing, in accordance with the principle of least disturbance of the original Si-0 lattice, is strikingly displayed in these rocks. Problems of classification and nomenclature are involved and receive due attention in the paper.