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PubMed2002

Growth of bioactive surfaces on dental implants.

Some metallic materials, such as pure titanium, Ti-6Al-4V, are used for dental and orthopedic implants under load-bearing conditions. However, they do not form a chemical bond with bone, which would achieve a good implant-bone fixation in service. In recent works, it has been demonstrated that an in vitro, chemically deposited, bone-like apatite layer with bone-bonding ability could be induced on a titanium surface. By reproducing that chemical procedure, in this work, a dense bone-like apatite layer was formed on the surface of the titanium in simulated body fluid. In addition, the different steps and kinetics of the layer-formation have been studied, because the observation of the samples in the wet state by means of the environmental scanning electron microscope has allowed the observation in situ of the apatite deposition process over a number of days. One of the most important features of the present study is that it can be carried out on a single titanium sample and the process is not interrupted at any stage. One of the main drawbacks of this chemical method is that the samples covered with apatite are susceptible to contamination by bacteria. The behavior of different types of antibiotics used to avoid this contamination has also been studied using the environmental scanning electron microscope. Finally, osteoblast cells have been cultured on the apatite-coated titanium samples to assess their biocompatibility.

Alloys↗

PubMed1993

Inhibition of calcium hydroxyapatite formation by polyamines.

The lithogenic potential of bile depends not only on supersaturation of solutes but also on the presence of pro- and anti-nucleating factors. For example, glycine-conjugated dihydroxy bile salt dimers are potent inhibitors of calcium hydroxyapatite precipitation that function by "poisoning" the nascent crystal. Although most inhibitors of apatite formation are anions, theoretically polycations should also be effective, and because significant concentrations of polyamines are present in bile, we have investigated the ability of these molecules to inhibit apatite formation. In vitro, each polyamine (2-10 mmol/l) was able to inhibit apatite formation, and the inhibiting power was correlated with ionic charge. Thus putrescine (2+) was the weakest inhibitor and spermine (4+) was the strongest. Mixtures of polyamines were less effective than were the individual polyamines, except at higher concentrations. Although polyamines were effective over short periods of time (270 min), over longer times (3 days) spermine was unable to prevent apatite formation. Using infrared spectroscopy, we found no evidence for interaction between phosphate ions and spermine in solution. Taken together, these results suggest that polyamines are modest inhibitors of apatite formation that likely function by retarding the dissolution of the intermediate amorphous calcium phosphate phase.

Bile↗

PubMed1977

Binding of dyes to chlorhexidine-treated hydroxyapatite.

The binding of some selected food dyes to hydroxyapatite with and without a coating of chlorhexidine was studied. The apatite had bound 0.6 mumol chlorhexidine per g dry weight. The bound chlorhexidine was in equilibrium with a free concentration of 115 microgram ml (128 micron). The dyes investigated were brilliant blue (FD&C Blue No. 1), indigo carmine (FD&C Blue No. 2), tartrazine (FD&C Yellow No. 5), sunset yellow (FD&C Yellow No. 6), amaranth (FD&C Red No. 2), and riboflavin. Riboflavin did not bind to either chlorhexidine-treated apatite or untreated apatite, whereas the other dyes showed a considerable affinity for chlorhexidine-treated apatite as compared with untreated apatite. Because the dyes with binding ability possess two or three acidic groups, and because riboflavin has none, it was suggested that the binding of the dyes is mediated by an interaction between the anionic groups of the dye molecules and the cationic groups of the chlorhexidine molecules. The results are discussed and related to the formation of the brownish discolorations seen on the teeth of patients using chlorhexidine mouthrinses. A mechanism to explain the development of tooth stains is proposed.

Amaranth Dye↗

PubMed2003

Synthesis of bioactive organic-inorganic nanohybrid for bone repair through sol-gel processing.

So-called bioactive ceramics have been attractive because they form bone-like apatite on their surfaces to bond directly to living bone when implanted in bony defects. However, they are much more brittle and much less flexible than natural bone. Organic-inorganic hybrids consisting of flexible organic polymers and the essential constituents of the bioactive ceramics (i.e., Si-OH groups and Ca2+ ions) are useful as novel bone substitutes, because of their bioactivity and mechanical properties analogous to those of natural bone. In the present study, organic-inorganic nanohybrids were synthesized from hydroxyethylmethacrylate (HEMA) and methacryloxypropyltrimethoxysilane (MPS), as well as various calcium salts. Bioactivity of the synthesized hybrids was assessed in vitro by examining their acceptance of apatite deposition in simulated body fluid (Kokubo solution). The prepared hybrids formed apatite in Kokubo solution when they were modified with calcium chloride (CaCl2) at 5 or 10 mol% of the total of MPS and HEMA. Deposition of a kind of calcium phosphate was observed for the hybrids modified with calcium acetate (Ca(CH3COO)2), although it could not be identified with apatite. The addition of glycerol up to 10 mol% of the total of MPS and HEMA or water up to 20 mol% as plasticizers did not appreciably decrease the acceptance of apatite formation of the hybrids. These findings allow wide selectivity in the design of bioactive nanohybrids developed by organic modification of the Si-OH group and calcium ion through sol-gel processing. Such nanohybrids have potential as novel bone substitutes with both high bioactivity and high flexibility.

Animals↗

PubMed1994

Strategies for improving the assessment of dental fluorosis: focus on chemical and biochemical aspects.

In order to assess fluoride accumulation and effects in developing dental tissues, one must determine the concentration profile of fluoride in the tissue and to assess separately the labile (i.e., free ions in fluid and ions associated with organic matter) and stable (i.e., incorporated into apatite lattice) pools of fluoride. Free fluoride ions in the mineralizing milieu markedly affect the driving force for precipitation and, as a result, the nature of precipitating crystals. The fluoride incorporated into the crystalline lattice increases the stability of the formed mineral. Improvement in the understanding of the mechanism of dental fluorosis requires more comprehensive information about the effects of fluoride on the ionic composition of the fluid phase, the nature of the initially precipitating mineral(s), the interactions between crystals and matrix proteins, and the enzymatic degradation of the proteins. Recent observations relevant to the role of fluoride in enamel formation include: (1) that there are threshold concentrations of fluoride below which the precipitation and hydrolysis of thin-platy octacalcium phosphate is facilitated but beyond which de novo apatite precipitation prevails; (2) that the presence of fluoride in the mineralizing milieu most likely affects the steady-state concentrations of mineral lattice ions; (3) that incorporation of fluoride into the stable pool is retarded by the presence of matrix proteins, particularly amelogenins, which inhibit the growth of apatite crystals; (4) that increasing the degree of fluoridation of apatite crystals enhances the adsorption of amelogenins onto the crystal surface, and (5) that amelogenins pre-adsorbed onto apatite crystals are more resistant to enzymatic cleavages by trypsin (used as a prototype of amelogeninases).

Ameloblasts↗

PubMed2000

Structure, composition, and maturation of newly deposited calcium-phosphate crystals in chicken osteoblast cell cultures.

Characterization of the very early calcium phosphate (CaP) crystals deposited in bone or in osteoblast cell cultures has been hampered by the overwhelming presence of organic matrix components and cells that obscure spectral analyses. We have overcome this problem using isolated protein-free crystals and have obtained new data including 31P nuclear magnetic resonance (NMR) spectra for the first time from mineral crystals deposited during osteoblast calcification in culture. Crystals were isolated from cultures at two time points: (a) at first calcium accumulation (day 8-10) and (b) after 60 days of culture, to assess maturational changes. The analyses show that the chemical composition overall and short range order of the early and mature crystals are characteristic of the apatite crystals found in young embryonic chick bone in vivo. No mineral phase other than apatite was detected by any of the methods used. 31P NMR spectroscopy identified the HPO4 groups as those present in bone apatite. Similar to bone apatites, no OH groups were detected by Fourier transform infrared (FTIR) spectroscopy. The temporal maturational changes in composition and structure of the mineral phase were difficult to assess because of the continuous deposition of crystals throughout culturing. The pathway of the maturational changes observed were similar to those occurring in chick bone in vivo and synthetic apatite crystals in vitro although to a much smaller extent.

Animals↗

PubMed2001

In vitro effect of hyperbaric oxygen on the chemolysis of infective stones.

BACKGROUND: In order to extend the feasibility of hyperbaric oxygen therapy in the urological field, the present study aimed to investigate the dissolution activity of human infective stones in UROCITRA solution under hyperbaric oxygen condition. METHODS: The dissolution activity of 7 struvite and 11 mixed struvite and carbonate apatite stones in UROCITRA solution were studied under 2.5 atmosphere (atm) hyperbaric oxygen (HBO) status in a Sigma I N-124 monoplace chamber. Another 7 struvite and 10 mixed struvite and carbonate apatite stones were also studied under normal condition. Chemolysis was performed in a drip device with a 150-ml/hour continuous flow rate. RESULTS: Under 2.5 atm HBO status, the PO2 of UROCITRA solution was 365 +/- 44 mmHg, which was significantly higher than that of tap water (113 +/- 62 mmHg) and UROCITRA solution (125 +/- 12 mmHg) under normobaric condition (p < 0.001). The decreases in the stone weight of struvite under normobaric condition were 31 +/- 8.8% after 2 h and 48 +/- 15% after 4 h of treatment. The HBO-enriched UROCITRA solution did not increase the dissolution activity as reflected by comparable decreases in the dried stone weight (31.2 +/- 14.6% and 54 +/- 19% at the 2nd and 4th post-treatment hours, respectively, p > 0.05). Similarly, there was no significant difference in the percent stone weight decrease of the mixed struvite and carbonate apatite stones under either HBO or normobaric condition. The dissolution responsiveness of struvite was significantly greater than that of the mixed struvite and carbonate apatite stones. CONCLUSIONS: The chemolysis of struvite in UROCITRA solution is significantly greater than that of the mixed struvite and carbonate apatite stones. However, the UROCITRA solution enriched with HBO does not enhance the dissolution of infective stones.

Calculi↗

PubMed1982

Electron spin resonance study of sound and carious enamel.

The present electron spin resonance (ESR) study aimed to investigate chemical alterations in enamel apatite associated with carious attacks. Enamel blocks were cut from sound areas and natural white spot lesions of human molar teeth and then X-irradiated at room temperature in air. Q-band ESR analysis of these samples showed the presence of two stable signals in the spectra recorded at room temperature. One of them has been identified at CO3-(3) centers, which originate from the carbonate ion substituting in the apatite lattice. The other signal is tentatively identified as O- defects in the hexad axis of apatite lattice. A comparison of the spectra between sound and carious samples demonstrated that the intensity ratios between the O- and the g parallel component of CO3-(3), R = O-/CO3-(3) (g parallel), are significantly higher in the carious samples than in the sound ones. This suggests that enamel apatite in the white spot lesions may have less carbonate ions in the crystal lattice, or have a higher producibility of the O- defects in its hexad axis. The observed alterations in enamel apatite may well be accounted for by remineralization playing a major role in the formation of white spot lesions, because this acid-dissolution study using irradiated enamel blocks showed that the R values do not increase but decrease in a simple process of demineralization.

Dental Caries↗

PubMed1997

Heterogeneous fluoridated hydroxyapatites partially substituted with fluoride ions.

The partially substituted fluoridated apatites H-FHAp0.5 and FH-HAp0.5 were synthesized heterngeneously by supplying fluoride at a concentration equivalent to half of the maximum value of fluorapatite during the initial or final half of the experimental period. Although X-ray diffraction patterns and SEM photos of H-FHAp0.5 and FH-HAp0.5 apatites were not significantly different, high-resolution electron microscopy showed quite different features; H-FHAp0.5 type apatite was an elongated hexagon with electron beam damage in the core, and FH-HAp0.5 type apatite was a rather wide hexagon analogous to fluorapatite. Energy dispersive spectroscopy attached to the SEM showed H-FHAp0.5 apatite to have a higher fluoride peak intensity than FH-HAp0.5. These results supported the previous speculations on the two different types of heterogeneous fluoridated hydroxyapatites: hydroxyapatite covered with fluorapatite and fluorapatite coverted with hydroxyapatite.

Crystallization↗

PubMed1998

Basic fibroblast growth factor adsorption and release properties of calcium phosphate.

Basic fibroblast growth factor (bFGF) is well known as a potent angiogenic factor playing a crucial role in wound-healing processes. Apatitic substrates such as hydroxyapatite and carbonated apatite (CA) could be potential carriers of growth factors because of their physicochemical similarities to bone mineral. These materials have been compared for their bFGF adsorption and release properties. The adsorption of the growth factor was higher on carbonated apatite than on hydroxyapatite, probably owing to environments with labile nonapatitic CO3(2-) and HPO4(2-) groups, along with a higher specific surface area which gives the CA a higher surface reactivity. These environments can be exchanged very rapidly, leading to the release of bFGF. The controlled release of adsorbed growth factor from carbonated apatite could provide means of improving bone healing in the future.

Adsorption↗

PubMed1999

Graded surface structure of bioactive titanium prepared by chemical treatment.

An NaOH treatment of pure titanium (Ti) forms a sodium titanate hydrogel surface layer with a smooth graded interface structure to the Ti metal substrate. Subsequent heat treatment at 600 degrees C of the NaOH-treated Ti forms an amorphous sodium titanate surface layer with a smooth graded interface structure similar to the Ti metal substrate. These treated Ti metals both form an apatite surface layer with a smooth graded interface structure to the Ti metal substrates in simulated body fluid (SBF). The smooth graded interface structures give a tight bond of the apatite layer to the substrates. Heat treatment at 800 degrees C of the NaOH-treated Ti forms crystalline sodium titanate and a rutile surface layer with a graded interface structure to the Ti metal substrate, which is intervened by a thick titanium oxide. This substrate forms an apatite layer with a graded interface structure to the Ti metal substrate, which is intervened by a thick titanium oxide in SBF. This irregular graded structure gives a less tight bond of the apatite layer to the substrate.

Apatites↗

PubMed2001

Osteoclastic resorption of biomimetic calcium phosphate coatings in vitro.

A new biomimetic method for coating metal implants enables the fast formation of dense and homogeneous calcium phosphate coatings. Titanium alloy (Ti6Al4V) disks were coated with a thin, carbonated, amorphous calcium phosphate (ACP) by immersion in a saturated solution of calcium, phosphate, magnesium, and carbonate. The ACP-coated disks then were processed further by incubation in calcium phosphate solutions to produce either crystalline carbonated apatite (CA) or octacalcium phosphate (OCP). The resorption behavior of these three biomimetic coatings was studied using osteoclast-enriched mouse bone-marrow cell cultures for 7 days. Cell-mediated degradation was observed for both carbonated apatite and octacalcium phosphate coatings. Numerous resorption lacunae characteristic of osteoclastic resorption were found on carbonated apatite after cell culture. The results showed that carbonated apatite coatings are resorbed by osteoclasts in a manner consistent with normal osteoclastic resorption. Osteoclasts also degraded the octacalcium phosphate coatings but not by classical pit formation.

Alloys↗

PubMed1983

Alizarin red S staining as a screening test to detect calcium compounds in synovial fluid.

A simple, rapid screening method using alizarin red S stain and ordinary light microscopy to detect microcrystalline or noncrystalline calcium phosphate salts was used on wet drop preparations of synovial fluids. This proved to be helpful in detecting apatite crystal clumps and small calcium pyrophosphate dihydrate (CPPD) crystals missed by polarized light. The staining was positive in 100% of synovial fluids from patients later proven to have apatite and/or CPPD deposition diseases. Apatite and CPPD crystals were commonly found together in the same fluids. In addition, some synovial fluids from patients with osteoarthritis, renal failure dialysis, rheumatoid arthritis, and gout also exhibited positive staining. The correlation of positive alizarin red S staining with radiologic evidence of osteoarthritis suggests that apatite crystals might be related to articular cartilage degeneration in different rheumatic diseases.

Anthraquinones↗

PubMed1990

Ca,P-rich layer formed on high-strength bioactive glass-ceramic A-W.

Glass-ceramic A-W, containing crystalline apatite and wollastonite in a MgO-CaO-SiO2 glassy matrix shows high bioactivity as well as high mechanical strength, but other ceramics containing the same kinds of crystalline phases in different glassy matrices do not show the same bioactivity. In order to investigate the bone-bonding mechanism of this type of glass-ceramic, surface structural changes of the glass-ceramics after exposure to simulated body fluid were analyzed with various techniques. A solution with ion concentrations which are almost equal to those of the human blood plasma was used as the simulated body fluid, instead of Tris-buffer solution hitherto used. For analyzing the surface structural changes, thin-film x-ray diffraction was used in addition to conventional techniques. It was found that a bioactive glass-ceramic forms a Ca, P-rich layer on its surface in the fluid but nonbioactive ones do not, and that the Ca, P-rich layer consists of carbonate-containing hydroxyapatite of small crystallites and/or defective structure. These findings were common to those of Bioglass-type glasses. So, we conclude that the essential condition for glass and glass-ceramic to bond to bone is the formation of the surface apatite layer in the body environment but it is not essential to contain apatite within the material. Bioactivity of glass and glass-ceramic can be evaluated in vitro by examining the formation of the surface apatite layer in the simulated body fluid described above.

Apatites↗

PubMed2003

Transmission electron microscopic study on setting mechanism of tetracalcium phosphate/dicalcium phosphate anhydrous-based calcium phosphate cement.

This work studied transmission electron microscopy on the setting mechanism of tetracalcium phosphate/dicalcium phosphate anhydrous (TTCP/DCPA)-based calcium phosphate cement. The results suggest the process for early-stage apatite formation as the follows: when TTCP and DCPA powders are mixed in the phosphate-containing solution, the TTCP powder is quickly dissolved because of its higher solubility in the acidic solution. The dissolved calcium and phosphate ions, along with those ions readily in the solution, are then precipitated predominantly on the surface of DCPA particles. Few apatite crystals were observed on the surface of TTCP powder. During the later stages of reaction, the extensive growth of apatite crystals/whiskers, with a calcium/phosphorous ratio very close to that of hydroxyapatite, effectively linked DCPA particles together and also bridged the larger TTCP particles. It is suggested that, when the large TTCP particles are locked in place by the bridging apatite crystals/whiskers, the CPC is set and would not dissolve when immersed in Hanks' solution after 20-40 min of reaction.

Apatites↗

PubMed2003

Formation and growth of clusters in conventional and new kinds of simulated body fluids.

Simulated body fluid (SBF) with ion concentrations approximately equal to those of human blood plasma has been widely used for the in vitro assessment of the bioactivity of artificial materials and for the formation of bonelike apatite on various substrates. Ion concentrations of conventional SBF (c-SBF) are, however, not exactly equal to those of blood plasma, and hence the apatite formed in c-SBF is not the same as bone apatite in its composition and structure. Recently, the present authors prepared new kinds of SBFs (r-SBF, i-SBF, and m-SBF) with ion concentrations nearer to those of blood plasma. The r-SBF and i-SBF have ion concentrations equal to those of blood plasma in total and dissociated amounts, respectively. The m-SBF has ion concentrations equal to those of blood plasma in total amount except for the HCO(-) (3) concentration, which was set to the saturated level with respect to calcite. In the present study, the stabilities of c-SBF, r-SBF, i-SBF and m-SBF were examined in terms of cluster formation in the fluids by means of dynamic light scattering photometry. The c-SBF and m-SBF were found to form only calcium phosphate clusters, whose initial hydrodynamic diameter was approximately 1 nm, and this did not change with storage time at 36.5 degrees C. Besides the calcium phosphate clusters, r-SBF and i-SBF formed calcium carbonate clusters, whose initial hydrodynamic diameters were 10-30 nm, and these increased significantly with storage time. The formation and growth of calcium carbonate clusters in r-SBF and i-SBF can be attributed to their supersaturation with respect to calcite. These indicate that r-SBF and i-SBF lack long-term stability. The m-SBF is recommended for the assessment of bioactivity of artificial materials as well as the formation of bonelike apatite on various substrates from the viewpoint of stability as well as similarity to blood plasma.

Apatites↗

PubMed2006

In vitro bioactivity of akermanite ceramics.

In this study, the bone-like apatite-formation ability of akermanite ceramics (Ca2MgSi2O7) in simulated body fluid (SBF) and the effects of ionic products from akermanite dissolution on osteoblasts and mouse fibroblasts (cell line L929) were investigated. In addition, osteoblast morphology and proliferation on the ceramics were evaluated. The results showed that akermanite ceramics possessed bone-like apatite-formation ability comparable with bioactive wollastonite ceramics (CaSiO3) after 20 days of soaking in SBF and the mechanism of bone-like apatite formation on akermanite ceramics is similar to that of wollastonite ceramics. The Ca, Si, and Mg ions from akermanite dissolution at certain ranges of concentration significantly stimulated osteoblast and L929 cell proliferation. Furthermore, osteoblasts spread well on the surface of akermanite ceramics, and proliferated with increasing the culture time. The results showed that akermanite ceramics possess bone-like apatite-formation ability and can release soluble ionic products to stimulate cell proliferation, which indicated good bioactivity.

Animals↗

PubMed1991

A role for osteocalcin in osteoclast differentiation.

Specific cellular interactions with components of the extracellular matrix can influence cellular differentiation and development of many tissues. The extracellular matrix of bone is composed of organic constituents and a solid phase of calcium and inorganic phosphate (apatite). When implanted subcutaneously in rats, particles of bone matrix (BPs) recruit progenitors that differentiate into multinucleated cells with osteoclastic features. Because BPs deficient in osteocalcin, a bone matrix protein, were less efficient at promoting osteoclast formation than were normal BPs, we directly examined the influence of osteocalcin on osteoclast differentiation. We evaluated tissue responses to particles of synthetic crystalline apatite alone (Ap), having many of the features of native apatite of mature bone, or to apatite prepared with osteocalcin (Ap/OC), bovine serum albumin (Ap/BSA) or rat bone collagen (Ap/Col). Twelve days after subcutaneous implantation in normal rats, Ap, Ap/BSA, and Ap/Col particles generated a mild foreign body reaction with multinucleated cells in direct contact with the particles; these cells were negative for tartrate-resistant acid phosphatase (TRAP) activity and lacked ruffled borders. In contrast, Ap particles containing approximately 0.1% osteocalcin were partially resorbed and they generated more multinucleated cells that were TRAP-positive, were immunoreactive with an antibody against tartrate-resistant purple acid phosphatase, and displayed ultrastructural features of active osteoclasts including ruffled borders and clear zones. These data support the hypothesis that osteocalcin may function as a matrix signal in the recruitment and differentiation of bone-resorbing cells.

Acid Phosphatase↗