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PubMed2000

Formation of bioactive functionally graded structure on Ti-6Al-4V alloy by chemical surface treatment.

An Al- and V-free sodium titanate hydrogel layer with a graded structure where the sodium titanate gradually decreases toward the interior, was formed on the surface of Ti-6Al-4V alloy, when the alloy was exposed to 5M NaOH solution at 60 degrees C for 24 h. This gel layer was transformed into an amorphous sodium titanate layer without giving considerable change in the graded structure, except a little increase in the depth of the oxygen distribution by a heat treatment at 600 degrees C for 1 h. The sodium titanate layer formed Ti-OH groups on its surface by exchanging its Na+ ion with H3O+ ion in simulated body fluid when soaked in the fluid, and thus formed Ti-OH groups induced the apatite nucleation. The apatite layer also formed a graded structure toward the substrate. The strong bond of the apatite layer to the substrate was attributed to this graded structure.

Journal Article↗

PubMed2001

Surface reaction of stoichiometric and calcium-deficient hydroxyapatite in simulated body fluid.

In the present study, the immersion behavior of two kinds of sintered HA with different Ca/P ratios in two different extracellular simulated solutions (Tris buffer and Hank's solutions) was investigated and compared. Results indicated that an as-received Ca-deficient HA (FHA) had a lower Ca/P ratio, larger linear shrinkage and higher density than a stoichiometric HA (MHA). When FHA powder was calcined at 900 degrees C, its Ca-deficient apatite structure was unstable and a significant amount of beta-TCP phase was formed. When heated to 1250 degrees C in air, the highly crystalline apatite structure of MHA was still stable without any noticeable decomposition. The FTIR spectra indicated that both immersed MHA and FHA in Hank's solution were gradually covered with a layer of precipitated apatite during immersion. When immersed in Tris buffer solution, neither HA showed significant changes in their FTIR spectra. SEM observation indicated that the precipitation rate on immersed FHA surface was much higher than that on MHA surface when immersed in Hank's solution. The weight loss and pH data confirmed the higher dissolution rate of FHA than MHA in Hank's solution.

Journal Article↗

PubMed2002

Effects of sodium hypochlorite solution on root dentine composition.

Sodium hypochlorite (NaOCl) solution,<or=5% w/v available chlorine (abbreviated subsequently to %), is widely used as an irrigant in root canal treatment of teeth, so its effects on dentine are of clinical importance. The effects of approximately 0.5%, 3% and 5% NaOCl solution on the composition of root dentine were studied at ambient temperature. For dentine powder treated for 30 min, depletion of the organic phase was confirmed by infrared spectroscopy. Apatite lattice parameters showed no significant change, but NaCl was also detected by X-ray powder diffraction. The low solubility of apatite mineral in the NaOCl solutions was demonstrated by the constant weight of bulk enamel specimens immersed for seven days. The stability of the mineral phase was confirmed by scanning microradiography (SMR), an X-ray attenuation method employing photon counting. Repeated SMR measurements of the local mineral content of bulk samples of root dentine and a synthetic hydroxyapatite aggregate during exposure to pumped NaOCl solutions for 100 h showed no mineral loss. As predicted from apatite chemistry, reaction of NaOCl with the mineral phase can be excluded as a primary factor in changes in mechanical properties of treated dentine. Effects of retention of NaCl on endodontic sealants requires further investigation.

Journal Article↗

PubMed2002

Effect of hydrolysis on the phase evolution of water-based sol-gel hydroxyapatite and its application to bioactive coatings.

In a previous report, we demonstrated a successful synthesis of crystalline hydroxyapatite (HA) through the use of a water-based sol-gel process. It was shown that the apatite can be obtained at temperatures generally below 400 degrees C, providing a great advantage for practical bioactive coating purposes. The influence of hydrolysis of phosphorus sol solution on the phase evolution of the resulting HA is the focus of this investigation. Experimental results show that, in the absence of acid catalyst, a long-term hydrolysis, i.e. >4 h, is required for better evolution of apatitic phase. Such a phase evolution is mainly attributed to an increased concentration of apatitic phase, rather than improved crystallinity in the calcined gels. With the aid of acid catalyst, we found that a well-crystalline HA can be synthesized over a time period shorter by 2-3 orders of magnitude than those without catalyst, i.e. a few minutes. In almost all cases, a small amount of tricalcium phosphate (TCP) was detected, which may be explainable by the formation of oligomeric derivatives of the phosphorus sol during synthesis, where calcium phosphate derivatives with lower Ca/P ratio than stoichiometry can be developed. By selecting an optimal sol as a dipping source, highly-porous dental root specimens were coated and a thin, dense, adhesive (upon finger-nail scratching test) coating was achieved after calcinations at 375 degrees C. An in vitro test also shows a bioactive character of the coating.

Journal Article↗

PubMed2002

Bioactivity and mechanical properties of polydimethylsiloxane (PDMS)-CaO-SiO2 hybrids with different calcium contents.

Polydimethylsiloxane (PDMS)-CaO-SiO(2) hybrids with starting compositions containing PDMS/(Si(OC(2)H(5))(4)+PDMS) weight ratio=0.30, H(2)O/Si(OC(2)H(5))(4) molar ratio=2, and Ca(NO(3))(2)/Si(OC(2)H(5))(4) molar ratios=0-0.2, were prepared by the sol-gel method. The apatite-forming ability of the hybrids increased with increasing calcium content in the Ca(NO(3))(2)/Si(OC(2)H(5))(4) molar ratio range 0-0.1. The hybrids with a Ca(NO(3))(2)/Si(OC(2)H(5))(4) molar ratio range 0.1-0.2 formed apatite on their surfaces in a simulated body fluid (SBF) within 12 h. The hybrid with a Ca(NO(3))(2)/Si(OC(2)H(5))(4) molar ratio of 0.10 showed an excellent apatite-forming ability in SBF with a low release of silicon into SBF. It also showed mechanical properties analogous to those of human cancellous bones. This hybrid is expected to be useful as a new type of bioactive material.

Journal Article↗

PubMed2003

Bioactivity of metallic biomaterials with anatase layers deposited in acidic titanium tetrafluoride solution.

A simple and versatile treatment was developed to provide various metallic biomaterials such as Ti, NiTi, Ta and SUS 316L stainless steel with in vitro bioactivity or ability to deposit carbonate-incorporated apatite in a simulated body fluid (Kokubo solution). A well-crystallized anatase layer deposited on the metallic biomaterials surfaces after soaking them at 60 degrees C for 24 h in an aqueous solution of titanium tetrafluoride (40 mM) whose pH was adjusted to 1.9 with HCl. The as-coated anatase layers did not deposit apatite. When heated at 300 degrees C they were so bioactive as to deposit apatite within 5 day(s) in the Kokubo solution. The trace amount of fluorine weakly bound in the as-coated anatase layers was suggested to be one of the factors that suppressed the bioactivity.

Journal Article↗

PubMed2003

Magnesium whitlockite, a calcium phosphate crystal of special interest in pathology.

Whitlockite (in fact magnesium whitlockite) is a calcium orthophosphate crystal in which, in biological conditions, magnesium is partly substituted for calcium. Identified in X-ray or electron diffraction patterns, it occurs in physiological or pathological conditions at extra or intratissular sites, mainly in tissues of non-epithelial origin. In a range of pathological calcifications investigated by X-ray diffraction, we noted that whitlockite appeared to be frequently associated with apatite, particularly in "dystrophic calcifications" of tuberculous origin. These personal observations could be correlated with documented data in oral pathology (dental calculus, salivary stones, and dental caries). Whitlockite deposits have also been reported in non-infectious conditions, such as in aortic media, cartilage, and bone tissue. Whereas the formation of both apatite and magnesium whitlockite appears to be caused by the binding of their constituting ions with proteolipids, magnesium inhibits apatite originating from amorphous calcium phosphate to the benefit of whitlockite formation. Possibly, the development of magnesium whitlockite may provide an interesting marker for magnesium metabolism. Further studies linking histology to crystallography might relate the crystal to issues, such as tuberculous calcifications or diseases of bone tissue, and might be useful for potential diagnostic orientation.

Calcinosis↗

PubMed2003

Bladder stones following SCI in the Sprague-Dawley rat.

OBJECTIVE: To develop a spinal cord injury (SCI) animal model for the study of bladder stones and compare this model with a non-SCI animal model. METHODS: Small pieces of catheters were implanted into the bladders of Sprague-Dawley rats as a nidus for bladder stone formation. Three weeks later, the rats underwent an SCI surgery (SCI transection or sham SCI). Control rats had SCI surgery, but no catheters were implanted into their bladders. MAIN OUTCOME MEASURES: Bladder stone number, weight, and composition were determined in two groups of SCI and sham SCI animals: Group A (recent spinal shock: 2 weeks post-SCI/sham SCI surgery) and Group B (out of spinal shock: 3 weeks to 3 months post-SCI/sham SCI surgery). A chi2 test was used to compare the incidence of bladder stones in SCI vs sham SCI animals. A Student t test was used to compare the weight of bladder stones in the 2 groups. RESULTS: Group A (recent spinal shock): Of the 20 SCI rats, 8 (40%) had stones. None of the sham SCI rats with implanted catheters (n = 5) had stones (0%). Group B (out of spinal shock): All 6 of the SCI rats with implanted catheters had stones (100%). Of the 10 sham SCI animals with implanted catheters, 3 (30%) had stones. Stones were more common in the SCI rats than in the sham SCI rats (chi2(1) = 4.9, P < 0.05). The mean weight of the bladder stones in SCI rats (42.2 +/- 16.3 mg) was greater than that in sham SCI rats (5.4 +/- 1.5 mg) (P < 0.01). Group C (controls: SCI surgery, but no catheter implanted): At 3 weeks post-SCI, control rats had no stones (n = 7); control rats at 3 months post-SCI also had no stones (n = 9). Stone composition in the 3 sham SCI animals was calcium apatite (90%) and calcium oxylate (10%). In the 14 SCI rats, 10 had struvite stones (100%), 1 had struvite (70%) and carbonate apatite (30%) stones, 1 had brushite (100)% stones, and 2 had carbonate apatite (> 90%) stones. CONCLUSION: Bladder stones occurred earlier and more frequently and attained a larger size in SCI rats with catheters compared with sham SCI rats with catheters. There were no stones in SCI rats without catheter implants, even at 3-month follow-up. The bladder stone composition in SCI rats was similar to that in humans with SCI. The Sprague-Dawley rat model appears to be an excellent animal model for the study of bladder stones following SCI.

Acute Disease↗

PubMed2000

Coherent scattering and matrix correction in bone-lead measurements.

The technique of K shell x-ray fluorescence of lead in bone has been used in many studies of the health effects of lead. This paper addresses one aspect of the technique, namely the coherent conversion factor (CCF) which converts between the matrix of the calibration standards and those of human bone. The CCF is conventionally considered a constant but is a function of scattering angle. energy and the elemental composition of the matrices. The aims of this study were to quantify the effect on the CCF of several assumptions which may not have been tested adequately and to compare the CCFs for plaster of Paris (the present matrix of calibration standards) and a synthetic apatite matrix. The CCF was calculated, using relativistic form factors, for published compositions of bone, both assumed and assessed compositions of plaster, and the synthetic apatite. The main findings of the study were, first, that impurities in plaster, lead in the plaster or bone matrices, coherent scatter from non-bone tissues and the individual subject's measurement geometry are all minor or negligible effects; and, second, that the synthetic apatite matrix is more representative of bone mineral than is plaster of Paris.

Adult↗

PubMed1992

Proteoglycan inhibition of calcium phosphate precipitation in liposomal suspensions.

The major proteoglycan in cartilage (aggrecan) is a complex macromolecule with numerous chondroitin sulphate, keratan sulphate, and oligosaccharide substituents. It has been proposed that this macromolecule has an important role in regulating mineralization in this tissue, a process which is initiated by the deposition of apatite in matrix vesicles. We have used a liposome-centred endogenous precipitation method as a model for matrix vesicle mineralization to study the effect of the rat chondrosarcoma aggrecan and its chondroitin sulphate and core protein components on apatite formation from solution. Precipitation was initiated by encapsulating buffered (pH 7.4) 50 mmol/l KH2PO4 solutions in the aqueous centres of 7:2:1 phosphatidylcholine:dicetylphosphate:cholesterol liposomes, adding 2.25-2.65 mmol/l Ca2+ and 1.5 mmol/l total inorganic phosphate (PO4) to the suspending medium (pH 7.4, 22 degrees C), then making the intervening lipid membranes permeable to the Ca2+ ions with the calcium ionophore X-537A. Aggrecan (0.5%) in the suspending medium had no effect on intraliposomal precipitation, but severely reduced (approximately 70% reduction at 24 h) its subsequent spread into the medium. The chondroitin sulphate and core protein were similarly inhibitory. The degree to which aggrecan and its constituent parts inhibited precipitation correlated with their capacity to bind Ca2+ ions. These findings suggest that functional groups in aggrecan blocked apatite growth by linking via Ca2+ bridges to growth sites on the crystal surfaces. Similar Ca-mediated interactions may well have a critical regulatory role in cartilage mineralization.

Aggrecans↗

PubMed2006

The ruffled border and attachment regions of the apposing membrane of resorbing osteoclasts as visualized from the cytoplasmic face of the membrane.

The aim of our present research was to visualize how the plasma membrane is modified and how the cytoskeleton interacts with the attachment and ruffled border regions of resorbing osteoclasts. In order to view the surface modification of membranes and associated cytoskeleton, we employed the method of cell-shearing combined with quick-freezing and rotary replication to expose and replicate an extensive area of the cytoplasmic face of the surface membrane of osteoclasts in contact with synthetic apatite as a substratum. The membrane apposed to the apatite was composed of three different domains: the attachment zone, ruffled border and the remainder. In the attachment zone, a highly organized actin filament network formed dot-shaped, F-actin rich adhesion sites, so-called podosomes, and the actin ring. The cytoskeletal filament of podosomes and actin ring appeared to be in direct contact with the cytoplasmic surface of the underlying membrane. Within the actin ring, individually recognizable podosomes were well preserved, which indicates that the actin ring was probably derived from the fusion of podosomes. After shearing at the ruffled border region, the ruffled border projections and membrane regions among the projections were left behind. These ruffled border projections contained the cytoskeletal network. These actin networks also appeared to be in direct contact with the inner side of the ruffled border membrane or in contact with it via membrane-associated particles. At the basal portion of the ruffled border, numerous clathrin-coated patches or pits were well preserved. Deeper clathrin-coated pits and vesicles were also found, which indicates an active site for receptor-mediated endocytotic events. Clathrin sheets were also observed in the cell periphery outside of the actin ring. This type of clathrin sheets adhered to the apatite substrate, but was not anchored to the actin microfilaments. Our study thus clearly visualized the interaction between the cytoskeletal filaments and the underlying membrane at the ruffled border, attachment zone and podosome in osteoclasts cultured on apatitepellets.

Animals↗

PubMed2001

Nanobacteria: controversial pathogens in nephrolithiasis and polycystic kidney disease.

Nanobacteria are unconventional agents 100-fold smaller than common bacteria that can replicate apatite-forming units. Nanobacteria are powerful mediators of biogenic apatite nucleation (crystal form of calcium phosphate) and crystal growth under conditions simulating blood and urine. Apatite is found in the central nidus of most kidney stones and in mineral plaques (Randall's plaques) in renal papilla. The direct injection of nanobacteria into rat kidneys resulted in stone formation in the nanobacteria-injected kidney during one month follow-up, but not in the control kidney injected with vehicle. After intravenous administration in rats and rabbits, nanobacteria are rapidly excreted from the blood into the urine, as a major elimination route, and damage renal collecting tubuli. Nanobacteria are cytotoxic to fibroblasts in vitro. Human kidney cyst fluids contain nanobacteria. Nanobacteria thus appear to be potential provocateurs and initiators of kidney stones, tubular damage, and kidney cyst formation. It is hypothesized that nanobacteria are the initial nidi on which kidney stone is built up, at a rate dependent on the supersaturation status of the urine. Those individuals having both nanobacteria and diminished defences against stone formation (i.e. genetic factors, diet and drinking habits) could be at high risk. Kidney cyst formation is hypothesized to involve nanobacteria-induced tubular damage and defective tissue regeneration yielding cyst formation, the extent of which is dependent on genetic vulnerability.

Gram-Negative Bacteria↗

PubMed1981

The intact surface layer in natural enamel caries and acid-dissolved hydroxyapatite pellets. An X-ray diffraction study.

The crystallographic features of various histological sites found in enamel carious lesions were studied by means of X-ray microbeam diffraction. The most interesting finding was the crystallinity of apatite crystals in the intact surface layer covering the demineralized lesions was higher than that of the crystals in the subsurface lesions or unaffected areas. Acid-dissolution experiments using synthetic hydroxyapatite pellets showed that a well mineralized layer was produced on the pellet surface under the condition that no Ca and PO4 ions were added to the initial acidic solution. Furthermore, X-ray diffraction analysis revealed that half-line breadth values of 004, 222, and 310 reflections of apatite pellets decreased, and their integrated peak intensities increased with dissolution time. These findings are in agreement with the results obtained in the study of enamel carious lesions, leading to the conclusion that the intact surface layer is formed by deposition of the mineral ions from dissolving subsurface lesions, and that this process is accompanied by the improvement in crystallinity of apatite crystals, possibly due to growth of the crystals.

Crystallography↗

PubMed1977

Interaction of hydroxyapatite and protein-coated hydroxyapatite with Streptococcus mutans and Streptococcus sanguis.

The present study showed that S. mutans and S. sanguis behaved like negatively-charged particles in their interaction with hydroxyapatite in vitro. Phosphate in the system inhibited bacterial uptake by apatite, whereas calcium increased the uptake. A layer of acidic protein inhibited the uptake of bacteria by hydroxyapatite. The opposite was true when a basic protein was first adsorbed to the apatite. A saliva film on the apatite decreased the uptake of bacteria, supporting the view that acidic proteins are selectively adsorbed by hydroxyapatite from saliva. The results indicate clearly that electrostatic forces may be involved in bacterial interaction with tooth surface.

Adsorption↗

PubMedDate not supplied

The effect of fluoride on the developing tooth.

This review aims to outline the effects of fluoride on the biological processes involved in the formation of tooth tissues, particularly dental enamel. Attention has been focused on mechanisms which, if compromised, could give rise to dental fluorosis. The literature is extensive and often confusing but a much clearer picture is emerging based on recent more detailed knowledge of odontogenesis. Opacity, characteristic of fluorotic enamel, results from incomplete apatite crystal growth. How this occurs is suggested by other changes brought about by fluoride. Matrix proteins, associated with the mineral phase, normally degraded and removed to permit final crystal growth, are to some extent retained in fluorotic tissue. Fluoride and magnesium concentrations increase while carbonate is reduced. Crystal surface morphology at the nano-scale is altered and functional ameloblast morphology at the maturation stage also changes. Fluoride incorporation into enamel apatite produces more stable crystals. Local supersaturation levels with regard to the fluoridated mineral will also be elevated facilitating crystal growth. Such changes in crystal chemistry and morphology, involving stronger ionic and hydrogen bonds, also lead to greater binding of modulating matrix proteins and proteolytic enzymes. This results in reduced degradation and enhanced retention of protein components in mature tissue. This is most likely responsible for porous fluorotic tissue, since matrix protein removal is necessary for unimpaired crystal growth. To resolve the outstanding problems of the role of cell changes and the precise reasons for protein retention more detailed studies will be required of alterations to cell function, effect on specific protein species and the nano-chemistry of the apatite crystal surfaces.

Amelogenesis↗

PubMed1989

Kinetics of acquisition and loss of calcium fluoride by enamel in vivo.

Two in vivo experiments were performed, concerning (1) the kinetics of the acquisition of calcium fluoride on enamel during daily rinses with a solution of 0.023% F as sodium fluoride, and (2) the loss of calcium fluoride from enamel slabs which had been topically treated with a neutral solution containing 0.9% F as sodium fluoride. Enamel slabs were carried in the mouth by 6 volunteers for 8 days in both experiments. Sound and etched enamel were included. (1) During mouthrinses moderate amounts of fluoride were acquired by sound enamel, and more as calcium fluoride than as fluoridated apatite, whereas on etched enamel, more fluoride was deposited as fluoridated apatite. On etched enamel there was also a tendency that the deposition of calcium fluoride levelled out whereas the incorporation of firmly bound fluoride continued. This may indicate that calcium fluoride was transformed into fluoridated apatite, probably through remineralization during pH cycling in plaque covering the etched enamel. (2) After single topical application, it was found that etched enamel initially took up more calcium fluoride than sound enamel, but also lost more during the 1st day of in vivo exposure. The loss of calcium fluoride was arrested after 1-2 days, on sound enamel at 70% and on etched enamel at 40% of the original level. It is suggested that the increased amounts of firmly incorporated fluoride in enamel originated from calcium fluoride on enamel, and that calcium fluoride is an important and clinically significant source of fluoride ions on enamel.

Acid Etching, Dental↗

PubMed1993

Notes on the dissolution of human dental enamel in dilute acid solutions at high solid/solution ratio.

The aim of the present study was to elucidate the nature of the relationship between enamel apatite and lesion fluid during demineralization. Powdered enamel in samples of 1.0 g was suspended in 3 ml of 10, 30, 50, or 70 mmol/l HCl under gentle agitation for up to 24 h at 20 degrees C. After 20 min and 24 h, pH and the concentrations of calcium and phosphate were determined and the degree of saturation with respect to various calcium phosphates calculated. The experiments were replicated 15 times using the same enamel samples. Twenty minutes after the start of dissolution, both pH and concentrations of calcium and phosphate had increased, and the solution became supersaturated with respect to hydroxyapatite, and in some runs also with respect to brushite. During the subsequent 23 h and 40 min, pH continued to increase, despite the supersaturation with respect to apatite, whilst the concentrations of calcium and phosphate decreased due to formation of apatite and, occasionally, brushite mineral. The data indicated that release of carbonate from enamel and its conversion to H2CO3 caused the increase in pH and thus, played a major role in the dissolution-reprecipitation process.

Calcium↗

PubMed1985

Ultrastructural study of epithelial cell attachment to implant materials.

Attachment of gingival tissues to the protruding post of an endosseous dental implant is of great importance for the prognosis of its clinical success. Little is known about the requirements an implant material must meet to secure a durable permucosal seal. The objective of this study, therefore, was to gain insight into the morphology of epithelial cell-implant interfaces for a number of well-known or potential implant materials. Guinea pig epithelial cells were cultured on gold, titanium, carbon, hydroxylapatite, carbonate apatite, and modified polystyrene substrates. The metallic and carbon substrates were obtained by vapor-phase deposition of thin films on polystyrene carriers. This technique allowed for the preparation of ultra-thin sections for transmission electron microscopy containing substrate as well as the cells adhering to it. The cultures on apatite were decalcified prior to sectioning. The results revealed tht as attachment structures, focal contacts, extracellular matrix contacts, and hemidesmosome-like contracts could be distinguished. Hemidesmosome-like contacts were only observed on apatite and polystyrene and not on the metallic or carbon surfaces. The results of this study suggest the existence of some, as yet unknown, property of the substrate that determines the nature and the structure of the contact site with epithelial cells.

Animals↗