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The structure of a complex, disordered type A–B carbonate apatite (CAp) of approximate composition Ca10(PO4)6-y(CO3)x+(3/2)y(OH)2-2x, x–0.7, y–0.6, synthesized at 3 GPa, 1400°C has been determined using single-crystal X-ray diffraction and FTIR spectroscopy at room temperature and pressure. Crystal data are: hexagonal, space group P63/m, Z=1; a=9.5143(3), c=6.8821(2) Å, V=539.5 Å3, and R=0.025. There are three structural locations for the carbonate ion. The channel carbonate is mainly in the closed vertical configuration of the P&3macr; structure, with two of its oxygen atoms close to the c-axis (A1 carbonate; IR bands at 1541 and 1449 cm-1), but subordinate amounts are also located in an open vertical configuration (A2 carbonate; IR bands at 1563 and 1506 cm-1). The type B carbonate ion is located close to the sloping faces of the PO4 tetrahedron (IR bands at 1474 and 1406 cm-1), confirming earlier inferences from polarized IR spectra. [Copyright &y& Elsevier]

The aim of this study was to detect, isolate and characterize the nanobacteria from human renal stones from a north Indian population, and to determine their role in biomineralization. Renal stones retrieved from the kidneys of 65 patients were processed and subjected to mammalian cell culture conditions. The isolated bacteria were examined using scanning (SEM) and transmission electron microscopy (TEM). They were characterized for the presence of DNA, proteins and antigenicity. The role of these bacteria in biomineralization was studied by using the 14C-oxalate based calcium oxalate monohydrate (COM) crystallization assay. We observed the presence of apatite forming, ultrafilterable gram negative, coccoid microorganisms in 62% of the renal stones. SEM studies revealed 60–200 nm sized organisms with a distinct cell wall and a capsule. TEM images showed needle like apatite structures both within and surrounding them. They were heat sensitive, showed antibiotic resistance and accelerated COM crystallization. A potent signal corresponding to the presence of DNA was observed in demineralized nanobacterial cells by flow cytometry. The protein profile showed the presence of several peptide bands of which those of 18 kDa and 39kDa were prominent. Apatite forming nanosized bacteria are present in human renal stones and may play a role in the pathophysiology of renal stone formation by facilitating crystallization and biomineralization. However, further studies are required to establish the exact mechanism by which nanobacteria are involved in the causation of renal stones. [ABSTRACT FROM AUTHOR]

X-ray and time of flight neutron diffraction data, FTIR and MAS-NMR spectra, and ICP-AES and carbonate analyses have been collected from a sodium-containing carbonate apatite (CO3 content 12.5(7) wt%). A structural model based on Holly Springs hydroxyapatite without CO32− ions showed an apparent reduction in the PO4 tetrahedral volume which is ascribed to CO32− replacing PO43− ions in the lattice. Four structural models from the literature with the CO32− ion explicitly modelled were fitted to the neutron diffraction data by the Rietveld method.The best fit was obtained with the CO32− ion in disorder between the mirror symmetry related faces of a vacant PO43− site and with the normal to the plane of the CO32− ion at ∼30° to the c-axis. This angle is consistent with results from previous polarised IR measurements on single crystals of francolite (a fluorocarbonate apatite) and human dental enamel. Further refinement of the model revealed a hitherto unknown atom site close to the unit cell origin, (possibly a water molecule). The refined hexagonal unit cell parameters from the neutron diffraction data were a=9.3446(3) A˚ and c=6.9199(4) A˚. [Copyright &y& Elsevier]

Electrolytically deposited carbonate apatite coating demonstrates higher strength but weaker support for bone marrow stromal cell attachment than do biomimetically deposited coatings. It is hypothesized that the incorporation of chitosan will increase the biocompatibility of electrolytic coating while maintaining its original strength. To verify this hypothesis, we formed a hybrid calcium phosphate/chitosan coating through electro-deposition. We found that the incorporation of chitosan influenced calcium phosphate formation and crystallization. Moreover, coating thickness and surface roughness decreased with increasing chitosan concentration. Hybrid coating exhibited an increased dissolution rate in both acidic and neutral simulated physiologic solution, whereas no significant difference on adhesive strength was found between the hybrid and original coatings (P > 0.05). Most importantly, the calcium phosphate/chitosan coating proved to be a more favorable surface for goat bone marrow stromal cell attachment than an unincorporated coating (P < 0.01). Considering its economic and simple production, a hybrid calcium phosphate/chitosan coating is thought to be an attractive candidate for future applications. [ABSTRACT FROM AUTHOR]

The determination of the components of the sialoliths is important both from the point of view of chances for a successful medical treatment of the patients and because the prevention of further re-occurrence of sialolithiasis depends upon the knowledge of the nature of the constituents of the concrements. Despite the fact that infrared spectroscopy is widely used for the determination of the composition of sialoliths, urinary calculi and bladder stones, we found no data for any chemometric method developed for such purposes. Here, a method is presented for quantitative determination of the content of salivary calculi composed of albumin and carbonate apatite (one of the most often found constituents in the analyzed calculi from the patients from Macedonia) using artificial neural networks (ANN). The results were checked on real samples using the standard addition method. The precision of the method was estimated using the relative standard deviation, which shows that it is suitable for routine analysis. [Copyright &y& Elsevier]

Biomimetically deposited octacalcium phosphate (OCP) and carbonate apatite (BCA) as well as electrolytically deposited carbonate apatite (ECA) were considered as promising alternatives to conventional plasma spraying hydroxyapatite. This study compared their physicochemical characteristics and cell attachment behavior. The physicochemical characteristics included scanning electron microscopy observation, X-ray diffraction analysis, Fourier transform infrared spectroscopy analysis, surface roughness, coating thickness, dissolution test and scratch test. Cell attachment tests included morphology observation with stereomicroscopy and scanning electron microscopy as well as cell number count with DNA content assay. The OCP coating had 100% crystallinity and was about 40 μm thick, composed of large plate-like crystals of 30 μm, with the lowest surface roughness (Ra=2.33 μm). The BCA coating had 60% crystallinity and was approximately 30 μm in thickness, composed of small crystals of 1–2 μm in size, with the highest surface roughness (Ra=4.83 μm). The ECA coating had intermediate characteristics, with 78% crystallinity, 45 μm thickness, crystals of 5–6 μm and an average roughness of 3.87 μm. All coatings could be seen by eyes dissolving quickly and completely into acidic simulated body fluid (simulated physiological solutions—SPS, pH 3.0) but slowly and incompletely into neutral SPS (pH 7.3). It was suggested that the main factor determining coating dissolution in acidic SPS was the solubility isotherm, while some other factors including crystallinity and crystal size joined to determine coating dissolution in neutral SPS. In regard to adhesive strength, results of scratch test showed the critical load at the first crack of coating (Lc1) was tightly related to crystal size as well as their arrangement, while the critical load at the total delamination of coating (Lc2) was also related to the coating thickness. The ECA coating had the highest values. Owing to higher dissolution rate and globular appearance, BCA coating demonstrated the best goat bone marrow stromal cells attachment at 1 day or 3 days, followed by OCP and ECA coating. [Copyright &y& Elsevier]

The aim of the present study was to study the mineral formation on a phosphorylated dental bonding agent using a mineralization inductive solution. Clearfil Photobond, which contained phosphate monomer, was cured by photo-irradiation and heat treated, and was then immersed in Hanks’ balanced salt solution (HBSS) with pH = 7·4 for 1, 3, 5, 7, 14, and 28 days at 37 °C. The white substances were deposited on the phosphorylated polymer, i.e. cured Photobond disk, after the immersion in HBSS. The white substances become visible after 3 days immersion. After 7 days immersion, surface of the phosphorylated polymer disk was almost covered with white substance layers. The measurement of white substances by means of X-ray diffraction, Fourier-transform infrared and electron probe microanalysis revealed that their main component was carbonate-containing hydroxyapatite. Scanning electron microscopy pictures showed that a large number of globules of hydroxyapatite were fused together, and that each globule was composed of a group of numerous thin-film form flakes uniting and/or clustering together. The results obtained in this study concluded that the presence of phosphonic acid and phosphate group of phosphorylated dental bonding agent enhanced the nucleation and growth of hydroxyapatite crystals on its surface. [ABSTRACT FROM AUTHOR]

More than half of the analyzed calculi from patients from Macedonia are composed of whewellite, weddellite and carbonate apatite (as single components or in binary or ternary mixtures). In order to develop a simple and satisfactorily reliable method for quantitative analysis of urinary calculi, the possibility was explored to employ artificial neural networks (ANNs) as a tool for such a purpose. By changing the number of input and hidden neurons, a search was made for the three-layered feed-forward ANN which would give the best performance. The root-mean-square errors (RMSE) for the test samples are: 0.035 for whewellite, 0.064 for weddellite and 0.078 for carbonate apatite. The accuracy of the method was checked using standard-addition method on real samples. The discrepancies between calculated and predicted mass fraction of constituents were in the range acceptable for use of the proposed method in clinical laboratories. [Copyright &y& Elsevier]

A new space group and structure are reported for type A carbonate apatite (CAp) of composition Ca10(PO4)6[(CO3)x(OH)2−2x], x&ges;0.5, synthesized at 2 GPa, 1400–1500°C. Crystal data are trigonal, space group P3¯, Z=1; x&ap;0.75, a=9.5211(3), c=6.8725(2) A˚, V=539.5 A˚3, R=0.030, and Dx=3.152 g/cm3; x&ap;0.50, a=9.4917(2), c=6.8758(3) A˚, V=536.5 A˚3, R=0.030, and Dx=3.150 g/cm3. In the P3¯ structure, the type A carbonate ion is ordered along the apatite channel at z=0.5. Two of the oxygen atoms of the carbonate ion lie close to the c-axis, with the plane of the ion canted ∼12°. FTIR spectra are similar to that of type A carbonate hydroxylapatite. The present structure may be an appropriate model for the orientation of the type A carbonate ion in bone and enamel. [Copyright &y& Elsevier]

Infection stones make up approximately 15% of urinary stone diseases and are thus an important group. These stones are composed of struvite and/or carbonate apatite. The basic precondition for the formation of infection stones is a urease positive urinary tract infection. Urease is necessary to split urea to ammonia and CO2. As a result, ammonia ions can form and at the same time alkaline urine develops, both being preconditions for the formation of struvite and carbonate apatite crystals. When these crystals deposit themselves infection stones form. If these infections are not treated and the stones are not removed, the kidney will be damaged. For stone removal modern methods are available, e.g. ESWL and/or instrumental urinary stone removal. Here especially less invasive methods are preferable. Any treatment must be adjusted to the patient individually. Patients should be examined frequently for recurrent urinary tract infections and stone recurrences and, newly arising infections must be resolutely treated. Good therapy and prophylaxis are possible with present-day treatment modalities. [Copyright &y& Elsevier]

Crystalline carbonate- and sodium-and-carbonate-substituted hydroxyapatite (CO3HAp and NaCO3HAp) powders were prepared at room temperature via a heterogeneous reaction between Ca(OH)2/CaCO3/Na2CO3 and (NH4)2HPO4 aqueous solution using the mechanochemical–hydrothermal route. X-ray diffraction, infrared spectroscopy, thermogravimetry, and chemical analysis were performed. Room temperature products were phase-pure CO3HAp and NaCO3HAp containing 0.8–12 wt% of carbonate ions in the lattice. Dynamic light scattering revealed that the median agglomerate size of the room temperature CO3HAp and NaCO3HAp powders was in the range of 0.35–1.6 μm with a specific surface area between 82 and 121 m2/g. Scanning and transmission electron microscopy confirmed that the carbonated HAp powders consisted of mostly submicron aggregates of nanosized, &ap;20 nm crystals. The synthesized carbonated apatite powders exhibit chemical compositions and crystallinities similar to those of mineral constituents of hard tissues and therefore are promising for fabrication of bone-resembling implants. [Copyright &y& Elsevier]

Abstract: Bone inducing agent (BIA) isolated from Saos-2 human osteosarcoma cells was added to an artificial bone substitute composed of 980°C-heated carbonate apatite (CAp) and Type I atelocollagen (AtCol) extracted from bovine tail skins (88/12 in wt/wt %), and a CAp-AtCol-BIA substitute was prepared as an osteoinductive bone substitute. Rat calvaria osteoblasts treated by the isolated BIA demonstrated significantly increased alkaline phosphatase (ALP) activity after 3 days (p < 0.05). In vitro cell attachment and proliferation and ALP activity were investigated for the bone substitute combined with BIA. Osteoblasts cultured onto the surface of the CAp-AtCol-BIA substitute demonstrated remarkable morphological changes such as radial spreading, flattening, and projecting filopodia after 5 days. In comparison with the substitute without BIA, osteoblasts grown in the BIA-combined CAp-AtCol substitute expressed significantly increased proliferation and ALP activity, respectively (p < 0.05). Both the substitutes combined with and without BIA were implanted into artificial defects created in rabbit radii. After 4 weeks, the CAp-AtCol-BIA substitute implanted lesion was completely replaced by regenerated host bone in radiological observation whereas the substitute without BIA was partially resorbed. No histologic abnormalities appeared in the substitute either with or without BIA. [ABSTRACT FROM AUTHOR]

Carbonate apatite (CO 3 Ap) is an inorganic component of bone and replaces by natural bone after implantation into the bone defect. Because of this unique characteristic, CO 3 Ap granules have been used in the dental field. However, washing out of granules from the bone defect area is an issue. The aim of this study was to set CO 3 Ap granules by mixing CO 3 Ap granules with acidic phosphate solutions and evaluate the influence of the pH and ion components of the solutions. When Na + was the counter ion, the amount of precipitated dicalcium phosphate dihydrate (DCPD) was small and the setting ability disappeared with increasing pH of the solutions. Alternatively, when the counter ion was Ca 2+ , the amount of precipitated DCPD was high and the setting ability was observed even at high pH. These results suggest the presence of Ca 2+ in the acidic phosphate solution is a key for fabricating CO 3 Ap granular cement.

The reconstruction of critical-sized segmental bone defects is a key challenge in orthopedics because of its intractability despite technological advancements. To overcome this challenge, scaffolds that promote rapid bone ingrowth and subsequent bone replacement are necessary. In this study, we fabricated three types of carbonate apatite honeycomb (HC) scaffolds with uniaxial channels bridging the stumps of a host bone. These HC scaffolds possessed different channel and micropore volumes. The HC scaffolds were implanted into the defects of rabbit ulnar shafts to evaluate the effects of channels and micropores on bone reconstruction. Four weeks postoperatively, the HC scaffolds with a larger channel volume promoted bone ingrowth compared to that with a larger micropore volume. In contrast, 12 weeks postoperatively, the HC scaffolds with a larger volume of the micropores rather than the channels promoted the scaffold resorption by osteoclasts and bone formation. Thus, the channels affected bone ingrowth in the early stage, and micropores affected scaffold resorption and bone formation in the middle stage. Furthermore, 12 weeks postoperatively, the HC scaffolds with large volumes of both channels and micropores formed a significantly larger amount of new bone than that attained using HC scaffolds with either large volume of channels or micropores, thereby bridging the host bone stumps. The findings of this study provide guidance for designing the pore structure of scaffolds., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Shibahara, Hayashi, Nakashima and Ishikawa.)

Carbonate apatite (CO 3 Ap), an inorganic component of human bone, has been clinically applied as an artificial bone substitute. In this study, the effects of the CO 3 content in CO 3 Ap on the replacement by new bone were studied by fabricating CO 3 Ap granules containing 0.9-8.3 wt% of CO 3 . The dissolution rate of CO 3 Ap in a weak acidic solution, mimicking the Howship's lacunae, was rapid for the CO 3 Ap granules containing a larger amount of CO 3 . Histological analyses demonstrated the rapid resorption in CO 3 Ap and replacement by natural bone tissue when the CO 3 content was increased. Therefore, the CO 3 content in CO 3 Ap is a key factor that influences the replacement of the bone tissue., (© 2021 John Wiley & Sons Ltd.)

The objective of this study was to investigate a bone graft substitute containing carbonate apatite (CO3Ap) to analyze bone replacement and the state of bone formation in vitro and in vivo compared with autogenous bone (AB) or control. An osteoclast precursor cell line was cultured with AB or CO3Ap, and morphological analysis using scanning electron microscopy and a tartrate-resistant acid phosphatase activity assay were performed. The right maxillary first and second molars of Wistar rats were extracted and compensated by AB or CO3Ap granules. Following implantation, the bone formation state was evaluated after 3, 5, 7, 14, and 28 days of surgery by micro-computed tomography and immunohistostaining. The osteoclast-like cell morphology was typical with many cell protrusions in the AB and CO3Ap groups. Additionally, the number of osteoclast-like cells formed in the culture increased in each group; however, there was no significant difference between the AB and CO3Ap groups. Five days after tooth extraction, osteoclasts were observed near CO3Ap. The bone thickness in the CO3Ap group was significantly increased than that in the control group and the bone formation in the CO3Ap group increased by the same level as that in the AB group. CO3Ap is gradually absorbed by osteoclasts in the extraction socket and is easily replaced by alveolar bone. The process of bone replacement by osteoclasts is similar to that of autologous bone. By observing the process of bone replacement in more detail, it may be possible to gain a better understanding of the bone formation and control the amount of bone after surgery. [ABSTRACT FROM AUTHOR]

Nanobacteria: An infectious cause for kidney stone formation. Background. Nanobacteria are cytotoxic, sterile-filterable, gram-negative, atypical bacteria detected in bovine and human blood. Nanobacteria produce carbonate apatite on their cell walls. Data on Randall's plaques suggest that apatite may initiate kidney stone formation. We assessed nanobacteria in 72 consecutively collected kidney stones from Finnish patients. Methods. Nanobacteria and kidney stone units were compared using scanning electron microscopy (SEM). Demineralized kidney stones were screened for nanobacteria using a double-staining method and a specific culture method. Isolated nanobacteria were analyzed for mineral formation in vitro with Ca and 85 Sr incorporation tests. Results. SEM highlighted the resemblance in size and morphology of nanobacteria and the smallest apatite units in the kidney stones. Nanobacterial antigens could be detected after the demineralization of the stones in 1 N HCl. Nanobacteria were surprisingly resistant to this treatment, and cultures could be established from 93.1% of the stones. Only struvite stones had common bacteria, in addition to the nanobacteria. When the results of all of the assays were combined, 70 of the 72 stones (that is, 97.2%) were nanobacteria positive. Although apatite stones indicated highest nanobacteria antigen signals, the overall nanobacteria positivity did not depend on the stone type. The isolated nanobacteria produced apatite stones in vitro , measured by Ca and 85 Sr incorporation. Conclusions. We propose that kidney stone formation is a nanobacterial disease analogous to Helicobacter pylori infection and peptic ulcer disease. Both diseases are initiated by bacterial infection and subsequently endogenous and dietary factors influence their progression. [ABSTRACT FROM AUTHOR]

Abstract Background RNA interference (RNAi) is a powerful approach in functional genomics to selectively silence messenger mRNA (mRNA) expression and can be employed to rapidly develop potential novel drugs against a complex disease like cancer. However, naked siRNA being anionic is unable to cross the anionic cell membrane through passive diffusion and therefore, delivery of siRNA remains a major hurdle to overcome before the potential of siRNA technology can fully be exploited in cancer. pH-sensitive carbonate apatite has recently been developed as an efficient tool to deliver siRNA into the mammalian cells by virtue of its high affinity interaction with the siRNA and the desirable size distribution of the resulting siRNA-apatite complex for effective cellular endocytosis. Moreover, internalized siRNA was found to escape from the endosomes in a time-dependent manner and efficiently silence gene expression. Results Here we show that carbonate apatite-mediated delivery of siRNA against PLC-gamma-2 (PLCG2) and calmodulin 1 (CALM1) genes has led to the sensitization of a human cervical cancer cell line to doxorubicin- and paclitaxel depending on the dosage of the individual drug whereas no such enhancement in cell death was observed with cisplatin irrespective of the dosage following intracellular delivery of the siRNAs. Conclusion Thus, PLCG2 and CALM1 genes are two potential targets for gene knockdown in doxorubicin and paclitaxel-based chemotherapy of cervical cancer.

The ESR spectrum of X-irradiated carbonated apatites precipitated from aqueous solutions was studied at carbonate contents ranging from approximately 5.4 up to 12.4 wt%. C- as well as C-enriched samples were prepared and examined with ESR after drying until constant weight at 25°C and 400°C. In these carbonated apatites, two CO radicals were detected, one of which is derived from B-type carbonate situated at a phosphate lattice site. The other CO most probably arises from CO ions situated at OH lattice sites. In contradistinction to the B-type contribution, the A-type contribution to the overall ESR signal decreases in absolute terms with increasing carbonate concentration. In addition, the line shape and the complete set of principal g-values of the A1-signal found in previous studles could be determined, corroborating the assignment of A1 to a surface O ion. [ABSTRACT FROM AUTHOR]

The ESR spectrum of X-irradiated carbonated apatites precipitated from aqueous solutions was studied as a function of their carbonate content and drying temperature. When the latter increases from 25 to 400 degrees C, the ESR spectrum is gradually modified and becomes similar to the spectrum of carbonated apatites, synthesized at high temperatures by solid state reactions. The latter ESR spectrum is dominated by CO3(3-)-contributions whereas the spectrum of precipitated samples dried at 25 degrees C can mainly be interpreted in terms of CO2-, CO3-, and O- ions. The behavior of these earlier-reported CO2-, CO3-, and O- centers is now studied as a function of drying temperature. In addition, the Spin Hamiltonian parameters of the CO3(3-) centers are determined and some other new paramagnetic radicals are discussed. It is shown that a CO3(2-) ion at a phosphate lattice site (B-type substitution) may give rise to either a CO2-, CO3-, or CO3(3-) radical on X-irradiation, depending on the sample preparation conditions. A surface CO3(2-) ion may cause a surface CO2-, CO3-, or O- radical. From the reported results it is not unambiguously clear whether the CO3(3-) ion detected in the samples with the relatively lowest carbonate content should be located on the surface or on a hydroxyl lattice site (A-type substitution). An important result is that the absolute concentration of the B-type CO3(3-) ion increases with increasing carbonate content as was also the case for the earlier reported B-type radicals (isotropic CO2- and CO3-). On the other hand, the absolute concentration of the surface radicals decreases with increasing carbonate content. The reported results show that similar deconvolution techniques can be applied in the future for the study of ESR spectra of calcified tissues. This will allow a more efficient phenomenological investigation of the latter. [ABSTRACT FROM AUTHOR]

The environment of carbonate ions in bones of different species (rat, rabbit, chicken, cow, human) was investigated by Fourier Transform Infrared Spectroscopy (FTIR) associated with a self-deconvolution technique. The carbonate bands in the v2 CO3(2-) domain show three components which were identified by using synthetic standards and different properties of the apatitic structure (ionic affinity for crystallographic locations, ionic exchange). The major component at 871 cm-1 is due to carbonate ions located in PO4(3-) sites (type B carbonate). A band at 878 cm-1 was exclusively assigned to carbonate ions substituting for OH-ions in the apatitic structure (type A carbonate). A band at 866 cm-1 not previously observed was shown to correspond to a labile carbonate environment. The intensity ratio of type A to type B carbonate appears remarkably constant in all bone samples. The 866 cm-1 carbonate band varies in its relative intensity in different species. [ABSTRACT FROM AUTHOR]

The ESR spectrum of X-irradiated carbonated apatites synthesized at low temperature was studied as a function of their carbonate content. Using 13C-enriched samples, four different carbonate-derived radicals and a surface O- ion could be identified. Isotropic CO3- and CO2- ions are present at a B site in the apatite lattice, and anisotropic CO3- and CO2- radicals are located at the surface of the crystallites. Only the isotropic ESR signals increase with increasing carbonate content. The anisotropic signal ascribed to a surface CO2- radical is mainly responsible for the so-called asymmetric ESR signal near g = 2. It is argued that this surface signal may still be composite and caused by several very similar CO2- ions. The consequences for phenomenological ESR studies of calcified tissues are discussed. [ABSTRACT FROM AUTHOR]

Synthetic carbonate-containing and carbonate-free hydroxyapatites (CO-HA and CO-free HA) have been investigated using ESR and IR absorption, together with X-ray diffraction and chemical analyses. Comparison of the IR spectra betweenC-enrichedCO-HA andCO-HA prepared at 100°C and at high pH suggested that the carbonate substitutes for PO but not for HPO. The substitution of CO for PO in this case resulted in elimination of hydroxyl ions in a hexad axis. The elimination of hydroxyl ions was found to be related to the decrease in crystallinity for the c-axis direction, although so far there has been no direct evidence for the existence of hydroxyl deficiencies. In the case of CO-free HAs prepared at 80°, 60°, 40°, and 20°C, the decrease in crystallinity accompanied by the decrease in the temperature for preparation was associated with the decrease in crystal size, and no significant elimination of hydroxyl ions would be expected in the absence of the carbonate. [ABSTRACT FROM AUTHOR]

When amorphous calcium phosphate (ACP) was transformed to crystalline hydroxyapatite (HA) in a series of aqueous slurry concentrations ranging from low to high, the higher slurry concentrations produced more Ca-deficient HA as measured by Ca/P ratio and heat-produced pyrophosphate. We feel that the excess solution phosphate produced in the higher slurry transformations results in lower Ca/P ratio HA. It has been suggested that an ACP is the precursor to bone apatite. Regulation of the in vivo ACP slurry concentration could then control the stoichiometry and, therefore, the metabolic activity of bone apatite. X-ray radial distribution function (RDF) analyses showed that CO substitution in HA creates far greater structural distortions than do Ca deficiencies. The latter, however, do produce small, but observable, structural distortions when compared to stoichiometric HA. It now seems clear that the RDF of bone apatite can be modeled by a synthetic, Ca-deficient, CO-containing HA. [ABSTRACT FROM AUTHOR]

Octacalcium phosphate (Ca8H2(PO4)6 . 5H2O) is considered to be precursor in the formation of apatite in bones and teeth; a crucial step for incorporation of impurities appears to occur during its hydrolysis. The present study examines the role that octacalcium phosphate plays in the process of incorporation of carbonate into apatite. Chemical, X-ray diffraction, and infrared techniques were used. When octacalcium phosphate is hydrolyzed in the presence of sodium and carbonate ions in aqueous media, approximately one sodium and one carbonate ion seem to substitute for a calcium and phosphate ion, respectively, in forming apatite, and the a axis is shortened. The infrared spectrum of the product indicates that the carbonate is in the type B site, which is presumed to be a phosphate site. This mechanism is of particular importance since the presence of carbonate in human enamel appears to be related to caries susceptibility. A structural mechanism for the incorporation of impurities during hydrolysis of octacalcium phosphate is presented. [ABSTRACT FROM AUTHOR]