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PubMed1985

Adsorption of zirconyl salts and their acids on hydroxyapatite: use of the salts as coupling agents to dental polymer composites.

Zirconyl methacrylate (I) and zirconyl-2-ethylhexanoate (II) were synthesized, and their adsorption isotherms from solutions onto synthetic hydroxyapatite were studied. The isotherms of methacrylic and 2-ethylhexanoic acids were also determined from the same solvents. The adsorption of I was irreversible from methylene chloride, and that of II was irreversible from cyclohexane. The adsorption in both cases was constant from solutions above a certain concentration, and exhaustive below this threshold concentration. Both compounds rendered the dried apatite powder extremely hydrophobic; however, the adsorbate was slowly washed off by excess water. The configuration of the adsorbate molecules, deduced from the maximum adsorption and other adsorption characteristics of the two compounds, indicated that: (i) in both cases the adsorbate may be held to the surface by concerted hydrogen bonding of the carboxylate and zirconyl oxygen atoms; and (ii) the hydrocarbon moieties in both adsorbates expose themselves toward the solution, thereby making the dried surface hydrophobic. The adsorptive behavior of the respective acids was similar to that of the salts. Polymer, filled with synthetic hydroxyapatite covered with irreversibly adsorbed I, had a diametral tensile strength about 50% greater than that of the polymer filled with untreated apatite. The strength of the composite was not affected by treatment of the apatite with II or with the acids.

Acids↗

PubMed1986

Enamel fluoride retention after DCPD and APF application and prolonged exposure to fluoride in vitro.

The effect of a topical fluoride regimen consisting of a four-minute pre-treatment with a saturated dicalcium phosphate dihydrate (DCPD) solution followed by a four-minute application of APF was compared with that of a four-minute application of APF alone with respect to the deposition of fluoride in enamel in an apatitic form in vitro. Following the topical applications, specimens were washed in either (1) an inorganic wash solution for 24 hrs or (2) an inorganic wash solution with 1 ppm F added for 28 days; specimens were then subjected to KOH extraction for 24 hrs. Fluoride-by-depth profiles revealed that the DCPD/APF treatment resulted in a significant increase in the apatitic F concentration of enamel to a depth of 20 microns, while APF application alone did not. All groups exposed to the 1 ppm F wash acquired significant amounts of apatitic F, with the differences between groups remaining relatively constant.

Acidulated Phosphate Fluoride↗

PubMed1986

Adsorption of benzoic acid on pure and cupric ion-modified hydroxyapatite: implications for design of a coupling agent to dental polymer composites.

The adsorption isotherms of benzoic acid on synthetic hydroxyapatite (containing about 1.5 monolayers of physisorbed water) were studied from ethanol, dimethylsulfoxide, p-dioxane, methylene chloride, and benzene to discern the role of solvent in the process. The adsorption is reversible from the first three solvents and follows the Langmuir plots. It is irreversible from the last two, and a constant amount of absorbent is removed from solutions above a certain concentration. The isotherms of potassium benzoate on the apatite from ethanol and dimethyl sulfoxide were reversible. The isotherms of the acid on cupric ion-modified apatite surfaces from ethanol and benzene were identical with those obtained on the pure hydroxyapatite. This may demonstrate that any "surface chelation" with the cation may not be a significant factor for adsorption to occur. The adsorptive behavior seems to depend upon the interplay of hydrogen-bonding among the solute, the solvent, and the hydrated apatite surface. The capability of a solvent to hydrogen-bond may determine whether adsorption from it will be reversible or irreversible. Based upon its compatibility with a solvent, the benzene ring is upright or lies flat on the surface. The adsorbed molecules rotate about the center of the carboxylate groups which are hydrogen-bonded to the surface. These factors should be considered in designing or selecting a suitable surface-active moiety for a coupling agent between tooth mineral and a restorative resin.

Adsorption↗

PubMed1987

Possible physico-chemical processes in human dentin caries.

This study correlated ultrastructural observations on the presence of beta-tricalcium phosphate (beta-TCP) in arrested dentin caries with physico-chemical observations on the in vitro formation of Mg-substituted beta-TCP. The ultrastructural studies were made using high-resolution transmission electron microscopy (TEM) with the capability of microdiffraction and microanalysis on sites less than 10 nm in diameter. Mg-substituted beta-TCP was obtained, by a precipitation method, from solutions with Mg/Ca molar ratios of 5/95 and higher. Such correlations led to the postulation of a possible chronological sequence of physico-chemical events occurring at the crystal level during the progress and arrest of caries in human dentin. It is suggested that the initial mechanism for the observed occurrence of large crystals of Mg-substituted beta-TCP and of apatite in the tubule lumen is due to the dissolution of the dentin mineral (a CO3- and Mg-rich calcium OH-apatite) and reprecipitation of Mg-substituted beta-TCP, followed by that of CO3- and Mg-poor apatite.

Calcium Phosphates↗

PubMed1987

The concomitant deposition of strontium and fluoride in dental plaque.

We have investigated the feasibility of incorporating Sr into dental plaque by means of an enzyme-dependent system known to increase Ca, P, and F levels in plaque. A solution containing Ca (20 mmol/L), P (12 mmol/L), MFP (4.7 mmol/L), F (0.3 mmol/L), and urea (500 mmol/L) was modified by equimolar replacement of Ca with 1, 2, 5, and 10 mmol/L Sr. Thin films of human salivary sediment incubated in these solutions showed increasing levels of acid-extractable Sr as the solution Sr increased. When the concentration exceeded 2 mmol/L, deposition of Ca, P, and F was reduced. In artificial plaque, grown on bovine enamel, from mixed human salivary organisms and treated with the solution containing 2 mmol Sr/L, there was a slightly smaller uptake of Ca, P, and Sr, but a greater uptake of F than in sediment treated with the same solution. Natural human plaque treated 12 times in vivo over three days with this solution (in the form of a mouthrinse) also showed substantial increases (from five- to 26-fold) in the concentrations of all four ions. Absolute levels of Ca, P, F, and especially Sr were, however, lower than those in the artificial plaque samples. (Ca + Sr)/P ratios suggested apatite deposition, and the correlation between amounts of Ca and Sr deposited in natural plaque samples suggested that Sr, like F, is structurally incorporated into this apatite. Fluctuations in the pH of natural plaque may promote apatite crystal maturation, causing a slow loss of Sr.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1995

Duration of dentinal tubule occlusion formed by calcium phosphate precipitation method: in vitro evaluation using synthetic saliva.

The use of a calcium phosphate precipitation method occluded dentin tubules with apatitic mineral and, thus, showed good potential for the treatment of dentin hypersensitivity. The aim of this study was to elucidate the occluding behavior of the precipitate in the oral environment. Dentin disks treated by the calcium phosphate precipitation method, and disks treated with potassium oxalate, NaF, and SrCl2 solutions, were immersed in synthetic saliva, which was regularly replenished so that ionic concentration would be maintained. Treatment of dentin disks by the calcium phosphate precipitation method immediately reduced dentin permeability to 6 +/- 8%. When the disk was immersed in synthetic saliva, dentin permeability remained low, even seven days after immersion. Scanning electron microscopic observation showed no distinct boundary line between the precipitate and intertubular dentin; this indicated further mineralization on the precipitate. Potassium oxalate treatment also reduced the dentin permeability to 8 +/- 3%. However, the dentin permeability gradually but steadily increased with immersion time, reaching 39 +/- 14% at seven days. To elucidate the mechanism underlying dentin permeability changes in synthetic saliva, we immersed the precipitates, i.e., apatitic mineral and calcium oxalate, in a fixed volume of synthetic saliva. When calcium oxalate was immersed in synthetic saliva, there was a large concentration of oxalate ions, indicating dissolution of the calcium oxalate; this phenomenon was ascribed to the increase in dentin permeability. In contrast, calcium and phosphate ions decreased when apatitic powder, the precipitate formed by the calcium phosphate precipitation method, was immersed in synthetic salvia. The decrease in the calcium and phosphate ions in synthetic saliva indicated further precipitation of calcium phosphate on the apatitc precipitate.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1996

Quantitative assessment of the efficacy of amorphous calcium phosphate/methacrylate composites in remineralizing caries-like lesions artificially produced in bovine enamel.

Recent studies show that methacrylate-based composites with amorphous calcium phosphate (ACP) as a filler can release supersaturating levels of calcium and phosphate ions in proportions favorable for apatite formation. These findings suggest that such composites could be effectively used as coatings for remineralizing teeth damaged by tooth decay. To examine this hypothesis, we tested composites in vitro for their efficacy to remineralize artificially formed caries-like lesions in extracted bovine incisors. Single 120-microns-thick sagittal tooth sections were placed in holders that exposed only the carious enamel surface. The exposed surfaces were coated with a 1-mm- to 1.5-mm-thick layer of the composite containing, by mass, 40% apatite, silica, or P2O7(-4)-stabilized ACP and 60% photoactivated resin comprised of Bis-GMA, TEGDMA, HEMA, and ZrM. The photocured composite-coated sections were immersed either in a remineralizing solution for 4 weeks at 37 degrees C (static model) or cyclically immersed in demineralizing (0.5 h) and remineralizing solutions (11.5 h) for 2 weeks (dynamic model). Quantitative digital image analysis of matched 102 microns x 220 microns areas from contact microradiographs taken of the sections before and after immersion showed that lesions coated with ACP-filled composites fractionally recovered 71% +/- 33% of their lost mineral compared with 14% +/- 13% for apatite controls in the static model and 38% +/- 16% compared with -6% +/- 24% in the dynamic model. The results suggest that sealants based on ACP-filled methacrylate composites have the potential to remineralize carious enamel lesions.

Animals↗

PubMed2005

The influence of X-ray radiation on the mineral/organic matrix interaction of bone tissue: an FT-IR microscopic investigation.

Fourier transform infrared microscopy was used to investigate human cortical bone samples before and after treatment with increasing doses of X-ray radiation. Especially the spectral region of the v1 and v3 phosphate vibrations of hydroxyapatite, the main mineral component of bone, and the region of the amide I and amide II vibrational bands due to the collagen extracellular matrix were examined. Major spectral changes in the phosphate region between 1250-1000 cm(-1) occur after irradiation doses between 1 and 4 Gray. These findings are explained by a decrease in size of mineral crystallites and by variances of the toichiometric/non-stoichiometric apatite composition. The Ca2+ /PO4(3-) /HPO4(2-) composition in the biological apatite is altered near the bone surface. The secondary structure of the collagen matrix is not affected by cumulative irradiation up to doses of 15 Gray as indicated by the unchanged frequency maximum and contour shape of the amide I band between 1600-1700 cm(-1) . However, side chain carboxylate groups of the collagen matrix that are involved in coordination with apatite bound calcium ions are partially removed by decarboxylation upon irradiation. Concomitantly, a loss of acidic phosphate groups due to a formation of phosphate groups with bound calcium is observed. These changes on a molecular level can be correlated with alterations in the mechanical properties of the bone samples, e.g. with an increased embrittlement as deduced from experiments with a scanning acoustic microscope.

Amides↗

PubMed1983

Changes in crystal size and orientation of acidic glycosaminoglycans at the fracture site in fractured necks of femur.

The aim of this study was to try to elucidate the increased susceptibility of the neck of femur to fracture. Quantitative polarised light microscopy has been applied to fresh, undecalcified sections of samples of bone taken from the site of fracture, in specimens taken at operation from patients with fractures of the femoral neck or osteoarthritic femoral heads or from the equivalent site from otherwise normal subjects at necropsy. In all 21 specimens of fractured necks of femur, but in none of the other specimens, relatively large crystals (up to 2.5 X 0.5 micrometres) were found close to the site of fracture; the properties of these crystals were compatible with their being apatite. Measurement of the natural birefringence of the collagen showed no difference in the orientation of the collagen in all three types of specimen. However, the orientation of acidic glycosaminoglycans, measured by the birefringence of alcian blue bound to these moieties, was 45 per cent lower in the specimens from fractured necks of femur than in the other specimens, even though the total content of acidic glycosaminoglycans was unchanged. Although the decreased orientation was most marked close to the site of fracture, it was still apparent 15 millimetres from that site. These changes were unlikely to be simply the sequelae of fracture since they were not found in traumatic fractures of other bones. Thus it is conceivable that changes in the orientation of the ground substance allow formation of relatively large crystals of apatite and that such crystals, in the microcrystalline mass of apatite, are the cause of the increased fragility of such bones.

Aged↗

PubMed2006

Three structural roles for water in bone observed by solid-state NMR.

Hydrogen-bearing species in the bone mineral environment were investigated using solid-state NMR spectroscopy of powdered bone, deproteinated bone, and B-type carbonated apatite. Using magic-angle spinning and cross-polarization techniques three types of structurally-bound water were observed in these materials. Two of these water types occupy vacancies within the apatitic mineral crystal in synthetic carbonated apatite and deproteinated bone and serve to stabilize these defect-containing crystals. The third water was observed at the mineral surface in unmodified bone but not in deproteinated bone, suggesting a role for this water in mediating mineral-organic matrix interactions. Direct evidence of monohydrogen phosphate in a (1)H NMR spectrum of unmodified bone is presented for the first time. We obtained clear evidence for the presence of hydroxide ion in deproteinated bone by (1)H MAS NMR. A (1)H-(31)P heteronuclear correlation experiment provided unambiguous evidence for hydroxide ion in unmodified bone as well. Hydroxide ion in both unmodified and deproteinated bone mineral was found to participate in hydrogen bonding with neighboring water molecules and ions. In unmodified bone mineral hydroxide ion was found, through a (1)H-(31)P heteronuclear correlation experiment, to be confined to a small portion of the mineral crystal, probably the internal portion.

Animals↗

PubMed2000

Initial evaluation of a ceramic form as a reconstructive material for bone defects.

Alumina form and a porous apatite, apaceram, were implanted in rat tibiae bone defects for up to 12 weeks and the tissue response was studied histologically as an initial evaluation of whether or not this ceramic form had potential as a reconstructive material for bone defects. We observed no bone formation inside the pores of porous apatite, even after 12 weeks, if the pores were deeper than 1.0 mm from the surface. In contrast, we observed bone tissue deep inside the alumina form as early as 2 weeks after implantation. However, the bone that formed around the alumina form did not directly contact with the frame of the alumina form, even though bone directly contacted with porous apatite. We concluded, therefore, that the ceramic form has potential value as a reconstructive material for bone defects. This potential value would be further increased if the ceramic form could be prepared with calcium phosphate-related materials.

Aluminum Oxide↗

PubMed1999

Bone implants--a challenge to materials science.

The review paper discusses the conditions for obtaining in vivo a composite from a synthetic, inorganic material and collagen fibres. Bone itself is a composite containing collagen fibres and hydroxoapatite crystals. The crystal size is, however, far smaller than can be made using conventional methods of ceramics technology. The paper discusses therefore the possibilities to synthesize the apatite in a gel. The requirements of initial load bearing can be met by forming the gel on the surface of glass particle, sintered to a porous body. In the pores calcium ions react with the gel to form (= SiO)Ca+ complexes. When the phosphate concentration in the pore is high enough to exceed the solubility product of apatite, the calcium-gel complexes release the calcium and highly dispersed apatite crystallites are precipitated in the gel. These give the gel the osteoconductive properties observed for bioactive glasses. Glass compositions, which give a gel surface enough hydrated to form calcium complexes, are discussed.

Bone Substitutes↗

PubMed2002

The crystallographic properties of the mineral phases of enamel and dentin in normal deciduous and permanent teeth.

OBJECTIVE: To investigate the crystallographic properties of the mineral phases of normal enamel and dentin (dental apatite) in deciduous and permanent teeth. METHODS: Three kinds of physical methods including X-ray diffraction (XRD), infrared absorption spectroscope (IR) and electron probe micro-analysis (EPMA) were utilized in this study. RESULTS: Dental apatite was not uniphase, but multiphase, which could be described as carbonate-substituted hydroxyapatite. Compared to dentin apatite, the higher crystallinity and expanded a-axis lattice parameters were found in enamel. Chemical analyses demonstrated that higher concentrations of Mg and CO(3)(2-) were found in dentin than those of enamel. But enamel had higher Cl content. CONCLUSIONS: The differences among enamel and dentin, in terms of lattice parameter and crystallinity may be partially attributed to the incorporation of Mg, CO(3)(2-) and Cl minor elements.

Dental Enamel↗

PubMed1989

[Experimental studies on the sealing properties of various kinds of root canal sealers in vitro (Part 3)].

In previous studies (Shikwa Gakuho 80: 473-485, 1471-1486, 1980), the authors have reported on sealing properties in vitro. But the recent development of many new sealers makes necessary a detailed reexamination at this time. The experimental materials were as follows; Zinc oxide eugenol sealer......Canals Calcium hydroxide eugenol sealer......CRCS, Dentalis KEZ Calcium hydroxide guaiacol sealer......FR Hydroxyapatite sealer......Finapec APC, Apatite root sealer TYPE III The experimental procedure employing a glass tube and the dye-penetration method was similar to the one used in previous studies. Results of the investigation; 1. Degrees of dye penetration were classified into 3 types i) Immediate penetration through the zone between the material and the glass tube within 2 days.--Apatite root sealer TYPE III, Dentalis KEZ ii) Little penetration within 12 hours but gradual penetration to the deep zone thereafter.--CRCS, Canals iii) Slight penetration within 7 days and then gradual penetration 1/5 of the way through the zone between the material and the glass tube.--Finapec APC 2. Dye penetrated through the material in the case of apatite root sealer TYPE III and FR.

Dental Leakage↗

PubMed1987

[Ultrastructural study of bone formation after bioapatite implantation in man].

Synthetic hydroxyapatite crystals (Bioapatite) were implanted in a vestibular longitudinal groove made in the alveolar bone, the periodontal membrane and the superficial root dentine of 2 human canines in the absence of periodontal disease. The healing process was followed in scanning as well as in transmission electron microscopy. At 6 months, the aggregate of synthetic hydroxyapatite crystals was surrounded by a fibrous connective tissue, devoid of inflammatory cells. Small apatite crystals, similar to the neighbouring bone crystals, were deposited between the Bioapatite crystals in the central area of the aggregates. These small crystals filled the intercrystalline spaces from the center to the periphery. The mineralization extended then directly in the collagen matrix (osteoid tissue) surrounding the synthetic apatite aggregates. Bone tissue was thus formed around the apatite implants. At 1 year, the thickness of the bone tissue formed around the synthetic hydroxyapatite aggregates was increased. It consisted of bone with a well-oriented collagen matrix, with osteocyte lacunae, osteocytes and interosteocytic canaliculi, with normal ultrastructure.

Alveolar Process↗

PubMed1985

X-ray microanalysis of urinary stones, a comparison with other methods.

A previous study of urinary stones by a combined electron microscopy demonstrated the potential of scanning electron microscopy and X-ray analysis as an analytic tool for urinary stones. Electron diffraction was chosen for the final confirmation of crystals in the study. Although electron diffraction is highly accurate for this purpose, it is desirable to establish the sensitivity of X-ray analysis for the identification of stone components relative to the more commonly used methods. Eighty six consecutive urinary stones were analyzed by X-ray analysis and the findings were compared with those of X-ray diffraction, infrared spectrometry and chemical analysis. The results indicate that X-ray analysis exceeds X-ray diffraction and infrared spectroscopy in its sensitivity for the identification of stone components several fold. This was largely due to the inability of the latter methods to detect apatite in more than half of the apatite containing stones. The findings in X-ray analysis had the best correlation with chemical analysis, which was applied mainly to the detection of apatite. X-ray analysis is particularly suited for the detection of rare and minor inorganic components of urinary stones such as silica and gypsum, and is obviously one of the most powerful tools for the analysis of urinary stones. Further application of X-ray analysis to urinary stone is likely to discern rare inorganic components of urinary stones overlooked by other methods.

Calcium Oxalate↗

PubMed1987

Mg2+-F-interaction during hydroxyapatite formation.

Two series of Mg-containing fluoridated hydroxyapatites with various fluoride contents were synthesized at 80 degrees C and pH 7.4 and compared with a corresponding Mg-free series. The Mg content of the apatites increased slightly with the degree of fluoridation despite the constant magnesium concentration in the feed solution. A small amount of magnesium significantly affected the crystallinity of synthetically fluoridated apatites. The patterns of crystallinity with the increase of fluoride content were unique in each series with different magnesium contents. These phenomena might have been caused by the Mg2+-F-interaction during the apatite formation.

Fluorides↗

PubMed1986

[Physicochemical analysis of subcutaneous calcifications in a case of Thibierge-Weissenbach syndrome].

A physicochemical study of subcutaneous calcium deposits was performed in a patient with typical Thibierge-Weissenbach syndrome which had begun, ten years previously, with Raynaud's phenomenon and sclerodactylia. Calcium deposits had progressively developed, forming large plates on the arms, flanks and thighs. In the course of the disease they had become ulcerated, exuding a white, chalky material. X-ray films and xerograms demonstrated the extent of these deposits. The calcium-phosphorus balance was normal, and the other clinical and laboratory examinations were concordant with a diagnosis of Thibierge-Weissenbach syndrome (calcinosis). Only systemic corticosteroid therapy slowed down the pathological process; calcium chelating agents (diphosphonate) proved ineffective. The physicochemical study showed that the deposits consisted of carbonated apatite type B with the following formula: Ca8.0(PO4)4.1(CO3)1.2(HPO4)0.8 The mineral substance seemed to be less reactive and more stable than normal bone. This would account for the total lack of effectiveness of all treatments, notably calcium chelating agents, on the course of the deposits. Treatments usually produce bone demineralization before they influence the calcium deposits. This study provides much more detailed information than was hitherto available on calcium deposits and on carbonate ion contents in the apatite phase. The presence of carbonates increases the solubility and reactivity of calcium apatite.

Calcinosis↗