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PubMed1997

Effect of calcium carbonate on clinical compliance of apatitic calcium phosphate bone cement.

Clinical requirements for calcium phosphate bone cements were formulated in terms of the initial setting time, the final setting time, the cohesion time, and the ultimate compressive strength. Two cement formulations were tested. Biocement F was made of a powder containing alpha-tertiary calcium phosphate, precipitated hydroxyapatite, and monetite. Biocement D powder also contained CaCO3. The liquid/powder (L/P) ratio of the cement paste and the accelerator concentrations (% Na2HPO4) in the cement liquid were varied. For Biocement F there was a small area of combinations of L/P ratio and percent Na2HPO4 for which all clinical requirements were satisfied. This area covered only pastes that could be applied as doughs. However, Biocement D showed a much larger area of full compliance and it covered both doughlike and injectable pastes.

Apatites↗
PubMed2003

Synchrotron X-ray microtomography (on a micron scale) provides three-dimensional imaging representation of bone ingrowth in calcium phosphate biomaterials.

This study used synchrotron X-ray microtomography on a micron scale to compare three-dimensional (3D) bone ingrowth after implantation of various calcium phosphate bone substitutes in a rabbit model. The advantage of using this new method for the study of biomaterials was then compared with histomorphometry for analysis of interconnection and bone ingrowth. The study focused on the newly formed bone-biomaterial interface. Macroporous Biphasic Calcium Phosphate (MBCP) ceramic blocks and two different injectable calcium phosphate biomaterials [an injectable bone substitute (IBS) consisting of a biphasic calcium phosphate granule suspension in hydrosoluble polymer and a calcium phosphate cement material (CPC)] were studied after in vivo implantation. Absorption or phase-contrast microtomography was performed with the dedicated set-up at beamline ID22. Experimental spatial resolution was between 1 and 1.4 microm, depending on experimental radiation. All calcium phosphates tested showed osteoconduction. IBS observations after 3D reconstruction showed interconnected bioactive biomaterial with total open macroporosity and complete bone ingrowth as early as 3 weeks after implantation. This experimentation was consistent with two-dimensional histomorphometric analysis, which confirmed its suitability for biomaterials. This 3D study relates the different types of bone substitution to biomaterial architecture. As porosity and interconnection increase, bone ingrowth becomes greater at the expense of the bone substitute: IBS>MBCP>CPC.

Animals↗
PubMed1997

Effect of calcium carbonate on the compliance of an apatitic calcium phosphate bone cement.

Clinical requirements for calcium phosphate bone cements were formulated in terms of the initial setting time, the final setting time, the cohesion time and the ultimate compressive strength. Three cement formulations were tested. The previously developed Biocement H was made of a powder containing alpha-tertiary calcium phosphate and precipitated hydroxyapatite. Biocement B2 powder was made by adding some CaCO3 to Biocement H, whereas Biocement B1 was made by adding some CaCO3 but with simultaneous adjustment of the amount of precipitated hydroxyapatite.The liquid/ powder ratio of the cement paste and the accelerator concentrations (percentage Na2HPO4) in cement liquid were varied. For Biocement H there was no combination of L/P ratio and percentage Na2HPO4 for which all clinical requirements were satisfied. However, there was an area of full compliance for Biocements B1 and B2, of which that for B1 was the largest. Therefore, Biocement B1 may be applied in clinical situations as those in orthopaedics, plastic and reconstructive surgery and oral and maxillofacial surgery, even when early contact with blood is inevitable.

Apatites↗
PubMed1998

Morphology and microstructure of electrochemically deposited calcium phosphates in a modified simulated body fluid.

Calcium phosphates were deposited on a pure titanium plate for various loading times under 1.3 and 12.9 mA/cm2 in a modified simulated body fluid at 52-92 degrees C. The plate-like crystals formed under 1.3 mA/cm2 were identified to be octacalcium phosphate (OCP) and/or carbonate-containing apatite. OCP converted to carbonate-containing apatite with the elapsing time of the loading current. The needle-like precipitates formed under 12.9 mA/cm2 were identified to be carbonate-containing apatite crystals elongated parallel to the c-axis direction. The degrees of crystallinity of the deposits formed under 1.3 mA/cm2 showed the highest value around 72 degrees C, whereas those under 12.9 mA/cm2 increased with the electrolyte temperature. The carbonate content of the deposits decreased with the electrolyte temperature and the flow current. The degree of crystallinity of the electrochemically deposited calcium phosphates decreased with the carbonate content.

Apatites↗
PubMed1994

Physical and chemical properties of resin-reinforced calcium phosphate cements.

OBJECTIVES: The purpose of this study was to improve the handling and physical properties of a self-setting, water-based calcium phosphate cement by combining it with polymerizable resins and to study the setting reactions involved. METHODS: Dual-cured composite cements were prepared from a calcium phosphate cement powder and dental monomers that contain carboxylated hydrophilic resins or resin/water mixtures. The setting reaction of the calcium phosphate cement in the presence of the resins was evaluated by pH measurements, infrared spectroscopy, diametral tensile strength, x-ray diffraction analysis, and scanning electron microscopy. RESULTS: Carboxylated resins were chosen because they can form ionic bonds to the mineral filler, which was confirmed by appearance of an infrared absorbance peak at 1552 cm-1 within 24 h after mixing due to the formation of a carboxylate salt. Hydroxyapatite did not develop in composites prepared from resin and calcium phosphate cement. However, composites from calcium phosphate cement, resin and water showed approximately 40% hydroxyapatite. The resulting composite cements have moderately high DTS of 14-15 MPa and high pH. SIGNIFICANCE: Hydrophilic acidic resins allows mixing with water and/or allow rapid diffusion of water into the resinous cement so that the dissolution and reprecipitation processes required for the conversion of the calcium phosphate components to hydroxyapatite can occur. The characteristics of the resulting composite cements suggest that the materials may be useful in pulp capping and/or cavity lining.

Calcium Phosphates↗
PubMedDate not supplied

Biomechanical comparison of conventional open reduction and internal fixation versus calcium phosphate cement fixation of a central depressed tibial plateau fracture.

OBJECTIVE: To evaluate the effect of calcium phosphate bone cement on stability and strength of the fracture repair in a central depressed tibial plateau fracture cadaveric model. DESIGN: Paired human cadaveric tibial specimens. SETTING: Biomechanics laboratory. PATIENTS: Uniform pure depression fractures of lateral tibial plateau were created in twenty human cadaveric tibial specimens. INTERVENTION: The first part of the study used thirteen pairs of tibiae in two groups: a control group receiving the conventional treatment of morselized bone graft and two cancellous screws and an experimental group receiving calcium phosphate bone cement only. The second part of the study used seven pairs of tibiae in two experimental groups: one receiving calcium phosphate bone cement with a more extensive void preparation and the other group receiving calcium phosphate bone cement with a more extensive void preparation and two screws. MAIN OUTCOME MEASUREMENTS: Each tibia was loaded on a Material Testing Systems machine from twenty newtons to 250 newtons for 10,000 cycles to simulate immediate postoperative load transmission to the tibial plateau. Specimens were then loaded to failure to determine the ultimate strength of the reconstruction. Displacement of the articular fragment and stiffness at each cycle were measured during dynamic loading. Peak load, deformation at peak load, and resistance to depression were measured during the load to failure. RESULTS: The treatment of depressed tibia plateau fractures with a calcium phosphate cement provides equivalent or better stability than conventional open reduction and internal fixation in pure depression tibial plateau fractures. If the fracture void is prepared by eliminating the cancellous bone under the subchondral plate, the results are further improved. CONCLUSIONS: This study suggests that the non-weight-bearing postoperative period may be significantly reduced without clinically significant articular collapse.

Absorptiometry, Photon↗
PubMed1997

Interaction of zinc with a synthetic calcium phosphate mineral.

As zinc has been included in several oral health products as an anticalculus and antiplaque agent, the interaction of zinc with a synthetic phosphate was investigated. The synthetic calcium phosphate used in this study was beta-tricalcium phosphate, or whitlockite, which is a major constituent of mature calculus. The aim of this work was to study the mechanism of uptake of zinc to this mineral. Zinc was readily taken up by the calcium phosphate to a maximum level of 13.9 mumol/m2. The interaction was reversible and followed a Langmuir adsorption isotherm. There was no concomitant release of calcium with zinc uptake. Inclusion of calcium in the exposure solution did however marginally depress the acquisition of zinc (12% max), but fluoride had no significant effect on uptake.

Adsorption↗
PubMed1994

Fourier transform Raman spectroscopy of synthetic and biological calcium phosphates.

Fourier-transform (FT) Raman spectroscopy was used to characterize the organic and mineral components of biological and synthetic calcium phosphate minerals. Raman spectroscopy provides information on biological minerals that is complimentary to more widely used infrared methodologies as some infrared-inactive vibrational modes are Raman-active. The application of FT-Raman technology has, for the first time, enabled the problems of high sample fluorescence and low signal-to-noise that are inherent in calcified tissues to be overcome. Raman spectra of calcium phosphates are dominated by a very strong band near 960 cm-1 that arises from the symmetric stretching mode (v1) of the phosphate group. Other Raman-active phosphate vibrational bands are seen at approximately 1075 (v3), 590 (v4), and 435 cm-1 (v2). Minerals containing acidic phosphate groups show additional vibrational modes. The different calcium phosphate mineral phases can be distinguished from one another by the relative positions and shapes of these bands in the Raman spectra. FT-Raman spectra of nascent, nonmineralized matrix vesicles (MV) show a distinct absence of the phosphate v1 band even though these structures are rich in calcium and phosphate. Similar results were seen with milk casein and synthetic Ca-phosphatidyl-serine-PO4 complexes. Hence, the phosphate and/or acidic phosphate ions in these noncrystalline biological calcium phosphates is in a molecular environment that differs from that in synthetic amorphous calcium phosphate. In MV, the first distinct mineral phase to form contained acidic phosphate bands similar to those seen in octacalcium phosphate. The mineral phase present in fully mineralized MV was much more apatitic, resembling that found in bones and teeth.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

A unique protonated phosphate group in bone mineral not present in synthetic calcium phosphates. Identification by phosphorus-31 solid state NMR spectroscopy.

The detailed chemical composition and microstructure of freshly deposited bone mineral, and how these properties change with maturation of the mineral, have been studied intensively and still remain controversial. For example, current analytical technology is inadequate for the unambiguous characterization of the monohydrogen phosphate ions in bone mineral. Using a differential cross polarization/magic angle spinning solid state nuclear magnetic resonance spectroscopy technique, we suppress the dominant orthophosphate (PO4-3) signal to reveal the spectra of the minor phosphate constituents. This method depends upon differences in the cross polarization time constants for phosphorus-31 nuclei in protonated and non-protonated phosphate ions. It is now possible for the first time to directly measure both the proportion of acid phosphate (HPO4-2) as well as the parameters which characterize its isotropic and anisotropic chemical shift. In bone from three species at several developmental stages, we have found a single type of acid phosphate species, identical in all of the specimens examined. The phosphorus-31 isotropic chemical shift of this acid phosphate group in bone mineral corresponds precisely with that of acid phosphate in octacalcium phosphate, and not with that of brushite. In contrast, the bone acid phosphate anisotropic chemical shift parameters are close to those of brushite, and differ significantly from those of octacalcium phosphate. The orthophosphate resonances of bone mineral, synthetic hydroxyapatite and synthetic octacalcium phosphate share identical chemical isotropic shifts, and similar chemical shift anisotropies. The implication of these results is that the intimate structure of the acid phosphate group in bone mineral is unique, and that none of the common synthetic calcium phosphates accounts well for all of the observed solid state phosphorus-31 NMR properties of bone mineral.

Animals↗
PubMed2004

Histopathological and cell enzyme studies of calcium phosphate cements.

New types of self-setting calcium phosphate cement (N-CPC), which do not contain tetracalcium phosphate, were recently developed. N-CPCs harden in 10 minutes with phosphate solution as the cement liquid, and form hydroxyapatite as the set product. The objectives of the present study were to evaluate the biocompatibility (Study I) and cell enzyme activity of N-CPCs and a conventional CPC (Study II). Four experimental cements were tested: (1) dicalcium phosphate anhydrous (DCPA) and calcium oxide; (2) DCPA and calcium hydroxide; (3) tricalcium phosphate and calcium carbonate; and (4) DCPA and tetracalcium phosphate. Phosphate solution was used as the cement liquid for cements (1)-(3), and water for cement (4). Sintered hydroxyapatite particles (5) were used as a control. The test materials were implanted subcutaneously in rats. Four weeks after operation, the animals were sacrificed and histopathological observations were performed. Cements (2) and (3) showed no inflammatory reaction, and were surrounded only by very thin fibrous connective tissues. The histopathological reactions of N-CPCs were nearly identical and were similar to (4) and (5). In addition, effects of alkaline phosphatase (ALP-ase) activity--invoked by the presence of cements (3) and (4)--on osteoblast-like cells derived from dog alveolar bone were also examined because ALP-ase activity is closely related to new bone formation. These results indicated that (3) and (4) were highly compatible with subcutaneous tissues and suggested that these cements may enhance new bone formation.

Acid Phosphatase↗
PubMed2004

Microstructural disassembly of calcium phosphates.

Microstructural factors may play a role in the osseointegration of calcium phosphates. In this paper, direct microstructural interactions between crystalline calcium phosphates and the biological milieu are reported. Degradation via exposure to osteoblast culture closely resembles in vivo interactions with subcutaneous tissues in a bovine model at early time periods. That these interactions were common to both experiments constitutes one of the few known examples of in vitro-in vivo correspondence. Interestingly, the degradation of phase pure hydroxyapatite (HA) in vitro was more rapid than that of biphasic HA in vivo. In both cases, grain extraction/pullout was frequently observed. This suggests a connection to smaller-scale observations of epitaxial CHA nucleation and growth on pre-existing HA grains. A microstructure in which the grain boundary is dissolving/corroding can apparently be disassembled by forces transmitted through biological structures. These observations are distinct from those of simple non-biological solutions and prove that biological environments can interact with the material beneath the ceramic-cell/ceramic-tissue interface. Many often ignored microstructural factors-grain size, shape, grain boundary strength and the presence of impurity phases-may in fact control degradation. We also suggest that even relatively modest initial grain sizes will, in combination with the mild/absent foreign body response to calcium phosphates, result in lengthy in vivo particle resistence.

Animals↗
PubMedDate not supplied

BS-SEM evaluation of the tissular interactions between cortical bone and calcium-phosphate covered titanium implants.

The improvement of the reliability of the contact between the osseous tissues and the implant materials has been tested by recovering the metallic implants with ceramic materials, usually calcium phosphates. In our study, the calcium phosphate recovering layers were deposited by means of a pulsed-laser deposition technique. Our aim was to to evaluate the tissue interactions established between cortical bone and titanium implants covered by five different layers, ranging from amorphous calcium phosphate to crystalline hydroxyapatite, obtained by altering the parameters of the laser ablation process. The surgical protocol of the study consisted in the simultaneous implantation of the five types of implants in both the tibial dyaphisis of three Beagle dogs, sacrificed respectively one, two and three months after the last surgical procedures. After the sacrifice, the samples were submitted to a scheduled procedure of embedding in plastic polymers without prior decalcification, in order to perform the ultrastructural studies: scanning microscopy with secondary and backscattered electrons (BS-SEM). Our observations show that both in terms of the calcified tissues appearing as a response to the presence of the different coatings and of time of recovering, the implants coated with crystalline calcium phosphate layers by laser ablation present a better result than the amorphous-calcium-phosphate-coated implants. Moreover, the constant presence of chondroid tissue, related with the mechanical induction by forces applied on the recovering area, strongly suggests that the mechanisms implied in osteointegration are related to endomembranous, rather than endochondral ossification processes.

Alloys↗
PubMed1982

Inorganic constituents of milk. III. The colloidal calcium phosphate of cow's milk.

Experiments involving the depletion of milk calcium phosphate (MCP) with EDTA have shown that it has a Ca to phosphate ratio of 1.61 +/- 0.04, close to that of dental enamel. The calcium phosphate also contains small amounts of citrate (citrate/Pi = 0.097 +/- 0.011 and Mg (Mg/Pi = 0.044 +/- 0.011). These experiments and model calculations indicate that the Ca binding capacity of casein is not reduced by mineralization with calcium phosphate and hence that ion binding sites and nucleation sites are distinct, or nearly so. Calculations of the ionic equilibria in the aqueous phase of milk show that there is an invariant ion activity product for a molecular formula close to that of dicalcium phosphate. It is suggested that MCP is a mixture of salts, with dicalcium phosphate a precursor of more basic salts such as octacalcium phosphate and hydroxyapatite.

Animals↗
PubMed1983

An intermediate state in hydrolysis of amorphous calcium phosphate.

The hydrolysis of previously prepared amorphous calcium phosphate (ACP) was studied in a solution "saturated" with ACP; this eliminated the initial consumption of acid due to ACP dissolution. The procedure established that conversion of high-concentration ACP slurry to an apatite involves two processes: the first process consumes acid and indicates the formation of a more acidic calcium phosphate intermediary with the solubility of octacalcium phosphate (OCP); the second process consumes base and indicates the conversion of the intermediary to apatite and, possibly, direct conversion of ACP to apatite. The thermodynamic analysis of the solution composition data suggests that ACP converts into a nonstoichiometric apatite when the OCP-like intermediary is formed, and a stoichiometric apatite is formed when no OCP-like intermediary is involved.

Calcium Phosphates↗
PubMed1993

Four calcium phosphate ceramics as bone substitutes for non-weight-bearing.

Calcium phosphate ceramics, beta-calcium pyrophosphate (Ca2P2O7), beta-tricalcium phosphate (Ca3(PO4)2), hydroxyapatite (Ca10(PO4)6(OH)2) and tetracalcium phosphate (Ca4(PO4)2O), were prepared. The calcium:phosphorus ratios and microporosities were 1 (31.6%), 1.5 (1.6%), 1.66 (1%) and 2 (34.6%) respectively. Samples (15 mm x 10 mm x 2 mm), abraded with No. 2000 alumina powder, were implanted into the tibial metaphysis of mature male rabbits. Failure load, when an implant detached from the bone or the bone itself broke, was measured. At 10 wk after implantation, the failure loads in beta-calcium pyrophosphate, beta-tricalcium phosphate, hydroxyapatite and tetracalcium phosphate were 31.65 +/- 9.90 N, 72.81 +/- 19.01 N, 49.49 +/- 17.25 N and 43.22 +/- 14.99 N respectively. At 25 wk after implantation, the values were 47.04 +/- 14.90 N, 71.34 +/- 19.50 N, 69.09 +/- 16.17 N and 62.03 +/- 18.62 N respectively. Histologically, bone bonding behaviour of calcium phosphate ceramics did not vary with the calcium:phosphorus ratio, as observed by contact microradiogram, Giemsa surface staining and scanning electron micrograph-electron probe micro analysis. There was no intervening soft tissue at the interface of bone and ceramics. Hydroxyapatite or tricalcium phosphate are used as bone substitutes. However, their mechanical strength is insufficient for weight-bearing and they are used as bone filler. This study showed that the apparent insignificance of strict calcium:phosphorus ratio with respect to the biological results greatly simplifies processing of calcium phosphate ceramics for clinical application. In clinical application, calcium phosphate ceramics with different Ca:P can be used as bone fillers for bone defects or bone cavities under non-weight-bearing conditions.

Animals↗
PubMed1988

Physiology of hard tissues in comparison with the solubility of synthetic calcium phosphates.

On the basis of the composition of the mineral in bone and the saturation level of blood plasma, with respect to slightly soluble calcium phosphates, it is shown that normal tissue fluids are not supersaturated with whole bone but with the minerals of dead bone. The phase controlling solubility in living bone is octocalcium phosphate, and the presence of this phase could regulate the calcium phosphate concentrations of the body fluids by a simple physicochemical equilibrium. It is explained how parathyroid hormone and calcitonine can act on osteocytes in such a way that shifts occur in this physicochemical equilibrium. It is also explained how the mineral of bone is affected by the activity of osteoclasts and osteoblasts during bone turnover. From this knowledge about the physiology of bone mineral, it is possible to predict the behavior of calcium phosphate bioceramics implanted in the body once their true solubility limits are known. Solubility studies have been carried out on hydroxyapatite, oxyhydroxyapatite, octocalcium phosphate, brushite, beta-tertiary calcium phosphate, and magnesium whitlockite. These studies indicate that the resorbabilities for implants of these materials are in the following order: magnesium whitlockite less than hydroxyapatite less than oxyhydroxyapatite less than beta-tertiary calcium phosphate. This order is consistent with data from implant studies now available in the literature.

Body Fluids↗
PubMed2005

Repair of the immature and mature craniofacial skeleton with a carbonated calcium phosphate cement: assessment of biocompatibility, osteoconductivity, and remodeling capacity.

BACKGROUND: The apatite compounds used most commonly in craniofacial reconstruction are highly crystalline and biologically inert ceramics. Because their capacity to be replaced by native bone is limited, they have found little application in repair of the growing craniofacial skeleton. Carbonated calcium phosphate cements more closely resemble the mineral phase of bone, thereby offering enhanced bioresorption and osteoconductivity, but their fate in the immature and mature craniofacial skeleton has not been investigated. METHODS: The authors hypothesized that the capacity for cell-mediated remodeling of carbonated calcium phosphate cements is based on (1) their crystallographic and compositional similarity to the mineral phase of bone and (2) the osteogenic capacity of the host. Four noncritical-sized calvarial defects were created in six 3-week-old and six 16-week-old Yorkshire pigs. The defects were repaired with autologous bone, sintered carbonated calcium phosphate cement disks with a higher crystal order, or carbonated calcium phosphate cement (Norian CRS; Synthes Maxillofacial, West Chester, Pa.). The fourth defect was left empty as a control. Specimens were harvested at 30 and 90 days postoperatively. RESULTS: Empty defects healed with dense fibroconnective tissue in all groups. Autologous bone grafts underwent complete remodeling and replacement with woven bone at both time points. Sintered carbonated calcium phosphate disks demonstrated no bony ingrowth or remodeling. In immature animals, carbonated calcium phosphate cement implants were progressively replaced with woven bone through osteoclast-mediated resorption and osteoblast-mediated bone formation. Only minimal remodeling of the carbonated calcium phosphate cement implants was observed in skeletally mature animals. CONCLUSIONS: The results of these experiments suggest that the extent of remodeling of carbonated calcium phosphate cement is dependent on both the composition of the implant itself and the osteogenic capacity of the host and that carbonated calcium phosphate cement may be used successfully for inlay applications in the immature craniofacial skeleton.

Animals↗
PubMed1999

Reconstruction of bone using calcium phosphate bone cements: a critical review.

The calcium phosphate cements (CPCs) are rapidly emerging as a new technology in craniofacial surgery and will soon impact many areas of orthopedic and maxillofacial reconstructive surgery as well. These materials are, in many ways, substantially different from the previously marketed dense, crystalline, hydroxyapatite (HA) ceramic materials of the 1980s. The CPCs are blends of amorphous and crystalline calcium phosphate compounds and set to produce HA. These materials 1) have x-ray diffraction spectra similar to the mineral phase of bone, 2) set endothermically at body temperature, 3) are capable of being injected into fractures or bone defects, 4) have compressive strengths equal to or greater than bone, 5) form chemical bonds to the host bone, and 6) may exhibit osteoconductive properties. This review provides an overall commentary on the different types of CPCs, emphasizing those materials currently on the market or soon to emerge in the marketplace.

Animals↗