Bioceramics 17

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Authors: Georg Berger, Renate Gildenhaar, Jutta Pauli, Heidi Marx
Abstract: This paper deals with calcium phosphate cements containing alkali to achieve higher solubility. Until now normally for all cements also if alkali was integrated the self-setting process leads to hydroxyapatite (HA) or calcium deficient HA (CDHA). In cases where fluid dispersions of HA were used for bone defect treatment the HA remains and do not acts self-hardening. The selfsetting cements show high compressive strength in comparison to the HA supplied as a paste. They show latent hydraulic behavior during the self-hardening process. The following storage in SBF for four weeks also did not lead to a strong change of the starting materials that were Ca2KNa(PO4)2 or Ca10[K/Na](PO4)7.
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Authors: Liam M. Grover, Uwe Gbureck, David Farrar, J.E. Barralet
Abstract: In this study the setting times, compressive strengths and microstructures of cements formed using pyrophosphoric acid solution and b-tricalcium phosphate (β-TCP; Ca3(PO4)2) were compared with those of cement formed using orthophosphoric acid solution and b-TCP. It was found that cement formed using pyrophosphoric acid solution set more slowly than that formed using orthophosphoric acid and could be mixed to a higher powder to liquid ratio, facilitating the production of cement exhibiting compressive strengths, without pre-compaction, as high as 25 MPa. The use of pyrophosphoric acid as opposed to orthophosphoric acid resulted in a marked change in the microstructure of the cement.
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Authors: I. Khairoun, A. Billon, G. Daculsi, Christian Merle, Jean Michel Bouler
Abstract: In this study a biodegradable polymer microspheres were used to make an alpha-TCP calcium phosphate bone cement macroporous. The biodegradable polymer microspheres were synthesised at the laboratory and a sieve fraction of this microspheres ranging between 100 and 300 microns was incorporated in a calcium phosphate cement, where the powder contained a-Ca3(PO4)2 (a-TCP). The microspheres content of the cement was 10 %. The cement pastes were prepared at liquid-to-powder ratios from 0.32 to 0.40 ml/g. X-ray diffraction and Infra-red spectroscopy was performed to analyse the reaction on powdered samples that were let to set at different times in a Ringer’s solution at body temperature. Mercury porosimetry has been used at the main method for porosity measurements. Scanning electron microscopy (SEM) was performed on fractured samples fro microstructural analysis. The microspheres seemed to retard slightly the cement setting and to reduce progressively the compressive strength after aging in aqueous solutions which were continuously refreshed. SEM pictures and XRD patterns of the samples after 1 and 4 weeks of aging showed that the microspheres were dissolved progressively. Mercury porosimetry measurements assessed at different times of aging showed an improvement in the total porosity and the pore diameter of the set material and confirmed SEM and XRD results.
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Authors: S. Shinzato, Takashi Nakamura, Koji Goto, Tadashi Kokubo
Abstract: A new bioactive bone cement (cGBC) consisting of crystallized MgO-CaO-SiO2-P2O5 glass beads and high-molecular-weight polymethyl methacrylate (hPMMA) has been developed to overcome the degradation seen with a previously reported cement (GBC) consisting of MgO-CaO-SiO2-P2O5-CaF2 glass beads and hPMMA. The purpose of the present study was to evaluate the degradation of cGBC using an in vivo aging test, and to compare the degradation of cGBC with that of GBC. Hardened rectangular specimens (20x4x3mm) were prepared from both cements. Their initial bending strengths were measured using the three-point bending method. GBC and cGBC specimens were then implanted into the dorsal subcutaneous tissue of rats, removed after 6 or 12 months, and tested for bending strength. The initial bending strengths (MPa) of GBC and cGBC were 141.9±1.8 and 144.4±2.4, respectively, while at 6 months they were 109.1±2.6 and 114.1±4.9, and at 12 months they were 109.1±3.2 and 113.1±3.3, respectively. Although the difference in initial bending strengths was not significant, the bending strength of cGBC was significantly higher than that of GBC at 6 and 12 months, indicating that cGBC is more resistant to cement degradation. The bending strengths of both GBC and cGBC decreased significantly from 0 to 6 months but did not change significantly thereafter. Thus, degradation of cGBC and GBC does not appear to continue after 6 months. We believe that cGBC and GBC are strong enough for use under weight-bearing conditions and that their mechanical strength (especially that of cGBC) is retained in vivo.
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Authors: K.J. Lilley, Adrian J. Wright, David Farrar, J.E. Barralet
Abstract: Brushite cement is more soluble than apatite cement in physiological conditions and therefore may be more resorbable in vivo. Brushite cement has been formed previously by mixing β-tricalcium phosphate, water and an acidic source of phosphate ions. However, brushite cement may be formed by the mixture of H3PO4 solution and poorly crystalline precipitated hydroxyapatite (HA). Several additives have been used to alter the physicochemical properties of brushite cement. In this study sulphate ions where added to the cement system by addition of ammonium sulphate to HA during HA preperation. Sulphate ions were found to alter the structure, composition and mechanical performance of cement.
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Authors: Kyung Sik Oh, Soo Ryong Kim
Abstract: Effect of the starting compostion was studied in bone cement containg coarse b-tricalcium phosphate (b-TCP) granules which was very dense and round. With respect to the mixing ratio between b-tricalcium phosphate and monocalcium monophophate (T:M), the properties such as setting time, density and compressive strength were measured. The properties of bone cement prepared from normal powdery b-TCP was strongly dependent on the initial mixing ratio (T:M). Though the compressive strength as well as density was maximum at T:M = 6:4, small departure of compostions from T:M=6:4 resulted in drastic decrease of compresive strength. On the contrary, in the specimens from granular b-TCP, compressive strength was much less deependent on the initial mixing ratio. Range of optimum compressive strength covered from T:M=6:4 to 8:2. Therefore, granular groups provided more degree of freedom to control other properties such as setting time while maintaing its compressive strength.
141
Authors: Hakan Engqvist, Lars Kraft, Håkan Spengler, Leif Hermansson
Abstract: The area of cements in dentistry is steadily growing with the introduction of new systems that need to be cemented to the tooth, e.g. new inlays and crowns. With the better properties of the implants there is a need for new cements with high bond strength, good esthetic and mechanical properties. The bioactive minerals have not been explored as dental cement. This paper investigates the strength, setting time and film thickness of a novel dental cement based on the biomineral Marokite (calcium aluminate) as bonding system. The reactive Marokite powder is mixed with glass filler (ratio of 1.9 by volume) and water (ratio of 0.4 by weight) to a paste, which hardens within 6 minutes and has a working time of 2 minutes. The compressive strength reaches 143 MPa after 24 hours and the flexural strength almost 40 MPa. When the film thickness is measured at the end of the working time it is about 50 µm. Compared to glass ionomer cement (Fuji Cem) and zinc phosphate cement (Harvad) the biomineral system has higher strength and comparable setting time and film thickness. The investigation shows that it is feasible to develop dental cements based on biominerals, in this case a Marokite based material. The cement complies with the given standards.
145
Authors: Masashi Mukaida, Masashi Neo, Y. Mizuta, Yasushi Ikeda, Takashi Nakamura
Abstract: High resolution X-ray CT is a powerful means for analyzing comprehensive ceramic biomaterials in a living body. The benefit of this method is that morphological and volume changes of implant materials can be evaluated without retrieve of the implant in an animal body, resulting in no killing of the animals and long term evaluation even more than one year. In this study, in situ techniques for observation of calcium phosphate cement is developed. Calcium phosphate cement (CPC) was implanted into a femur and under skin of a rat. The volume and morphology change of the CPC were repeatedly measured using the same rat for more than 12 months. The 3-dimentional (3-D) structures of the CPC were imaged and reconstructed from hundreds of 2-D cross sectional CT images, which were obtained at one time by a 360 degree rotation of the sample. The structure of the CPC was visualized with 3-D, and the volume were numerically analyzed by using a 3-D structure analyzing computer software, which enabled two-value processing and estimation of the quantities of the CPC. Moreover some of the CPC samples were retrieved and were observed by SEM. In the results, the surface of the calcium phosphate cement changed from smooth to jagged with increasing implanted period. The CPC volume implanted into bone was gradually decreased with increasing implanted period. The volume loss was 8 % after 12 months. The CPC volume under skin after 1 month increased by 7 %. After that the volume gradually decreased in next 3 months. Absorption process of CPC in a rat will be discussed.
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Authors: S.B. Cho, Sang Bae Kim, Keon Joon Cho, Ill Yong Kim, Chikara Ohtsuki, Masanobu Kamitakahara
Abstract: Novel PMMA-based bone cement using bioactive sol-gel derived CaO-SiO2 powder in order to induce bioactivity as well as to increase its mechanical property. The novel PMMA-based bone cements formed apatite on their surfaces in Simulated Body Fluid(SBF). In the present study, a change in mechanical property of the cement was evaluated using SBF. Before soaking in SBF, its compressive strength showed 80.6±2.1MPa. After soaking in SBF for 2 weeks, 8weeks and 9 weeks, its compressive strength were changed to 83.6±1.6MPa, 87.3±2.4MPa and 85.6±1.8MPa, respectively. It is clear that from the above result, there is no decrease in its compressive strength within 9 weeks soaking in SBF. That it hardly decreases in compressive strength of 7P3S bone cement in SBF is due to the relative small amount of gel powder or its spherical shape and monosize. Therefore, the newly developed PMMA-based cement can bond to the living bone and also be effectively used as bioactive bone cement without decrease in mechanical property.
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Authors: J.A. Delgado, I. Harr, Amisel Almirall, Sergio del Valle, Josep A. Planell, M.P. Ginebra
Abstract: In this work an injectable and self setting calcium phosphate/albumen foam is developed. The effect of both the amount of albumen and the particle size of the starting a-tricalcium phosphate (a-TCP) powder on the injectability of the cement paste is studied. X-ray diffraction (XRD) and infrared (IR) analysis of the samples reveal that the hydrolysis of a-TCP to calcium deficient hydroxyapatite (CDHA) is not affected by the addition of albumen. A foamed structure formed by spherical pores with diameters between 100 and 500 µm is observed by SEM. This porous structure is maintained after injection of the paste, although some deformation of the pores is produced due to the extrusion process. The injectability of the cements is increased by the presence of albumen as compared with cements prepared in the same conditions but without foaming agent.
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