O. Bermúdez

Effective formulations for the preparation of calcium phosphate bone cements

In the system CaO−P2O5−H2O 13 different solids with varying Ca/P ratios are known. In addition calcium phosphates containing other biocompatible constituents like Na, or K, or Mg or Cl or carbonate, are known. Therefore, a large number of combinations of such compounds is possible which might result in the formation of calcium phosphate cements upon mixing with water. However, the number of calcium phosphates possibly formed by precipitation at room or body temperatures is limited to 12, which should limit the number of suitable combinations. In this study more than 450 different combinations of reactants have been investigated. The results were evaluated on the basis of the following criteria: (a) was the intended reaction product formed? (b) was the final setting time shorter than 60 min? (c) was the compressive strength after soaking for 1 day in Ringers solution at 37°C higher than 2 MPa? We found that 15 formulations satisfied all of these criteria. The distribution of cements synthesized in this way was 3 DCPD type, 3 CMP type, 6 OCP type and 3 CDHA type cements. The DCPD type cements were acidic during setting and remained that for a long time afterwards. CDHA type cements were neutral or basic during setting, and remained neutral after completion of the reaction. The OCP type cements were neutral both during and after setting. Two CMP type cements were basic both during and after setting. In this study compressive strengths were found up to 90 MPa. Also, in the literature values up to 90 MPa have been reported for this type of cement. Taking into account the excellent biocompatibility and the good osteoconductivity of calcium phosphates and the fact that these calcium phosphate cements can be injected into the site of operation, it may be expected that these materials will become the materials of choice for bone replacement and augmentation. Their suitability for the fixation of metal endoprostheses for joint replacement should be investigated as well.

Compliance of an apatitic calcium phosphate cement with the short-term clinical requirements in bone surgery, orthopaedics and dentistry

An apatitic calcium phosphate cement was developed containing a nucleator in its powder and an accelerator in the liquid and having an initial setting time of 7.5 min and a final setting time of 12.5 min according to testing with Gillmore needles at room temperature. At body temperature the initial setting time is 6 min, after which the wound can be closed. The dough time (during which it can be deformed without damaging its microstructure) is 4 min. Therefore, the time lost during an operation with this material is 2 min. The product does not shrink or expand during setting, neither is there a thermal effect; it does not swell or disintegrate upon exposure to aqueous fluids after initial setting. Upon soaking in Ringers solution the product obtains a final compressive strength of 40 MPa and 65% of that strength is reached within 6 h at body temperature. Cytotoxicity is absent. Applications are envisaged in bone surgery, orthopaedics and dentistry, a.o. for acceleration of the osseointegration of metal endoprostheses.

Compressive strength and diametral tensile strength of some calcium-orthophosphate cements: a pilot study

More than 100 different formulations of calcium-orthophosphate cements were subjected to determinations of the compressive strength and the diametral tensile strength after storage at room temperature for 24 h under 100% relative humidity (RH). It was found that setting occurred on more than 15 combinations of reactants. Further, it was shown that the mechanical properties of the cements which were obtained were also dependent on the water/powder ratio, the content of seed material and the storage conditions. Other factors which are thought to be of importance are the particle form and the particle size of the powder constituents as well as the addition of modifiers.

Development of some calcium phosphate cements from combinations of α-TCP, MCPM and CaO

From previous studies it is known that alpha-tertiary calcium phosphate (α-TCP), monocalcium phosphate monohydrate (MCPM) and calcium oxide form cements upon mixing combinations of them with water. In this study some formulations were optimized with respect to the particle size of the constituents, their molar ratio, amounts of hydroxyapatite or beta-tertiary calcium phosphate (β-TCP) added and the water/powder ratio. Three suitable products were obtained. Product 1 had a relatively short setting time and might be suitable as a dental cavity liner or for filling parodontological pockets or for filling alveolar cavities to prevent alveolar ridge resorption. Products 2 and 3 may be more suitable for orthopaedic purposes. Their compressive strength being 35 and 12 MPa, respectively, after soaking for 1 day in Ringers solution at 37°C. Product 1 reaches its full strength within 4 h, whereas products 2 and 3 take about 12 h and 10 h, respectively.

Development of an octocalcium phosphate cement

From previous studies it is known that alpha-tertiary calcium phosphate and dicalcium phosphate form a cement upon mixing with water. In this study this cement was optimized in terms of the milling of the constituents, their molar ratio, the amount of hydroxyapatite added and the water/powder ratio. The optimum Ca/P molar ratio of the cement mixture was 1.36±0.03. X-ray diffraction showed the reaction product to be octocalcium phosphate. Addition of precipitated hydroxypatite of over 3% diminished the final strength of the cement significantly. However, admixtures of only 2% of precipitated hydroxyapatite (a) kept the final compressive strength at 30±5 MPa after soaking in Ringers solution at 37°C, (b) diminished the initial setting time from 27.5 to 10 min and the final setting time from 65 to 40 min, (c) diminished the time in which the final strength was reached from 36 to less than 14 h. The tensile strength of this cement is 19±1% of its compressive strength. The optimum water/powder ratio as found in this study was 0.30 g/g.

Optimization of a calcium orthophosphate cement formulation occurring in the combination of monocalcium phosphate monohydrate with calcium oxide

In a previous study it has been found that mixtures of monocalcium phosphate monohydrate MCPM and calcium oxide CaO set upon mixing with water. In this study it was found that the optimum composition for such a mixture is a Ca/P molar ratio of 1.35±0.02. The milling procedure for preparation of the powder of this cement was also optimized. the optimum water/powder ratio appeared to be 0.53±0.01. Amounts of precipitated hydroxyapatite up to 7% by weight increased the compressive strength and the diametral tensile strength of the cement. The maximum values found for these properties were 6 and 1.6 MPa, respectively. Finally, it was found that the cement obtained its maximum strength within 5 h but this diminished upon further soaking in Ringers solution at 37°C until after 10 weeks of soaking the strength was decreased to 62% of the maximum value.

Common ion effect on some calcium phosphate cements

Abstract Four calcium phosphate cements were selected to investigate whether the use of aqueous solutions of CaCl2, Na2HPO4 or NaH2PO4.2H2O instead of water had any effect on their properties. One cement was sensitive for the CaCl2 solution, two others for the phosphate solutions, and the fourth cement was insensitive to all three solutions. The setting times were reduced considerably. However, the strength values after soaking the cements in Ringers solution for 1 day at 37°C decreased with the use of an accelerator. The use of phosphate solutions changed the pH of the cement slurry slightly during setting, whereas the CaCl2 solution had no effect on the pH.

Compliance of a Calcium Phosphate Cement with Some Short-term Clinical Requirements

ABSTRACT Short-term clinical requirements proposed for calcium phosphate cements are: (1) initial setting time between 4 and 8 min, (2) final setting time between 10 and 15 min, (3) maximum attainable strength, and (4) attainment of this maximum strength within the shortest possible time. From previous studies it was known that the setting times of a calcium phosphate cement made of α-TCP could be controlled by using solutions of Na 2 HPO 4 as cement liquid and that the strength could be improved by controlling the milling. Combinations of these factors were used to find out whether the cement derived from α-TCP could be brought to complete compliance. It could be concluded: (a) that compliance to requirements 1 and 2 simultaneously was possible, (b) that this caused a drop in the maximum compressive strength from 70 to 45 MPa, and (c) that at body temperature the maximum strength is achieved much faster than at room temperature.

Chloride- and alkali-containing calcium phosphates as basic materials to prepare calcium phosphate cements

Combinations of an alkali-containing calcium phosphate-like rhenanite, sodium whitlockite or calcium potassium phosphate and a chloride-containing calcium phosphate-like spodiosite or chloroapatite with or without additions of other calcium phosphates like monocalcium phosphate monohydrate, dicalcium phosphate or dicalcium phosphate dihydrate were made and mixed with water into pastes. The setting time of these pastes was determined. After soaking for a day in Ringers solution at 37 degrees C the compressive strength and the diametral tensile strength were determined. Two of the combinations tried in this study resulted in the formation of cements at room temperature. One cement was of the type dicalcium phosphate, whereas the other gave octocalcium phosphate as the solid reaction product. The byproducts formed were an aqueous solution of NaCl and one of K2HPO4, respectively. Applications for bone repair and augmentation are envisaged.

Preparation and properties of some magnesium-containing calcium phosphate cements

Attempts were made to prepare magnesium-containing calcium phosphate cements. These were successful at the composition CaMg2(PO4)2xH2O. X-ray diffraction showed that such a compound is not formed but that the cement consists of magnesium phosphate precipitated on the calcium phosphate admixture. The pH of this formulation is around 10 during setting and after. The cement is injectable. Its setting time is about 10 min. In this study compressive strength values were as high as 11 MPa and the diametral tensile strength was over 2 MPa. Animal experiments must show whether it is suitable for replacement or augmentation of bone in non-load bearing situations.