In the system CaO-P,O,-H,O 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 Ringer's 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.

Calcium orthophosphates which either can. be formed by precipitation at room or body temperatures or by reactions at higher temperatures have been reviewed. Most formulations of cements contain at least one or more acidic components and one or more basic components which react when the powder is mixed with water. Several combinations of reactants are possible in the systems of calcium phosphates and even combinations with calcium phosphates containing sodium, potassium, magnesium, zinc, carbonate or chloride are thought to be useful. Furthermore, other compounds can be added as accelerators or retarders of the setting reaction or as promoters of bone ingrowth. In this study, over 100 formulations have been tested on their ability to set upon mixing with water. The initial and final setting times were measured with Gilmore needles.

No abstract

No abstract

No abstract

No abstract

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.

No abstract