JOURNAL OF MATERIALS SCIENCE LETTERS 14 41995) 4-5 Dimensional and thermal behaviour of calcium phosphate cements during setting compared to PMMA bone cements E. FERNANDEZ, M. P. GINEBRA, O. BERMODEZ*, M. G. BOLTONG, F. C. M. DRIESSENS, J. A. PLANELL Dept. of Materials Science and Metallurgy, UPC, ETSEIB,Avda. Diagonal 647, E 08028-Barcelona, Spain The use of PMMA bone cements for the fixation of metal endoprostheses in hip and knee surgery is quite successful. However, the average lifetime of such provisions is limited to about 12 years, which according to some investigators is mainly due to the PMMA cement [1]. During setting these materials develop temperatures far above body temperature so that the adjacent bone tissue becomes necrotic. Furthermore, they shrink due to polymerization and thus allow for micromovements of the prosthesis directly after the operation. That the gap between bone and cement becomes filled with fibrous tissue after some time does not inhibit these micromove- merits. Often the combined effect of these events is formation of particular debris and ultimately loosen- ing of the prosthesis by osteolysis. For these reasons, investigators have been search- ing for an alternative bone cement which does not have these disadvantages. Some authors propose glass ionomer cements [2], others composites of BIS-GMA resins with glass filler particles [3] or with hydroxyapatite filler [4] or cements made of a glass powder with an aqueous solution of ammonium phosphate [5]. In our laboratory calcium phosphate cements are being developed [6, 7]. The purpose of the present study was to measure the dimensional and the thermal behaviour of six of these calcium phosphate cements and to compare them with the behaviour of some commercial brands of PMMA bone cement. The active ingredients and the nucleator phases used in composing the powders of the six calcium phosphate cements are listed in Table I. They were either bought on the market or prepared from basic commercial products by ceramic technology as described elsewhere [6]. The composition of the cement powders and certain characteristics of the cements are given in Table 1I. For comparison the commercial PMMA bone cements CMW-1 (CMW Laboratories, Exeter, England) and ROSTAL (Industrias Quirtlrgicas de Levante, Paterna, Valen- cia, Spain) were used. The ultimate temperature during setting was measured with the method recommended for acrylic bone cements according to ASTM standard F451-86. In analogy with gypsum materials we expected TABLE I Ingredients used for the composition of the cement powders of the calcium phosphate cements used in this study Name Abbreviation Formula Monocalcium phosphate, monohydrate MCPM Dicalcium phosphate DCP Dicalcium phosphate dihydrate DCPD m-Tertiarycalcium phosphate or-TCP Precipitated hydroxyapatite PHA Chloroapatite CA Sodium whitlockite SWH Calcium potassium phosphate CPP Magnesium oxide Ca(HzPO4)2-H20 CaHPO 4 CaHPO4.2H20 Ca3(PO4)z CaI0(PO4)6(OH)2 Cal0(PO4)6C12 Cal0Na(PO4)7 CaKP04 MgO TABLE II Composition of the cement powders and their reaction products for the six calcium phosphate cements of this study Active Nucleator added Reaction Code ingredients Ca/P (%) product M14 SWH, CA, MCPM 1.00 DCPD 40 DCPD F36 DCP, o:-TCP 1.33 PHA 4 OCP ~ R45 MCPM, CaKPO4 1.33 PHA 20 OCP H90 MCPM, cr-TCP 1.33 PHA 4 OCP FI72 or-TCP 1.50 PHA 2 CDHA b V2 MCPM, MgO 0.50 PHA 43 CaMg2(PO4) 2 ~OCP = octocalcium phosphate Cas(HPO4)2(PO4)4.5H20. bCDHA = calcium deficient hydroxyapatite Cag(HPO4)(PO4)5OH. *At present: Universidad del Cauca, Popayan, Colombia. 4 0261-8028 ~ 1995 Chapman & Hall