JOURNALOF MATERIALS SCIENCE: MATERIALS IN MEDICINE 13 (2002) 17±22 Curing characteristics of acrylic bone cement N.J.DUNNE 1 ,J.F.ORR 2 1 School of Mechanical and Manufacturing Engineering, Dublin City University, Glasnevin, Dublin 9, Republic of Ireland 2 School of Mechanical and Manufacturing Engineering, The Queen's University of Belfast, Stranmillis Road, Belfast, BT9 5AH, Northern Ireland Commercialacrylicbonecementsaresuppliedastwocomponents,apolymerpowderanda liquidmonomer.Mixingofthetwocomponentsisfollowedbyaprogressivepolymerization oftheliquidmonomertoyieldasolidmass,ahighlevelofheatbeinggeneratedduringthis exothermicreaction.Theexposureofbonetohightemperatureshasledtoincidencesof bonenecrosisandtissuedamage,ultimatelyresultinginfailureoftheprosthetic®xation. Theaimofthisstudywastodeterminethethermalpropertiesoftwoacrylicbonecementsas theyprogressthroughtheirpolymerizationcycles.Itwasalsofeltthattherewasaneedto quantifythevariationsinthecuringcharacteristicsasafunctionofpreparingbonecement bydifferenttechniques,handmixingandvacuummixing.Anumberofparameterswere calculatedusingthedatagatheredfromtheinvestigation:peaktemperature,cure temperature,curetime,andthecumulativethermalnecrosisdamageindex.Theresults showthetemperaturepro®lerecordedduringpolymerizationwaslowestwhenthecement waspreparedusingtheHowmedicaMix-KitI 1 system:36  CforPalacosR 1 and41  Cfor CMW 31 respectively.Whentheacryliccementswerepreparedinanyvacuummixingsystem therewasevidenceofanincreaseinthecuretemperature.Themainfactorthatcontributed tothisriseintemperaturewasanimbalanceinthepolymerpowder:liquidmonomerratio, therewasahighincidenceofunmixedpowdervisibleinthemixingbarrelofsome contemporaryvacuummixingdevices.Observingthethermalcharacteristicsofthe polymethylmethacrylate(PMMA)bonecementsassessed,itwasfoundthatparticular formulationsofbonecementsaresuitedtocertainmixingmethodologies.Itisvitalthatafull investigationisconductedonacementmixing/deliverysystempriortoitsintroductioninto theorthopaedicmarket. # 2002 Kluwer Academic Publishers 1. Introduction The exposure of bone to high temperatures has become quite common, especially with the increasing use of acrylic bone cement. With regard to total hip arthro- plasty, many authors have commented on the temperature problem induced by the curing polymethyl methacrylate (PMMA) cement mass. It has been shown that three factors can affect bony tissue as a consequence implants using PMMA bone cement [1, 2]: * Polymerization temperature of bone cement; * Cyto-toxicity of the liquid monomer; * Diminished vascularity of the bone due to surgical reaming of the medullary canal. It has been cited by DiPisa et al. [3] that the temperature at the bone-cement interface is a function of: * The quantity of heat produced by the bone cement; * The rate at which the heat is produced [4]; * The thermal conductivity and thermal capacity of the bone, prosthesis and the cement [5, 6]; * The initial conditions of the bone/cement prosthesis system, including initial and ambient temperature, and preparation of the cement [7]. Polymerization temperatures range from 40  C to 110  C. Meyer et al. [8] recorded that setting bone cement never exceeded 110  C, Revie et al. [9] quoted a mean exothermic temperature of 67.46  C for an unloaded specimen, Huiskes [10] showed that interface tempera- tures could reach as high as 100±120  C. Revie et al. [9] observed that the cement layer thickness and position of the site of measurement are two factors that in¯uence the exothermic curing temperature. Meyer et al. [8] found that the maximum temperature generated was 107  C for an cement mantle of 10 mm and 60  C for a mantle of 3 mm. Sih et al. [11] showed that for a cement thickness of 1 mm the temperature was 41  C and for 5 mm 56  C, and for a cement thickness of 6±7 mm 60  C. Moritz and 0957±4530 # 2002 Kluwer Academic Publishers 17