one cement to cyclical load<strong>in</strong>g is extremelysignificant and is a subject of many ongo<strong>in</strong>g studies[8-14]. Also, <strong>PMMA</strong> has been widely used as amodel for studies of fatigue and fracture <strong>in</strong>polymers. Effects of different factors have been<strong>in</strong>vestigated, whereas variable amplitude load<strong>in</strong>goffer <strong>in</strong>sight <strong>in</strong> its behavior from aspects of fatigueand crack propagation. The load<strong>in</strong>g curve <strong>in</strong> Fig. 5consists of both elastic and plastic contribution,while the unload<strong>in</strong>g curve is purely elastic andallows calculations of elastic modulus andhardness. <strong>Bone</strong> cements have a more complicatedstructure if compared to pure <strong>PMMA</strong>, withpreviously polymerised beads <strong>in</strong> a softer matrixwhich cures on implantation, and other componentssuch as particles of barium sulphate or zirconia tomake the cement visible <strong>in</strong> radiographs. Thismicrostructural complexity means that the cementmay behave very differently from pure <strong>PMMA</strong>.There are several commercially available bonecement mixtures and they have beencomprehensively studied both <strong>in</strong> laboratory andcl<strong>in</strong>ical practice. However, there are still featuresthat need to be enhanced and <strong>in</strong>dentation tests canbe used for further understand<strong>in</strong>g of its behavior.Cl<strong>in</strong>ical failure of the cement occurs over long timeperiods, and this implies that the crack growth rateis very low, perhaps as low as 10 -12 m/cycle. It isclear from Fig. 6 that cracks did not occur <strong>in</strong> thistest<strong>in</strong>g and that edges are smooth and clearlymarked with well shaped impr<strong>in</strong>t. Therefore, valuesof hardness H IT and elastic modulus E IT of bonecement sample can be taken as valid. Micro<strong>in</strong>dentation method can be used for measur<strong>in</strong>g ofelastic modulus and hardness of prepared bonecement mixtures <strong>in</strong> a short period of time.5. CONCLUSIONCharacterization of bone cement to cyclical load<strong>in</strong>g isextremely significant and is a subject of manyongo<strong>in</strong>g studies. Studies showed that one of the ma<strong>in</strong>reasons of cement failure mechanism is related tofatigue failure and fatigue crack propagation.Indentation represents flexible mechanical test<strong>in</strong>g dueto its simplicity, m<strong>in</strong>imal specimen preparation andshort time needed for tests. Devices with depthsens<strong>in</strong>g possibilities, such as CSM Nano IndentationTester, enable determ<strong>in</strong>ation of hardness, elasticmodulus, plastic stress-stra<strong>in</strong> behavior and/or creepbehavior directly us<strong>in</strong>g the tester, without the need tomeasure contact impressions.Results obta<strong>in</strong>ed with<strong>in</strong> this study were fullycomparable with the literature data found for <strong>PMMA</strong>and commercial bone cements. Micro <strong>in</strong>dentationmethod can be used for measur<strong>in</strong>g of elastic modulusand hardness of prepared bone cement mixtures. 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