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roots - international magazine of endodontology

I industry report _ NiTi files anatomical shape of the root canal during the entire treatmentprocedure.Incaseofresistanceorblocking inthecanal,thefilesbypassthisstresssituationbythe spiralschangingtheircross-section.Afteruse,thefile is subjected to new temperature conditions during autoclaving. The effect of heat automatically returns the instrument to its original shape. However, if the uniformspiralstructurecannolongerbereproduced, then the file is plastically deformed and should no longer be used. For the first time it is possible to visi- blydifferentiatebetweenelasticandplasticdeforma- tion with the naked eye, which considerably adds to application safety in the dental practice. Regardless of short set-up times or frequent changes in person- nel, even ENDO beginners can quickly scrutinise and assess the situation without a doubt—a considerable advantageinoftenstressfuldailytreatmentroutines. _Like a Phoenix from the ashes The reason why Nitinol can be trained so reliably liesinitsinnerstructure.NiTialloysdisplaytwocrys- tallographic phases: the austenite phase at high temperatures, and the martensite phase at rather lower temperatures. In the martensite phase, Niti- nolcanbebentintocomplicatedstructureswithout effort.Withoutfurtherexternalinfluences,thebent NiTi file with ‘controlled memory’ effect therefore remainsinthispositionatroomtemperature.Inthe austenite phase, i.e. at higher temperatures, the material can adopt its original structure and the molecules form a cubic face-centred lattice struc- ture.Heatinducesthephasetransformationandthe file returns to its original condition during sterilisa- tion.Thiscontrolledbounce-backeffectcanevenbe demonstrated directly using a conventional lighter. When placed over the flame, the heated instrument visibly changes from its bent form back to the clas- sicalstraightfileshapeinonlyafewseconds(Fig.5). Based on these insights, COLTENE presented its HyFlex CM file series for the first time in 2011. The abbreviation ‘CM’ stands for the above described ‘controlled memory’ effect. This special property results in an up to 300% higher fatigue resistance comparedwithconventionalNiTifiles,withanadded highlight:theHyFlexCMexcelsthroughitsextreme flexibility. Due to its special characteristics, the file adapts perfectly to prevailing canal anatomies and thus considerably reduces the risk of perforation. In addition, the instrument moves perfectly in the centre of the canal. This effectively prevents a shift in course or via falsa. The result is perfect cleaning and preparation of the root canal for subsequent Fig. 4_Plastic deformation of metal. 44 I roots1_2015 Fig. 4 Fig. 3 Fig. 3_Change in molecular structure.

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