Issue 28

A. Brotzu et alii, Frattura ed Integrità Strutturale, 28 (2014) 19-31 ; DOI: 10.3221/IGF-ESIS.28.03 21 M ATERIALSANDTECHNIQUE his study has been carried out on two different Ni-Ti rotary instruments manufactured byMICRO-MEGA ® and namedHERO 642 ® . The two instruments, shown in Fig. 1 (red, the biggest, and yellow, the smallest), present as main difference the root cross sectional diameter, the yellow instrument is 0.75 mm in diameter while the red is 1.0mm in diameter. Both instruments have been observedwith a ScanningElectronMicroscope (SEMHITACY S-2500, KEVEXEDSmicroprobe). DSC analysis has been carried out in order to identify possible phase transition of the Ni-Ti material. Figure 1 : InvestigatedMICRO-MEGAHERO642 rotary instruments. In order to test these instruments, root canal treatments have been simulated employing the Perspex simulator shown in Fig. 2. Tests have been carried out with an equipment for root canal treatment manufactured by NSH (ENDO-MATE DT) with the following standard settings: rotation speed 140 rpm, torque 3.0Ncm. Tests have been carried out at room temperature with or without the use of an aqueous lubricant gel whose composition is object of a patent request. Yellow instruments were also testedwith another lubricant available off the shelf, based onUrea Peroxide andEthileneDiamine Tetracetic Acid. Rheological analyses were performed at 23 °C using a rheometer equipped with a Peltier system for temperature control and a measurement system at parallel plates, to highlight the differences between the two types of lubricant by deformation control. In addition, heat capacities of the two gels at different temperaturesweremeasured. The fatigue test procedure consists in the repetitionof 30 second cycles. After each cycle the instruments is removed from the Perspex simulator and cleaned inorder to eliminate plastic debris and to identify potential macroscopic defects. Figure 2 : ENDO-TRAINING-BLOC employed as simulator. Every four cycles the simulator is replaced because the canal is enlarged by mechanical processing and thus it does not offer resistance any longer. It has been observed that during the first cycle the rotary instrument reaches only the half of the canal, during the second cycle it reaches the bottom of the canal, during the other 2 cycles the instrument works only to enlarge the canal. The insertion of rotary instrument must be as parallel as possible to the canal entrance and the operator has to be particularly accurate inserting andmaintaining the tool in the root canal with regular up and downmovement, necessary in order to avoid the seizing of the instruments inside the simulator . T