DIFFERENTIAL SCANNING CALORIMETRIC (DSC) ANALYSIS OF ROTARY NICKEL-TITANIUM (NiTi) ENDODONTIC FILE (RNEF)

The superelastic working temperature of rotary nickel-titanium (NiTi) endodontic file (RNEF) is thermodynamically limited to within approximately 20K above its austenitic-finish transformation temperature (A_f) [1]. While DSC studies of RNEF has been reported [2-3], some were carried out over 5 years ago and that regional A_f characterization along the entire length of RNEF is not available.

This study determined the variation in A_f along the length span of RNEF. Three commercial brands of 4% taper RNEF: GTX (#20, 25mm, Dentsply Tulsa Dental Specialties,Tulsa, OK), K3 (#25, 25mm) and TF (Twisted File #25, 27mm) (Sybron Kerr, Orange, CA) were cut into segments at 4mm increment from the working tip. Regional specimens were encased in aluminum pan without crimping, and measured for heat-flow against empty pan over thermal heat-cool cycling, generally with continuous heating or cooling (5°C/min) and 5-min hold at set temperatures (start, finish temperatures): GTX: -55°C, 90°C; K3: -55°C, 45°C; TF: -55°C, 60°C  by Thermal Analysis (TA) Differential Scanning Calorimeter. Data were analyzed by software (Universal Analysis). A_f values were obtained by intersection of the tangent of the steepest endothermic slope at the austenitic-end with the baseline extension of the heating curve. This experiment demonstrated regional differences in A_f along the length of GTX and K3, but not apparently of TF.  A contributory effect of regional difference in strain-hardening due to grinding and machining during manufacturing is proposed.

References

[1] Y Liu, SP Galvin. Criteria for pseudoelasticity in near-equiatomic NiTi shape memory alloys. Acta Mater, 45:4431-4439, 1997.                                                                                          [2] G Kuhn, L Jordan. Fatigue and mechanical properties of nickel-titanium endodontic instruments. J Endod, 28:716–20, 2002. 2002.                                                                          [3] WA Brantley , TA Svec , M Iijima , JM Powers, TH Grentzer. Differential scanning calorimetric studies of nickel titanium rotary endodontic instruments after simulated clinical use.  J Endod, 28:774–8, 2002.