Phase transformation behaviour and bending property of twisted nickel-titanium endodontic instruments

Aim To investigate the relationship between phase transformation behaviour and bending property of nickel-titanium endodontic instruments manufactured by a twisting process. Methodology The phase transformation behaviour and bending property of Twisted Files (TF; SybronEndo, Orange, CA, USA) and K3 (SybronEndo) with.06 taper and size 30 tip were investigated. K3 was used as control group. Phase transformation behaviour was estimated by differential scanning calorimetry (DSC). Transformation temperatures were calculated from the DSC curve. Bending load of the instruments was measured by cantilever-bending test at 37°C. Data were analysed by Student's t-test and Mann-Whitney U-test. Results The phase transformation temperatures of TF were significantly higher (P<0.05) than those of K3. The bending load values were significantly lower for TF than that of K3 (P<0.05), both in the elastic and super-elastic ranges. Conclusions The new method of manufacturing NiTi instruments by twisting coupled with heat treatment might contribute to the increased phase transformation temperatures and superior flexibility.