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Effect of Design and Heat Treatment on the Mechanical Properties of NiTi Rotary Instruments

Seok Woo Chang,Soram Oh, Hyun-Jung Kim, Bong-Ki Jeon, Kee-Yeon Kum, Hiran Perinpanayagam

Adult Background/purpose: NiTi files have been manufactured with various designs and heat treatments. This study aimed to determine the effects of design and heat treatment on the mechanical properties of NiTi instruments. Materials and methods: ProFile, Profa File Gold, ProTaper Universal, ProTaper Gold, Profa Taper Gold, and ExactTaper H (n=44/brand) were subjected to bending, buckling, cyclic fatigue and torsional resistance tests (n=10/brand/test). Instrument surfaces were examined with scanning electron microscopy (SEM) (n=2/brand), and phase transformation behavior studied by differential scanning calorimetry (DSC) (n=2).

Results: ProFile and Profa File Gold showed a concave triangular crosssection with radial lands, while other NiTi files had a convex triangular crosssectional design. DSC curves revealed that austenitic transformationfinishing temperature of Profa File Gold, ProTaper Gold, Profa Taper Gold and ExactTaper H were above 37°C. ProTaper Universal, Profa Taper Gold, and ExactTaper H presented the highest bending resistance. ProTaper Universal showed the highest buckling resistance, elastic modulus, and the lowest cyclic fatigue resistance. ExactTaper H exhibited the highest cyclic fatigue resistance and ultimate torsional strength. ProTaper Gold and ExactTaper H showed the greatest angle of rotation until fracture and consisted of mainly R-phase at room temperature.

Conclusion: NiTi instrument’s mechanical properties were affected significantly by both design and heat treatment.