Microstructural and mechanical characterizations of new Ni-Ti endodontic instruments

Laurence Jordan,Anthony Sultan,Philippe Vermaut,N Schryvers,J Van Humbeeck

doi:10.1051/matecconf/20153303005

Abstract

NiTi alloys have been used for many years in dentistry, especially in endodontology. High flexibility of NiTi alloys, compared to the stainless steel one, has made of NiTi the alloy of choice for the new generation of shaping files. Despite the improvement of file design, endodontic NiTi instruments are not perfect and the risk of fracture during use is still a concern. In recent years, several new thermomechanical processes have been developed to optimize the structure of NiTi alloys, in particular, the development of treatments named “M-wire”, “R phase” and “CM wire” technologies. According to the manufacturers, these innovative treatments may improve the flexibility and the fatigue life of endodontic instruments. In the present work, new generations of these files have been characterized using DSC and bending tests and compared to a conventional NiTi file. The new endodontic instruments seem to improve the instrument properties. Hypotheses on the microstructural modifications due to specific thermomechanical treatments are proposed.

Highlights

NiTi alloys have been used for many years in dentistry, especially in endodontology [1]
“M-wire” would be produced by applying “specific tensions and heat treatments at various temperatures” [4,5]; “R phase” instruments would be “twisted by a thermal process” during the R-Phase transformation [5,6] and “Controlled Memory (CM) wire” would be a novel NiTi alloy using a special thermomechanical process that controls the memory of the material [5,7]
For “CM wire” instrument, DSC cooling curve presented three step transformations: A→R followed by a weak peak corresponding to a first transformation to martensite (*M1) and a third peak corresponding to the formation of a second martensite M2

Summary

Introduction

NiTi alloys have been used for many years in dentistry, especially in endodontology [1]. The great flexibility of NiTi alloys gives the endodontic instrumentation undeniable qualities compared to that of stainless steels. It provides safer preparations, even in the canals with curvatures. “M-wire” would be produced by applying “specific tensions and heat treatments at various temperatures” [4,5]; “R phase” instruments would be “twisted by a thermal process” during the R-Phase transformation [5,6] and “CM wire” would be a novel NiTi alloy using a special thermomechanical process that controls the memory of the material [5,7]. The alloy is solution treated (between 600 and 900°C) and aged around 400°C [8,9]

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Conclusion