Int J Cur Res Rev | Vol 9 • Issue 15 • August 2017 32 Effect of Cryogenic Treatment on Fracture Resistance of Nickel Titanium Rotary Instruments a Systematic Review Kumar Ujjwal 1 , Anamika C. Borkar 2 , Piyush Oswal 3 , Karan Bhargava 3 1 Post Graduate, Dr. D.Y. Patil Dental College & Hospital, Pune, India; 2 Professor & PG Guide, Dr. D.Y. Patil Dental College & Hospital, Pune, India; 3 Senior Lecturer, Dr. D.Y. Patil Dental College & Hospital, Pune, India. ABSTRACT Introduction: Endodontic instruments upon rotation are subjected to both tensile and compressive stresses in curved canals. This stress is localized at the point of curvature. It has been demonstrated that the continuous cycle of tensile and compressive forces in the area of curvature of the canal to which (Nickel Titanium) NiTi rotary instruments are subjected produce a very de- structive form of loading, causing cyclic fatigue and eventually fracture of the instrument. 2 The aim of this study is to conduct a systematic review on the effect of cryogenic treatment on fracture resistance of nickel titanium rotary instruments. Methods: Two Internet sources of evidence were used in the search of appropriate papers satisfying the study purpose: the National Library of Medicine (MEDLINE PubMed) and Google Scholar, Google and manual search using DPU college library resources. All cross reference lists of the selected studies were screened for additional papers that could meet the eligibility criteria of the study. Results: Preliminary screening consisted total of 54 articles out of which 24 articles were selected. The papers were screened independently by two reviewers. At first the papers were screened by title and abstract. As a second step, full text papers were obtained when they fulfilled the criteria of the study aim. Any disagreement between the two reviewers was resolved after ad- ditional discussion. Finally 3 articles were included in this study. Conclusions: Within the limitations of this study we can conclude that the cryogenic treatment increases the fracture resistance of nickel titanium rotary instruments. Key Words: Treatment, Fracture Resistance, Nickel-Titanium Rotary Instruments Corresponding Author: Kumar Ujjwal, Post Graduate, Dr. D.Y. Patil Dental College & Hospital, Pune, India. Mob: 9021451669; Email: guptaujjwal05@gmail.com ISSN: 2231-2196 (Print) ISSN: 0975-5241 (Online) DOI: 10.7324/IJCRR.2017.9156 Received: 19.05.2017 Revised: 16.06.2017 Accepted: 20.07.2017 INTRODUCTION Nickel-titanium alloy exhibits the unique properties of shape memory (SM) and pseudoelasticity. 1 It is well known that in- strument separation occurs either by brittle fracture (cyclic fatigue) or by ductile fracture (torsional fatigue). Endodontic instruments upon rotation are subjected to both tensile and compressive stresses in curved canals 2 . This stress is localized at the point of curvature. It has been demonstrated that the continuous cycle of tensile and compressive forces in the area of curvature of the canal to which NiTi rotary instruments are subjected produce a very destructive form of loading, caus- ing cyclic fatigue and eventually fracture of the instrument 2 . Despite the extreme flexibility, 4 these thermomechanically processed NiTi instruments undergo permanent plastic defor- mation, especially while reusing the smaller size instruments 5,6 due to inadequate martensite content. Cryogenic treatment is a supplementary procedure of subjecting stainless steel 7,8 and superelastic NiTi 3 to subzero temperatures that affects the entire bulk of the material rather than the accessible surface alone. One of the mechanisms proposed behind the improve- ment in properties following cryogenic treatment is the com- plete martensitic transformation from the austenite phase. 9 It has been proved that deep cryogenic treatment (DCT) at a soaking temperature of up to −185°C increases the martensite content of SM NiTi alloys by a similar mechanism. 10 Previ- ous studies have been done evaluating the effect of cryogenic IJCRR Section: Healthcare Sci. Journal Impact Factor 4.016 ICV: 71.54 Review Article