Introduction: Nitinol (NiTi) is the most interesting smart material used in orthopedic surgery and production of artificial muscles. Considering its medical applications, Nitinol biocompatibility is, therefore, quite important. This issue is discussed in this paper.Methods: Nitinol alloy experimentally produced by melting and casting under vacuum, plus imported commercial AO samples were implanted in limb tissue of a number of male rats. Twenty one days after the implantation, fibroblast and fibrosis formation in the tissues around the alloy were studied.Results: The amount of the alloy that was corroded under the experimental invitro conditions was acceptable. The biocompatibility of the experimentally made alloy implanted in limb tissue was nearly similar to that of the imported alloy.Conclusion: According to the results obtained, utilization of Nitinol in medicine is scientifically justifiable. Possibilities of its wide industrial and medical applications favorably support the mass production of the alloy in the country, and its biocompatible parallels that of the imported material.

Aim: In the constantly evolving field of orthodontics, it is necessary to develop cost-effective materials to cater to weaker socioeconomic sections of society. This study used the low-cost superelastic NiTi archwires, which were customized as an alternative to Copper NiTi archwires, and compared them regarding alignment efficiency and pain perception after initial alignment. Methods: Thirty-six patients were randomly assigned to two groups in terms of initial archwires: group 1: 0. 014-inch preformed Copper NiTi archwire and group 2: 0. 014-inch customized superelastic NiTi archwire. Changes in the alignment of the six anterior teeth were measured for 4 months at T0, T1, T2, T3, and T4 using the modified Little’s irregularity index. Patients were asked to complete the Pain Questionnaire with the VAS scale. Friedman’s test and Wilcoxon’s signed-rank test were used to compare the two groups, and the Mann-Whitney U test was used for intergroup comparison of the modified Little’s irregularity index. P<0. 05 was considered as significant. Results: Groups 1 and 2 exhibited no significant differences (P>0. 05) when alignment efficiency was compared at different time intervals. Patients reported less pain perception and were more comfortable with customized superelastic NiTi archwires compared to Copper NiTi archwires (P<0. 01). Conclusion: Customized superelastic NiTi archwires demonstrated alignment efficiency similar to Copper NiTi archwires but significantly reduced pain perception. Therefore, they could be a viable alternative for minimizing pain in the initial alignment phase of fixed orthodontic treatment.

Background and Aim: NiTi rotary instruments have been extensively used in the preparation of curved root canals, due to their superelastic quality, These instruments are less susceptible to unexpected fracture as compared to their stainless steel counterparts. However, unexpected fracture of NiTi instruments under complex stress within curved canals can lead to serious problems. The aim of this investigation was to identify and evaluate the various failure mechanisms which can cause fracture of NiTi rotary instruments under clinical conditions.Materials and Methods: The causes of failure of two brands of Hero and Profile rotary files have been studied. A total of 1133 instruments that failed during clinical use were collected from several dental clinics, after inspection under a stereomicroscope, all instruments were classified as either plastically deformed or fractured. The fracture surfaces of all broken instruments were examined following ultrasonic cleaning in ethanol and acetone, 30 minutes each. The fracture surfaces of more than 70 broken instruments were subjected to fractographic analysis using a scanning electron microscope. Results: More than 68% of the 1133 specimens were fractured. Stereomicroscopic inspection showed three failure mechanisms for the studied instruments: fracture, plastic deformation due to bending and torsion and a combination of both mechanisms. Based on fractographic observations, microvoid coalescence and cyclic stable crack growth by striation formation were identified.Conclusion: According to these results, excessive plastic deformation and fracture may be considered as the two main mechanisms responsible for the failure of NiTi rotary instruments.

Introduction: Irregularities and defects on NiTi endodontic instruments originating from the manufacturing process can lead to the structural collapse and fracture of these instruments during treatment. To assess the cause of instrument wear and fracture, as well as increasing fracture incidence, destructive and non-destructive methods have been used for the analysis of surfaces and internal structures of new and used NiTi instruments. The aim of this systematic review was to undertake a detailed analysis of the methods used to evaluate the surface and internal microstructure of endodontic instruments. Methods and Materials: The scientific literature was comprehensively and systematically searched in the MEDLINE (PubMed), Web of Science, Cochrane Library, Scopus, and LILACS/BBO databases for studies published up to June 9, 2019. The eligibility criteria was based on the PICO (Patient, Intervention, Comparison, and Outcome) strategy with the question “ What is the best method for structural analysis of endodontic files? ” Two aspects were considered for inclusion in this study: (i) endodontic instruments and (ii) methods for structural analysis of NiTi instruments. Results: Based on the inclusion criteria, 94 articles were selected. The results showed that although specific methods have been used for qualitative and/or quantitative structural analysis of NiTi instruments, no study addressed both the surface and internal structure of the instruments at the same time. According to this review, the need to compare the methodologies used in the selected articles has been identified; however, each type of method used has its own limitation on the analysis of both the surface and the internal structure of the instruments. Conclusions: The comparison between the different types of methodologies used in the studies revealed the reliability and the limitations of the methods employed for structural analysis of endodontic instruments; thus assisting us in determining their validity.