Cutting efficiency of heat‐treated nickel–titanium single‐file systems at different incidence angles

Cutting efficiency of Reciproc R25 (REC) and Reciproc blue R25 (REB) at different inclinations was evaluated. Sixty new files were tested at 90°, 70° and 45° of inclination in relation to the sample (n = 10), using a customised machine. All files were activated in reciprocation against standardised gypsum blocks for 120 s. Cutting efficiency was determined by measuring the block weight loss with an analytical balance and measuring the length of the block surface cut using a digital calliper. Data were statistically analysed (two‐way ANOVA, Bonferroni t‐test) with the significance level set at P < 0.05. There was no difference for REC among the tested angles. REB had no statistical difference between 90° and 70°; however, its cutting efficiency significantly increased at 45°. There was a significant difference between REC and REB at 45° only. Under these conditions, increased file inclination to 45° and blue heat treatment improved cutting efficiency of reciprocating files.     

Efficiency of multi-strand steel,superelastic Ni-Ti and ion-implanted Ni-Ti archwires for initial alignment

In a clinical trial involving 155 dental arches with irregularity > 5 mm, the rate of alignment was used to compare the alignment efficiency of 16 mil superelastic Ni-Ti versus 17.5 mil triple-stranded steel archwires, and to determine whether ion implantation of the Ni-Ti wire improved its performance. Subjects were randomly assigned to archwire types; both 18 and 22 slot edgewise appliances were employed. Pre-treatment equivalence of the experimental groups was verified. Anterior irregularity was determined monthly (using Little's irregularity index) until it decreased below 2 mm, and the elastomeric ligatures were replaced at each appointment. Effective tooth movement occurred with each of the archwire types. There were no significant differences among wires, but the rate of alignment was significantly faster in the lower arch for subjects with the 22 slot appliance.     

Comparison of cyclic fatigue resistance of novel nickel‐titanium rotary instruments

New files (ProTaper Next/HyFlex/OneShape) are made from novel nickel‐titanium (NiTi) alloys/treatments. The purpose of this study was to compare the cyclic fatigue resistance of these new instruments with that of Revo‐S instruments. Four groups of 20 NiTi endodontic instruments were tested in steel canals with a 3 mm radius and a 60° angle of curvature. The cyclic fatigue of the following NiTi instruments with a tip size 25 and 0.06 taper that were manufactured with different alloys was tested: ProTaper Next X2 (M‐Wire), OneShape (conventional NiTi), Revo‐S Shaping Universal (conventional NiTi) and HyFlex 25/0.6 (controlled memory NiTi wire). A one‐way anova and post‐hoc Tukey's test (α = 0.05) revealed that the HyFlex files had the highest fatigue resistance and the Revo‐S had the least fatigue resistance among the groups (P < 0.001).     

A review of instrumentation kinematics of engine‐driven nickel–titanium instruments

Over the years, NiTi alloys have become indispensable materials in endodontic treatment. With technological advancements in metallurgy, manufacturers have attempted to produce instruments with enhanced features. In parallel with these developments, endodontic motors have undergone improvements in terms of torque control and kinematics that are adjustable in different directions. This review presents an overview of the advancements in instrumentation kinematics and the effect of instrumentation kinematics on root canal shaping procedures and instrument performance. The literature search for this narrative review was conducted in Google Scholar, Scopus, PubMed and Web of Science using the keywords ‘kinematics and endodontics’ and ‘reciprocation and endodontics’. In addition, historical literature was searched using the keyword ‘nickel–titanium and endodontics’. Overall, 143 articles were included up to 2015.     

Comparison of the Mechanical Behavior between Controlled Memory and Superelastic Nickel-Titanium Files via Finite Element Analysis

IntroductionThe aim of this study was to evaluate the flexibility and torsional stiffness of a controlled memory (CM) nickel-titanium (NiTi) file and compare its mechanical responses with those of a superelastic NiTi file with the same geometry using finite element simulation.MethodsA commercially available instrument with a tip size of 30 and a 0.06 taper was selected for this study. The geometric model for finite element analysis was generated by micro–computed tomographic scanning, and the data for the constitutive model of controlled memory NiTi were obtained from the literature. The numeric analysis was performed in ABAQUS (SIMULIA, Providence, RI) with boundary conditions that were based on the ISO 3630-1 specification.ResultsThe CM NiTi file exhibited the least bending moment and maximum stress value (523 MPa) under 45° bending simulation. However, the least torsional stiffness was calculated for this same instrument.ConclusionsThe higher flexibility and potential fatigue resistance of the CM NiTi files were confirmed, indicating that this new technology represents an improvement in the mechanical behavior of the rotary NiTi files.     

Influence of electrochemical polishing on the mechanical behaviour of nickel‐titanium rotary files

The purpose of this study was to evaluate the influence of electrochemical polishing on the cyclic fatigue, cutting efficiency and surface topography of Miltex nickel‐titanium rotary files. A group of files were submitted to electrochemical polishing. New files and polished files were tested for flexural fatigue and for cutting efficiency. Scanning electron microscopy observations of all files were carried out to compare the surface morphologies of polished and new files. The t‐test was used to compare the groups for cutting efficiency. Scanning electron microscopy analysis indicated that the polishing resulted in more regular surfaces in relation to the new files. Electropolished files attained a significantly higher number of cycles to fracture than new unpolished files. No statistical difference exists between the groups in relation to the cutting efficiency (t‐test, P < 0.05). The polished files keep their integrity for a significantly higher number of cycles to fracture than the new files, without compromising cutting efficiency.     

Methods and models to study nickel–titanium instruments

Over the past two decades, nickel–titanium (NiTi) instruments have become an important part of the armamentarium for root canal treatment. They are increasingly used by generalists and specialists to facilitate the cleaning and shaping of root canals. Despite the advertising claims of superiority of design for some NiTi rotary systems, few have been supported by objective well‐designed studies in the literature. A variety of experiments with different models and methods have been developed for studying the properties of NiTi instruments and how they fulfil these mechanical goals. One of the main issues is how to make a rational choice for the best study model that is relevant. This article aims to present an overview of those methods and devices that have been used in endodontic literature for studying NiTi files.