The endodontic literature contains a plethora of studies on static and dynamic cyclic fatigue resistance tests performed on a large array of rotary or reciprocating nickel-titanium endodontic instruments. It was the aim of this review to summarize the currently available evidence to point out the different outcomes from static versus dynamic tests and to assess whether cyclic fatigue tests provide useful data and information for clinical practice. An electronic literature research in the database PubMed was performed using appropriate search terms, and the titles and abstract were screened for relevance. Language was restricted to English. The review reveals marked differences between the results obtained in static and dynamic tests, and also, the results for the same instruments assessed either under static or dynamic experimental conditions are widely inconsistent. Between the lowest and the highest value for one and the same pathfinding instrument was a factor of about 123 when cyclic fatigue was assessed either under static or dynamic experimental conditions. Moreover, standard deviations of up to 30% have been reported. Environmental temperature has a 500% impact on the lifetime of instruments. In conclusion, fatigue resistance tests conducted under room temperature should be regarded as having little meaning and the scientific and clinical benefits of fatigue resistance tests are very limited. These data should be provided by the manufacturer of the instruments.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/iej.13182

A critical appraisal of studies on cyclic fatigue resistance of engine-driven endodontic instruments.

Comparison of Cyclic Fatigue Resistance of 5 Heat-treated Nickel-titanium Reciprocating Systems in Canals with Single and Double Curvatures.

According to the Global Burden of Disease (GBD) 2015, around 3.5 billion people suffer from dental diseases. The treatment of these disease requires either a specific dental device or a material which are usually subjected to stress and corrosion of the oral environment due to varying temperature, pH, occlusion, and masticatory forces. Various smart materials have emerged in the biomedical field because of their superior properties compared to conventional alloys. However, Nickel-Titanium (Ni-Ti) alloys with nearly equi-atomic composition have a long-standing history of successful use in dentistry because of their shape memory (SM) and superelastic (SE) properties with excellent cytocompatibility and corrosion resistance. The SM property offers preferable control of the transition temperature range (TTR) near the oral temperature providing multiple actuation. The SE property has revolutionized orthodontic treatment by delivering light and continuous physiological forces to the teeth, thereby improving patient comfort. The SE property of Ni-Ti alloy has been extensively used to produce orthodontic archwires and endodontic files as they exhibit higher flexibility compared to conventional stainless-steel alloy. However, the duration and type of heat treatment performed on these devices have been reported to modify their thermo-mechanical properties, producing adverse effects. Besides this, the devices are also subjected to short-term cooling or heating, sterilization, and disinfection protocols that creates a corrosive environment. Thus, thermo-mechanical properties and the influence of oral environment on various commercially available Ni-Ti alloy dental devices have been briefly explored and discussed. Besides orthodontic archwire and endodontic files, other Ni-Ti alloy-based dental devices are also reviewed, such as Shape memory Ni-Ti alloy sleeve for Abutment System, SM Ni-Ti alloy palatal expander, and SM Ni-Ti alloy porous dental implant. Thus, this manuscript aims to provide a concise assessment of the properties of SE and SM Ni-Ti alloys and their evolution in the field of dentistry. • Large population suffers from dental diseases. • Among the smart materials, Ni-Ti alloys have been successfully used in dentistry. • Shape memory offers control of transition temperatures near to oral temperature. • Superelasticity delivers light and continuous physiological forces to the teeth. • Thermomechanical treatment and oral environment create undesirable device behavior. 

Superelastic and Shape memory equi-atomic Nickel-Titanium (Ni-Ti) alloy in Dentistry: A Systematic Review

Torsional, Static, and Dynamic Cyclic Fatigue Resistance of Reciprocating and Continuous Rotating Nickel-Titanium Instruments

Instrument failure during root canal preparation is still a concern among endodontists. However, it remains unclear whether the use of more martensitic alloys or the cross-sectional design parameters (i.e., core mass) significantly improve fracture resistance. The aim of the study was to evaluate the impact of core mass and alloy on dynamic cyclic fatigue resistance of nickel-titanium endodontic instruments in matching artificial canals at body temperature. Two groups were tested. (A) taper 0.04: F360 (Komet, Lemgo, Germany), Twisted file (Sybron Endo, Glendora, CA, USA) (=TF), JIZAI (Mani, Tochigi, Japan) (=J_04) (all size #25) and the variable tapered TruNatomy (Dentsply, Ballaigues, Switzerland) (size #26) (=TN). (B) size #25; taper 0.06: (Mtwo (VDW, Munich, Germany), JIZAI (Mani) (=J_06), and variable tapered Hyflex EDM OneFile (Coltene Whaledent, Altstatten, Switzerland) (=HF). Time, number of cycles to fracture (NCF), and number and length of fractured fragments were recorded and statistically analysed using ANOVA Student-Newman-Keuls, Kruskal–Wallis or Chi-square test (significance level = 0.05). (A) TN showed the significantly shortest time until fracture, followed by TF, F360 and J_04 which also differed significantly, while NCF showed the following order: F360 0.05). While all Mtwo instruments fractured, only four instruments failed in the other groups (p < 0.05). Within the limitations of this study, alloy and cross-sectional design (i.e., core mass) were critical factors regarding instrument failure, but none of these factors could be determined as a main parameter for increased or decreased time, and cycles to fracture. Rather, it seemed to be the interaction of multiple factors (e.g., longitudinal and cross-sectional design, alloy, and rotational speed) that was responsible for differences in the time and cycles to fracture. Nonetheless, all instruments had lifetimes that allow safe clinical use. However, the superiority or inferiority of an instrument with regard to cyclic fatigue based on laboratory results—even when identical trajectories are guaranteed—may be considered questionable, as the characteristics and design parameters of the instruments vary considerably, and the experimental setups lack additional clinical parameters and thus clinical relevance.

Effect of Core Mass and Alloy on Cyclic Fatigue Resistance of Different Nickel-Titanium Endodontic Instruments in Matching Artificial Canals.

Effects of Sodium Hypochlorite Concentration and Temperature on the Cyclic Fatigue Resistance of Heat-treated Nickel-titanium Rotary Instruments.

An interconnection between tissue inflammation and regeneration has been established through the regulation of defense and repair mechanisms within diseased dental tissue triggered by the release of immune-resolvent mediators. To better our understanding of the role of specific pro-resolving mediators (SPMs) in inflamed human bone marrow-derived mesenchymal stem cells (hBMMSCs), we studied the effects of Resolvin E1 (RvE1) and Maresin 1 (MaR1) in lipopoly-saccharide (LPS) stimulated hBMMSCs. The hBMMSCs were divided into five different groups, each of which was treated with or without SPMs. Group-1: negative control (no LPS stimulation), Group-2: positive control (LPS-stimulated), Group-3: RvE1 100 nM + 1 μg/mL LPS, Group-4: MaR1 100 nM + 1 µg/mL LPS, and Group-5: RvE1 100 nM + MaR1100 nM + 1 μg/mL LPS. Cell proliferation, apoptosis, migration, colony formation, Western blotting, cytokine array, and LC/MS analysis were all performed on each group to determine the impact of SPMs on inflammatory stem cells. According to our data, RvE1 plus MaR1 effectively reduced inflammation in hBMMSCs. In particular, IL-4, 1L-10, and TGF-β1 activation and downregulation of RANKL, TNF-α, and IFN-γ compared to groups receiving single SPM were shown to be significantly different (Group 3 and 4). In addition, the LC/MS analysis revealed the differentially regulated peptide’s role in immunological pathways that define the cellular state against inflammation. Inflamed hBMMSCs treated with a combination of Resolvin E1 (RvE1) and Maresin 1 (MaR1) promoted the highest inflammatory resolution compared to the other groups; this finding suggests a potential new approach of treating bacterially induced dental infections.

/pdf/anti-inflammatory-effect-of-specialized-proresolving-lipid-1vo99qaa.pdf

Anti-Inflammatory Effect of Specialized Proresolving Lipid Mediators on Mesenchymal Stem Cells: An In Vitro Study

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Effects of Sodium Hypochlorite Concentration and Temperature on the Cyclic Fatigue Resistance of Heat-treated Nickel-titanium Rotary Instruments.

Anti-Inflammatory Effect of Specialized Proresolving Lipid Mediators on Mesenchymal Stem Cells: An In Vitro Study