Various heat-treated nickel–titanium rotary instruments evaluated in S-shaped simulated resin canals

AbstractBackground/purposeHeat treatment of nickel–titanium (NiTi) alloy produces a better arrangement of the crystal structure, thereby leading to increased flexibility and improved fatigue resistance or plastic behavior. This study aimed to assess the performance of various heat-treated NiTi rotary instruments in S-shaped resin canals.Materials and methodsForty S-shaped resin canals were instrumented (10/group) with either Twisted Files (R-phase), WaveOne (M-wire), Hyflex CM, or V Taper 2H (CM-wire) with the same apical size and taper (25/0.08). Each S-shaped resin canal was scanned both before and after instrumentation with microcomputed tomography. Changes in canal volume and transportation were evaluated at regular intervals (0.5 mm). Differences between instruments at the apical curve, coronal curve, and straight portion of the canals were analyzed statistically.ResultsAll tested instruments caused more transportation at the coronal rather than apical curvatures, with the exception of Twisted Files for which apical transportation was the highest for any instrument or location (P<0.05). The transportation was mostly influenced by the alloy type rather than their cross-sectional characteristics (P<0.05). The volumetric increase after instrumentation was similar for all tested instruments at the apical curve (P>0.05), whereas Hyflex CM created the most conservative preparations at the coronal curve (P<0.05). At the straight portion, volumetric changes were largest for Twisted Files and smallest for V Taper 2H (P<0.05).ConclusionAmongst heat-treated NiTi instruments, the CM-wire based instruments created the most favorable preparations in S-shaped resin canals

The effect of cyclic fatigue on the hardness of new NiTi endodontic files : a nanoindentation study

Objective: The purpose of this study was to compare the flexibility and cyclic fatigue of ProTaper Universal (PTU; Dentsply Tulsa Dental Specialties, Tulsa, OK) and ProTaper Gold (PTG; Dentsply Tulsa Dental Specialties, Tulsa, OK) in relation to their phase transformation behavior, as well as to determine the effect of cyclic fatigue on the nanohardness with a nanoindentation method. Hypotheses: PTG and PTU have similar flexibility and fatigue resistance. Cyclic fatigue has no effect on the hardness of both PTG and PTU NiTi rotary endodontic instruments. Methodology: PTU and PTG instruments were subjected to rotational bending at a curvature of 40° and a radius of 6mm. The number of cycles to fracture (NCF) was recorded. According to the ISO 3630-1 specification, 45° bending tests was used to determine the flexibility. Unused and fractured instruments were studied by differential scanning calorimetry. The hardness and modulus of elasticity of new files, fractured instruments and instruments stressed to 50% of the NCF for sizes S1, F1 and F2 were measured with the use of a nanoindenter. Results: PTG had a cyclic fatigue resistance superior to PTU in all sizes (P <.001). The fractured files of both PTU and PTG showed the typical fracture pattern of fatigue failure. Bending load results for PTG were significantly lower than that for PTU (P <.05). The differential scanning calorimetry analyses showed that PTG instruments had a higher austenite finish temperature (50.1°C ± 1.7°C) than the PTU instruments (21.2°C ± 1.9°C) (P <.001). There were no significant differences in the austenite finish between unused files and instruments subjected to the fatigue process. There were statistically significant differences in nanohardness and elastic modulus between PTU and PTG groups (P < 0.05). Conclusions: Within the limitation of this study, PTG files were significantly more flexible and resistant to fatigue than PTU files. PTG exhibited different phase transformation behavior than PTU, which may be attributed to the special heat treatment history of PTG instruments. The fatigue process had no significant effect on the hardness and elastic modulus of both NiTi instrument. PTG may be more suitable for preparing canals with sudden curvature.Dentistry, Faculty ofGraduat

Lateral and axial cutting efficiency of instruments manufactured with conventional nickel-titanium and novel gold metallurgy.

AIM: To isolate the effect of metallurgy in lateral and axial cutting efficacy against plastic and bovine dentine substrates by comparing two rotary systems with identical design but manufactured with either conventional nickel-titanium or heat-treated gold alloy. METHODOLOGY: A total of 258 ProTaper Universal (PTU) and ProTaper Gold (PTG) Shaping instruments were used. Bending behaviour was assessed to determine the appropriate displacement associated with a 2 N force in lateral cutting. Ten instruments of each type were used in lateral action for 60 s against bovine dentine or plastic substrates four consecutive times producing four notches in each specimen. Ten further instruments of each type were used in on axial action in four standardized simulated root canals fabricated from 4-mm thick plastic or dentine discs. Both tests were performed at 300 rpm in a computer-controlled testing platform. Notch area and torsional load were compared with Student\u27s t-tests. Repeated measures ANOVA was used to compare cutting efficiency across the four different time-points. Pearson correlation coefficients between substrates were also determined. RESULTS: For lateral action, all three PTG instruments cut significantly more effectively (P \u3c 0.05) than PTU on the plastic substrate. S1 and S2 PTG cut significantly more after 120 and 180 s (P \u3c 0.05) on bovine dentine substrate. For axial action, S1 and S2 PTG were significantly more efficient in cutting at 180 s on plastic and 120 s on bovine dentine (P \u3c 0.05). CONCLUSION: Instruments made from heat-treated nickel-titanium gold alloy had equal or greater cutting efficiency when compared to those made from conventional nickel-titanium

Physical properties and hydration behavior of a fast-setting bioceramic endodontic material

Background: To investigate the physical properties and the hydration behaviour of the fast-setting bioceramic iRoot FS Fast Set Root Repair Material (iRoot FS) and three other endodontic cements. Methods iRoot FS, Endosequence Root Repair Material Putty (ERRM Putty), gray and white mineral trioxide aggregate (G-MTA & W-MTA), and intermediate restorative material (IRM) were evaluated. The setting time was measured using ANSI/ADA standards. Microhardness was evaluated using the Vickers indentation test. Compressive strength and porosity were investigated at 7 and 28 days. Differential scanning calorimetry (DSC) was employed for the hydration test. Results iRoot FS had the shortest setting time of the four bioceramic cements (p < .001). The microhardness values of iRoot FS, ERRM Putty and MTA increased at different rates over the 28 days period. At day one, ERRM Putty had the lowest microhardness of the bioceramic cements (p < .001), but reached the same level as MTA at 4, 7 and 28 days. The microhardness of iRoot FS was lower than that of W-MTA at 7 and 28 days (p < .05). The porosity of the materials did not change after 7 days (p < .05). The compressive strength values at 28 days were significantly greater for all bioceramic groups compared to those at 7 days (p < .01). ERRM Putty had the highest compressive strength and the lowest porosity of the evaluated bioceramic cements (p < .05), followed by iRoot FS, W-MTA, and G-MTA, respectively. DSC showed that iRoot FS hydrated fastest, inducing an intense exothermic reaction. The ERRM Putty did not demonstrate a clear exothermic peak during the isothermal calorimetry test. Conclusions iRoot FS had a faster setting time and hydrating process than the other bioceramic cements tested. The mechanical properties of iRoot FS, G-MTA and W-MTA were relatively similar.Applied Science, Faculty ofDentistry, Faculty ofNon UBCMaterials Engineering, Department ofOral Biological and Medical Sciences (OBMS), Department ofReviewedFacult