ProTaper Universal F2 Research Articles

Electrochemical dissolution and retrieval of broken NiTi endodontic files from root canal using chloride based isotonic fluids as electrolytes - An in vitro study.

The electrochemical dissolution method of instrument retrieval emphasizes on the dissolution of the instrument rather than sacrificing dentine. Most of the studies conducted for electrochemical dissolution used fluoride-containing electrolytes and were performed inside a beaker. In this study, we used chloride-based fluids as electrolytes. Fifty extracted mandibular first premolars were divided into five groups based on the electrolytes used. Canals were enlarged to ProTaper Universal F2, and files were intentionally broken inside the canal. These specimens were subjected to electrochemical characterization by applying the potential of 9V for 20 min. Optical images were taken to assess the change in surface topography. The results were analyzed statistically by one-way analysis of variance (analysis of variance [ANOVA]). The rate of dissolution based on the electrolyte used decreased in the following order, viz. Tyrode's solution>artificial saliva>normal saline>Ringer's lactate/physiological serum. Apart from fluoride, chloride-based electrolytes could be an efficient alternative.

Structural Assessment of Endodontic Files via Finite Element Analysis

A methodology for the structural assessment of Nickel-Titanium (Ni-Ti) endodontic files and a novel approach to predict their fatigue behavior using finite element method (FEM) were proposed. ProTaper-Universal F1 and F2 endodontic files were selected due to availability of extensive test data needed for the validation of the methodology. Bending and torsional loadings were analyzed since these provide essential data for the structural integrity assessment for the endodontic files. High-definition FEM models and their computationally efficient idealized versions were developed. The results for the bending and torsional stiffness of the F1 endodontic file agreed with the literature data validating the proposed methodology. Hysteresis energy density was shown to give promising results as a predictor of low cycle fatigue failure. The predictions with the idealized models matched those of the high-definition models, justifying the proposed idealizations. The validated models demonstrated that F2 has 60% higher bending and torsion resistance and 7% higher hysteresis energy density per cycle with respect to F1, leading to the conclusion that F1 has a lower structural stiffness but a longer fatigue life as compared to F2. In summary, the developed methodology allows for the structural and durability evaluation of various design parameters for Ni-Ti endodontic files.

Dynamic cyclic fatigue resistance of NiTi instruments in a double-curved stainless steel canal with variable distances of displacement

The present study aimed to measure the number of cycles to fracture (NCF) of different instruments using pecking motion at constant and varying distances of movement at body temperature. This study included 20 files from each brand: ProTaper Universal F2, ProTaper Next X2, and WaveOne Gold Primary (Dentsply Sirona, Maillefer, Ballaigues, Switzerland). Instruments from each brand were divided into two groups (ten files for each group) that experienced constant or variable distances in a stainless-steel artificial double-curved canal in a platform that ensured that the instrument rotated at a stable temperature with a minimum fluctuation of the environment. While running, the platform was programmatically controlled to move at any desired distance of instrument displacement to simulate the clinical pecking motion at variable distances. The files were rotated using proprietary programs. The times to fracture were recorded and then transformed into the number of cycles to fracture (NCF). Data were analyzed using Minitab with proper tests. All fragments were observed under a scanning electron microscope to capture and describe the characteristics of the fracture surface. The WaveOne Gold had the highest NCF, while the ProTaper Universal had the lowest NCF. The manufacturer brands and the modes of displacement of the experimental instrument showed interactive effects. The fracture surface revealed no striation. A new design, material, mode of rotation, and different distances of movement have certain effects on the cyclic fatigue resistance of the instrument.

Comparison of Er:YAG laser and ultrasonic in root canal disinfection under minimally invasive access cavity.

The disinfection of root canal through minimally invasive access cavity remains questionable. This in vitro study compared the effectiveness of three disinfection measures including conventional irrigation, ultrasonic assisted irrigation, and erbium:yttrium-aluminum-garnet (Er:YAG) laser assisted irrigation through conventionally or minimally invasive access. Sixty-six extracted maxillary first molars were randomly divided into group 1 conventionally invasive access group (CIA) and group 2 computer-guided minimally invasive access group (MIA). Each group was further randomly divided into three subgroups, (A) conventional irrigation (CI), (B) passive ultrasonic agitation (PUI), and (C) Er:YAG laser activated irrigation (LAI). Enterococcus faecalis (E. faecalis) infection model was established inside all root canals after instrumentation was performed up to ProTaper Universal F2. After various disinfection methods, microbial samples were collected from root canals by paper tip method and cultured, and colony forming units (CFU) values of each sample were calculated. Then the root canals were enlarged to the size of F3, after which dentin debris was collected from the F3 file. After dilution and culturing, the CFU value was calculated for each group. Two-way analysis of variance (ANOVA) was performed to test the interaction. The results revealed a significant antagonism (F = 3.394, P = 0.043). The bacterial CFU counts of group B and group C were significantly less than that of group A (P < 0.05), and there was no significant difference between group B and C (P > 0.05). Additionally, group 2A was better than group 1A (P < 0.05); there was no significant difference between group 1B and group 2B, group 1C and group 2C (P > 0.05). Comparison of the bacterial CFU counts in dentin debris after disinfection, the results revealed a significant antagonism (F = 7.224, P = 0.002), and group C had the least. The disinfection effect of Er:YAG laser or ultrasonic assisted computer-guided minimally invasive access is similar to conventionally invasive access, and Er:YAG laser is better than ultrasonic in removing bacteria from dentinal tubules and is easy to operate, which is more suitable for minimally invasive root canal treatment.

The effectiveness of rotary and reciprocating techniques in curved root canals retreatment: a micro-CT analysis.

Introduction: Different NiTi rotary systems have been developed to improve efficiency and retreatment success rates. Aim: To evaluate the Protaper Universal retreatment system and WaveOne instrument in removing the filling material from curved canals during retreatment. Materials and Methods: Thirty mesial root canals of extracted human mandibular molar teeth were randomly allocated into 2 groups (n=15). In the PT group, retreatment was performed with ProTaper Universal Retreatment according to the manufacturer’s instructions. In the WO group, was used WaveOne Primary. ProTaper Universal F2 and F3 were used to achieve the apical diameter in both groups. The samples were scanned by micro-computed tomography pre and postoperatively to evaluate the filling material remaining. The percentage of material filling was compared between groups using Student’s T test and in the same group among thirds was compared using Kruskal-Wallis followed by Dunn’s post hoc test. Results: The filling material remaining was not statistically different between the groups (p≥0.05). The apical third presented a greater amount of remaining filling material when compared with the cervical third for both groups (p&lt;0.05). Conclusion: Rotary and reciprocating techniques can effectively, but not completely, remove the filling materials from the root canal system. The apical third presented a more significant amount of remaining filling material.

Effect of sonic irrigation activation at different frequencies in smear layer removal; An in vitro experimental study

Introduction: The aim of this study was to compare the vibration/oscillation frequencies of WaterPik and EndoActivator devices and their effectiveness in smear layer (SL) removal.Materials and Methods: The root canal of 60 single-rooted extracted human premolars were prepared until ProTaper Universal F2 file, and randomly grouped according to the irrigation activation technique used: EndoActivator group; WaterPik group; manual dynamic agitation (MDA) group; and control group (conventional irrigation with no activation). The vibration/oscillation frequencies of EndoActivator and WaterPik devices were measured using a digital tachometer. Electron microscopy images of all specimens were evaluated for SL removal according to a modified Hülsmann scoring system. Data were statistically analyzed.Results: The mean vibration frequency of the EndoActivator was significantly higher than that of WaterPik (200.6 ± 2.1 and 185.2 ± 2.744 Hz, respectively). A significant difference was detected in the SL removal along the full length of the canal between the experimental and control groups (P < 0.001). EndoActivator and MDA groups had significantly more samples with no to minimum SL at the coronal and middle thirds compared to the apical third, whereas there was no significant difference among the thirds in the WaterPik group. At the apical third, the WaterPik group had significantly more samples with no to minimum SL (60%) than WaterPik and MDA groups (20% and 26.7%, respectively).Conclusion: WaterPik was as effective as MDA and EndoActivator in SL removal, with better performance at the apical third, probably attributed to the lower vibration/oscillation frequency of WaterPik.

Effects of Root Canal Curvature and Mechanical Properties of Nickel-Titanium Files on Torque Generation

IntroductionThis study aimed to compare the torque generated by 4 different files in root canals with 4 different curvature angles. MethodsFour brands of nickel-titanium (NiTi) endodontic files were selected: WaveOne Primary (Dentsply Sirona, Ballaigues, Switzerland), WaveOne Gold Primary (Dentsply Sirona), ProTaper Universal F2 (Dentsply Sirona), and ProTaper Next X2 (Dentsply Sirona). A tempered steel block containing artificial canals with 4 different canal curvatures (15°, 25°, 35°, and 45°) was constructed. Each file was used according to the manufacturer’s instructions in the dynamic model, with an added 15 axial up-and-down movements of 4 mm at the end of the canal. The generated torque was recorded, and the total and maximum torque values were measured. Two-way analysis of variance and the Duncan post hoc comparison test were performed at a significance level of 95%. ResultsA significant correlation between the curvature angle and the type of file system was observed (P < .05). As the degree of canal curvature increased, the generated total and maximum torque increased. At 15° and 25°, the NiTi files with reciprocating motion generated a higher total and maximum torque than files with continuous rotation. ProTaper Universal of conventional NiTi alloy showed the steepest increase in the generated total and maximum torque with the increasing curvature angle. The ProTaper Next file had the lowest torque values at the higher canal angles of 35° and 45° (P < .05). ConclusionsDespite the study limitations, it can be concluded that root canal curvature, design, and heat treatment of NiTi files and file kinematics affect the generated torque during instrumentation.

Effect of synchronous irrigation on cyclic fatigue of nickel-titanium instrument in the dynamic and static models.

To evaluate the effect of synchronous water irrigation on the fatigue resistance of nickel-titanium instrument. A standardized cyclic fatigue test models were established, and five types of nickel-titanium instruments (PTU F1, WO, WOG, RE, and M3) were applied. Each instrument was randomly divided into two groups (N = 12). There was synchronous water irrigation in the experimental group, and no water irrigation in the control group. Besides, ProTaper Universal F1 was randomly divided into 10 groups (N = 20). In the static group, nickel-titanium instruments were divided into one control group (no irrigation, N = 20) and six experimental group (irrigation, N = 20) based on different flow rate, angle and position; while in the dynamic group, instruments were divided into one control group (no irrigation, N = 20) and two experimental group (irrigation, N = 20) based on different flow rate. The rotation time (Time to Failure, TtF) of instruments was recorded and analyzed. According to the static experiments, the TtF of instruments in all experimental groups was significantly higher than that in the static control group. Besides, the dynamic tests of PTU F1 showed that the TtF in the experimental group was significantly higher than that in the dynamic control group. Compared with control group, the TtF in the experimental groups increased by at least about 30% and up to 160%. The static and dynamic tests of PTU F1 showed that the TtF of nickel-titanium instrument in all experimental groups was significantly higher than that in the control group. However, there was no significant difference between any two experimental groups. Regardless of dynamic or static model, TtF with irrigation was longer than that with non-irrigation, indicating that synchronous irrigation can increase the fatigue resistance of nickel-titanium instrument. However, different irrigation conditions may have the same effect on the fatigue resistance.

Effect of flushing temperature on preparation ability of rotary nickel-titanium files.

The effect of flushing at different temperatures on the preparation ability of rotary nickel-titanium files was investigated to provide guideline for clinical application. Sixty ProTaper Universal F1 rotary nickel-titanium files were randomly divided into three groups treated by flushing at 6°C, 23°C, and 40°C. Root canal preparation was conducted by step-by-step method on standardized nickel-titanium instrument fracture models. During preparation, the thrust force was set as 10 N, and water was continuously flushed. The motor speed was 350 rpm (rounds per minute), and the torque was 3.0 N cm. When the set torque was reached, the motor automatically rotated in the reverse direction and was pulled out. Root canal preparation was performed using ProTaper Universal F1 rotary nickel-titanium files treated by flushing. The numbers of rotations before the device was fracture were 429.33 ± 214.68, 821.92 ± 410.43, and 1304.92 ± 297.81, respectively. When each root canal was completed, the numbers of instrument rotations were 272.15 ± 88.30, 188.85 ± 34.36, and 163.41 ± 16.18, respectively. Rank sum test and analysis of variance were performed by IBM SPSS Statistics v21.0 software, and both of them were p < 0.01, indicating that the number of cycles to failure (NCF) and the number of instrument rotations for each root tube were statistically different at the three temperatures. The self-made resin-simulated curved root canal can replace the real root canal to complete the root canal preparation experiment. The group of nickel-titanium files treated by flushing at 23°C can prepare more root canals and prolong the life of nickel-titanium files than at 6°C. When flushing was done at 40°C, the number of root canals prepared by nickel-titanium files was the highest, and it was not easy to damage the instrument, but lateral perforation occurred easily during root canal preparation.

Mechanical Tests, Metallurgical Characterization, and Shaping Ability of Nickel-Titanium Rotary Instruments: A Multimethod Research

IntroductionThis study aimed to compare the mechanical and metallurgical properties and shaping ability of different rotary systems using a multimethod approach. MethodsNew NeoNiti A1 (Neolix SAS, Châtres-La-Forêt, France), HyFlex EDM One File (Coltène/Whaledent, Altstätten, Switzerland), ProTaper Gold F2 (Dentsply Maillefer, Ballaigues, Switzerland), and ProTaper Universal F2 (Dentsply Maillefer) rotary instruments were tested regarding cyclic fatigue, torsional resistance, design, and morphologic characteristics using scanning electron microscopy, metal alloy characterization using differential scanning calorimetry, and energy-dispersive X-ray spectroscopy. Additionally, their shaping ability on the preparation of 48 canals of maxillary molars was evaluated using micro–computed tomographic technology. Mechanical and metallurgical analyses were compared using analysis of variance post hoc Tukey tests, whereas the independent Student t test was used to compare the shaping ability of the ProTaper systems or the thermomechanically treated instruments. The significance level was set at 5%. ResultsThe highest cyclic fatigue was observed with the NeoNiti and HyFlex EDM instruments (P > .05), whereas HyFlex EDM had the highest angular rotation to fracture (P < .05). Scanning electron microscopic/energy-dispersive X-ray spectroscopic analyses confirmed similarities in the instruments’ design and an almost equiatomic composition of the systems. Differential scanning calorimetry showed that ProTaper Gold had higher transformation temperatures than ProTaper Universal, whereas a similar transformation was observed between NeoNiti and HyFlex. Micro–computed tomographic analysis revealed that, despite the fact that none of the systems was able to prepare all root canal walls, no statistical differences were observed in either ProTaper systems (P > .05) or the thermomechanically treated instruments (P > .05). ConclusionsApart from differences in the mechanical tests and metallurgical characterization, systems with comparable instrument dimensions and preparation protocols showed a similar percentage of untouched surface areas in the root canal preparation of maxillary molars.

Evaluation of fluoride and sodium hypochlorite solutions during the electrochemical dissolution of conventional NiTi instruments and Gold thermomechanically treated NiTi instruments.

To compare the dissolution time of two solutions, a fluoride solution and a sodium hypochlorite solution, both saturated with sodium chloride, during the electrochemical dissolution of instruments consisting of conventional nickel-titanium alloy and Gold thermomechanically treated nickel-titanium alloy. Two solutions, an NaF solution consisting of 12gL-1 NaF with 180gL-1 NaCl and an NaOCl solution consisting of 2.5% NaOCl with 180gL-1 NaCl, were evaluated in a polarization test of a sample of 48 ProTaper Universal F1 (PTU F1) and WaveOne Gold Small (WOGS) instruments. The electric potentials were 0.5V and 5V for the NaF and NaOCl solutions, respectively. The electrochemical cell consisted of three electrodes for the polarization test of the PTU F1 and WOGS instruments, which had 6mm of the tip immersed in the test solutions. The electric current was recorded for 540s. If complete dissolution of the immersed tip occurred in less than the expected time, the experiment was considered complete. The time variations (in seconds) of the instruments in the solutions were measured. Data were subjected to statistical analysis using the Mann-Whitney, Kruskal-Wallis and Dunn tests. The corrosion patterns of the instruments were evaluated by scanning electron microscopy (SEM). The NaF and NaOCl solutions were associated with significantly different (P=0.000) dissolution times of the instrument, with mean values of 12.96s and 83.63s, respectively. There was no significant difference (P=0.649) in dissolution time between the PTU F1 and WOGS instruments. NaF and NaOCl solutions were able to electrochemically dissolve PTU F1 and WOGS instruments. However, the NaF solution achieved dissolution in significantly less time.

Evaluation of Flexibility, Microstructure and Elemental Analysis of Some Contemporary Nickel-Titanium Rotary Instruments.

BACKGROUND:Contemporary nickel-titanium (NiTi) rotary endodontic instruments had a revolutionary impact on the success of root canal treatment.AIM:To evaluate the flexibility, microstructure and elemental analysis of four different recent NiTi rotary instruments, namely; Wave One Gold, TF adaptive, HyFlex EDM and Gr_Reciproc Blue compared to conventional Protaper Universal (F2).MATERIAL AND METHODS:The NiTi rotary files were subjected to cantilever bending test to evaluate their flexibility. The microstructural characteristics and elemental analysis were examined via scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDX).RESULTS:The TF adaptive, HyFlex EDM and Wave One Gold endodontic files showed significantly lower cantilever bending values (i.e., higher flexibility) than Protaper F2 and Gr_Reciproc Blue (p < 0.05). The SEM micrographs showed that the bulk of all examined files showed multiple striations due to the cutting process, on the other hand, their external surfaces were different: The Protaper Universal F2 showed multiple voids, while the TF Adaptive surface exhibited more uniform structure. The Hyflex EDM had a crater-like surface, whereas Wave one Gold showed machining grooves with minimum defects, while Reciproc Blue displayed machining grooves with random scratch lines. There was a significant difference in bulk and surface elemental analysis of the various examined files, yet composed mainly of the same elements.CONCLUSION:Chemical composition, heat treatment, manufacturing process and geometrical design of the NiTi rotary instrument have a great influence on their flexibility and microstructure.

Comparison of Screw-In Forces during Movement of Endodontic Files with Different Geometries, Alloys, and Kinetics.

This study compared the maximum screw-in forces of various instruments during their movements. Forty simulated canals in resin blocks were randomly divided into four groups (n = 10): ProTaper Universal F2, ProTaper Gold F2, WaveOne Primary, and WaveOne Gold Primary. To standardize a lumen size, all artificial canals were prepared with ProTaper Universal F1. The rotation speed was set at 350 rpm with an automated 4 mm pecking motion at a speed of 1 mm/s. The pecking depth was increased by 1 mm for each pecking motion until the file reached the working length. During instrumentation, screw-in forces were automatically recorded by customized software. Maximum screw-in forces were analyzed by one-way ANOVA and Tukey’s post hoc comparison with the significance level at 0.05. WaveOne Gold files generated the lowest maximum screw-in forces, followed by ProTaper Gold, WaveOne, and ProTaper Universal (p < 0.05). Under the condition of this study, heat-treated nickel–titanium (NiTi) files with smaller cross-sectional area, fewer contact points, and reciprocating movements resulted in a lower screw-in effect.

Effectiveness of different irrigation systems in the presence of intracanal-separated file.

The aim of this study was to evaluate conventional syringe irrigation and three different irrigant activation techniques' effectiveness for smear layer removal in the absence and presence of intracanal-separated file (SF) fragment. Mandibular anterior teeth (160 total) with single canal were used and each root canal preparation was finished with the ProTaper Universal F1. The samples were randomly divided into eight equal groups with n = 20 in each group. The Protaper Universal F3 file was used to simulate intracanal file separation in four groups. To remove the smear layer, final irrigation for each group was performed with conventional syringe irrigation (CSI), EndoActivator, Vibringe, and passive ultrasonic irrigation (PUI). The roots were divided into two longitudinal parts and evaluated with scanning electron microscopy, and two observers scored smear layers at 1, 2, and 3 mm away from the minor foramen. The data were analyzed using the Kruskal-Wallis and Mann-Whitney U tests (p < .05). PUI significantly removed the smear layer better at all levels than other nonseparated file groups (p < .05). In the presence of intracanal SF, PUI had the most efficiency loss. Sonic techniques and CSI revealed statistically better smear layer removal efficiency than PUI at 3 mm level in the presence of SF (p < .05). The intragroup score analysis at all levels revealed that there were less smear layers at 3 mm than at 1 mm in all SF groups (p < .001). As a conclusion, sonic/ultrasonic methods did not yield better irrigant by-passing than CSI in the presence of intracanal SF.

Effect of NaOCl solution on the cyclic fatigue resistance of traditional and heat-treated file systems

Aim: To compare the cyclic fatigue resistance at distilled water and %5.25 NaOCl of immersed ProTaper Gold (Dentsply Sirona, Ballaigues, Switzerland) and ProTaper Universal (Dentsply Sirona, Ballaigues, Switzerland) file systems.Material and Methods: The ProTaper Gold F2 (25.06v taper) and ProTaper Universal F2 (25.06v taper) file systems were immersed in distilled water andNaOCl for 5 minutes. After immersion process files were rotated at artificial canal with 60O curvature and a 5-mm radius until fracture occurred. Time to fracture and fractured lengths were recorded. Data were analyzed statistically using independent t-tests. Statistical significance was set at P .05. Results: ProTaper Gold files had a significantly higher resistance to cyclic fatigue than ProTaper Universal files (P .05). When ProTaper Universal immersed in distilled water showed higher resistance to cyclic fatigue than immersed in NaOCl solution (P .05).Conclusion: ProTaper Gold system more resistant than ProTaper Universal system to cyclic failure. The effect of NaOCl were higher on the ProTaper Universal system.Keywords: Corrosion, cyclic fatigue; NaOCl; ProTaper Gold; ProTaper Universal.

Failure Analysis and Reliability of Ni–Ti-Based Dental Rotary Files Subjected to Cyclic Fatigue

The cyclic fatigue resistance of ProTaper Universal (PTU), ProTaper Gold (PTG), and ProTaper Next (PTN) nickel titanium (NiTi) rotary files was evaluated. Fifteen instruments of each type were selected, totaling 195 files. The instruments were rotated until fracture in an artificial canal with dimensions corresponding to the dimensions of each instrument tested: +0.1 mm in width and 0.2 mm in depth, an angle of curvature of 45°, a radius of curvature of 5 mm, and a center of curvature 5 mm from the instrument tip. The fracture surfaces of three representative samples of each subgroup were examined using scanning electron microscopy (SEM). Time to fracture was analyzed via analysis of variance and Tukey’s tests (P &lt; 0.05). PTG F1 and F2 had significantly higher resistance than PTU F1 and PTN X2, and PTU F2 and PTN X3, respectively. PTN X2 showed a significantly higher resistance than PTU F1. The PTG series demonstrated superior cyclic fatigue (CF) behavior compared with that of the PTU and PTN series.

Environmental Temperature Drastically Affects Flexural Fatigue Resistance of Nickel-titanium Rotary Files

IntroductionThe aim of the present study was to analyze how a low environmental temperature can affect the fatigue life of instruments made by different types of heat-treated nickel-titanium alloys. MethodsThe flexural cyclic fatigue of 40 new specimens for each of the following systems was tested for cyclic fatigue resistance: ProTaper Universal F2 (Dentsply Maillefer, Ballaigues, Switzerland), ProTaper Gold F2 (Dentsply Tulsa Dental Specialties, Tulsa, OK), Twisted Files SM2 (SybronEndo, Orange, CA), Mtwo #25.06 (VDW, Munich, Germany), and Vortex Blue #30.04 and #40.06 (Dentsply Tulsa Dental Specialties). Instruments were tested at 2 different environmental temperatures: 20°C (±2°C) for room temperature (RT) group and −20°C (±2°C) for the cooled environment (CE) group (n = 20). The number of cycles to failure (NCF) and the length of the fractured fragment (FL) were recorded. The means and standard deviations of NCF and FL were then calculated; NCF data were statistically analyzed using a paired t test between groups RT and CE for each instrument tested (P < .05), whereas FL data were analyzed using analysis of variance (P < .05). ResultsThe mean NCF values measured were significantly higher for the CE groups than the RT groups in all the systems tested (P < .05). The increase in cyclic fatigue resistance varied from 274%–854%. No differences in FL were registered among the different groups (P < .05). ConclusionsA low environmental temperature determines a drastic increase in the flexural fatigue resistance of NiTi endodontic instruments manufactured with traditional alloy and different heat treatments.

Influence of clinical use on physical-structural surface properties and electrochemical potential of NiTi endodontic instruments.

To investigate the surface morphology and electrochemical potential of superelastic (SE), M-Wire (MW) and shape memory technology (SMT) NiTi instruments before and after single clinical use invivo. A total of 60 ProTaper Universal F2 (PTU-SE), ProTaper Next X2 (PTN-MW), Typhoon (TYP), Hyflex (HF) and Vortex Blue (VB), the last three SMT, and size 25, .06 taper (n=6 of each type) files were examined. Scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS) and electrochemical potential analysis were employed before and after clinical use. Statistical analysis was performed with one-way analysis of variance and Bonferroni's post hoc test. Significance was determined at the 95% confidence level for both tests. SEM observations of new instruments indicated the presence of marks left by the machining process during manufacturing and EDS revealed the existence of an oxide coating on shape memory instruments. After clinical use, the five types were associated with propagation of transverse cracks 3mm from the tip. The surface oxide layer of TYP, HF and VB instruments had microcracks in multiple directions, whilst TYP and HF had fragmentation in chip form of the oxide layer. EDS analysis demonstrated a significant reduction of the oxide layer in shape memory instruments, except for VB. Electrochemical potentials were higher for shape memory instruments than for M-Wire and superelastic NiTi instruments, respectively (P<0.05). It appears that shape memory technology NiTi instruments have a dysfunctional oxide layer after clinical use. Additionally, they featured higher electrochemical potential relative to NiTi instruments manufactured from M-Wire, and conventional superelastic NiTi alloy.

Influence of Cyclic Flexural Deformation on the Torsional Resistance of Controlled Memory and Conventional Nickel-titanium Instruments

IntroductionThe aim of this study was to evaluate the influence of cyclic deformation on the torsional resistance of controlled memory (CM) nickel-titanium files in comparison with superelastic (SE) instruments with similar geometric and dimensional characteristics. MethodsNew 30/.06 HyFlex (HF; Coltene/Whaledent, Inc, Cuyahoga Falls, OH), Typhoon (Clinician's Choice Dental Products, New Milford, CT), RaCe (FKG, La-Chaux De Fonds, Switzerland), and ProTaper Universal F2 instruments (F2; Dentsply Maillefer, Ballaigues, Switzerland) were assessed. The diameter and pitch length were measured along the active part of the instruments. The number of cycles to failure (Nf) in flexural fatigue and the torsional resistance were evaluated for new files (n = 10). Ten new instruments of each type were fatigued to 3/4 of their fatigue life and then submitted to torsion until rupture. Data were analyzed using 1-way analysis of variance (α = .05). ResultsNew CM files had a significantly higher Nf when compared with SE instruments; HF exhibited the highest value (P = .001). The mean torque value for F2 was the highest (P = .001). CM files precycled to 3/4 Nf had a significantly lower torque than the new files (HF: P = .003, Typhoon: P = .001), whereas the SE instruments displayed no significant differences (F2: P = .059, RaCe: P = .079). ConclusionsCyclic flexural loading significantly reduced the torsional resistance of CM instruments.

The Effects of Torsional Preloading on the Torsional Resistance of Nickel-titanium Instruments

IntroductionThis study evaluated the effect of torsional preloading on the torsional resistance of nickel-titanium (NiTi) endodontic instruments. MethodsWaveOne Primary (Dentsply Maillefer, Ballaigues, Switzerland) and ProTaper Universal F2 (Dentsply Maillefer) files were used. The ultimate torsional strength until fracture was determined for each instrument. In the phase 1 experiment, the ProTaper and WaveOne files were loaded to have a maximum load from 2.0 up to 2.7 or 2.8 Ncm, respectively. In the phase 2 experiment, the number of repetitions of preloading for each file was increased from 50 to 200, whereas the preloading torque was fixed at 2.4 Ncm. Using torsionally preloaded specimens from phase 1 and 2, the torsional resistances were calculated to determine the ultimate strength, distortion angle, and toughness. The results were analyzed using 1-way analysis of variance and Duncan post hoc comparison. The fracture surfaces and longitudinal aspect of 5 specimens per group were examined under a scanning electron microscope. ResultsAll preloaded groups showed significantly higher ultimate strength than the unpreloaded groups (P < .05). There was no significant difference among all groups for distortion angle and toughness. Although WaveOne had no significant difference between the repetition groups for ultimate strength, fracture angle, and toughness, ProTaper had a higher distortion angle and toughness in the 50-repetition group compared with the other repetition groups (P < .05). Scanning electron microscopic examinations of the fractured surface showed typical features of torsional fracture. ConclusionsTorsional preloading within the ultimate values could enhance the torsional strength of NiTi instruments. The total energy until fracture was maintained constantly, regardless of the alloy type.