Sang Won Kwak

Safety of the Factory Preset Rotation Angle of Reciprocating Instruments

INTRODUCTION This study aimed to investigate the torsional resistance of 2 reciprocating nickel-titanium instruments (Reciproc [VDW, Munich, Germany] and WaveOne [Dentsply Maillefer, Ballaigues, Switzerland]) operated at the maximum rotating angle in a proprietary motor. METHODS With the file tip secured at various levels (3, 4, or 5 mm) of Reciproc R25 and WaveOne Primary, the distortion angles and torsional loads were monitored during counterclockwise movement at 2 rpm until fracture (n = 10 at each level) for a load-distortion graph. The rotation angles and loads at the beginning point of the plateau, the ultimate torsional strength, final fracture angle, and toughness were determined. The data were analyzed using 1-way analysis of variance and the Tukey post hoc test at α = .05. The lateral longitudinal aspect and the fracture cross-section of each specimen were examined by scanning electron microscopy after the test. RESULTS The rotation angle at the beginning point of the plateau was significantly greater for a binding site farther away from the tip of the instrument for both systems (P < .05), and all were greater than 170° (preset in the dedicated motor from manufacturer). The ultimate strength and toughness also increased significantly at levels farther away from the instrument tip (P < .05). All specimens showed typical topographic features of torsional fracture, including the circular abrasion marks and fibrous dimples near the rotation center after the test. CONCLUSIONS It was determined that the 2 brands of reciprocating files are safe when operated at the rotational angle in the proprietary motor.

Physicochemical Properties of Epoxy Resin-Based and Bioceramic-Based Root Canal Sealers

Three bioceramic sealers (EndoSequence BC sealer, EndoSeal MTA, and MTA Fillapex) and three epoxy resin-based sealers (AH-Plus, AD Seal, and Radic-Sealer) were tested to evaluate the physicochemical properties: flow, final setting time, radiopacity, dimensional stability, and pH change. The one-way ANOVA and Tukeys post hoc test were used to analyze the data (P = 0.05). The MTA Fillapex sealer had a highest flow and the BC Sealer presented a flow significantly lower than the others (P < 0.05). The BC Sealer and MTA Fillapex samples were not set in humid incubator condition even after one month. EndoSeal MTA had the longest setting time among the measurable materials and Radic-Sealer and AD Seal showed shorter setting time than the AH-Plus (P < 0.05). AH-Plus and EndoSeal MTA showed statistically higher values and MTA Fillapex showed statistically lower radiopacity (P < 0.05). BC Sealer showed the highest alkaline pH in all evaluation periods. Set samples of 3 epoxy resin-based sealers and EndoSeal MTA presented a significant increase of pH over experimental time for 4 weeks. In conclusion, the bioceramic sealer and epoxy resin-based sealers showed clinical acceptable physicochemical properties, but BC Sealer and MTA Fillapex were not set completely.

Mechanical Properties of Various Heat-treated Nickel-titanium Rotary Instruments

Aim The purpose of this study was to compare the bending stiffness, cyclic fatigue, and torsional fracture resistances of heat‐treated and conventional nickel‐titanium rotary instruments. Methods V‐Taper 2 (VT2; #25/.08), V‐Taper 2H (V2H; #25/.06), Hyflex CM (HCM; #25/.06), HyFlex EDM (HDM; #25/variable taper), and ProTaper Next X2 (PTN; #25/variable taper) were tested. The bending stiffness was measured with the customized device (AEndoS), and the files (n = 15) were fixed at 3 mm from the tip and bent at 45° with respect to their long axis. Cyclic fatigue resistance was tested by pecking and rotating instruments (n = 15) in artificial canal with a 7.8‐mm radius and 35° angle of curvature until fracture. The ultimate torsional strength and toughness were estimated by using AEndoS. The file tip of 5 mm was fixed between resin blocks and driven clockwise at 20 rpm until fracture. The results were analyzed by using one‐way analysis of variance and Duncan post hoc comparison. The fracture surfaces and longitudinal aspect of each group were examined under the scanning electron microscope. Results CM‐wire instruments had lower bending stiffness than others. HDM showed the highest cyclic fatigue resistance, followed by VTH and HCM (P < .05). VT2 showed the highest ultimate strength, followed by HDM, VTH‐PTN, and HCM. HDM and VT2 showed significantly higher toughness than VTH, HCM, and PTN (P < .05). Scanning electron microscope analysis showed typical fractographic features of cyclic fatigue and torsional fractures. Conclusions CM‐wire instruments showed higher flexibility and cyclic fatigue resistance than M‐wire and conventional nickel‐titanium instruments. Large cross‐sectional area and conventional nickel‐titanium showed high torsional resistance. HighlightsCM‐wire instruments showed higher residual angles than M‐wire and conventional NiTi.CM‐wire exhibited lower bending stiffness than M‐wire and conventional NiTi.Hyflex EDM had significantly higher fatigue resistance than M‐wire and conventional NiTi.Hyflex EDM and V‐Taper2 exhibited higher torsional resistance than other files.SEM examinations showed typical features of cyclic fatigue and torsional fracture.

Screw-in forces during instrumentation by various file systems

Objectives The purpose of this study was to compare the maximum screw-in forces generated during the movement of various Nickel-Titanium (NiTi) file systems. Materials and Methods Forty simulated canals in resin blocks were randomly divided into 4 groups for the following instruments: Mtwo size 25/0.07 (MTW, VDW GmbH), Reciproc R25 (RPR, VDW GmbH), ProTaper Universal F2 (PTU, Dentsply Maillefer), and ProTaper Next X2 (PTN, Dentsply Maillefer, n = 10). All the artificial canals were prepared to obtain a standardized lumen by using ProTaper Universal F1. Screw-in forces were measured using a custom-made experimental device (AEndoS-k, DMJ system) during instrumentation with each NiTi file system using the designated movement. The rotation speed was set at 350 rpm with an automatic 4 mm pecking motion at a speed of 1 mm/sec. The pecking depth was increased by 1 mm for each pecking motion until the file reach the working length. Forces were recorded during file movement, and the maximum force was extracted from the data. Maximum screw-in forces were analyzed by one-way ANOVA and Tukeys post hoc comparison at a significance level of 95%. Results Reciproc and ProTaper Universal files generated the highest maximum screw-in forces among all the instruments while M-two and ProTaper Next showed the lowest (p < 0.05). Conclusions Geometrical differences rather than shaping motion and alloys may affect the screw-in force during canal instrumentation. To reduce screw-in forces, the use of NiTi files with smaller cross-sectional area for higher flexibility is recommended.

Debris extrusion by glide-path establishing endodontic instruments with different geometries

Background/purpose Glide-path preparation is an important step during initial endodontic procedure to reduce shaping-instrument fracture. The aim of this study was to evaluate the amount of apically extruded debris produced by glide-path preparation instruments with different geometric designs. Materials and methods Forty teeth extracted for periodontal reasons were randomly divided into four groups (n = 10). The working length was standardized at 17 mm from the apical foramen by a flattening reference point. The glide-path was created using repetitive up-and-down movement three times with one of following four selected instruments: One G, ProGlider, a size 15 ScoutRace, and a size 15 stainless-steel K-file. To collect the apically extruded debris, the customized apparatus was used, and the collected debris was stored in an incubator. The weight of the debris was measured using an analytical balance with an accuracy of 0.00001 g. The data were analyzed by one-way analysis of variance and Duncans multiple comparison test at a significance level of 95%. Results The ProGlider group produced significantly less debris extrusion relative to the other groups (P < 0.05). The One G and ScoutRace groups showed no significant difference, but debris production was lower than that observed for the stainless-steel group (P < 0.05). Conclusion Creating the glide-path using nickel-titanium rotary files produced lower amounts of debris extrusion than using manual stainless-steel files. The progressive taper design of ProGlider, the center-off cross-section of One G, and the alternative-pitch design of ScoutRace may have increased the efficiencies of debris removal with minimal extrusion during glide-path preparation. Glide-path preparation using NiTi rotary files have better clinical efficiency than the manual stainless-steel file.

Effect from Rotational Speed on Torsional Resistance of the Nickel-titanium Instruments

Introduction: The purpose of this study was to evaluate differences in torsional resistance using up‐regulated speed of rotational spindle. Methods: Three NiTi rotary instrument systems were selected in this study: K3XF (SybronEndo, Glendora, CA), BLX (B&L Biotech, Ansan, Korea), and OneShape (MicroMega, Besançon, France). The tip size and taper for all files were #25 and 0.06. Experimental groups (n = 10/group) were assigned to 2‐, 60‐, 350‐, and 600‐rpm groups by the rotational speed of spindle. Forty new files were used for each test. The file tip of 5‐mm length was secured between brass plates. While keeping the file straight, it was rotated clockwise at a constant rotational speed until fracture occurred. The parameters of torsional resistance, torsional load (Ncm), and distortion angle (°) were measured using an AEndoS‐k (DMJ System, Busan, Korea), and the toughness until fracture was computed from these data. The 1‐way analysis of variance test was used to analyze the torsional resistance at a significance level of 95%. All fractured fragments were observed under a scanning electron microscope to evaluate the topographic features of the fractured surfaces. Results: No significant difference in torsional resistance was found among groups when they were compared for ultimate strength at the maximum torque, fracture angle, and toughness. Scanning electron microscopic examination of the fractured cross‐sectional surfaces revealed typical features of torsional fractures, concentric abrasion marks, and fibrous dimples from the torsional center. Conclusions: Under the conditions of the study, the torsional resistances of the rotary instruments were not affected by the rotational speed. HighlightsThe difference of torsional resistance was evaluated according to the up‐regulated speed of rotational spindle.Four conditions of rotational speed (2, 60, 350, and 600 rpm) were applied.The conventional nickel‐titanium alloy (BLX and OneShape) and the R‐phase heat‐treated alloy (K3XF) were tested.The different speeds of rotation did not change the torsional resistance of the rotary files.

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

Introduction: This study evaluated the effect of torsional preloading on the torsional resistance of nickel‐titanium (NiTi) endodontic instruments. Methods: WaveOne 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. Results: All 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. Conclusions: Torsional 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. Highlights:The effects of torsional preloading in various conditions on the torsional resistance of nickel‐titanium (NiTi) endodontic instruments were investigated.Two NiTi instrument systems, WaveOne Primary made from M‐wire from a reciprocating system and ProTaper Universal F3 made from conventional NiTi from a continuous rotation system, were used in this study.All preloaded groups showed significantly higher ultimate strength than the unpreloaded groups. There was no significant difference among all groups for distortion angle and toughness.Scanning electron microscopic examinations of the fractured surface showed typical features of torsional fracture. The total energy until fracture was maintained constantly, regardless of the alloy type.

Vibrations Generated by Several Nickel-titanium Endodontic File Systems during Canal Shaping in an Ex Vivo Model

Introduction: This study aimed to compare the vibration generated by several nickel‐titanium (NiTi) file systems and transmitted to teeth under 2 different motions (continuous rotation motion and reciprocating motion). Methods: Sixty J‐shaped resin blocks (Endo Training Bloc‐J; Dentsply Maillefer, Ballaigues, Switzerland) were trimmed to a root‐shaped form and divided into 2 groups according to the types of electric motors: WaveOne motor (WOM, Dentsply Maillefer) and X‐Smart Plus motor (XSM, Dentsply Maillefer). Each group was further subdivided into 3 subgroups (n = 10 each) according to the designated file systems: ProTaper Next (PTN, Dentsply Maillefer), ProTaper Universal (PTU, Dentsply Maillefer), and WaveOne (WOP, Dentsply Maillefer) systems. Vibration was measured during the pecking motion using an accelerometer attached to a predetermined consistent position. The average vibration values were subjected to 2‐way analysis of variance as well as the t test and Duncan test for post hoc comparison at the 95% confidence interval. Results: Both motor types and instrument types produced significantly different ranges of average vibrations. Regardless of the instrument types, the WOM group generated greater vibration than the XSM group (P < .05). Although PTN and PTU did not show significant differences, the WOP group showed significantly greater vibration than the other groups regardless of motor types (P < .05). Conclusions: Under the limitations of this study design, the reciprocating NiTi file system may generate greater vibration than the continuous rotation NiTi file systems. The motor type also has a significant effect to amplify the vibrations. HighlightsVibrations generated by 3 NiTi files and transmitted to the artificial teeth were measured.Instruments with reciprocating motion, continuous rotation, or swaggering motions were compared.The reciprocating motion generated greater vibration than the continuous rotation motion.The WaveOne motor may generate greater vibration than the X‐Smart Plus motor.

Effect of the Glide Path Establishment on the Torque Generation to the Files during Instrumentation: An In Vitro Measurement

Introduction: The purpose of this study was to compare in vitro torque generation during instrumentation with or without glide path establishment. Methods: Endo‐training resin blocks with J‐shaped canals were randomly divided into 2 groups according to glide path establishment (with or without) and subdivided into 2 subgroups with shaping instruments (WaveOne [Dentsply Maillefer, Ballaigues, Switzerland] or WaveOne Gold [Dentsply Maillefer]) (n = 15). For the glide path–established group, the glide path was prepared using ProGlider (Dentsply Maillefer). During the instrumentation with WaveOne or WaveOne Gold, in vitro torque was measured. The acquired data were analyzed with software. The maximum torque and total torque (the sum of the generated torque) were calculated. The data were statistically evaluated using 2‐way analysis of variance and the Duncan post hoc comparison to examine any correlation of torque generation with glide path establishment and nickel‐titanium instruments. The significance level was set at 95%. Results: The generated total torque by WaveOne Gold was significantly reduced by glide path establishment (P < .05), whereas glide path establishment did not induce significant changes in the maximum torque for both file systems. WaveOne Gold with a glide path showed the lowest total torque generation among all groups (P < .05). WaveOne generated a higher maximum torque than WaveOne Gold regardless of the establishment of a glide path (P < .05). Conclusions: Under the limitations of this study, glide path establishment and the mechanical property of instruments have a significant influence on torque generation. It is recommended to create the glide path and use a flexible file to reduce torque generation and, consequently, the risk of file fracture and root dentin damage.

Cutting efficiency of apical preparation using ultrasonic tips with microprojections: confocal laser scanning microscopy study

Objectives The purpose of this study was to compare the cutting efficiency of a newly developed microprojection tip and a diamond-coated tip under two different engine powers. Materials and Methods The apical 3-mm of each root was resected, and root-end preparation was performed with upward and downward pressure using one of the ultrasonic tips, KIS-1D (Obtura Spartan) or JT-5B (B&L Biotech Ltd.). The ultrasonic engine was set to power-1 or -4. Forty teeth were randomly divided into four groups: K1 (KIS-1D / Power-1), J1 (JT-5B / Power-1), K4 (KIS-1D / Power-4), and J4 (JT-5B / Power-4). The total time required for root-end preparation was recorded. All teeth were resected and the apical parts were evaluated for the number and length of cracks using a confocal scanning micrscope. The size of the root-end cavity and the width of the remaining dentin were recorded. The data were statistically analyzed using two-way analysis of variance and a Mann-Whitney test. Results There was no significant difference in the time required between the instrument groups, but the power-4 groups showed reduced preparation time for both instrument groups (p < 0.05). The K4 and J4 groups with a power-4 showed a significantly higher crack formation and a longer crack irrespective of the instruments. There was no significant difference in the remaining dentin thickness or any of the parameters after preparation. Conclusions Ultrasonic tips with microprojections would be an option to substitute for the conventional ultrasonic tips with a diamond coating with the same clinical efficiency.