Stress Generation during Pecking Motion of Rotary Nickel-titanium Instruments with Different Pecking Depth

Three-Dimensional Printed Teeth in Endodontics: A New Protocol for Microcomputed Tomography Studies

This study aimed to describe a support material removal protocol (SMRP) from inside the root canals of three-dimensional printed teeth (3DPT) obtained by the microcomputed tomography (microCT) of a natural tooth (NT), evaluate its effectiveness by comparing the 3DPT to NT in terms of internal anatomy and behaviour toward endodontic preparation, and evaluate if 3DPT are adequate to assess the differences between two preparation systems. After the SMRP, twenty 3DPT printed by PolyJet™ were microCT scanned before preparation and thereafter randomly assigned into two groups (n = 10). One group and NT were prepared using ProTaper Gold® (PTG), and the other group with Endogal® (ENDG). MicroCT scans were carried out after preparation, and the volume increase, volume of dentin removed, centroids, transportation, and unprepared areas were compared. For the parameters evaluated, no significant differences were found between the 3DPT and NT before and after preparation (p > 0.05), and no significant differences were found between the 3DPT PTG group and the 3DPT ENDG group (p > 0.05). It can be concluded that the SMRP described is effective in removing the support material SUP706B™. PolyJet™ is adequate for printing 3DPT. Furthermore, 3DPT printed with high-temperature RGD525™ have similar behaviour during endodontic preparation with PTG as the NT, and 3DPT can be used to compare two preparation systems.

Finite element study of the fatigue behaviour of nickel-titanium endodontic files utilised with pecking motion technique

The purpose of the study is to evaluate the influence of the pecking motion (reciprocal axial motion) surgical technique on the durability behaviour of the Nickel-Titanium endodontic files using Finite Element Analysis (FEA). A commonly used endodontic file, ProTaper Universal F2, is selected for the study. Root canal treatment procedure is simulated on a test-bench (simulated root canal) proposed by G. Gambarini for cyclic fatigue loading of endodontic files with and without the pecking motion via FEA. The hysteresis energy density is used as evaluation criteria for low cycle fatigue life estimation of Shape Memory Alloy files. In an additional study, the root canal treatment procedure is also simulated for an FEA model of a molar tooth with significant root canal curvature to understand the influence of the realistic curvature of a root canal on the fatigue behaviour of endodontic files. For the simulated root canal, analysis accurately predicts the endodontic file's failure location, and fatigue life estimation based on the hysteresis energy density is shown to increase significantly with the introduction of the pecking motion, an observation confirmed by reported experimental results. Molar tooth simulations reveal greater file fatigue resistance than in simulated root canals, confirming the pecking motion's efficacy in enhancing file durability, even in real root canal conditions. Simulations indicate that the pecking motion technique increases the fatigue life of endodontic files for simulated as well as real root canals and the hysteresis energy is confirmed as an acceptable parameter to quantify fatigue life of Nickel-Titanium endodontic files.

The Role of Pecking Motion Depths in Dynamic Cyclic Fatigue Resistance: In Vitro Study

OBJECTIVE

This is the first study evaluating the impact of different pecking motion depths on dynamic cyclic fatigue resistance of different endodontic instruments.

METHODS

Four nickel-titanium systems (Hyflex EDM OneFile 25/. ∼; Rotate 25/0.6; Mtwo 25/0.6; Reciproc Blue R25) were tested. Forty instruments from each group were subjected to 4 different pecking movements to evaluate their cyclic fatigue resistance. The distances for the pecking motion were 3-mm forward and backward, 1-mm (3-mm forward and 2-mm backward), 2-mm (4-mm forward and 2-mm backward), and 3-mm (5-mm forward and 2-mm backward). Speeds were 100 and 200 mm/min for the descending and ascending motion, respectively. The times to fracture (TtF) in seconds were recorded for each instrument. Data were statistically analysed by using 2-way ANOVA and Bonferroni multiple comparison post hoc test (P < .05).

RESULTS

All instruments had a significant increase in cyclic fatigue resistance during the forward dynamic motion compared with the axial continuous. Overall, the heat-treated instruments reported higher fatigue strength than the untreated files (P < .05). Reciproc Blue and Hyflex EDM showed higher TtF in the forward movements of 1-/2-mm and 2-mm (P < .05), respectively while Mtwo 25.06 and Rotate 25.06 in the forward movement of 3-mm (P < .05).

CONCLUSIONS

Within the limits of this in vitro study, the pecking motion depths had varying impacts on the cyclic fatigue resistance of instruments. Reciproc Blue and Hyflex EDM performed significantly better with pecking motions of 1-and 2-mm. Improving endodontic instrument durability through specific pecking depths has the potential for improving clinical performance and reducing instrument failures.

Impact of pecking amplitude on cyclic fatigue of new nickel-titanium files

OBJECTIVES

The aim of this study is to determine the cyclic fatigue resistance of Mtwo Minimal in static and dynamic tests, with different amplitudes of pecking movements, at intracanal temperature.

MATERIALS AND METHODS

Two hundred new 25-mm Mtwo Minimal rotary files (#10/0.035, #17.5/0.045, #25/0.05, #40/0.03, #45/0.03) were tested in static and dynamic cyclic fatigue tests at 35°C (±1°C). An artificial stainless-steel canal was used. In the dynamic mode, axial movements were set at 1 and 3 mm. The number of cycles to fracture (NCF) was recorded and statistically analyzed by one-way analysis of variance (p < 0.05).

RESULTS

The 3-mm dynamic test showed significantly increased NCF than the other tests for the #10/0.035, #17.5/0.045, and #25/0.05 files (p < 0.05). The #40/0.03 and #45/0.03 files showed no significant differences in all the tests (p > 0.05).

CONCLUSION

Mtwo Minimal showed higher cyclic fatigue resistance in the dynamic test than the static test, except for the larger instruments. The 3-mm pecking amplitude increased the cyclic fatigue resistance of the smaller instruments.

Screw-in force, torque generation, and performance of glide-path files with three rotation kinetics

We aimed to evaluate the screw-in force, torque generation, and performance of three nickel-titanium (NiTi) glide-path files with different rotational kinetics. ProTaper Ultimate Slider (PULS) and HyFlex EDM Glide-path (HEDG) files were used for canal shaping with constant rotation (CON) or the alternative rotation technique (ART). In the ART mode, the NiTi file was periodically rotated at a speed of 1.5 times faster than that in the CON mode. WaveOne Gold Glider was used with reciprocating motion (WOGG_RCP). Sixty J-shaped resin blocks were assigned to five groups: PULS_CON, PULS_ART, HEDG_CON, HEDG_ART, and WOGG_RCP (n = 12). Glide-path preparation was performed using an automated pecking device. During glide-path preparation, the screw-in force and clockwise and counterclockwise torques were recorded and the number of pecking motions required to reach the working length was determined. The centering ratio was calculated after glide-path preparation using stereomicroscopic images. Data were analyzed using one-way analysis of variance with the Games-Howell post hoc test and the Kruskal-Wallis test with Bonferroni correction. PULS_ART generated a lower maximum screw-in force than PULS_CON. The average number of pecking motions required to reach the working length by HEDG_ART was lower than that by HEDG_CON. The mean centering ratios of PULS_CON and HEDG_CON were - 0.04 and - 0.06, respectively, while those of PULS_ART, HEDG_ART, and WOGG_RCP were 0.09, 0.01, and 0.08, respectively. The ART mode reduced the screw-in force of PULS and enabled faster glide-path preparation with the HEDG file.

A novel model to evaluate the fatigue resistance of NiTi instruments: Rotational and axial movement at body temperature

To develop a model to test cyclic fatigue resistance of TruNatomy instruments undergoing rotational and axial movement at body temperature. A total of 288 Prime and Medium instruments were subjected to cyclic fatigue testing in simulated canals (at 37°C) using a model with either rotational movement only or rotational and axial movement simultaneously. Two different sized canals and three different types of curvatures were tested for each instrument (30/0.04 and 30/0.06 for Prime; 38/0.04 and 40/0.06 for Medium). The number of cycles to failure (fatigue resistance) was recorded. Rotational and axial movement of instruments led to greater fatigue resistance compared with rotational movement alone. Apical curvatures led to greater fatigue resistance than curvatures in the coronal and middle third. The developed dynamic model at body temperature to evaluate fatigue resistance of instrument closer simulates clinical scenarios.

Effect of Different Downward Loads on Canal Centering Ability, Vertical Force, and Torque Generation during Nickel-Titanium Rotary Instrumentation

This study aimed to examine how downward loads influence the torque/force and shaping outcome of ProTaper NEXT (PTN) rotary instrumentation. PTN X1, X2, and X3 were used to prepare J-shaped resin canals employing a load-controlled automated instrumentation and torque/force measuring device. Depending on the torque values, the handpiece was programmed to move as follows: up and down; downward at a preset downward load of 1 N, 2 N or 3 N (Group 1N, 2N, and 3N, respectively; each n = 10); or upward. The torque/force values and instrumentation time were recorded, and the canal centering ratio was calculated. The results were analyzed using a two-way or one-way analysis of variance and the Tukey test (α = 0.05). At the apex level, Group 3N exhibited the least canal deviation among the three groups (p < 0.05). The downward force was Group 3N > Group 2N > Group 1N (p < 0.05). The upward force, representing the screw-in force, was Group 3N > Group 1N (p < 0.05). The total instrumentation time was Group 1N > Group 3N (p < 0.05). In conclusion, increasing the downward load during PTN rotary instrumentation improved the canal centering ability, reduced the instrumentation time, and increased the upward force.

Improvement and analysis of mechanistic modeling of root canal preparation by a computer-based method

BACKGROUND AND OBJECTIVE

Root canal preparation is a cutting process between nickel-titanium (Ni-Ti) file and root canal, which aims to remove the bacteria and to keep teeth from infection. A mechanistic model in root canal preparation is proposed to investigate the mechanical mechanism of Ni-Ti file, which is essential to prevent physical and thermal damage on root canal.

METHODS

First, the mathematic modeling is introduced based on oblique cutting theory, which the loading condition of Ni-Ti file is derived from each cutting element by expressing a function of geometric parameters. For the modeling improvement, a cutting simulation algorithm (CSA) based on Boolean operation is proposed to achieve the complicated cutting situation between root canal and Ni-Ti file instantaneously. After establishment of model, the predictive precision is verified by conducting in vitro experiments. Eighteen artificial root canals were prepared in 6 mm straight and 2 mm C-shaped curved specification with 0.3 mm diameter, which was a single canal for each position, all the canals do not have connections with each other. During experiments, root canals were prepared using Wave One Gold (GWO) instruments with reciprocating rotational motion. Different influential factors (curvatures of root canal and movements of Ni-Ti file) and cutting parameters (feed rate and spindle speed) were analyzed by conducting a series of simulations under the mechanistic model.

RESULTS

Experiment results show that the predictive error of thrust force based on the proposal model is around 15%. The thrust force will increase dramatically after Ni-Ti file gets into craved canal. It can be indicated that the curvatures of root canal, movements of Ni-Ti file have a strong influence on root canal preparation. 20° increasement of curved degrees can lead to the 0.73 N increase of thrust force, while pecking movement can decrease 19.88% of thrust force compared with continues one. Furthermore, investigation on pecking distance represent that 2-1 mm movement can effectively reduce the thrust force of 15.82% compared to 4-2 mm movement.

CONCLUSION

Based on simulation results, 2-1 mm pecking movement is recommended for dentists compared with 4-2 mm pecking movement or continues movement. In addition, this paper provides a novel insight of interactive mechanism between Ni-Ti file and root canal, so as to contribute to both the theoretical and practical research by elucidating mechanisms and providing quantitative predictions that can be validated. Compared with conventional analytical model, both calculated precision and efficiency are improved in the proposed model.

Impact of Radial Lands on the Reduction of Torque/Force Generation of a Heat-Treated Nickel-Titanium Rotary Instrument

This study investigated the impact of a one-sided radial-landed cross-sectional design of a heat-treated nickel-titanium rotary instrument (JIZAI, MANI, Japan; JZ) on torque/force generation and canal-shaping ability, using an experimental non-landed instrument (non-landed JZ) for comparison. Both instruments had tip sizes of 25 and 0.04 or 0.06 taper and were similar in metallurgy and geometry, except for the presence/absence of a radial land. Twenty J-shaped simulated resin canals were instrumented in a two-instrument single-length sequence using an automated root canal instrumentation device with a torque/force analyzing unit. Pre- and post-instrumentation images of the resin canals were analyzed for canal-centering ability at 0–3 mm from the apex. The mean centering ratio was not significantly different between JZ and non-landed JZ (p > 0.05). In the 2nd instrumentation, JZ showed a significantly smaller torque compared with the non-landed JZ (p < 0.05). Regardless of instrumentation sequence, JZ showed a significantly smaller maximum upward force, representing screw-in force (p < 0.05), and a larger maximum downward force (p < 0.05) than the non-landed JZ. JZ generated smaller screw-in forces and had similar canal-centering ability compared with the non-landed JZ.

Torque Generation of the Endodontic Instruments: A Narrative Review

As the use of nickel-titanium (NiTi) file systems for root canal therapy has become popular; hence, knowledge and understanding of the characteristics of NiTi files is essential for dentists. Unintended sudden fracture can occur during root canal shaping, and it is important to understand the conditions that may cause instrument fractures. Torque is defined as the force required to rotate the NiTi file and can be considered of as a parameter for the stress generated. The endodontic engine maintains a constant rotational speed by adjusting torque regardless of the root canal conditions. The process of root canal shaping by rotary instruments is a series of actions that requires torque and generates stress to both the teeth and the NiTi instruments. The generated stress may induce the strain accumulation on NiTi instrument and the canal wall and lead to the development of microcrack in the instrument and dentinal wall. Therefore, understanding of torque and stress generated is important to prevent the fractures to the instrument and the teeth. This stress has been measured using various experimental approaches, including microcrack observation by using a microscope or computed tomography, attaching strain gauges to the teeth, and finite element analysis. This review focuses on the stress generated to the teeth and the instrument during instrumentation under various experimental conditions. The factors related to torque generation are also discussed.

Influence of pecking frequency at working length on the volume of apically extruded debris: A micro-computed tomography analysis

Background/purpose

There is no consensus to date on how many repetitive pecking motions at working length (WL) should be regarded as optimal during instrumentation. Therefore, this study aimed to evaluate the effect of pecking frequency at WL on the volume of apically extruded debris using three single-file systems in curved, oval-shaped canals.

Materials and methods

Forty-five single-rooted mandibular premolars with curved, oval-shaped canals were prescanned by micro-computed tomography, anatomically paired-matched, and randomly divided among three groups (n = 15 each): Reciproc Blue (RB), WaveOne Gold (WOG) and XP-endo Shaper (XPS). Samples were embedded in agarose gel to collect extruded debris. After preparation to the WL, each sample was rescanned after one, two, four, 10, and 20 pecking motions at WL, respectively. The debris volume was innovatively calculated by a modification of an existing method using micro-computed tomography. The apical preparation size was also measured. Data were compared using a two-way repeated-measures analysis of variance.

Results

All single-file systems extruded debris apically, irrespective of the pecking frequency at WL. The extruded debris volume correlated positively with the minor foramen size (P < 0.05); both increased with pecking frequency for each single-file system (P < 0.05). The minor foramen size corresponded to the instrument tip size when reaching the WL once.

Conclusion

To produce less debris extrusion and obtain a predictable foramen size corresponding to the instrument tip size, a single pecking motion may be preferred when using single-file systems. Caution should be exercised when applying the current results to clinical situations.

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

INTRODUCTION

This study aimed to compare the torque generated by 4 different files in root canals with 4 different curvature angles.

METHODS

Four 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%.

RESULTS

A 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).

CONCLUSIONS

Despite 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.

Analysis of Torque and Force Induced by Rotary Nickel-Titanium Instruments during Root Canal Preparation: A Systematic Review

The aim of this review was to provide a detailed literature analysis of torque and force generation during nickel-titanium rotary root canal instrumentation. We followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. An electronic search was performed using in PubMed and in journals for articles published in English from 1987 to June 2020 on studies that investigated dynamic torque and force in vivo or in vitro. We assessed article titles and abstracts to remove duplicates, and the titles and abstracts of the remaining articles were screened for eligibility. Full texts were read to verify eligibility by considering predetermined inclusion and exclusion criteria. Fifty-two out of 4096 studies met the inclusion criteria, from which we identified 26 factors that influence torque or force generation. Factors associated with higher torque or force generation and supported by multiple studies with mostly consistent results included convex triangle cross-sectional design, regressive taper, short pitch length, large instrument size, small canal size, single-length preparation technique, long preparation time, deep insertion depth, low rate of insertion, continuous rotation (torque), reciprocating motion (force), lower rotational speed and conventional alloy. However, several factors are interrelated, which obscured the independent effect of each factor, and there was insufficient scientific evidence supporting the influence of some factors.

Comparison of canal transportation and centering ability of manual K-files and reciprocating files in glide path preparation: a micro-computed tomography study of constricted canals

Background

Optimum Glide Path (OGP) is a new reciprocating motion aiming to perform efficient glide path preparation in constricted canals. The aim of this study was to investigate and compare manual and OGP movement in terms of canal transportation and centering ability in glide path preparation of constricted canals.

Methods

Thirty constricted mesial root canals of mandibular molars, with initial apical size no larger than ISO#8, were selected and negotiated with #6–#8 K-files under the microscope. Canals were randomly divided into two experimental groups: Group 1 (MAN, n = 15): Glide path was established by using #10-#15 stainless steel K-files manually; Group 2 (OGP, n = 15): #10-#15 Mechanical Glide Path super-files were used with OGP motion (OGP 90°, 300 rpm). Each instrument was used to prepare only 2 canals (as in one mesial root). Canals were scanned before and after glide path preparation with micro-computed tomography (micro-CT) to evaluate root canal transportation and centering ratio at 1, 3 and 5 mm levels from the root apex. File distortions and separations were recorded. Paired t-test was used to statistically evaluate the data (P < .05).

Results

Group 2 showed a significantly lower transportation value than group 1 at 1-mm and 3-mm levels (P < .05), however the difference at 5-mm level was not significant. There was no significant difference regarding the centering ratio between the groups. Six #10 K-files were severely distorted in group 1, while no file separation or distortion was found in group 2.

Conclusions

OGP motion performed significantly less canal transportation (apical 3 mm) and file distortion during glide path establishment in constricted canals comparing to manual motion, while the centering ability between the two was similar.

Clinical relevance

OGP reciprocating motion provides a safer and efficient clinical approach compared to traditional manual motion in glide path establishment with small files in constricted canals.

Ex-Vivo Comparison of Torsional Stress on Nickel-Titanium Instruments Activated by Continuous Rotation or Adaptive Motion

This study aimed to evaluate the effect of adaptive motion applied to conventional nickel-titanium (NiTi) rotary instruments on torsional stress generation during shaping procedure. One hundred and twenty mesio-buccal canals of molars were randomly assigned to two groups according to the kinetics; adaptive motion (AD) and continuous rotation (CR). Each group was divided into four subgroups (n = 15) according to the NiTi instrument systems: HyFlex EDM, One Curve, Twisted File Adaptive, and ProTaper Next. A glide path was established with PathFile #1, for each file group being used with either of the kinetic movements. During the instrumentation with the designated motion and file system, the generated torque was measured via the control unit and acquisition module. Based on the acquired data, the maximum and total torque were calculated. The data were statistically analyzed using Kruskal–Wallis and Mann–Whitney tests at a significance level of 95%. The maximum and total torque generated by all instruments were significantly reduced by the adaptive motion (p < 0.05). In the CR group, HyFlex EDM generated the highest maximum and total stress. In the AD group, HyFlex EDM showed the highest maximum torsional stress, and One Curve showed the highest total torsional stress (p < 0.05). The TF Adaptive instrument with adaptive movement produced the lowest maximum and total torsional stress (p < 0.05). Under the conditions of this study, the use of adaptive motion would be useful to reduce the torsional stress of instrument and root dentin. The reduction of torsional stress through adaptive motion may enhance the durability of instruments and reduce the potential risk of dentinal cracks.

Force and vibration generated in apical direction by three endodontic files of different kinematics during simulated canal preparation: An in vitro analytical study

During root canal shaping, pain could result from the high level of force or vibration generated. This could be related to file kinematics or geometry. In the present study, a comparison is made between forces and vibrations generated by endodontic files having three different kinematics. Square pillar resin blocks were used as simulated root canals to study forces and vibrations generated by the file having reciprocating motion (WaveOne Gold), transline motion (Self-Adjusting File), and rotary motion (2Shape). The forces and vibrations were measured using the dynamometer and accelerometer, respectively. Recorded time domain signals were processed in MATLAB to calculate the root mean square value. A one-way analysis of variance and Tukey's test for post hoc comparison at 95% confidence interval were applied over the root mean square data of different files. From a statistical analysis of the file systems, the null hypotheses could not be accepted (P < 0.05) as 95% of the confidence interval. Differences between the means were statistically significant. The root mean square values of force and vibration for WaveOne Gold significantly exceeded those of Self-Adjusting File, 2Shape1, and 2Shape2 while the root mean square values of vibration for 2Shape1 and 2Shape2 were significantly less than the Self-Adjusting File; however, the root mean square value of force for the 2Shape2 was significantly more than for the Self-Adjusting File. Under the present experimental conditions, significant differences in the root mean square values of force and vibration of the three endodontic files of different kinematics have been observed. The WaveOne Gold file system generated higher apical force and vibration than the transline and rotary file system.