Cyclic Fatigue Resistance of One Curve, 2Shape,ProFile Vortex,Vortex Blue,and RaCe Nickel-Titanium Rotary Instruments in Single and Double Curvature Canals

Introduction

The aim of this study was to evaluate and compare the resistance to cyclic fatigue of the new One Curve (OC) instrument in double (S-shaped) and single curvature canals compared with other nickel-titanium rotary instruments.

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.

Blue Treatment Enhances Cyclic Fatigue Resistance of Vortex Nickel-Titanium Rotary Files

Introduction

The aim of the present study was to evaluate the difference in cyclic fatigue resistance between Vortex Blue (Dentsply Tulsa Dental, Tulsa, OK) and Profile Vortex nickel-titanium (Dentsply Tulsa Dental) rotary instruments.

Methods

Two groups of nickel-titanium endodontic instruments, ProFile Vortex and Vortex Blue, consisting of identical instruments in tip size and taper (15/.04, 20/.06, 25/.04, 25/.06, 30/.06, 35/.06, and 40/.04) were tested. Ten instruments from each system and size were tested for cyclic fatigue resistance, resulting in a total of 140 new instruments. All instruments were rotated in a simulated root canal with a 60° angle of curvature and a 5-mm radius of curvature of a specific cyclic fatigue testing device until fracture occurred. The number of cycles to failure and the length of the fractured tip were recorded for each instrument in each group. The mean values and standard deviation were calculated, and data were subjected to 1-way analysis of variance and a Bonferroni t test. Significance was set at the 95% confidence level.

Results

When comparing the same size of the 2 different instruments, a statistically significant difference (P < .05) was noted between all sizes of Vortex Blue and Profile Vortex instruments except for tip size 15 and .04 taper (P = 1.000). No statistically significant difference (P > .05) was noted among all groups tested in terms of fragment length.

Conclusions

Vortex Blue showed a significant increase in cyclic fatigue resistance when compared with the same sizes of ProFile Vortex.     

Low Environmental Temperature Influences the Fatigue Resistance of Nickel-titanium Files

Introduction

The purpose of this study was to evaluate the effect of different temperatures (0°C, 10°C, 22°C, 37°C, and 60°C) on the cyclic fatigue life of nickel-titanium (NiTi) files using a new fatigue test model in zirconium oxide.

Root Canal Preparation and Enlargement Using Thermally Treated Nickel-Titanium Rotary Systems in Curved Canals

IntroductionThe purpose of this study was to evaluate root canal preparation and apical enlargement of curved canals using rotary heat-treated and heat/surface-treated systems by micro–computed tomographic imaging.MethodsCurved mesial root canals (n = 48) of mandibular molars (20°–40°) were prepared using ProDesign Logic (PDL; Easy Equipamentos Odontológicos, Belo Horizonte, MG, Brazil) 25/.01 and 25/.06 or HyFlex EDM (HFEDM) 10/.05, HyFlex CM 20/.04, and HFEDM 25/.08. Apical enlargement was performed using PDL 40/.05 or HFEDM 40/.04. Scanning (9 μm) was performed before and after preparation and after apical enlargement using micro–computed tomographic imaging. Volume, percentage of volume increase, debris, untouched root canal surface, and centering ability were analyzed. Statistical analysis was performed using Mann-Whitney, Wilcoxon, and unpaired t tests (α = .05).ResultsHFEDM promoted a higher volume increase of the root canals than PDL after preparation and after apical enlargement (P < .05). The apical enlargement promoted a significant decrease in debris and untouched surface in both groups (P < .05). The percentage of debris and untouched surface were similar between HFEDM and PDL after preparation and after apical enlargement (P > .05). Both systems promoted centered canals (P > .05).ConclusionsHFEDM instruments promoted greater volume of the root canal than PDL. However, the cleaning ability of the instruments was similar. The apical increase up to size 40 with both instruments provided less debris and untouched surfaces and allowed centralization of the curved root canals.     

Cyclic Fatigue Resistance of Rotary and Reciprocating Nickel-Titanium Instruments Subjected to Static and Dynamic Tests

IntroductionThis study compared the static and dynamic cyclic fatigue resistance of contemporary nickel-titanium instruments with different kinematic, metallurgic, and design features to establish whether the fatigue-reducing effect of the pecking motion differs among different nickel-titanium instruments.MethodsProTaper Gold (PTG), Hyflex EDM (EDM), Reciproc Blue (RPB), and WaveOne Gold (WOG) files were divided into 2 groups of 10 for the static and dynamic cyclic fatigue resistance tests. A stainless steel artificial canal with 1.5-mm inner diameter, 60° angulation, and 3-mm radius of curvature was used. In the dynamic cyclic fatigue resistance test, speeds were set at 100 and 200 mm/min for the descending and ascending motion, respectively. The number of cycles to fracture (NCF) was calculated, the fractured lengths were recorded, and fractographic analysis of the fractured surfaces was carried out by scanning electron microscopy. Data were analyzed statistically with the Kruskal-Wallis test with Bonferroni correction (alpha = 0.05).ResultsThe RPB and EDM showed significantly higher NCF in the static and dynamic cyclic fatigue resistance tests (P < .05). The dynamic cyclic fatigue resistance test showed significantly higher NCF than the static cyclic fatigue resistance test in the PTG and EDM (P < .05). There was no significant difference between the RPB and WOG (P > .05).ConclusionsIn the experimental condition where the ascending speed was higher than the descending speed, the dynamic cyclic fatigue resistance was significantly higher than the static cyclic fatigue resistance in continuous rotary instruments, but not in reciprocating instruments.     

Effect of Curvature Location on Fatigue Resistance of Five Nickel-titanium Files Determined at Body Temperature

IntroductionThe purpose of this study was to evaluate the effect of 5 different curvature locations on the fatigue resistance of thermomechanically treated nickel-titanium (NiTi) files and superelastic NiTi files at body temperature and to document the corresponding phase transformations.MethodsEndoSequence (ES; Brasseler USA, Savannah, GA), EndoSequence CM (ESCM, Brasseler USA), K3 (SybronEndo, Orange, CA), K3XF (SybronEndo), and Vortex Blue (VB; Dentsply Tulsa Dental Specialties, Tulsa, OK) NiTi files (size 25/.04) were subjected to fatigue tests inside customized artificial canals containing a curvature of 60° and a 3-mm radius. There were 5 different canals based on the location of initial curvature; these included groups in which the distance between the canal orifice and the location of the curvature (DOC) was 5, 6, 8, 10, and 11 mm. The model canal was immersed in water at 37°C ± 1°C. The number of cycles to failure (N_f) was recorded, and the fracture surface of the fragments was examined by scanning electron microscopy. Two unused files of each brand were examined by differential scanning calorimetry.ResultsThe N_f was highest in the 10-mm and 11-mm DOC groups and lowest with the 5-mm and 6-mm DOC groups (P < .05). ESCM files had the highest fatigue resistance followed by the VB, K3XF, K3, and ES files (P < .05). ESCM files had the highest N_f (P < .05), and ES and K3 files had the lowest N_f (P < .05) depending on the curvature location. Two endothermic peaks were observed on the heating curve of the heat-treated files (ESCM, K3XF, and VB).ConclusionsThe location of the canal curvature had a significant effect on the fatigue resistance of both heat-treated and superelastic NiTi files. The fatigue life of files in the coronal curve was quite short.     

Cyclic Fatigue Resistance of Multiused Reciproc Blue Instruments during Retreatment Procedure

IntroductionRoot canal retreatment procedure may reduce the mechanical resistance of nickel-titanium instruments and increase the frequency of instrument fracture. The aim of the present study was to evaluate the effect of multiuse of Reciproc Blue R25 instruments on cyclic fatigue resistance during retreatment procedure in mandibular molar teeth.MethodsForty-eight Reciproc Blue R25 files were included in the study. In control group, 12 new Reciproc Blue R25 instruments were subjected to cyclic fatigue test by using a stainless steel artificial canal with a 90° angle and 3-mm radius of curvatures. In experimental groups, Reciproc Blue R25 files (n = 12) were used to remove the root canal filling (RCF) material of 1, 2, and 3 molar teeth, respectively. Then cyclic fatigue tests of these 36 instruments were performed. The number of cycles to fracture (NCF) and the length of the fractured fragment were calculated for each instrument. Working time for retreatment procedures was determined in seconds with a digital chronometer. The data were analyzed by using one-way analysis of variance followed by post hoc Tukey test and mixed-effect analysis (P = .05).ResultsNo significant difference was found between NCF values of new and first time used files (P > .05), but NCF values of new and first time used files were significantly higher than those of second and third time used files (P < .05). The second and third time used files revealed no difference (P > .05). As the number of uses increased, the average time for retreatment procedure statistically extended (P < .05).ConclusionsReciproc Blue R25 instrument can be used to remove RCF material of 2 molar teeth. However, because of its decreased NCF values, multiple use over 2 molars may not be suggested.     

Cyclic fatigue resistances of Hyflex EDM,WaveOne gold,Reciproc blue and 2shape NiTi rotary files in different artificial canals

The aim of the present study was to compare the cyclic fatigue resistances of HyFlex EDM (HEDM), WaveOne Gold (WOG), Reciproc Blue (RB), and 2Shape (TS) NiTi systems having different metallurgic properties. HEDM, WOG, RB, and TS instruments were rotated in artificial canals which were made of stainless steel with an inner diameter of 1.5 mm, 45°, and 90° angles of curvatures and a radius of curvature of 5 mm until fracture occurred, and the time to fracture (TTF) was recorded in seconds. Also, number of cycles to fracture was calculated (NCF). Data were statistically analyzed using Kruskal–Wallis and t test. The statistical significance level was set at P < 0.05. When comparing the TTF of all the instruments tested in the artificial canal with 45° curvature, RB had statistically the highest cyclic fatigue resistance followed by HEDM and TS (P < 0.05), while the WOG showed the lowest cyclic fatigue resistance (P < 0.05). In artificial canal with 90° curvature, RB showed a significantly higher cyclic fatigue resistance than the other tested files (P < 0.05), while there was no significant difference among the TS, WOG and HEDM groups (P > 0.05). When the NCF values were taken into consideration, HEDM reported a significantly higher cyclic fatigue resistance than TS in both canal curvatures analyzed (P < 0.05). Within the limitations of the present study, RB NiTi files showed statistically higher cyclic fatigue resistance in artificial canals with 45° and 90° than the other NiTi files tested.     

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

IntroductionThe goal of this study was to compare the cyclic fatigue resistance of 5 heat-treated nickel-titanium files in reciprocating movement with the same tip size and different cross sections.MethodsFive groups (WaveOne [Dentsply, Ballaigues, Switzerland], WaveOne GOLD [Dentsply], RECIPROC [VDW, Munich, Germany], RECIPROC BLUE [VDW GmbH, Munich, Germany], and TF [Sybron Endo, Glendora, CA] Adaptive) of 24 files each of the rotary files were examined. Cyclic fatigue resistance was compared between groups by determining the time needed to fracture and the number of cycles to failure in a cyclic fatigue testing device with 2 different curvatures, the first with a 5-mm radius of curvature and a 60° angle and the second with a double curvature, coronal curvature of 60° angle and a radius of 5 mm, and an apical curvature of 70° angle and a 2-mm radius. Scanning electron microscopic evaluation was performed at the fracture sites to investigate the types of fracture.ResultsRECIPROC BLUE group had a higher mean time to fracture followed by RECIPROC and WaveOne GOLD for both single and double curvature. WaveOne had a higher mean time to fracture in a single curvature canal than TF Adaptive, whereas the opposite was true for a double curvature canal. Both RECIPROC groups were significantly greater in cyclic fatigue resistance in comparison with all other groups (P < .05). WaveOne GOLD was significantly greater than the WaveOne and TF Adaptive groups (P < .05).ConclusionsRECIPROC BLUE files exhibited significantly greater cyclic fatigue resistance compared with other files tested in an S-shaped artificial canal.     

Cyclic Fatigue Resistance of Nickel-Titanium Reciprocating Instruments after Simulated Clinical Use

IntroductionThe aim of this study was to evaluate the cyclic fatigue resistance of different heat-treated nickel-titanium reciprocating instruments in 2 different situations: new and used instruments after preparing 3 curved canals.MethodsA total sample of 60 nickel-titanium instruments of 3 systems (n = 20 per system) were used in this study: ProDesign R (tip 25, 0.06 taper; Easy Dental Equipment, Belo Horizonte, Brazil), Reciproc Blue (tip 25, 0.08v taper; VDW, Munich, Germany), and WaveOne Gold (tip 25, 0.07v taper; Dentsply Sirona, Ballaigues, Switzerland). Thirty new instruments (n = 10 per system) were used to prepare 90 curved single-rooted mandibular premolars (n = 30). Each instrument was used to prepare 3 root canals, and after each canal preparation the instrument was ultrasonic cleaned and submitted to autoclave sterilization procedures. The other 30 instruments (n = 10 per system) were kept without use. Then, the new and used instruments were subjected to the cyclic fatigue test in an artificial canal with a 30° angle and a 5-mm radius of curvature. The time and number of cycles to fatigue were recorded. Data were analyzed using the unpaired t test for intragroup comparison. For intergroup comparison, analysis of variance and the Tukey test for multiple comparisons were used.ResultsThe intergroup comparison of new instruments showed that ProDesign R had the highest cyclic fatigue resistance followed by Reciproc Blue and WaveOne Gold (P < .05). Regarding the used instruments, WaveOne Gold had the lowest cyclic fatigue resistance (P < .05). The intragroup comparison between new and used instruments showed that WaveOne Gold and ProDesign R presented a significant reduction in the cyclic fatigue resistance after simulated clinical use (P < .05); no difference was found with the Reciproc Blue instruments (P > .05).ConclusionsProDesign R had the highest cyclic fatigue resistance, whereas WaveOne Gold had the lowest for new and used instruments. Simulated clinical use affected the cyclic fatigue resistance of ProDesign R and WaveOne Gold but not of Reciproc Blue instruments.     

Static Cyclic Fatigue Resistance in Abrupt Curvature,Surface Topography,and Torsional Strength of R-Pilot and ProGlider Glide Path Instruments

IntroductionThis study aimed to compare ProGlider (Dentsply Sirona, Ballaigues, Switzerland) and R-Pilot (VDW, Munich, Germany) instruments in terms of their cyclic fatigue resistance using an artificial stainless steel canal showing an abrupt apical curvature, torsional resistance according to the ISO specification, and topographic changes on the instrument surface after glide path management in mesial canals of mandibular first molars with the abrupt curvature selected based on their micro–computed tomographic examination.MethodsEighty instruments were used: 40 ProGlider (size 0.16, .02v taper) and 40 R-Pilot (size 0.125, .04 taper) instruments. The cyclic fatigue resistance was tested in a static test model using an artificial canal with an abrupt apical curvature (angle of curvature of 90° and radius of curvature of 2 mm). The torsional resistance test was performed according to ISO 3630-1 specifications. To determine surface topography of the unused and used instruments, mesial root canals of mandibular molars with an abrupt apical curvature were selected to prepare a glide path with either the ProGlider or R-Pilot instrument. An optical profilometer and scanning electron microscopy were used to determine the surface properties. Normally distributed torsional and cyclic resistance data were analyzed using the Student t test, whereas quantitative data obtained by the optical profilometer were analyzed with the Kruskal-Wallis H test with a 5% significance threshold.ResultsThe R-Pilot showed significantly higher cyclic fatigue and torsional resistance than the ProGlider (P < .05). Angular deflection values were similar between instruments (P < .05). Measurements made from the blade area showed that the surface roughness values of the ProGlider were larger. Cutting blade measurements showed that unused instruments had significantly greater roughness values than used ones (P < .05). Although there was a 14% increase between the blade edge radii of the used and unused R-Pilot instruments, this difference was determined as 61% in ProGlider instruments.ConclusionsThe R-Pilot exhibited greater cyclic fatigue strength than the ProGlider when tested in an artificial canal with an inner diameter of 1.0 mm and an abrupt apical curvature. Torsional resistance of the R-Pilot was higher than the ProGlider, but the angular deflection values were similar. Glide path preparation in a mesial root canal with an abrupt apical curvature did not increase the surface roughness of both instruments but resulted in a greater blade edge radius.     

Fracture Resistance of Heat-Treated Nickel-Titanium Rotary Files After Usage and Autoclave Sterilization: An In Vitro Study

IntroductionThis study aimed to evaluate the dynamic cyclic fatigue resistance of heat-treated nickel-titanium (NiTi) files after usage and autoclaving.MethodsTwo heat-treated NiTi file systems with tip sizes of #25 (ie, ProTaper Gold F2 [Dentsply Sirona, Charlotte, NC] and TruNatomy Prime [Dentsply Sirona]) were selected. Files of each system were divided into 3 experimental subgroups (n = 10). For subgroup 1, new files were tested to establish the baseline number of cycles to failure (NCF). For subgroup 2, files underwent canal instrumentation in a simulated J-shaped canal block with 35° of curvature and a 16.5-mm length. The simulated canals were pre-enlarged using stainless steel files #10K and #15K. After instrumentation, the files were tested. For subgroup 3, files underwent canal instrumentation as in subgroup 2 followed by autoclave sterilization and then were tested for cyclic failure. The cyclic fatigue test was performed in dynamic pecking motion under body temperature. The time to fracture was recorded and calculated into NCF. Fracture fragment lengths were measured using a digital microcaliper. Statistical analysis was conducted using the independent t test and multifactorial analysis of variance with 95% significance. Scanning electron microscopy was used to examine the topographic characteristics after cyclic fatigue tests.ResultsThere were no significant differences between file systems in subgroup 1 using new files (P < .05). Although PG reduced the NCF after use, TN showed a significantly increased NCF (P < .05). However, after sterilization, TN showed a reduced NCF compared with the used one (P < .05).ConclusionsCyclic loading by usage and heat treatment during sterilization may result in different cyclic fatigue resistance according to the geometry and alloy characteristics.     

Effects of Conservative Access and Apical Enlargement on Shaping and Dentin Preservation with Traditional and Modern Instruments: A Micro-computed Tomographic Study

IntroductionThis ex vivo study aimed to evaluate the shaping abilities and preservation of dentin with traditional and modern instruments after using sizes 25 and 40 in oval canals of mandibular incisors with conservative access.MethodThirty mandibular incisors with single straight oval canals were selected and assigned into 2 groups (n = 15) according to the instrument system used during preparation, Slim Shaper (SS) plus Apical Shaper (AS) and Protaper Gold (PG). The samples were subjected to micro-computed tomography before and after preparation with sizes 25 and 40. The shaping parameters evaluated included canal volume and surface area, amount of unprepared root canal walls, and reduction in pericervical dentin.ResultsCanal volume and surface area were significantly increased after enlargement with each instrument size (P < .01). The percentage of unprepared areas showed a significant intragroup decrease after using PG F2 and F4 or SS 3 and AS (P < .05). Intergroup comparison showed no significant differences. Pericervical dentin was reduced in all groups. The intragroup comparison only revealed a significant reduction (P < .01) between PG F2 and F4. In addition, a significant decrease in pericervical dentin (P < .05) was observed between PG F4 40/.06 and AS 40/.03. No significant differences were observed between PG F2 25/.08 and SS 3 25/.04.ConclusionIncreasing the instrumentation size from 25 to 40 significantly reduces the percentage of unprepared areas regardless of the system used. In addition, using a modern system with a regressive taper allows the maintenance of pericervical dentin without compromising shaping efficacy in the apical third of the mandibular incisors with oval canals and conservative access.     

Mechanical Properties of Various Glide Path Preparation Nickel-titanium Rotary Instruments

Introduction

The aim of this study was to compare the cyclic fatigue, torsional resistance, and bending stiffness of single-file glide path preparation nickel-titanium instruments.

Optimum Shaping Parameters of the Middle Mesial Canal in Mandibular First Molars: A Finite Element Analysis Study

IntroductionThis study investigated the effect of shaping parameters of 2 different configurations of middle mesial canals (MMCs) on the biomechanical behavior and life span of a mandibular first molar using finite element analysis (FEA).MethodsA mandibular molar with an independent MMC and another with a confluent MMC were scanned via micro-computed tomography, and FEA models were produced. For each tooth, an intact model and 5 experimental models were produced that differed by parameters of how the MMC was shaped: unshaped MMC, 25/.04, 25/.06, 30/.04, and 30/.06. Cyclic loading of 50 N was applied on the occlusal surface in vertical and oblique scenarios, and the number of cycles until failure (NCF) was compared with the intact models. In addition, mathematical analyses evaluated the stress distribution patterns and calculated maximum von Mises and maximum principal stresses.ResultsFor both the independent and confluent MMC models, shaping the MMC reduced the NCF. The lifelog percentage of models was inversely proportional with radicular shaping parameters during the vertical and oblique loading scenarios. The shaping size of 30/.06 resulted in lower lifelog percentage than the cases with shaping size of 25/.04 in both of the independent and confluent MMC models. For all models, oblique loading reduced NCF more than vertical loading.ConclusionShaping the MMC should be kept as conservative as 25/.04. Also, whether the MMC is independent or confluent is a deciding factor in whether to increase the apical diameter or the root canal taper when larger shaping parameters are needed.     

Duration of ultrasonic activation causing secondary fractures during the removal of the separated instruments with different tapers

Objectives

The aim of the present study was to determine the effect of taper (.08, .06, and .04) of separated K3XF instruments on duration taken for the secondary fracture formation during ultrasonic activation.

Materials and methods

Ten 25/.08 K3XF (SybronEndo, Orange, CA, USA), ten 25/.06 K3XF, and ten 25/.04 K3XF instruments were used for the study. The apical 5 mm of the instruments was cut to simulate the fragments in root canals. Fragments of the instruments were sandwiched between two straight dentin blocks. An ultrasonic tip was used to cause a secondary fracture of the fragment. The time needed for the secondary fracture was recorded for each instrument. The data were statistically analyzed using the Kruskal-Wallis H test (alpha = 0.05).

Results

Secondary fractures occurred in all instruments. In the .08 taper group, secondary fractures took longer than in the case of the .06 and the .04 taper groups (P < 0.05). There were no significant differences between the .06 and the .04 taper groups in terms of the time required for the occurrence of a secondary fracture (P > 0.05).

Conclusions

In the .08 taper group, secondary fracture took longer time than in the case of the .06 and the .04 taper groups due to its larger cross-sectional area involved.

Clinical relevance

Typically, when removing separated instruments, a much lower power setting is chosen. The purpose of this in vitro study was to determine which tapered files were more resilient to secondary fracture, thus allowing a higher power setting to be chosen. Thus, the results of the present study cannot be used in clinical practice. If the clinician knows the taper of the broken file, the clinician should be very careful with regard to secondary fractures when using ultrasonics to remove the separated smaller tapered instruments.

     

Comparison of Cyclic Fatigue Resistance of Nickel-Titanium Coronal Flaring Instruments

IntroductionThe purpose of this study was to compare the cyclic fatigue resistance of coronal flaring instruments.MethodsThree groups of nickel-titanium (NiTi) endodontic coronal flaring instruments were tested in steel canals with a 3-mm curvature radius and 60° (n = 18) and 45° of curvature (n = 18). The cyclic fatigue of the following NiTi instruments was tested: ProTaper Sx (Dentsply Maillefer, Ballaigues, Switzerland), HyFlex 25.08 (Coltene-Whaledent, Allstetten, Switzerland), and Revo-S SC1 (Micro-Mega, Besancon, France). The length and diameter of the fractured fragment and the total area of the fractured surface of each instrument were measured. The data were then statistically analyzed using a 1-way analysis of variance and the post hoc Tukey test (α = .05).ResultsAt the 60° of curvature, Revo-S had the highest fatigue resistance, HyFlex had the second highest fatigue resistance, and ProTaper Universal had the least fatigue resistance. At the 45° of curvature, the Revo-S and HyFlex showed superior cyclic fatigue resistance compared with the ProTaper. The length of the fracture fragment of the ProTaper instrument was longer than that of the other groups at the 60° of curvature. At the 45° of curvature, the length of the fracture fragment of the ProTaper and HyFlex instruments was longer than that of Revo-S. The mean diameter and surface area of the HyFlex instruments in the fractured part was higher than that of other groups at both angles of curvature.ConclusionsThe Revo-S SC1 and HyFlex 25.08 instruments showed better cyclic fatigue resistance than the ProTaper Sx instrument.     

Influence of the apical enlargement size on the endotoxin level reduction of dental root canals

Gram-negative bacteria play an essential role in endodontic infections because they have virulence factors such as endotoxin. Due to its potential cytotoxic activity, special attention has been given to the removal/neutralization of this endotoxin in the root canal system.

Objective

The aim of this study was to evaluate the influence of the apical enlargement size (AES) by using rotary instruments on the endotoxin level reduction of dental root canals.

Material and Methods

Forty root canals of the mandibular premolar teeth were used. Escherichia coli endotoxin (055: B55) was inoculated into thirty root canals. Ten teeth served as the negative control group. After the incubation period, the first endotoxin samples were collected from the root canals with a sterile/apyrogenic paper point for the analysis of the endotoxin units (EU/mL) present before instrumentation (S1). Specimen instrumentation was performed with the Mtwo^® rotary system in the sequence 10/.04, 15/.05, 20/.06, 25/.06, 30/.05, 35/.04 and 40/.04. To monitor the effectiveness of increasing apical enlargement on endotoxin removal, the second endotoxin samples were collected from all the root canals after instrumentation with the following instruments: #25/.06- (S2); #30/.05- (S3); # 35/.04- (S4); and #40/.04- (S5). Limulus amebocyte lysate (LAL) was used to quantify the levels of endotoxin. The results were statistically compared by using repeated measures of ANOVA with post hoc Tukey testing.

Results

Increasing levels of endotoxin removal was achieved by large sized apical enlargement: S2 (AES #25/.06)- 89.2%, S3 (AES #30/.05)- 95.9%, S4 (AES #35/.04)- 97.8% and S5 (AES #40/.04)- 98.2%. Substantial reduction of endotoxin content was obtained in S4 and S5 compared to S2 (p<0.05), however, the root canal preparation was not able to eliminate the endotoxin.

Conclusions

Under the conditions of this study, it was concluded that the reduction of endotoxin levels of the dental root canals could be predicted by increasing the apical enlargement size.     

Influence of Continuous or Reciprocating Motion on Cyclic Fatigue Resistance of 4 Different Nickel-Titanium Rotary Instruments

IntroductionThe aim of this study was to evaluate the resistance to flexural fatigue of Reciproc R25 (VDW, Munich, Germany), WaveOne Primary (VDW, Munich, Germany), Mtwo (Sweden & Martina, Padova, Italy), and Twisted File (TF; SybronEndo, Orange, CA) instruments used in continuous rotation or in 2 different reciprocating motions.MethodsA total of 180 nickel-titanium files from 4 brands marketed, 2 for use in reciprocating motion (ie, Reciproc R25 and WaveOne Primary) and 2 for use in continuous rotation (ie, Mtwo and TF both taper .06/0.25 tip diameter), were tested. Forty-five instruments for each brand were divided into 3 groups (n = 15) on the basis of the motion tested: continuous rotation (group 1: 300 rpm) and reciprocal motion (group 2: “RECIPROC ALL” mode and group 3: “WAVEONE ALL” mode). The resistance to cyclic fatigue was determined by counting the number of cycles to failure in a 60° curve with a 5-mm radius. Data were analyzed through 2-way analyses of variance.ResultsThe cyclic fatigue resistance of the 2 reciprocating motion instruments (ie, “RECIPROC ALL” and “WAVEONE ALL”) was significantly higher than the continuous rotation in each brand (P < .001). No significant difference was observed in cyclic fatigue between the 2 different reciprocal motions tested in each brand (P > .05). When considering the appropriate clinical motion for each brand, no significant difference in cyclic fatigue was found between TF, Mtwo, and Reciproc R25 instruments, whereas the cyclic fatigue resistance of WaveOne files was less than the other 3 brands (P < .05).ConclusionsReciprocal motion showed a significantly higher cyclic fatigue resistance in all brands compared with continuous rotation. No differences were found between the 2 reciprocating motions.