Twisted File Research Articles

Propagation of preexisting dentinal microcracks after root canal preparation using rotary, reciprocating, and adaptive instruments: An ex vivo microcomputed tomographic analysis

ABSTRACT Aim: To evaluate the propagation of preexisting dentinal microcracks after instrumentation with ProTaper Universal (PTU), ProTaper Gold (PTG), Twisted File Adaptive (TFA), and Reciproc Blue (RB) instruments by micro-CT imaging. Methods: The mesial roots of 60 mature human mandibular molars were cut out approximately 10 mm from the apex. The roots were then divided randomly into four groups (n = 15) based on file system used: PTU, PTG, TFA, and RB. Before and after canal shaping, roots were scanned with micro-CT. The preinstrumentation cross-sectional slices were examined to ascertain the presence of preexisting dentinal microcracks in apical 10 mm of radicular dentine. Postinstrumentation, the extension of preexisting dentinal microcracks was assessed and compared with corresponding preinstrumentation image to determine the grade of propagation. Postinstrumentation, the propagation of preexisting dentinal microcracks were categorized into three grades: nonpropagated dentinal microcracks (Grade 1), incomplete propagation (Grade 2), and complete propagation (Grade 3). Results: The PTU system showed a significantly higher propagation of preexisting dentinal microcracks compared to PTG, TFA, and RB system (P ≤ 0.05). All the instrumentation systems showed propagation of preexisting dentinal microcracks into Grade 2 cracks. Grade 3 propagation was seen in PTU, PTG, and RB systems. The number of Grade 2 dentinal microcracks were significantly higher than Grade 1 dentinal microcracks for the PTU system (P ≤ 0.05). Conclusion: Root canal instrumentation promotes propagation of preexisting dentinal microcracks. As compared to conventional nickel-titanium file systems, reciprocating and thermally treated file systems may less likely result in propagation of dentinal microcracks.

Micro-computed tomography analysis of shaping ability of nickel-titanium instruments activated by continuous rotation or adaptive motion.

This study assessed the ability of Twisted File Adaptive (TFA), TruNatomy (TRN) and VDW.Rotate (VR) instruments activated by continuous rotation (CR) and adaptive motion (AM) to shape curved root canals. Thirty mandibular molars with two separate mesial canals 20°-40° curved were collected and scanned using micro-computed tomography (μCT). The canals were then randomly assigned into six groups (n = 10): TRN, VR or TFA instruments activated by CR or AM. TRN groups 17.02, 20.04 and 26.04; VR groups 15.04, 20.05 and 25.06; TFA groups were shaped consecutively using 15K-file, 20.04 and 25.06. After they were shaped, the canals were scanned again. The volume of removed dentin, canal transportation and centring ratio were calculated μCT images. All data were analysed using the Kruskal-Wallis test or one-way analysis of variance (p < 0.05). With both kinematics, the TRN instrument removed the least amount of dentin, the VR-CR and the TFA-AM removed the most (p < 0.05). The transportation and centring ratios among all groups were similar (p > 0.05). The volume of dentin removed, the diameter or design features of the instruments and different kinematics did not affect the centring ratio and the amount of transportation and remained within safe limits. All three instruments activated by either kinematics were found to have similar effectiveness in shaping curved root canals.

Micro-computed tomographic evaluation of the shaping ability of three nickel-titanium rotary systems in the middle mesial canal of mandibular first molars: an ex vivo study based on 3D printed tooth replicas

BackgroundThe preparation of the middle mesial (MM) canal of mandibular molars represents a challenge because it is often curved, narrow, and close to the root concave. The purpose of this study was to evaluate the ex vivo shaping ability of 3 nickel-titanium (NiTi) rotary systems in the MM canal using 3D printed resin tooth replicas.MethodsA permanent mandibular first molar with a MM canal was acquired from a pool of extracted teeth and reproduced by a 3D printer. The resin tooth replicas (n = 18) were equally assigned to 3 groups for the evaluation of the shaping abilities of 3 NiTi rotary systems (OneShape [OS], Twisted Files [TF], and ProTaper Gold [PTG]) according to the manufacturer’s recommendations. The tooth replicas were scanned by micro-computed tomography (micro-CT) twice before and after instrumentation of the mesiobuccal (MB), mesiolingual (ML), and MM root canals. After 3D reconstruction, the canal straightening, change of root canal volume and surface area, the mesial and distal canal wall thickness and canal transportation at the levels of 1, 2, and 3 mm below furcation were assessed. One-way variance analysis and Turkey’s post hoc test were used for comparisons of the means among different groups, and paired-t test was used to compare the mesial and distal sides of the mesial roots.ResultsAs compared with OS and TF, the use of PTG in preparation of MM canals resulted in significantly more straightening of canal curvature (p < 0.05), greater post-instrumentation canal volume and surface area, and thinner mesial and distal remaining canal wall thickness at 1, 2 and 3 mm below furcation (all p < 0.05). Regarding the root canal transportation in the mesiodistal direction, there was no significant difference among the 3 instruments (all p > 0.05) after the preparation of the MB and ML canals. However, in the MM canal, more pronounced transportation was detected in the PTG group at 2 mm below furcation, and in the TF group at 3 mm below furcation as compared with the other 2 systems (both p < 0.05).Conclusions3D printed tooth replicas have the advantages of consistency and can be an ideal model to evaluate the shaping ability of different instruments in the MM canal. OS and TF files performed similarly and both are appropriate for shaping the MM canal, while PTG may cause excessive and uneven resin removal, especially near the furcation, and may lead to root fragility and procedural errors.

Cutting efficiency and corrosion resistance of heat-treated endodontic files after various disinfection protocols.

The aim of this study is to evaluate the effect of various disinfection protocols on the cutting efficiency and chemical composition of ProTaper, Twisted File, Twisted File Adaptive, and Hedström files. Four experimental groups (n = 10) were presoaked in either enzymatic solution or 1% sodium hypochlorite for 30min, followed by either 5 or 15min of ultrasonic cleaning and then autoclaved. Resin-simulated canals with a single curvature of 38-40° were prepared by each instrument system. Cutting efficiency of each instrument was analyzed by subtracting the final weight from the initial weight of the resin blocks. Chemical compositions were studied by field emission scanning electron microscopy and X-ray energy-dispersive spectrometry. The cutting efficiency of Hedström, ProTaper, and Twisted File instruments decreased compared to their control groups (p < 0.05) whereas it did not change for Twisted File Adaptive. More corrosion was detected with longer ultrasonication time. No difference was observed regarding the pre-soaking media. Disinfection protocols exerted a significant overall effect on the performance of Hedström, ProTaper, and Twisted File instruments. Corrosion, microcracks, and crevices were evident on all tested instruments after disinfection protocols applied. All disinfection protocols, regardless of the pre-soaking media used or the ultrasonic cleaning time applied, have some effect on the cutting efficiency and the surface characteristics of the files.

The Influence of Nickel-Titanium (Ni-Ti) Rotary Instrument Systems on Debris and Smear Layer Formation in Endodontic Procedures: An In Vitro Scanning Electron Microscopy Study.

Background Successful endodontic treatment relies on the effective removal of debris and the prevention of smear layer formation within the root canals. The choice of nickel-titanium (Ni-Ti) rotary instrument systems can significantly impact these outcomes. Aim This study aims to evaluate and compare the debris and smear layer formation in root canals of extracted mandibular second premolar teeth following instrumentation with the ProTaper Universal (Dentsply Sirona,Charlotte, NC) (Group II), Twisted File (Kerr Endodontics, Gilbert, AZ) (Group III), and XP Endo (FKG Dentaire,La Chaux-de-Fonds, Switzerland) (Group IV) Ni-Ti rotary instrument systems. Methods In this in vitro study, 60 extracted mandibular second premolar teeth were randomly divided into four groups, each containing 15 teeth. Group I served as the control with no instrumentation. Groups II, III, and IV were instrumented with the ProTaper Universal rotary file, the Twisted File, and the XP Endo file systems, respectively. Debris and smear layer formation were evaluated through scanning electron microscopy (SEM), and photomicrographs were scored using a standardized index. Results Group II (ProTaper) exhibited the highest mean debris and smear layer scores, with values of 3.50 and 2.70, respectively. Group IV (XP Endo) demonstrated the least debris and smear layer formation, with mean scores of 2.65 and 2.08, respectively. Statistical analysis confirmed significant differences among the groups for both debris and smear layer formation. Conclusion The results highlight the practical importance of selecting appropriate Ni-Ti rotary instrument systems to minimize debris and smear layer formation during endodontic procedures. The XP Endo file system showed promise as a favorable choice in this regard, but further clinical research is needed to validate these findings.

Comparison of four different file systems in terms of transportation in S-shaped canals and apically extruded debris.

This study evaluated transportation and extruded debris during preparation using different instruments. Sixty resin blocks with S-shaped canals and 60 extracted teeth were separated into four groups (n = 15), which were instrumented with Reciproc Blue, XP-endo Shaper, WaveOne Gold, and Twisted File Adaptive. For evaluating transportation, pre- and post-preparation images were obtained under a stereomicroscope and superimposed with digital software. The distance between the inner and outer canal walls was measured. For the evaluation of debris extrusion, the samples were placed in Eppendorf tubes and instrumented using one of the four rotary files. The initial weight was subtracted from the post-instrumentation weight to determine the amount of extruded debris. The Kruskal-Wallis and Dunn multiple tests were performed. For transportation, no significant difference was found between the XP-endo Shaper-Twisted File Adaptive systems and between Reciproc Blue-WaveOne Gold groups (P > 0.05). The XP-endo Shaper and Twisted File Adaptive techniques led to significantly less transportation compared to the other systems (P < 0.05). Regarding debris extrusion, the XP-endo Shaper system extruded significantly less debris than the other groups (P < 0.05). XP-endo Shaper extruded less debris compared to other groups, while XP-endo Shaper and Twisted File Adaptive caused less transportation than other files.

Exploring the Efficacy of 6 Preparation Systems for Achieving Minimal Root Canal Transportation: A Micro-CT Investigation

IntroductionThis study aimed to assess the canal transportation with 6 preparation systems. MethodsSixty curved mesial roots of mandibular molars were scanned, and their root canals (n = 20 per group) were prepared with XP-endo Shaper, BioRace, ProTaper Next, Twisted File Adaptive, Reciproc, or Reciproc Blue systems. After preparation, a new scan was conducted, and transportation was determined by comparing the geometric center of the canal in 13,542 cross-sectional slices. The transport direction frequencies were recorded, and linear transport were compared using a Univariate GLM model and Tukey honestly significant difference tests (α = 5 %). ResultsTransportation was affected by the preparation system and root third (P < .05), with no significant effect observed for the root canal (P > .05). The Twisted File Adaptive had the highest transport (P < .05), and the lowest transports were observed with XP-endo Shaper, ProTaper Next, and BioRace (P < .05). Reciproc Blue and Reciproc showed intermediate results (P < .05). The apical and coronal third exhibited the lowest and highest transportation, respectively (P < .05). A significant interaction was observed between the preparation system and root third (P < .05). In the coronal third, transportation was mostly toward the disto-inside direction, whereas in the middle and apical thirds, transportation was predominantly toward the mesio-outside direction. ConclusionsXP-endo Shaper had the lowest mean linear transportation followed by the ProTaper Next, BioRace, Reciproc Blue, and Reciproc systems. The Twisted File Adaptive system had the worst performance. The direction of transportation was generally toward the inner aspect of the canal at the coronal third and toward the outer aspect of the curve at the middle and apical thirds.

Comparative evaluation of nickel titanium rotary instruments on canal transportation and centering ability in curved canals by using cone beam computed tomography: An in vitro study

The aim of this study was to compare canal transportation and centering ability of different nickle titanium systems using Cone beam computed tomography in curved canals. Ninety mandibular molars with angle of curvature ranging from 10°– 40° were randomly allocated into six experimental groups containing 15 teeth in each group. Preinstrumentation scans were taken with CBCT with constant exposure parameters before and after instrumentation. Six grouped specimens were instrumented with Wave One, Twisted File, Hyflex CM, K3XF, ProTaper Next, NeoNiTi file respectively. Post instrumentation the specimens were scanned by CBCT to obtain postoperative images. The amount of root canal transportation and centering ability of the instrument were determined. Statistical analysis on collected data was performed using One way analysis of ANOVA, and post-hoc Tukey test (p&amp;#60;0.0.5). K3XF group showed significantly higher transportation values in the apical third (2mm) than TF group (p=0.01) and Hyflex CM group (p=0.03). The coronal transportation values are higher than the apical values but with no significant difference between them (p&amp;#62;0.05). There was no significant difference in centering ratio values between the six groups (p&amp;#62;0.05) at any of the level.: All the file systems can be safely used, showing satisfactory preservation to the original canal shape with preference of TF files.

Impact of nickel-titanium instrument heat treatment on the precision of an inbuilt electronic apex locator and endodontic motor

Numerous nickel-titanium alloys have been designed by manufacturers, however there is little information on the precision of integrated EAL when utilized with various NiTi thermal processes to determine working length.An integrated EAL and endomotor assembly is utilized in this study to assess ex vivo the effects of different thermal processes on NiTi instruments.This study used 20 extracted human maxillary incisors. The visual approach was used to establish the working length (WL) control. WL was measured during cleaning and shaping using rotary files consisting of the Reciproc, Reciproc Blue, Wave One Gold, Twisted File Adaptive, and Hyflex CM systems using 0.25 diameter instrument size.Fisher's exact test and the Kruskal-Wallis statistic tests were used in the analysis of the information at hand.Heat treatment of NiTi rotary instruments has no significant impact on the EAL's accuracy (P &amp;#62; 0.051).The precision of WL estimation using an EAL incorporated with the endomotor was unaffected by the use of thermal processes.

Phase transformation behavior and mechanical properties of HyFlex EDM nickel-titanium endodontic rotary instrument: Evaluation at body temperature

Background/purposeTemperature-dependent phase compositional changes influence the mechanical properties of heat-treated nickel-titanium (NiTi) rotary instruments. This study evaluated the phase composition, bending properties, and cyclic fatigue resistance of HyFlex EDM NiTi rotary instruments against differently heat-treated and non-heat-treated NiTi instruments at body temperature (BT). Materials and methodsHyFlex EDM OneFile (EDM) instruments, heat-treated HyFlex CM (CM) and Twisted File (TF) instruments, and non-heat-treated K3 instruments (size #25/.08) were subjected to differential scanning calorimetry, and the martensitic, R-phase, and reverse transformation starting and finishing temperatures were determined. A cantilever bending test and a cyclic fatigue test were conducted at BT (37 °C ± 1.0 °C), and the bending load and number of cycles to failure (NCF) were recorded. Statistical analysis was performed using Kruskal–Wallis and Mann–Whitney U tests (α = 0.05). ResultsTF and K3 had reverse transformation finishing temperatures lower than BT, while those for EDM and CM were higher than BT. The bending loads at a 0.5 mm deflection were in the order of EDM < TF < CM < K3 (P < 0.05), and those at a 2.0 mm deflection were EDM < CM and TF < K3 (P < 0.05). EDM had the highest NCF among the four instruments (P < 0.05). ConclusionThe EDM instrument had a reverse transformation finishing temperature higher than BT indicating its martensite/R-phase composition at BT. The EDM instrument had superior flexibility and greater resistance to cyclic fatigue than the CM, TF, and K3 instruments at BT.

Effects of Autoclave Sterilization on Cyclic Fatigue Resistance in 5 Types of Rotary Endodontic Instruments: An In Vitro Study.

BACKGROUND Rotary endodontic instruments are increasingly used in root canal treatment and have replaced stainless steel manual files. Cyclic fatigue is the cyclic loading of stress to produce deformation or fracture. This study aimed to evaluate and compare the effects of autoclave sterilization on cyclic fatigue in 5 types of rotary endodontic instruments. MATERIAL AND METHODS ProTaper Universal, BioRace, ProTaper Next, Twisted File, and HyFlex CM instruments were included in this study. Each type included 96 instruments, divided into 4 groups according to the number of sterilization cycles (0, 1, 3, 5). After sterilization, each group of instruments was divided into 2 subgroups and tested for cyclic fatigue in 2 simulated canals (45 degrees both and 2 radii, 2 mm and 5 mm). The number of cycles to failure (NCF) was calculated, and statistical analyses were carried out using the t test, Mann-Whitney U test, and ANOVA, followed by the Tukey post hoc test (p<0.05). Fracture surfaces were analyzed using scanning electron microscopy (SEM). RESULTS Within the group of non-sterilized instruments, ProTaper Universal showed significantly lower resistance to cyclic fatigue compared to the other types of instruments (p<0.001). After repeated sterilization, a significantly higher mean of NCF was observed for BioRace (p<0.001), ProTaper Next (p<0.001), Twisted File (p<0.001), and HyFlex CM (p<0.001) compared to ProTaper Universal. The resistance of HyFlex CM was significantly higher compared to the other types of instruments (p<0.001). CONCLUSIONS The findings from this study showed that autoclave sterilization of newer rotary endodontic instruments could increase resistance to cyclic fatigue.

Elimination of E. faecalis and C. albicans Biofilm: A Comparison Between Single and Multiple File Systems in an Ex Vivo Study

To evaluate whether the WaveOne Gold and Reciproc single file instrumentation systems, are effective in reducing the microbial load of a mixed biofilm and the cleaning of apical third compared to the Twisted File Adaptive system (multiple-file system). Seventy mesial roots of the first and second molars were included and randomly divided into three experimental groups (n=20, n=10 controls). Biofilms were formed inside canals over 31 days. After instrumentation with the unique file systems, WaveOne Gold and Reciproc and the multiple file system Twisted File Adaptive, using 2.25% sodium hypochlorite as an irrigant in all cases, a count of colony forming units was performed using serial dilutions, cleaning of the apical third was evaluated using scanning electron microscopy. Comparisons amongst groups were made by using parametric and non-parametric statistics, according to a normal or non-normal data distribution, respectively. No significant differences in the reduction of the microbial load after employing a single-file system in comparison to the multiple-file system were found; in addition, the cleaning of the apical third was similar for the three different instrumentation systems. The single-file system is equal in effectiveness compared with the multiple-file system in reducing the microbial load.

Apically extruded debris of different file systems used with various kinematic movements during retreatment: An in vitro study.

This study aimed to examine the amount of apically extruded debris and time during retreatment with five current file systems, which exhibit various kinematic movements. One hundred upper central incisors were shaped with manual files and filled using the thermoplastic injection method. The root canal fillings in each group (n=20) were removed using the Genius (GN), ProTaper Next (PTN), Reciproc (RCP) Blue, Tango-Endo (TE) and Twisted File Adaptive (TFA) file systems. The apically extruded debris was collected in preweighed Eppendorf tubes. Time to reach working length and total time were also recorded. The PTN, RCP Blue and TFA instruments caused significantly less apically extruded debris and shorter total retreatment time than the GN and TE file systems (p < 0.05). The time to reach the working length was the shortest in the PTN group compared to the other groups (p < 0.05). All file systems extruded debris while removing the root canal filling.

In vitro evaluation to quantify extruded debris during filing with three different systems

Aim: This study was planned to quantitatively estimate the amount of pushed off debris during instrumentation with three commercial files. Materials &amp; Methods: Maxillary central incisors were chosen by simple random sampling. Only freshly extracted teeth were entertained for sampling procedure. For the ease of study and grouping, all samples were further divided into three study groups. This was solely based on available latest and economical NiTi files. Consequently in group I, canal cleaning and shaping was performed ProTaper Next system files. Authors attempted this in given recommended sequential manner as directed by manufacturer. In group II, Twisted File Adaptive adaptive files were engaged for canal procedures in the recommended sequence. In group III, Reciproc R25 file system was checked for the similar factors. Results: Statistical analysis was done using statistical software ‘Statistical Package for the Social Sciences (SPSS)’. The recorded data was subjected to suitable statistical tests to obtain p values and mean. P ≤ 0.05 was considered as statistically significant. Mean values of pushed out debris was 0.00047 grams, 0.00058 grams and 0.00050 grams in group I, II and III respectively.

Several Shaping Characteristics of OneCurve Continuously Rotating System versus Three Different Kinematic Systems: ProTaper Universal, Twisted File Adaptive and WaveOne Gold

Several Shaping Characteristics of OneCurve Continuously Rotating System versus Three Different Kinematic Systems: ProTaper Universal, Twisted File Adaptive and WaveOne Gold

COMPARISON OF FOUR DIFFERENT ENDODONTIC ROTARY SYSTEMS IN TERMS OF CYCLIC FATIGUE

Objectives: The aim of this study was to compare four endodontic rotary systems in terms of cyclic fatigue. Material and Methods: 25/.08 Twisted File (TF), TF Adaptive, Reciproc and WaveOne rotary files were used to test the cyclic fatigue strength in this study. Four different artificial canals, compatible with the file size and taper, were created, with the curvature angle and radius of 450-2 mm, 600-2 mm, 450-5 mm and 600-5 mm, respectively. The front surface of the artificial canals was covered with a removable glass plate. The files were operated in the canals according to their own working principles until they fractured. The fracture time was determined by using a chronometer with 1/100 second accuracy and the cyclic fatigue strength was evaluated according to the time until fracture occurs. A total of 40 files, 10 in each canal, were used in each group. SPSS program was used for statistical analysis. Mann-Whitney U test was applied for pairwise comparisons. Bonferroni correction was applied and P&amp;lt;0.008 was considered as statistically significant. Results: In all canals, fracture time was the highest for Reciproc files, followed by WaveOne, TF Adaptive and TF files, respectively. For the canal curvature of 450-2 mm, the Reciproc files were significantly more resistant to fracture than the others. While there was no significant difference between TF Adaptive and TF, WaveOne was significantly more resistant than both groups. In canals with the curvature of 600-2 mm and 450-5 mm Reciproc and WaveOne were significantly more resistant to fracture than TF Adaptive and TF. In addition, TF Adaptive was significantly more resistant than TF. For the curvature of 600-5 mm, the difference between all groups was significant. Conclusions: Regardless of the canal curvature, the Reciproc exhibited the highest cyclic fatigue strength, while the TF showed the lowest fatigue strength.

Influence of solvent use on apical extrusion during removal of Resilon™ from root canals

Background/Aim. During retreatment, filling material and debris may extrude and trigger an inflammatory reaction of periapical tissues. Resilon? has not been investigated in terms of solvent use and influence on apical extrusion during retreatment. This study evaluated the amount of apically extruded debris during Resilon? removal using ProTaper, Twisted File and Hedstrom instruments, with and without solvent. Methods. In total, 72 extracted teeth with single canal were used. Canals were prepared with ProTaper Universal (F2) and filled with Resilon? and RealSeal sealer, before being assigned randomly to 6 groups (n=12 each). Retreatment in groups 1, 2 and 3 was done with ProTaper, Twisted File or Hedstrom instruments, without solvent; in groups 4, 5 and 6 the same instruments were used with chloroform. Apically extruded debris was collected in a simulated periapical environment and assessed visually. Additionally, the time required for retreatment was recorded. Data were analysed statistically using Mann-Whitney U test, with a significance level of 0.05. Results. There were no significant differences in apical extrusion debris between groups (p &gt; 0.05) regarding solvent use. Rotary instruments, without solvent, were associated with significantly less debris extrusion when compared with hand files (p &lt; 0.05). When solvent was used, rotary instruments caused higher degree of extruded material, that was similar to the results of hand instruments. Conclusion. Within the limitations of this study, the use of rotary instruments without solvent resulted in a lower degree extrusion of Resilon ? material compared to hand instruments, while greater caution is advised in the presence of solvent when rotary instruments are used to remove this material.

Dentinal Microcrack Formation by Different Rotary Endodontic File Systems: An In-vitro Study

Introduction: During endodontic treatment, biomechanical preparation of the root canals constitutes one of the prime steps to enable bacterial eradication, irrigant percolation and three dimensional obturation of the canal space. Currently used rotary endodontic instruments generate stresses in the dentinal walls as microcracks and craze lines which can eventually precipitate vertical root fractures. This endangers the prognosis of an endodontically treated tooth or can even lead to tooth extractions. Aim: To compare dentinal micro-crack formation during biomechanical preparation by different Nickel-Titanium rotary endodontic instruments, Reciprocating single file system and Self-Adjusting File (SAF) using a stereomicroscope. Materials and Methods: The study was a randomised controlled trial conducted for a total duration of two months. A total of eighty extracted human mandibular molars with intact mesial roots were selected. Endodontic access was achieved. Hyflex CM file (Coltene), One Shape file (Micromega), Twisted File (TF; SybronEndo, Orange, CA), One endo file (Nano endo), ProTaper Next file (Dentsply Maillefer), Reciproc file (VDW) and SAFs were used to prepare the samples, leaving ten teeth unprepared which served as control. Sectioning of the prepared samples were carried out perpendicular to their long axes at 9, 6 and 3 mm. Under 40X magnification of a stereomicroscope, digital images of each section were recorded with the aid of a digital camera. Examination of each specimen was carried out by two operators to verify the presence of dentinal defects/microcracks. The statistical analysis was done by Chi-square test. Results: Except the control group, all the remaining groups recorded the presence of dentinal defects. The incidence of cracks was highest in One Endo (40%) followed by One Shape, Twisted (30%), Protaper Next (23.33%), Reciproc (10%), Hyflex (6.6%), SAF (3.3%) and control (0%). A significant difference was found for the cracks in coronal section between the file systems (p=0.0001). Conclusion: Usage of nickel titanium rotary instruments leads to the formation of microcracks or craze lines in root dentine. Instruments which have Matellurgical (M) wire or Controlled Memory (CM) wire in their metallurgy result in fewer formations of micro-cracks. When compared to multiple rotary files system, a reciprocating file led to the induction of lesser number of radicular cracks. SAF creates minimal cracks as compared to other file systems.

Comparative evaluation of cyclic fatigue resistance of file systems based on different manufacturing technologies after exposure to NaOCl and multiple sterilization cycles

Aim: To comparatively evaluate in vitro the cyclic fatigue resistance of different file systems based on different manufacturing technologies after exposure to NaOCl and multiple sterilization cycles.Materials and Methods: Sixty new Nickel − Titanium (NiTi) rotary files were selected and divided into five groups (n = 12) based on different manufacturing technology. These groups were: Protaper Universal (GPT) (DentsplyMaillefer, Ballaigues, Switzerland) Protaper Next (GPTN) (Dentsply, Tulsa, OK, USA), Twisted files (GTF) (Sybron Endo, Orange, CA, USA), Neoniti (GNL) (Neolix, France), and Hyflex CM (GHCM) (Coltene/whaledent inc., 235 Ascort Parkway, Cuyahoga falls, OH, USA). Files were sterilized in an autoclave at 121°C at 15 psi for 15 min and exposed to 5.0% NaOCl solution for 30 s before cyclic fatigue testing till instrument fracture using a standardized grooved block assembly with the artificial canal at 90° angle of curvature using a 16:1 reduction hand-piece powered by a torque-controlled motor. This whole procedure of autoclaving, immersion in sodium hypochlorite solution and rotating in a stainless steel assembly was repeated again and again until the file fractured.Results: The highest mean for the number of cycles before fracture was observed with Neoniti (GNL) and lowest for Hyflex CM (GHCM). The difference between GPT vs GTF, GPTvs GNL, GNLvs GHCM; GPTNvs GTF, GPTNvs GNL, GPTNvs GHCM; GTFvs GNL, GTFvs GHCM and GNL VS GHCM was statistically significant, whereas the difference between GPTvs GPTN was statistically nonsignificant.Conclusion: Neoniti and twisted file systems resisted the maximum number of cycles to fracture at 90° angle of curvature after exposure to 5% sodium hypochlorite solution and multiple autoclaving cycles. Hyflex CM showed the least resistance in the similar conditions.

Comparative evaluation of the effect of hand file, different nickel-titanium retreatment files, and self-adjusting file system on the incidence of dentinal microcrack formation during the removal of root canal filling material: An in vitro stereomicroscopic study

Aim: The aim of the study is to evaluate the effect of hand files, rotary nickel-titanium files, and self-adjusting file (SAF) on the incidence of crack formation during retreatment. Materials and Methods: Eighty extracted human mandibular molar teeth with intact mesial roots were selected. They were divided into 8 groups of 10 teeth each; Group 1: Control, Group 2: Obturated control, Group 3: Hand files, Group 4: ProTaper Universal Retreatment, Group 5: Twisted File Adaptive, Group 6: Reciproc Blue, Group 7: XP-endo Finisher R, Group 8: SAF system. All teeth had the coronal portions and distal roots removed by a diamond-coated disc with water cooling, leaving roots approximately 13 mm in length. Except for Group 1, all canals were similarly instrumented and obturated at an apical size of 40.02. Retreatment was performed in each group according to manufacturer's recommendations except for Groups 1 and 2. The roots were sectioned horizontally at 3, 6, and 9 mm from the apex with a low-speed saw. Stereomicroscopic evaluation of the sections was done to assess the presence or absence of defects. Results: The groups that were not retreated (Groups 1 and 2) showed no defects. Hand files showed the least number of defects followed by the SAF. Reciproc Blue showed the most dentinal defects. Conclusion: All NiTi instruments tend to induce various degrees of dentinal damage during retreatment procedures. The SAF and hand instrumentation presented satisfactory results with minimal dentinal microcracks.