Rotary Nickel-titanium Endodontic Instruments Research Articles

A SEM/EDS evaluation of debris removal of used rotary Ni-Ti endodontic files by four different cleaning solutions

PurposeThe aim of this study was to compare the efficacies levels of four cleaning solutions for removing debris from rotary Nickel-Titanium (Ni–Ti) endodontic instruments. Materials and methodsTwelve instruments that fractured during ex vivo instrumentation were used. Fractured surfaces were investigated by SEM before and after 3, 6 and 9 min of ultrasonic cleaning in 17 % EDTA.3NaOH (Group A), 2.5 % NaOCl (Group B), Dentasept 3H Rapide (Group C) and ZymeX™ (Group D) solutions. EDS analyses of selected files from all four groups of untreated and ultrasonically cleaned samples were performed to assess the elemental composition of the alloy surfaces. ResultsSEM analysis revealed that after 9 min of ultrasonic agitation, all four investigated solutions had cleaned fractured surfaces. However, some low-atomic-number regions exhibited random distributions on the fractured surfaces. EDS analyses indicated that only C was retained on surface after 9 min of ultrasonic cleaning. This finding was common in all tested groups. ConclusionsAll four investigated solutions substantially removed debris from the surfaces of the Ni–Ti files and were considered appropriate for clinical practice.

Factors Affecting the Cyclic Fatigue of Heat-Treated NiTi Rotary File: A Review

Clinicians face a major problem when a Nickel-Titanium (NiTi) rotary endodontic instruments fracture occurs inside the canal during treatment. It is time consuming for removal of these separated instruments, in addition to its technical difficulty. So for these reasons it is important to reduce the risk of file fracture. As a sequel, several attempts have been made to improve the mechanical features of NiTi rotary files, like changes in speed of operation, changing the geometric and dimensional characteristics, and several different metal treatments. The revolution of new heat-treated NiTi instruments opens a new era for basic, clinical and scientific research. This article concerns mostly with environmental and heat-treated factors, irrigation and type of rotation and their effects on heat-treated NiTi instruments found in most studies.

Phase transformation and mechanical properties of heat-treated nickel-titanium rotary endodontic instruments at room and body temperatures

BackgroundThe aim of this study was to evaluate the phase composition, phase transformation temperatures, bending property, and cyclic fatigue resistance of different heat-treated nickel-titanium (NiTi) rotary instruments with the same tip diameter and taper at room (RT; 25 ± 1 °C) and body (BT; 37 ± 1 °C) temperatures.MethodsFive heat-treated NiTi rotary instruments, HyFlex EDM (EDM), HyFlex CM (CM), Vortex Blue (VB), RE file CT (RE) and JIZAI, and a non-heat-treated NiTi rotary instrument (Mtwo) with a size 40, 0.04 taper were investigated. Temperature-dependent phase transformation was examined with differential scanning calorimetry (DSC). The bending loads of the instruments at RT and BT were evaluated using a cantilever-bending test. Cyclic fatigue resistance at RT and BT was measured using a dynamic test, during which the instruments were rotated in combination with a 2-mm back-and-forth motion in an artificial curved canal, and the number of cycles to failure (NCF) was determined. The results were analyzed using two-way repeated measures analysis of variance, a simple main effect test, and the Bonferroni test (α = 0.05).ResultsDSC results indicated that EDM and Mtwo were primarily composed of martensite/R-phase and austenite, respectively, while the other heat-treated instruments were composed of a mix of martensite/R-phase and austenite at the tested temperatures. Regardless of the temperature setting, the bending loads of heat-treated instruments were significantly lower than those of Mtwo (p < 0.05). EDM showed the lowest bending loads and highest NCF at both temperatures (p < 0.05). CM, VB, and JIZAI showed significantly higher bending loads at BT than at RT (p < 0.05). The NCF of all the heat-treated instruments, except VB, was lower at BT than at RT (p < 0.05). At BT, the NCF of CM, VB, RE, and JIZAI were not significantly higher than that of Mtwo (p > 0.05).ConclusionsHeat-treated NiTi instruments exhibited lower bending loads and higher NCF values than Mtwo. However, this tendency was less pronounced at BT than at RT, especially in the NCF values of instruments with a mixture of martensite/R-phase and austenite phases at the tested temperatures.

Impact of endodontic irrigants on surface roughness of various nickel-titanium rotary endodontic instruments

BackgroundThe aim of the current study is to assess the surface roughness of several recent nickel-titanium (Ni-Ti) rotary endodontic instruments, namely: Protaper next (PTN); Hyflex CM (CM); Hyflex EDM (EDM); WaveOne gold (WOG); and trunatomy (TN), before and after application of 5.25% sodium hypochlorite (NaOCl) irrigant solution.MethodsIn this in vitro study, five recently introduced rotary endodontic instruments of different metallurgical properties and designs were subjected to Atomic Force Microscopy (AFM) analysis, and then each file was rotated in 5.25% NaOCl for 15 min., with speed and torque according to manufacturer’s instructions. The instruments were then subjected to AFM analysis again. The surface roughness average (Sa) parameter was calculated. Data were analyzed by Paired T test, One-way ANOVA and Tukey tests.ResultsThere was a statistically significant decrease in the surface roughness of all rotary endodontic instruments after immersion in irrigants (P ≤ 0.05).ConclusionThe new TN and PTN instruments showed the least surface roughness. All tested Ni-Ti rotary endodontic instruments after irrigants exposure showed a varying increase in surface roughness.

A critical evaluation of physical and manufacturing properties of genuine and counterfeit rotary nickel-titanium endodontic instruments.

Rotary nickel-titanium (NiTi) instruments are made to exacting standards and are costly to manufacture, and quality control is paramount. Consequently, unauthorized factories make counterfeit instruments that are less expensive and may therefore be attractive to dentists. Little information exists about the metallurgy and manufacturing quality of such instruments. There is the potential for counterfeit instruments to be at higher risk of fracture during treatment, thereby compromising clinical outcomes. The aim of this study was to evaluate physical and manufacturing properties of genuine and counterfeit ProTaper Next™ and Mtwo® rotary NiTi instruments. This study investigated the metallurgical properties, manufacturing quality, microhardness and number of cycles to failure of two commonly used rotary NiTi systems and compared them with counterfeit products purporting to be genuine articles. Counterfeit instruments were found to be inferior in manufacturing standards and were less resistant to cyclic fatigue when compared to genuine instruments. Counterfeit rotary NiTi instruments may be less efficient at preparing root canals and may be at higher risk of fracture during endodontic treatment. Dentists must be aware that, although less expensive, counterfeit instruments may be of dubious manufacturing quality and at higher risk of fracture if used in patients. © 2023 Australian Dental Association.

Effects of sodium hypochlorite on corrosion of the rotary nickel-titanium endodontic instruments - SEM analysis

Introduction/Objective. of this study is to use scanning electron microscopy (SEM) analysis to examine surfaces of new and same sets of Ni-Ti instruments after canal preparations, to check their suspectability to corrosion. Methods. In this study, we used five different endodontic Ni-Ti instruments: K3, Mtwo, ProTaper Universal, HyFlex and BioRaCe. Instruments were analyzed before and after preparation of canals of different curvature, using SEM (150?2000 ?). Results. Corrosion of the working part was observed in 5.5% of new Ni-Ti instruments of the K3 system (apical and middle segment), in 5.5% of Mtwo instruments (apical third), and in 11.1% of ProTaper Universal systems (apical and middle third). Corrosion was not observed on the new instruments of the HyFlex and BioRaCe kits. After instrumentation, disinfection, and sterilization, corrosion was observed in all sets of K3 and ProTaper Universal systems and in all HyFlex instruments of the first group. Corrosion was observed in the HyFlex system in the second group in 16.7% of instruments (apical and middle third) and in the third 83.3% in the apical and 66.7% in the middle segment. In the Mtwo set, corrosion was observed in 16.7% of instruments in the first (apical and middle third), in the second group in 33.3% of instruments in the apical part and 50% in the middle third, while in the third group, corrosion was observed in 16.7% of instruments in the middle third of instruments. Conclusion. Rotary Ni-Ti instruments K3 and ProTaper Universal are susceptible to corrosion in a very high percentage. Ni-Ti systems with post-heat treatment of the working part (HyFlex) are somewhat more resistant to corrosion, while in Ni-Ti systems with electropolished surface (BioRaCe), corrosion is not observed.

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.

Testing Cyclic Fatigue Resistance of Nickel Titanium Rotary Endodontic Instruments: A Validation Study for a Minimum Quality Criterion in a Standardized Environment

Introduction: Cyclic fatigue resistance of rotary endodontic instruments has been extensively studied in the last two decades, yet with no standardization. While new low-cost instruments are now manufactured, a standard is lacking to guarantee a minimum quality. This study aimed to validate a new model for CF testing through a fixture proposed for ISO Specification 3630-1 and to establish a minimum quality standard based on testing conditions and material characteristics.Materials and methods: Size 25/0.06 instruments of ProFile Vortex (PF) and Vortex Blue (VB) were run until failure in curved metallic fixtures (5 or 7.5 mm radius) built according to a proposal for an additional test for the ISO 3630-1 standard. High resolution videos were recorded, number of cycles to failure (NCF) registered and apical fragments measured with a digital caliper. Surface strain was determined from test dimensions and fragment lengths. Mean life, β and η parameters were calculated with Weibull analysis. NCF data were compared using student's t-tests and referenced to a minimum required cycles at fracture (Cmin) based on austenite finish temperatures, testing temperature and deformation.Results: VB instruments were statistically more resistant than PF in both 7.5 mm radius curve (p = 0.001) and 5 mm radius curve (p = 0.002) simulated canals. Weibull probability plots showed higher mean life for VB than PV. NCF for both instruments were higher than Cmin.Conclusions: The NCF results in this study support the findings of previous studies where VB and PF were compared. The novel test design appears a suitable addition to ISO 3630-1.

Advancement of Mechanical Properties of Nickel-Titanium Rotary Endodontic Instruments by Spring Machining on the File Shaft

Nickel-titanium (NiTi) endodontic rotary instruments are used extensively in root canal procedures by both general dentists and specialists. However, their vulnerability to fracture is the major reason for clinicians’ concern regarding their use. The objective of this study was to investigate the potential effects of spring machining of the file shaft on the fatigue and torsional resistances of NiTi rotary instruments. Three types of NiTi rotary systems with (S) and without (NS) spring machining were used in this study (n = 15 each): a spring file (SPR; #25/.06, SPR-S, SPR-NS), a ProTaper Next X2 (PTN; #25/variable taper, PTN-S, PTN-NS), and a ProTaper Gold F2 (PTG; #25/variable taper, PTG-S, PTG-NS). Spring machining was adjusted on the 6 mm of each file system’s shaft via a laser cutting process. The number of rotation cycles until fracture (i.e., cyclic fatigue resistance), ultimate torsional strength, the distortion angle, and the toughness of each subgroup were estimated with specially designed devices. The results were analyzed using a paired t-test at a significance level of 95%. NiTi rotary instruments with spring machining exhibited a higher cyclic fatigue resistance than instruments without spring machining. The groups with spring machining exhibited a higher toughness and larger distortion angle than the groups without it (p < 0.05). In conclusion, spring machining on the shank of NiTi instruments may provide a stress-bearing area and attenuate the torsional and cyclic fatigue of NiTi rotary instruments.

Impact of Endodontic Instrumentation on Surface Roughness of Various Nickel-Titanium Rotary Files.

Objectives The aim of the present study was to evaluate the surface roughness (SR) of various nickel-titanium (NiTi) rotary endodontic instruments (ProTaper Next [PTN], WaveOne Gold [WOG], and ProTaper Gold [PTG]) before and after root canal instrumentation. Materials and Methods For each type (PTN, WOG, and PTG), the endodontic instrumentation was performed using extracted mandibular molar teeth’s curved mesial root canals (curvature: 20–40 degrees) after determining the working length. Each NiTi file was cleaned, and sterilized following preparation of four root canals and characterized for surface properties before and after endodontic instrumentation using a contact-mode three-dimensional surface profiler. The data were analyzed statistically using Statistical Package for the Social Sciences for SR parameters including average surface roughness value (Sa), root mean square roughness (Sq), and peak to valley height (Sz). Results Preinstrumentation assessment revealed a significant difference for all the three SR variables (p < 0.05) for the cutting blade and the flute area. WOG instruments showed the highest SR values ( p = 0.000). The postinstrumentation assessment revealed significant differences in SR values in the blade and the flute between the three groups ( p < 0.05), with WOG and PTG exhibiting the highest values in the blade and flute sections, respectively. Conclusions The SR parameters of intact PTN, WOG, and PTG NiTi files vary and that was increased following the endodontic instrumentation.

Cyclic Fatigue Resistance of Various Nickel-titanium Rotary Endodontic Instruments at Body Temperature: An in Vitro Study

Introduction: The purpose of this study was to compare the cyclic fatigue of different types of nickel-titanium rotary files at body temperature. Methods: Four types of rotary instruments with tip size 0.25 were used: HyFlex EDM (OneFile, variable taper, Colten/Whaledent), ProTaper Gold (F2, 0.08 taper, Dentsply), XP-endo Finisher (zero tapers, FKG Dentaire) and 2Shape (TS2, 0.06 taper, Micro-Mega). Ten files for each instrument were tested for cyclic fatigue at body temperature and rotated until fracture occurred in a simulated canal with an angle curvature of 60°, a radius curvature of 5 mm, and a canal width of 1.5 mm. Four groups were formed for all instruments (total number = 40). The number of cycles to fracture and the length of fractured fragment were recorded, and statistical analysis was completed using analysis of variance with significance at a (p-value &lt; 0.05). Results: The cyclic fatigue resistance of the HyFlex EDM OneFile was significantly greater than the other instruments, while that of the 2Shape TS2 was significantly lower (p &lt; 0.05). Conclusion: Within the limitations of this study, the HyFlex EDM OneFile was more resistant to cyclic fatigue than the XP-endo Finisher, ProTaper Gold F2 and 2Shape TS2 files

Use of rotary Nickel Titanium endodontic instruments by Dental practitioners in Pondicherry: A questionnaire-based study.

Use of rotary Nickel Titanium endodontic instruments by Dental practitioners in Pondicherry: A questionnaire-based study.

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

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

The Effect of Temperature on Cyclic Fatigue of Nickel-titanium Rotary Endodontic Instruments

IntroductionThis study examined the effect of different temperatures on the cyclic fatigue of nickel-titanium rotary files. MethodsThree groups of nickel-titanium rotary files (EF group [EdgeFile; EdgeEndo, Albuquerque, NM], VB group [Vortex Blue; Dentsply Tulsa Dental Specialties, Tulsa, OK], and ESX group [ESX; Brasseler USA, Savannah, GA]) of size 25 with a .04 taper and 25-mm length were tested in a metal block that simulated a canal curvature of 60° and a 5-mm radius curvature. The block was submerged in a water bath filled with water at 3°C, 22°C, 37°C, and 60°C. At each temperature, 30 files from each group were rotated at 500 rpm in the block. The number of cycles to fracture (NCF) was calculated. Statistical analysis was completed using a 1-way analysis of variance with significance at P < .05. ResultsVB group showed a significant decrease in NCF as the temperature increased from 3°C to 60°C. The ESX group showed a significant decrease in NCF as the temperature increased from 3°C to 37°C. The EF group showed a significant increase in NCF from 3°C to 22°C and a significant decrease in NCF from 22°C to 37°C. For each temperature, the EF group showed higher NCF than the VB group, which showed higher NCF than the ESX group. ConclusionsIn this in vitro study, temperature was found to significantly affect the cyclic fatigue of nickel-titanium rotary files. At each tested temperature, NCF was the highest for the EF group followed by the VB group and lowest for the ESX group. Future cyclic fatigue studies should be conducted at body temperature.

Effect of heat treatments on Ni-Ti endodontic files

Three brands of rotary nickel-titanium endodontic instruments with some comparable geometric features but with different cross-section (similar tip size and same taper of .04) were selected for this study: MTwo .04(35) (VDW GmbH, Germany), K3 .04(30) (SybronEndo, Mexico) and K3XF .04(30) (SybronEndo, Mexico). K3XF is made from novel R-phase heat-treated metal alloy while all other files were made from traditional Ni-Ti alloy. The instruments were analysed under the following conditions: i) as-received (AR), ii) heat treated at 350°C, iii) heat treated at 400°C. The transformation temperatures were determined by differential scanning calorimeter (DSC). Compared to conventionally K3 and MTwo files, R-phase heat treatment K3XF file showed higher transformation temperatures. These results also showed that heat treatments increase the transformation temperatures.

Undergraduate Teaching for Using Rotary Nickel-titanium Endodontic Instruments

Aim: To evaluate students’ perceptions and self-assessment of their experience, theoretical knowledge and practical abilities to use rotary nickel-titanium endodontic instruments. Methodology: A questionnaire was filled by fourth- and fifth-year students in Faculty of Dental Medicine, Sofia, Bulgaria. Data concerning self- assessment of theoretical knowledge and practical experience were gathered. Results: Students’ self-assessment of practical experience was not influenced by the time of education. High appreciation for increase of amount/time of practical training and inclusion of more cases and more rotary NiTi systems was determined. University lectures alone or in combination with non-university lectures were found to have greatest influence on students’ knowledge of rotary NiTi instruments. University practical lessons were estimated as the main source for acquiring practical skills. In the course of education preference for rotary NiTi instruments remained unchanged, although majority of students felt more confident in usage of hand stainless-steel instruments. A good understanding of general topics related with use of NiTi rotary systems was demonstrated. Almost all respondents estimated work with rotary NiTi instruments as less strenuous and time saving. Conclusion: Students assess implementation of rotary nickel-titanium instrument in undergraduate curriculum as positive. Their practical experience is highly influenced by the university training classes. Majority of students prefer using rotary NiTi instruments, but feel deficiency in confidence for using them. Increased number of lectures and wider variety of topics related to rotary NiTi systems are advocated. Knowledge of more rotary systems has to be incorporated into lectures and practical training.

Enhancement of NiTi superelastic endodontic instruments by TiO2 coating

Rotary nickel-titanium (NiTi) endodontic instruments were coated with a nanometric flexible TiO2 layer through dip-coating sol-gel. Control groups and coated samples of superelastic NiTi instruments model RaCe 25/0.06 (0.25mm tip-diameter, 6% conicity) were comparatively investigated with respect to the cutting efficiency, fatigue life, and corrosion resistance. Results showed an improvement in cutting efficiency for the coated samples and a high resistance to corrosion in NaClO. The coated instruments showed a better performance in fatigue life after corrosion.

Mechanical behavior of deep cryogenically treated martensitic shape memory nickel-titanium rotary endodontic instruments.

Objectives:The aim of this study was to investigate the role of deep cryogenic treatment (DCT) on the cyclic fatigue resistance and cutting efficiency of martensitic shape memory (SM) nickel–titanium (NiTi) rotary endodontic instruments.Materials and Methods:Seventy-five HyFlex® CM instruments were randomly divided into three groups of 25 each and subjected to different DCT (–185° C) conditions based on soaking time: DCT 24 group: 24 h, DCT 6 group: 6 h, and control group. Each group was randomly subdivided for evaluation of cyclic fatigue resistance in custom-made artificial canals (n = 15) and cutting efficiency in plexiglass simulators (n = 10). The cyclic fatigue resistance was measured by calculating the number of cycles to failure (NCF) and cutting efficiency was measured using the loss of weight method.Results:Increase in NCF of instruments in DCT 24 group was highly significant (P < 0.01; Tukey's honest significant difference). There was no difference in weight loss of plexiglass simulators in all the groups (P > 0.05; one-way analysis of variance). In conclusion, deep dry cryogenic treatment with 24 h soaking time significantly increases the cyclic fatigue resistance without affecting the cutting efficiency of SM NiTi endodontic instruments.Materials and Methods:Seventy-five HyFlex® CM instruments were randomly divided into three groups of 25 each and subjected to different DCT (–185° C) conditions based on soaking time: DCT 24 group: 24 h, DCT 6 group: 6 h, and control group. Each group was randomly subdivided for evaluation of cyclic fatigue resistance in custom-made artificial canals (n = 15) and cutting efficiency in plexiglass simulators (n = 10). The cyclic fatigue resistance was measured by calculating the number of cycles to failure (NCF) and cutting efficiency was measured using the loss of weight method.Results:Increase in NCF of instruments in DCT 24 group was highly significant (P < 0.01; Tukey's honest significant difference). There was no difference in weight loss of plexiglass simulators in all the groups (P > 0.05; one-way analysis of variance). In conclusion, deep dry cryogenic treatment with 24 h soaking time significantly increases the cyclic fatigue resistance without affecting the cutting efficiency of SM NiTi endodontic instruments.

Deformation and fracture of K3 rotary nickel-titanium endodontic instruments after clinical use.

The aim was to evaluate the incidence and type of defects that occurred with K3 rotary nickel-titanium instruments during routine clinical use. A total of 2397K3 (G-PACKS, SybronEndo, West Collins, Orange, CA, USA) instruments were collected from a graduate endodontic clinic over 21months. All the instruments were limited to a maximum use of 30 canal preparations. The collected instruments were measured by a digital caliper to determine whether any fractures had occurred and then were visually inspected for deformation and fracture under a stereomicroscope. The surfaces of fractured instruments were further evaluated under a scanning electron microscope. Data were analysed using chi-square test and Kruskal-Wallis test. The incidence of instrument defect was 5.63%, consisting of 3.59% fractures and 2.05% deformations. The defect rates of 0.04 and 0.06 files were statistically higher than the other taper groups (P<0.003) except for 0.08 files (P>0.05). For the fractured instruments, 63.95% failed from flexural fatigue, whilst 36.05% failed from torsion. Flexural fracture was the major mode of fracture for instruments with larger taper. A routine check for instrument integrity particularly for 0.04 and 0.06 files at high magnification is recommended after each clinical use.

Influence of Heat Treatment of Nickel-Titanium Rotary Endodontic Instruments on Apical Preparation: A Micro–Computed Tomographic Study

IntroductionThe aim of this study was to make a 3-dimensional comparison of the canal transportation and changes in apical geometry using micro–computed tomographic imaging after canal preparation with K3 (SybronEndo, Orange, CA) and K3XF (SybronEndo) file systems. MethodsTwenty-eight mandibular molars were randomly divided into 2 groups according to the rotary system used in instrumentation: K3 or K3XF. The specimens were scanned by micro–computed tomographic imaging before and after instrumentation. Images before and after instrumentation from each group were compared with regard to canal volume, surface area, and structure model index (SMI) (paired t test, P < .05). After instrumentation, the canals from each group were compared regarding the changes in volume, surface area, SMI, and canal transportation in the last 4 apical mm (t test, P < .05). ResultsInstrumentation with the 2 rotary systems significantly changed the canal volume, surface area, and SMI (P < .05). There were no significant differences between instrument types concerning these parameters (P > .05). There were no significant differences between the 2 groups with regard to canal transportation in the last 4 apical mm (P > .05). ConclusionsBoth rotary systems showed adequate canal preparations with reduced values of canal transportation. Heat treatment did not influence changes in root canal geometry in the apical region.