Change In Working Length Research Articles

Loss of working length in curved canals with rotary nickel–titanium instruments and reciprocating files

ABSTRACT Aim: The aim of the study was to investigate the change of working length in curved molar root canals after preparation with rotary nickel–titanium instruments and reciprocating files. Materials and Methods: Thirty human-extracted maxillary and mandibular molars with curved roots were selected, with the help of a radiographic platform, a constant object sensor distance was arranged to take a digital radiograph of each tooth for determining the angle of curvature of the roots by Schneider’s method. The teeth were divided into Groups I, II, and III based on the instrumentation, ProTaper group, Reciproc group, and control group, respectively. Preoperative and postoperative working length was determined and compared using cone-beam computed tomography. The difference was determined statistically using one-way anova analysis. Results: There was minimum loss of working length found when instrumentation was done with Reciproc files compared with ProTaper. Conclusion: Reciprocating instruments can be an effective alternative used in the preparation of severely curved canals.

Beş Farklı Nikel-Titanyum Döner Eğe Sisteminin Yapay Kanallarda Şekillendirme Etkinliklerinin Karşılaştırmalı Olarak Değerlendirilmesi

Objectives: The aim of this study was to compare the simulated canal shaping efficiencies of five different NiTi rotary file systems.
 Materials and Methods: In the study, 100 transparent resin blocks with J-shaped canals were randomly divided into five groups (n=20). Simulated canals were shaped with VDW.Rotate (VR), TruNatomy (TRN), HyFlex CM (HF), EdgeFile X7 (EF), or ProTaper Next (PTN) files. Ten measuring points were detected on the pre- and post-preparation images taken from the blocks and superimposed. After preparation, the total canal width and the amount of transportation were calculated for the determined measuring levels. Zipping and ledge formation, instrument fracture and deformation, and change in working length were evaluated. The data were statistically analyzed with the Kolmogorov-Smirnov test, one-way ANOVA, Tukey test, Chi-Square test, and a Monte Carlo version of the Fisher Exact tests. The error level was taken as 0.05.
 Results: There were significant differences between the groups at all measuring levels in terms of total canal width after instrumentation (p = 0.001). Significant differences in the amount of transportation were found between the groups (p = 0.001) except at levels 4 (p = 0.169) and 10 (p = 0.054). Zip and instrument fractures did not occur in any group. 3 EF size 25/.04 files were deformed (p = 0.021). There was no significant difference between the groups in terms of ledge formation and working length change (p > 0.05).
 Conclusions: According to findings obtained in the study, transportation occurred at all 10 measuring levels with all file systems used. HF and EF systems were found to be more reliable in terms of transportation in the middle and coronal regions. Wider canal preparation was obtained with the PTN system in the middle and coronal regions.

Shaping Ability of Reciproc Blue Versus One Curve in Curved Canal: An In-Vitro Study.

The introduction of nickel-titanium (NiTi) rotary instruments improved the root canal preparation of the narrow and curved root canals, especially after the introduction of thermomechanical treated (NiTi) alloys that have a high flexibility to prepare the curved canal reducing the common clinical complication, such as fracture, the change of the original shape of the root canal as a result of the change in the curvature of the curved root canal, the change of the working length which caused by the creation of the ledges, canal transporting and zipping especially in medium and highly curved canal. This study aimed to compare the shaping ability of two heat-treated nickel-titanium single file systems using reciprocation motion and rotary motion in curved canals.Materials and methodsThirty extracted human teeth with one curved root at 25 to 56 degrees were used, two NiTi single file systems were used to prepare the curved root canal in two groups: Reciproc R25 (Munich, Germany: VDW) group (n=15) and One Curve (Besancon, France: Micro-Mega) group (n=15). Curved root canal instrumentation outcomes were evaluated using cone-beam computed tomography (CBCT). Kruskal-Wallis with Bonferroni post hoc test was used to assess differences between working length, the angle and radius of curvature after instrumentation.ResultsThere was a significant difference in angle and radius of curvature (-1.83° One Curve, -2.25° Reciproc blue and -0.18 mm One Curve, -0.19 mm Reciproc blue, respectively) (p<0.05) after instrumentation for both One Curve and Reciproc blue groups, and there was no significant difference in working length change (-0.16 mm One Curve, -0.32 mm Reciproc blue) after instrumentation of both One Curve and Reciproc blue groups (p>0.05).ConclusionThe Reciproc blue single file system with reciprocation movement and One Curve with continuous movement cause a significant difference in curvature and radius of curved root canal affecting the original shape of the root canal with no significant difference in working length of the curved root canal.

Does The Working Length Change When Using The XP-Endo Shaper File at Different Operating Temperatures?

Introduction: This study was directed to evaluate the effect of different operating temperatures on the change in working length when using the XP-endo shaper file. Methods: A total of 20 plastic blocks with16 mm curved canals were used in this study. The working length was adjusted to be 15 mm using a customized Teflon stopper (10mm in length) which was used with all files in the study. The preparation was done using the XP-endo shaper file (FKG, La Chaux-de-Fonds, Switzerland) according to the manufacturer’s instructions. The blocks were divided into 2 groups: Group 1: body temperature, Group 2: room temperature. Pre and post instrumentation imaging of the blocks was done using the stereomicroscopy at 8x. The images were superimposed to create a composite image on which the evaluation of working length change was done. Mann-Whitney U test was used to compare the change in working length in the two groups. Results: There was no statistically significant difference between the two groups (P ≤ 0.05). Conclusions: Within the parameters of this study, although both groups showed an increase in working length when using the XP-endo shaper file, the operating temperature did not have an effect.

An Adaptive Roller Speed Control Method Based on Monitoring Value of Real-Time Seed Flow Rate for Flute-Roller Type Seed-Metering Device.

In order to obtain desirable crop yields, grain seeds need to be sown at the optimal seed amount per hectare with uniform distribution in the field. In previous grain sowing processes, the seeding rates are controlled by the rotational speed of the flute roller which significantly effects the uniform distribution of the seeds due to disturbances, such as the reduction of the seeds’ mass in the hopper and the change of working length of the flute roller. In order to overcome the above problem, we developed an adaptive roller speed control system based on the seed flow rate sensor. The developed system can monitor and feedback actual seeding rates. In addition, based on the monitoring value of the real-time seeding rates, an adaptive roller speed control method (ARSCM), which contains an algorithm for calculating the seeding rate with a compensation, was proposed. Besides, the seeding performance of the ARSCM and that of the conventional roller speed control method (CRSCM) were compared. The results of constant-velocity experiments demonstrated that the accuracy (SA) and the coefficient of variation (SCV) of the seeding rates controlled by the ARSCM were 94.12% and 6.77%, respectively. As for the CRSCM, the SA and SCV were 89.00% and 8.95%, respectively. Under variable-velocity conditions, the SA and SCV of the proposed system were 91.58% and 11.08%, respectively, while those of the CRSCM were 88.48% and 13.08%, respectively. Based on the above results, this study concluded that the ARSCM is able to replace the CRSCM in practical sowing processes for the optimal and uniform seed distribution in the field.

Contradictory working length effects in locked plating of the distal and middle femoral fractures―a biomechanical study

BackgroundWorking length have been reported to affect the plate stress and fixation stiffness. However, the results of previous studies have been controversial. The present study was to determine working length effects on different locations of femoral bone gap. MethodsFive composite femurs with wide bone gaps at five levels (G1, 2, 3, 5, and 7), were fixed with locking plates. G1-3, G5 and G7 represented gaps at distal femur, distal-middle femur and middle femur respectively. Strain gauges were applied near the screw holes. The plate-bone constructs were loaded through a hemicylinder on the femoral head with total constraints at the distal femur. The micro-strains, axial stiffness and interfragmentary motions were recorded. Then the locking screws were removed one by one and the tests were re-run. The working length effects were compared and correlated. FindingsIn distal femurs (G1-3), long working length was negatively correlated with the highest strains (r = −0.97, −0.95 and − 0.95, p < 0.01) and axial stiffness (r = −1, −0.96 and −0.99, p < 0.01). In distal-middle femurs (G5), as the working length increased, the highest strain decreased initially and then increased (r = 0.81, p = 0.026) and the axial stiffness decreased (r = −0.98, p < 0.01). In middle femurs (G7), the highest strain and gap motions were much higher than that in the other groups and not significantly correlated with the working length change. InterpretationLong working length could reduce the highest plate strain in distal femurs, but had no significant effects in middle femurs. The working length effects were markedly affected by the loading and boundary conditions.

Comparative Study of Four Endodontic File Systems to Assess Changes in Working Length during Root Canal Instrumentation and the Effect of Canal Curvature on Working Length Change

IntroductionThe aim of this study was to compare a reduction in working length and area of canal enlargement resulting from instrumentation with Hedström (Kerr Dental, Orange, CA), K (Kerr Dental), ProTaper Next (Dentsply Sirona, York, PA), and TF Adaptive (Kerr Dental) files. The effect of the canal curvature on the working length and area of canal enlargement was also assessed. MethodsA total of 80 plastic canal models were used, 40 with a canal curvature of 10° and another 40 with a canal curvature of 30°. Instrumentation of 10 models with a 10° canal curvature and 10 models with a 30° canal curvature was performed using each of the file systems up to size 25. Working length measurements were taken before and after instrumentation with each file type and size. Twenty composite images were made from superimposition of pre- and postpreparation photographs, and the difference in area was calculated using ImageJ software (National Institutes of Health, Bethesda, MD). ResultsProTaper Next rotary files and TF Adaptive files produced the smallest reduction in the working length and the least canal enlargement followed by Hedström files and K files, respectively. The degree of canal curvature increased the working length reduction by a significant amount when K files and ProTaper Next rotary files were used, and the degree of curvature increased canal enlargement by a significant amount when K files were used. ConclusionsNickel-titanium rotary files produced more favorable results than stainless steel hand files in terms of maintaining a consistent working length and producing minimal canal enlargement. Hedström files performed significantly better than K files in terms of working length reduction and canal enlargement.

A comparative study of root canal shaping using protaper universal and protaper next rotary files in preclinical dental education.

BackgroundDentistry has undergone an evolution in endodontics practice caused by the advancement of rotary techniques for root canal preparation and their subsequent incorporation into the teaching of dentistry undergraduates. This research aimed to evaluate the shaping ability of third-year dental students as their first experience in rotary instrumentation using ProTaper Universal (PTU) and ProTaper Next (PTN) (Dentsply Maillefer) rotary instruments in simulated curved canals.MethodsForty students instrumented 200 simulated canals with a 40° curvature in resin blocks according to the manufacturer’s instructions with PTU and 39 students and 195 canals with PTN files. The canals were prepared at a speed of 300 rpm using a 16:1 reduction hand-piece powered by an electric motor (Xsmart; Dentsply Maillefer). The final apical preparation was set to F2 for the PTU and X2 for the PTN group. The change in canal curvature was evaluated based on Schneider technique using the AutoCAD 2007 software on post-digital photographs. The incidence of instrument fracture and deformation, the incidence of ledge, the change in working length (WL), and the working time were noted. The data were analyzed with Student’s t-test and Chi-Square test at a significance level of 0.05 using SPSS.ResultsPTN maintained the original canal curvature better, resulting in fewer fractures and ledges, and shaped the canals faster than the PTU (P < 0.05). The mean curves of the resin canals after the instrumentation for the PTU and PTN groups were 24.03° ± 3.14° and 25.64° ± 2.72°, respectively. Thirty-three (17.4%) PTU and 18 (9.3%) PTN files fractured (p < 0.05). Nine (4.5%) PTU and 2 (2.6%) PTN deformed (p > 0.05). The change in WL after instrumentation was 0.97 mm ± 0.95 mm in PTU and 0.96 mm ± 0.80 mm in PTN (p < 0.05). The mean times were 627 s ± 18 s for PTU and 379 s ± 18 s for PTN (p < 0.000).DiscussionPTN can be recommended in severely curved root canals in terms of maintenance of the original canal curvature, superior instrument fracture and fewer ledges. Even if training before preparation provides an acceptable level of canal shaping for preclinical students, the use of NiTi rotary instruments should be included in the undergraduate dental curriculum, contributing to an increase in the quality of root canal shaping and, consequently, to an improvement of the clinical experience of students.

Research of dependence of electrodynamic characteristics of the crack which have been cut in the rectangular wave guide, from change of its sizes and position

Electrodynamic characteristics of the crack which have been cut in a wide wall of a rectangular wave guide are investigated.In resonant and non-resonant wave guide slot-hole aerials, one of the reasons of loss of capacity of a signal is a mismatch of entrance resistance of cracks with wave resistance of a wave guide. Possibility of reduction of influence of the specified lack by change of electrodynamic characteristics of a crack is offered.By a technique outlined in [1] dependency diagrams of active сonductivity crack radiations in a wave guide and from a wave guide, jet conductivity and factor of reflexion of a crack from its arrangement, the geometrical sizes and change of working length of a wave are constructed. The analysis of the received results from the point of view of possibility of maintenance of reduction of losses of capacity of a signal of a wave guide slot-hole radiator is carried out.Possibility of maintenance of radiation of a crack in single-mode operation in the set range of frequencies with low factor of reflexion under condition of change of the geometrical sizes and crack position is shown. We specify recommendations about a purposeful choice of the sizes of a crack (width, length) and its positions in a wide wall of a wave guide. Reliability of settlement results is confirmed by their convergence on units of measure and check in boundary conditions.

Root canal shaping by single-file systems and rotary instruments: a laboratory study.

The aim of this study was to compare the shaping ability of two single-file systems and conventional rotary instruments in severely curved root canals of extracted human molars. Mesiobuccal canals of 120 mandibular molars with angles of curvature ranging between 25(°) and 35(°) and radii of curvature from 5 to 9 mm, were divided into three groups (n=40). In each group the canals were instrumented with either WaveOne (W), Reciproc (R) or ProTaper (P). The time required for canal shaping and the frequency of broken instruments were recorded. The standardized pre and post-instrumentation radiographs were taken to determine changes in working length (WL) and straightening of canal curvature. The presence of blockage or perforation was also evaluated. Data were analyzed using the one-way analysis of variance (ANOVA) and post-hoc Tukey's test. The level of significance was set at 0.05. Both single-instrument systems reduced the canal preparation time by approximately 50% (P<0.05). No incidence of broken instruments from single-file systems was reported; however, two F2 instruments in the P group were broken (P<0.05). Reduction in WL and straightening of canal curvature was observed in all three systems with the highest scores belonging to P system (P<0.05). No case of blockage or perforation was found during shaping in any group. Single-file systems shaped curved canals with substantial saving in time and a significant decrease in incidence of instrument separation, change in WL, and straightening of canal curvature.

Working length changes in curved canals after coronal flaring by using rotary files and hand file: An in vitro study

Aim:This in vitro investigation examined the effect of early coronal flaring (CF) and late CF on the working length (WL) in curved root canals.Background:The objective of this study was to determine if canal length is altered as a result of CF in curved canals of molar roots.Study Design:The conditions compared were combinations of (a) stainless steel hand files using Gates Glidden (G. G.) drills (SS) versus nickel-titanium rotary files (Ni-Ti); and (b) early CF (flaring completed before WL determination) versus late CF (flaring completed after WL determination). Selected were 90 canals of extracted maxillary or mandibular first molars (mesial root of mandibular molars and the mesiobuccal root of the maxillary molars) from three groups. CF was accomplished for the SS group using G. G. drills and for the Ni-Ti group using rotary ProTaper and Hero Shaper files. WL was determined by a digital vernier caliper before CF, immediately after CF, and again after canal preparation.Statistical Analysis:A repeated measures analysis of variance (ANOVA) test and a Tukey's multiple prosthoc test were used for this study.Results:Results indicated that WL decreased for all canals as a result of canal preparation. The mean decrease in WL was significantly greater for the SS group (−0.77 ± 0.42 mm) than for the Ni-Ti groups (−0.33 mm ± 0.44). Less change in WL occurred in all groups when initial WL was determined after CF.Conclusion:WL in curved canals consistently decreases during the course of instrumentation. Clinician should keep this in mind for better treatment outcome.

A comparison of the shaping ability of reciprocating NiTi instruments in simulated curved canals

ObjectivesThe study was to compare the shaping ability of Reciproc (VDW) and WaveOne (Dentsply Maillefer) instruments compared with ProTaper, Profile and hand instrument during the preparation of simulated root canals.Materials and MethodsFive groups (n = 5) were established. Reciproc, WaveOne, ProTaper, Profile and K file (K-flexo file) were used to prepare the resin simulated canals. A series of preoperative and postoperative images were taken by a microscope and superimposed in 2 different layers. The amount of resin removed from both the inner and the outer sides of the canal was measured to the level of 10 mm from the apical tip, with a 1 mm increment.ResultsThe mean of resin removal from the inner canal wall was not different from the outer canal wall for Reciproc and WaveOne groups at apical third (1 - 3 mm level). There was no difference in the change of working length and maintenance of canal curvature. NiTi instruments are superior to stainless-steel K file in their shaping ability.ConclusionsWithin the limitation of this present study, Reciproc and WaveOne instruments maintained the original canal curvature in curved canals better than ProTaper and Profile, which tend to transport towards the outer canal wall of the curve in the apical part of the canal.

Comparison of apical transportation and change of working length in K3, NRT AND PROFILE rotary instruments using transparent resin block

Objectives: The purpose of this study is to compare the apical transportation and working length change in curved root canals created in resin blocks, using 3 geometrically different types of Ni-Ti files, K3, NRT, and Profile. Materials and Methods: The curvature of 30 resin blocks was measured by Schneider technique and each groups of Ni-Ti files were allocated with 10 resin blocks at random. The canals were shaped with Ni-Ti files by Crown-down technique. It was analyzed by Double radiograph superimposition method (Backman CA 1992), and for the accuracy and consistency, specially designed jig, digital X-ray, and CAD/CAM software for measurement of apical transportation were used. The amount of apical transportation was measured at 0, 1, 3, 5 mm from 'apical foramen - 0.5 mm' area, and the alteration of the working length before and after canal shaping was also measured. For statistics, Kruskal-Wallis One Way Analysis was used. Results: There was no significant difference between the groups in the amount of working length change and apical transportation at 0, 1, and 3 mm area (p = 0.027), however, the amount of apical transportation at 5 mm area showed significant difference between K3 and Profile system (p = 0.924). Conclusions: As a result of this study, the 3 geometrically different Ni-Ti files showed no significant difference in apical transportation and working length change and maintained the original root canal shape.

Change of working length in curved molar root canals after preparation with different rotary nickel-titanium instruments

Aim:The purpose of this study was to investigate change of working length in curved molar root canals after preparation with Profile, ProTaper and K3 Rotary Nickel-Titanium (Ni-Ti) instruments.Materials and Methods:One hundred and eighty maxillary and mandibular molars were divided into group I having root curvature angle <300 and group II having root curvature angle >300 comprising 90 teeth in each group based on Schneider's method. Group II and I were further divided into sub group A, B and C having 30 teeth each based on type of instrument used. Profiles, ProTaper and K3 Rotary Ni-Ti files were used to prepare mesial and buccal roots of molars. Radiography platform was made to allow technique for constant object to film distance and object to sensor distance. Conventional access opening was prepared in each tooth. Preoperative and postoperative working length was measured to an accuracy of 0.1 of mm on Dexis 3.0 direct digital radiograph's onscreen measurement device.Results:Mean loss of working length varied from 0.28 to 0.92 mm. Highest working length loss was seen in ProTaper followed by K3 files and Profiles, which is statistically significant.

An In Vitro Comparison of Profile GT and GTX Nickel-Titanium Rotary Instruments in Apical Transportation and Length Control in Mandibular Molar

Introduction Profile GT files have been redesigned and are now marketed as GTX nickel-titanium rotary files. Methods A double-digital radiographic technique was used to compare apical transportation (AT) and change in working length (CWL) between Profile GT and GTX rotary files. Mesiobuccal canals of 40 extracted mandibular molars were instrumented by either rotary system. The central axes of preoperative (15 K) and master apical rotary file (30/.04) were digitally superimposed. AutoCAD was used to measure AT at 0, 1, and 3 mm from WL. The distance from the file tip to the set WL indicated any CWL. Analysis of variance test showed no significant differences between groups in AT. Results CWL in GTX (−0.25 ± 0.42) group was significantly greater than in Profile GT group (0.17 ± 0.30). Conclusions The AT results indicate that the newly designed GTX rotary instruments are as effective as the older Profile GT instruments.

A Comparison of Apical Transportation and Length Control between EndoSequence and Guidance Rotary Instruments

Introduction The aim of this study was to evaluate apical transportation and working length changes after instrumentation using EndoSequence (Brasseler USA, Savannah, GA) and Guidance V-taper (Guidance Endo, Albuquerque, NM) rotary files. Methods Forty-four mesiobuccal and mesiolingual canals of extracted mandibular first and second molars were instrumented by using EndoSequence or Guidance NiTi rotary files. Group 1 ( n = 22) was instrumented with EndoSequence #30/.06, #25/.06, and #20/.06 files in a crown-down technique until apical enlargement with #25/.06 was achieved at the working length. Group 2 ( n = 22) was instrumented with Guidance #30/.10, #25/.08, and #20/.06 files in a crown-down method until apical enlargement with #25/.08 was reached. A double digital radiographic technique was used to measure the loss of working length and canal transportation at 0, 1, and 3 mm from the working length. Measurements were analyzed by using repeated-measures analysis of variance. Results The average amount of transportation at 0, 1, and 3 mm was 0.077 mm, 0.039 mm, and 0.040 mm for the EndoSequence group and 0.066 mm, 0.046 mm, and 0.05 mm for the Guidance group, respectively. The loss of working length was 0.001 mm for the EndoSequence group and −0.002 mm for the Guidance group. Conclusion There was no statistically significant difference in the loss of working length or transportation at the measured level between EndoSequence and Guidance rotary files.

A comparative study of four rotary NiTi instruments in preserving canal curvature, preparation time and change of working length

The purpose of this ex vivo study was to compare working time, working length changes and shaping effects using ProTaper, ProFile, FlexMaster and Mtwo rotary instruments. A total of 96 mesiobuccal roots of the first maxillary molars were prepared using these instruments. Using pre and post-radiographs, canal curvature and working length were measured. In addition, the time required for canal preparation was recorded. Data was statistically analysed using one-way anova and Duncan's post-hoc tests. ProTaper significantly lessened the canal curvature (P < 0.001), and Mtwo rotary instruments took significantly less instrumentation time (P < 0.001). No significant difference was observed between the four groups in changing working lengths (P = 0.081). According to the results of the study, the Mtwo rotary instruments required significantly less instrumentation time, and the ProTaper significantly changed the canal curvature.

A Comparative Study on Rotary Mtwo Versus Passive Step Back of Hand K-File in Preparation of Extracted Curved Root Canals

INTRODUCTION: The preparation of the root canal space includes debridement, shaping and apical preparation. These procedures are challenging and constitute. The recent introduction of automated techniques for canal preparation has created considerable interest. The aim of this study was to test shaping ability of one hand instrumentation (passive step-back technique) and new rotary NiTi system (Mtwo instrumentation) in curved root canals. MATERIALS AND METHODS: A total number of 40 curved molars selected for this in vitro study, 20 canals for each group. The mean of canal curvature in studied groups was similar. After preparation of access cavity, samples were divided into two groups. A custom made block was used for standardization of radiograph beam angel before and after preparation. In group 1, samples instrumented with passive step-back technique using stainless steel K-file, Gates Glidden and Pesso reamers. Mtwo NiTi rotary file and Endo IT power driven motor were used for instrumentation of samples in group 2. Transportation of canals curvature (loss of primary curvature) after canal preparation was assessed for each sample with the aid of AutoCAD 2007 software. Stereomicroscope provided data for measurement of changes in working length after canal preparation. RESULTS: The mean of changes in canals curvature (canal transportation) and mean of working length changes in group 1 (passive step-back technique) were 11.77 degree and 0.202 mm (P<0.001) and in group 2 (rotary Mtwo) were 5.58 degree and 0.202 mm (P<0.001). According to the present results, the original canal curvature was maintained significantly better with automated Mtwo files than with hand instrumentation. CONCLUSION: These can be hypothesized that the instrumentation with Mtwo NiTi rotary file preserves the canal curvature adequately.

Working length changes following straight-line access and different coronal flaring methods

Introduction: The purpose of this in vitro study was to compare working length (WL) changes after straight-line access (SLA) and different coronal flaring (CF) methods. Materials and Methods: Coronal access preparations were made (without SLA) in molar teeth to allow access to 120 canal orifices with a hand file. The suitable cusp and root tips were then flattened to facilitate reproducible and accurate measurements. WL was determined before and after SLA and after different methods of CF. These methods consisted of: stainless-steel (SS) hand files + NiTi hand files, SS hand files + Gates Glidden burs (GG) (#1 to #3), (#3 to #1), GG in step-back manner and crown-down manner without using SS hand files and NiTi rotary orifice shapers. Data was analyzed by paired T-test and coefficient of variance. Results: The mean difference in WL changes after SLA was statistically greater than other methods of CF (P<0.001). The mean difference of WL after CF, in SS hand files + GG (#3 to #1) group was significantly different with SS hand files + NiTi hand files group (P<0.004) and NiTi rotary group (P<0.04). Also the mean changes of WL in SS hand files + NiTi hand files group was significantly different with GG (#1 to #3) group (P<0.01). Conclusion: It is better to established working length after SLA. Least changes in WL was occurred with NiTi rotary orifice shapers after coronal flaring. (Iranian Endodontic Journal 2008;3:57-61)

Shaping Abilities of Two Different Engine-Driven Rotary Nickel Titanium Systems or Stainless Steel Balanced-Force Technique in Mandibular Molars

The purpose of this study was to compare apical transportation, working-length changes, and instrumentation time by using nickel-titanium (Ni-Ti) rotary file systems (crown-down method) or stainless steel hand files (balanced-force technique) in mesiobuccal canals of extracted mandibular molars. The curvature of each canal was determined and teeth placed into three equivalent groups. Group 1 was instrumented with Sequence (Brasseler USA, Savannah, GA) rotary files, group 2 with Liberator (Miltex Inc, York, PA) rotary files, and group 3 with Flex-R (Union Broach, New York, NY) files. Pre- and postoperative radiographs were superimposed to measure loss of working length and apical transportation as shown by changes in radius of curvature and the long-axis canal angle. Sequence rotary files, Liberator rotary files, and Flex-R hand files had similar effects on apical canal transportation and changes in working length, with no significant differences detected among the 3 groups. Hand instrumentation times were longer than with either Ni-Ti rotary group, whereas the rotary NiTi groups had a higher incidence of fracture.