The Effect of Access Cavity Designs and Sizes of Root Canal Preparations on the Biomechanical Behavior of an Endodontically Treated Mandibular First Molar: A Finite Element Analysis

IntroductionThis study aimed to compare the biomechanical properties of a mandibular first molar with different endodontic cavity designs and increasing sizes of root canal preparations using finite element analysis (FEA).MethodsThe experimental finite element models were designed with 3 different endodontic access cavities and 2 sizes of canal preparations: traditional access cavity, conservative access cavity, and truss access cavity and #30/.04 and #40/.04 of root canal preparations. Vertical and oblique loads were applied with a 250-N static force to simulate masticatory forces. Mathematical analysis was performed to evaluate the stress distribution patterns. Maximum von Mises (VM) stresses were assessed at the occlusal surface; cervical line; and 1 , 3, 5, and 7 mm from the root apices.ResultsDecreasing the size of the access cavity was associated with a higher magnitude of cervical stresses. The magnitude of VM stresses was maximum at the 7-mm level and was minimum at the 1-mm level from the root apex. Increasing the size of the access cavity was associated with the transmission of stresses to a further apical direction regardless of the extent of root canal enlargement. The root canal enlargement from #30 to #40 increased radicular VM stresses within all models.ConclusionsWithin the limitations of this study, conservative and truss access designs preserved a significant volume of tooth structure. The extent of root canal enlargement should be as small as practical without jeopardizing the biologic objectives of root canal treatment.     

Effect of Access Cavities and Canal Enlargement on Biomechanics of Endodontically Treated Teeth: A Finite Element Analysis

IntroductionThe purpose of this study was to investigate the influence of access cavities and tapers of canal preparations on fracture resistance of endodontically treated first molars by finite element method and Weibull analysis.MethodsOn the basis of the micro–computed tomography data of maxillary first molar, the models of endodontically treated teeth with conservative endodontic cavity, traditional endodontic cavity, and 4 tapers of canal preparations (0.02, 0.04, 0.06, and 0.08) were created. Four static loads (800 N in total) were applied vertically to the contact points. The stress distributions of maximum principal stress were recorded and analyzed. Weibull analysis was performed to analyze the failure risk in enamel and dentin.ResultsThe stress distributions of maximum principal stress on occlusal surfaces were similar. In cervical region, the tensile stress was mainly concentrated on mesiobuccal root and root furcation. The finite element analysis and Weibull analysis showed that conservative endodontic cavity significantly reduced the maximum principal stress in cervical region and the failure probability, compared with traditional endodontic cavity. No significant difference was detected among tapers of prepared canals.ConclusionsPreserving coronal dentin by using conservative endodontic cavity significantly reduced the concentration of tensile stress and the failure probability of dentin, although the maximum principal stress and failure probability were less affected by taper of canal preparation.     

The Impact of TruNatomy and ProTaper Gold Instruments on the Preservation of the Periradicular Dentin and on the Enlargement of the Apical Canal of Mandibular Molars

IntroductionThis study aimed to evaluate the preservation of periradicular dentin and the enlargement of the apical canal of mandibular molars with TruNatomy (Dentsply Sirona, Ballaigues, Switzerland) and ProTaper Gold (Dentsply Sirona) instruments.MethodsTwenty mandibular molars were scanned in a micro–computed tomographic device, anatomically paired, and distributed into 2 groups (n = 10). In the ProTaper Gold group, mesial and distal canals were prepared up to F2 (25/.08v) and F3 (30/.09v) instruments, whereas in the TruNatomy group, mesial and distal canals were enlarged up to the prime (26/.04v) and medium (36/.03v) instruments, respectively. After a new scan, the surface area, volume, unprepared areas, transportation, percentage of dentin removal, and dentin thickness parameters were calculated. Data were compared between groups using the Mann-Whitney test, the Student t test, and the nonmetric multidimensional scaling test with alpha set at 5%.ResultsNo difference was found between groups regarding unprepared canal areas and the reduction of dentin thickness (P > .05). Transportation was lower than 0.1 mm in all groups, and statistical differences were observed only at the apical third of the mesiobuccal canal with lower values in the TruNatomy group. ProTaper Gold removed more dentin than TruNatomy at the coronal level of mesial roots (1.8% and 1.0%, respectively) (P < .05).ConclusionsTruNatomy and ProTaper Gold were efficient for performing canal preparation in mandibular molars. The tested systems were similar in terms of untouched canal walls and remaining dentin thickness and slightly different in the apical transportation of mesial canals and the percentage of dentin removal at the coronal third but without clinically significant errors.     

Changes in compaction stress distributions in roots resulting from canal preparation

AIM: To examine if canal enlargement with instruments of controlled taper leads to more uniform stress distributions within a root, thereby reducing fracture susceptibility. METHODOLOGY: Finite element models of a mandibular incisor were constructed with round and oval canal profiles, based on measurements from extracted teeth. The shapes of rotary nickel-titanium instruments (ProTaper F1, F2, and F3 and ProFile size 30, 0.04 taper and size 30, 0.06 taper; Dentsply Maillefer) were superimposed on the canals. Equivalent stresses and circumferential stresses in the root were calculated for a compaction load. RESULTS: The highest stresses were found at the canal wall. Round canals showed lower uniform distributions, whilst oval canals showed uneven distributions with high concentrations at the buccal and lingual canal extensions and greater stresses in the coronal and middle thirds than in the apical third. Preparation of round canals introduced only small circumferential stress increases in the apical half; preparation of oval canals produced substantial reductions where the canal was enlarged to a smooth round shape. Even where fins were not completely eliminated, the maximum stresses were still reduced by up to 15%. External distal and mesial surfaces of roots with oval canals showed moderate stress concentrations that were minimally affected by preparations, whilst stress concentrations emerged on roots with round canals when preparation sizes increased. CONCLUSIONS: The potential for reducing fracture susceptibility exists as a result of round canal profiles achieved and smooth canal taper. Even when fins were not contacted by the instrument, stresses within the root were lower and more evenly distributed than before preparation.     

The Effect of Different Access Cavity Designs in Combination with WaveOne Gold and TruNatomy Instrumentation on Remaining Dentin Thickness and Volume

IntroductionThe purpose of this study was to evaluate and compare 2 different access cavity designs in combination with 2 popular single-file preparation systems to see which combination preserves dentin, more specifically pericervical dentin, best. The minimum remaining dentin thickness and dentin volumes were evaluated pre- and postinstrumentation.MethodsSixty extracted human mandibular molars were selected and randomly divided into 2 different access cavity design preparation groups: traditional access cavities (n = 30) and conservative access cavities (n = 30). Within each cavity preparation design group, the 30 teeth were divided into 2 instrumentation groups (WaveOne Gold Primary; Dentsply Sirona, Ballaigues, Switzerland [n = 15] and TruNatomy Prime, Dentsply Sirona [n = 15]). Samples were scanned using micro–computed tomographic imaging before and after access cavity preparation as well as after final endodontic instrumentation. The pericervical remaining dentin thickness and dentin volume changes were evaluated and compared.ResultsConservative access cavity designs resulted in more favorable remaining dentin thickness. The least amount of mean dentin volume loss was also recorded in the conservative access cavity preparation groups regardless of the preparation instrumentation.ConclusionsIn terms of the remaining pericervical dentin thickness and dentin volume reductions, the authors conclude that conservative access cavity designs preserve dentin best.     

Rotary Versus Reciprocation Root Canal Preparation: Initial Clinical Quality Assessment in a Novice Clinician Cohort

Introduction

Reports comparing clinical outcomes using nickel-titanium (NiTi) reciprocating instruments with other instrumentation modalities are scarce. This study examined initial shaping outcomes after an instrumentation change of root canal instrumentation technique in a doctor of dental surgery educational program. Student characteristics, faculty/student ratio, facility, and overall endodontic treatment guidelines remained unchanged.

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

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

Middle Mesial Canal Preparation Enhances the Risk of Fracture in Mesial Root of Mandibular Molars

IntroductionThe aim of this investigation was to evaluate the effect of the presence and preparation of middle mesial (MM) canals on the fracture resistance of the mesial root of mandibular molars.MethodsForty intact mesial roots of mandibular first molars having 2 (n = 20) or 3 (n = 20) independent canals from the furcation level for up to at least 5 mm apically were selected based on preoperative micro–computed tomographic scanning. The selected roots were then distributed into 2 experimental (n = 10) and 2 control groups (n = 10) according to the root length, canal configuration (2 or 3 independent canals), and root thickness at the furcation level. In the experimental groups 1 (2 independent canals) and 3 (3 independent canals), root canals were enlarged up to the ProTaper Next X3 rotary instrument (Dentsply Sirona, Ballaigues, Switzerland), whereas in groups 2 (2 independent canals) and 4 (3 independent canals) root canals were not prepared. The specimens were embedded in acrylic resin after their surfaces were coated with a thin layer of silicone and subjected to a fracture strength using a universal testing machine. The types of fracture extension and course were recorded and statistically compared with the chi-square test, whereas fracture strength was analyzed using 1-way analysis of variance and post hoc Tukey tests (α = 5%).ResultsNo statistical difference in fracture strength was observed between nonprepared roots with 2 (group 2, 696.1 ± 186.3 N) or 3 (group 4, 558.4 ± 154.6 N) independent canals (P > .05), whereas the lowest values were obtained in the prepared roots with an MM canal (groups 3, 377.1 ± 77.2 N) (P < .05). The mean fracture strength observed in the prepared roots with 2 canals (group 1, 528.4 ± 134.3 N) showed no statistically significant difference compared with nonprepared roots with 3 canals (group 4, 558.4 ± 154.6 N) (P > .05). The chi-square test revealed no significant differences in fracture extent, types, and courses among groups (P > .05). Fracture extensions in all groups were mostly central and buccal-central types, whereas the highest frequency of fracture course was the curved and zigzag types.ConclusionsThe fracture resistance of the mesial roots of the mandibular molars decreased after the preparation of mesial canals with large-tapered instruments. Preparation of the MM canal further diminished the fracture resistance of the mesial roots. The resultant fracture displayed a distinct pattern in the buccolingual plane.     

Matching the Dimensions of Currently Available Instruments with the Apical Diameters of Mandibular Molar Mesial Root Canals Obtained by Micro–computed Tomography

IntroductionThis micro–computed tomographic study investigated the original anatomic diameters of the apical portion of mandibular molar mesial canals and matched them to the dimensions of instruments that are currently available and commonly used for apical preparation.MethodsOne hundred eight mandibular molar mesial roots with Vertucci type IV configuration were scanned by micro–computed tomographic imaging, and the largest anatomic diameter of both mesial canals at 1, 2, 3, and 4 mm short of the apical foramen was measured. Canal diameters were compared with the dimensions of 10 endodontic instruments for simulation of preparation 1 mm short of the apical foramen. Accordingly, the instruments with a diameter larger than the largest canal diameter were regarded as having the potential to prepare 100% of the canal walls at each specific point or over the 4-mm apical segment.ResultsAt 1 and 2 mm short of the apical foramen, a 45/.02 instrument had a larger diameter than the mesiobuccal canal diameter in 73% and 55% of the teeth, respectively. Corresponding figures for the mesiolingual canal were 65% and 55%. When the entire 4-mm apical segment was considered, a 40/.06 instrument had better results, being larger than the apical canal in about 20% of the specimens. Overall, 78% of the apical canals would not be completely prepared by any instrument. Based on the mean (median) anatomic diameters, the adequate instrument dimensions would be 40/.10 (40/.08) for mesiobuccal canals and 45/.08 (40/.09) for mesiolingual canals.ConclusionsThe dimensions of the available instruments are not compatible with complete apical preparation in the majority of cases. The ideal instrument size/taper to include all the canal walls in apical preparation is too large and may not be safe for clinical use.     

Effect of root canal treatment procedures with a novel rotary nickel titanium instrument (TRUShape) on stress in mandibular molars: a comparative finite element analysis

The aim of this study was to investigate and compare, via finite element analysis (FEA), the effects of endodontic access and canal preparation on stress distribution under functional loading of a mandibular molar treated with novel (TRUShape) and conventional (Vortex) rotary root canal preparation instruments. Identical plastic mandibular molars with natural anatomy had all 4 canals shaped with either TRUShape or a conventional rotary, Vortex (#20 and #30, both by Dentsply Tulsa Dental). Finite element analysis was used to evaluate stress distribution in untreated and treated models. Micro-computed tomography (MCT) of the extracted teeth shaped in vitro was used to inform the FEA model regarding the geometry of root canals and external surfaces. Modeling the intact periodontal support and cancellous/cortical bone was based on anatomical data. Profiles of average and maximum von Mises stresses in dentin of the four treated conditions under functional loading were compared to the untreated model. This comparison was performed for each tooth model with and without root canal obturation and composite restoration. On average, the dentin sections with the most changes after preparation were located in the access cavity, with average stress increase up to +5.7, +8.5, +8.9, and +10.2 % for the TRUShape #20, Vortex #20, TRUShape #30 and Vortex #30, respectively, relative to the untreated model. Within the root canal system, the average stress differences were smaller than <5 % with lower values for TRUShape preparation. A reduction of the average stress in the access cavity was observed as an effect of the composite restoration, while about the same von Mises stress’ profiles were found into the root canal. In this finite element analysis, preparation of the access cavity resulted in increased von Mises stresses under functional occlusal load. The limited (up to 0.7 %) retained radicular dentin in the TRUShape versus the Vortex cavity proved effective in reducing masticatory stresses. The bonded restoration modeled in this study only partially counterbalance the combined effects of access cavity and root canal preparation.     

Micro-Computed Tomographic Evaluation of Canal Transportation and Centering Ability of 4 Heat-Treated Nickel-Titanium Systems

IntroductionThis study aimed to evaluate and compare canal transportation and centering ability of 4 different root canal preparation systems produced with thermal treatments by means of micro–computed tomographic imaging.MethodsEighty mesial canals of human extracted mandibular molars were selected based on similar morphologic parameters and were randomly assigned to 4 experimental groups (n = 20) according to the canal instrumentation technique: HyFlex CM (HCM [Coltène-Whaledent, Allstätten, Switzerland]), HyFlex EDM (HEDM [Coltène-Whaledent]), WaveOne Gold (WOG [Dentsply Sirona, Ballaigues, Switzerland]), and OneCurve (OC [Micro-Mega, Besancon, France]). The specimens were scanned before and after root canal preparation using X-ray micro-computed tomographic imaging at a resolution of 19.9 μm. Apical transportation and centering ability were then analyzed at 3 different levels: 3 mm, 5 mm, and 7 mm from the apex, representing the apical, midroot, and coronal thirds of the root, respectively. One-way analysis of variance and Kruskal-Wallis tests were used to statistically compare the groups. The significance level was set at 5%.ResultsHCM caused less canal transportation than WOG at the 3-mm level in both the buccal and lingual canals (P < .05). Also, HCM resulted in less canal transportation than WOG and OC at the 7-mm level regarding lingual canals. No statistically significant differences were recorded between the groups when the mean centering ratios were compared.ConclusionsThe 4 evaluated systems safely prepared root canals causing minimal canal transportation and producing relatively centered preparations. In terms of canal transportation, HCM performed better than WOG at the apical level and better than WOG and OC at the coronal level.     

Syringe Irrigation in Minimally Shaped Root Canals Using 3 Endodontic Needles: A Computational Fluid Dynamics Study

IntroductionThe aim of this study was to compare the irrigant flow in curved root canals prepared to various apical sizes by constant-taper or variable-taper instruments during syringe irrigation with 3 endodontic needles at 2 different flow rates.MethodsTwo matched curved mesial root canals of human mandibular molars were imaged by micro–computed tomographic imaging after preparation to apical size 20, 25, and 30/.06 taper either by constant-taper or variable-taper instruments. A Computational Fluid Dynamics model was used to simulate the irrigant flow in the 2 root canals prepared to each apical size during syringe irrigation with a 30-G open-ended needle and 30-G and 31-G closed-ended needles at 0.05 and 0.15 mL/s.ResultsThe irrigant could not penetrate up to the working length in root canals prepared to apical size 20 or 25/.06 taper. The 30-G open-ended needle combined with the low flow rate allowed the irrigant to reach the working length in size 30/.06 taper root canals while maintaining a relatively low apical pressure, but the wall shear stress was very low. The 31-G closed-ended needle combined with the high flow rate also delivered the irrigant to the working length in size 30 root canals and developed higher wall shear stress, but the apical pressure was also higher.ConclusionsSyringe irrigation using 30-G and 31-G needles was compromised in minimally shaped root canals.     

Biomechanical Behavior and Life Span of Maxillary Molar According to the Access Preparation and Pericervical Dentin Preservation: Finite Element Analysis

IntroductionThis study investigated the significance of pericervical dentin after coronal canal flaring on the biomechanical behavior and life span of a maxillary molar using finite element analysis (FEA).MethodsIn addition to the intact tooth (IT) model, 4 experimental FE models were designed: conservative access cavity model (CON), and 3 models with different radicular preparations for the coronal 4 mL considering 3 instruments: ProTaper SX model (SX), OneFlare model (OF), and Gates-Glidden model (GG). Cyclic loading of 50 N was applied on the occlusal surface and number of cycles until failure (NCF) was compared with the IT model. Mathematical analysis was done to evaluate the stress distribution patterns and calculated maximum von Mises (VM) and maximum principal stresses.ResultsAccess cavity preparation (CON) decreased NCF significantly when compared with the IT model (93.99%). The coronal preparation of the root canal did not have a significant effect even when the preparation was taken to the extreme (GG: 92.02%). VM analysis confirmed apical dispersion of stresses, with maximum value registered on the occlusal surface in the GG model (7.88 MPa), and minimum on the IT model (7.01 MPa). The furcation area showed higher maximum principal stresses, yet stress values remained minimal and distributed over larger surfaces with the progressive enlargement among models.ConclusionsWithin the limitations of this study, coronal canal flaring affects tooth integrity minimally, and when loading conditions lie within normal functional ranges, tooth structure has the capacity to disperse increasing stresses over a wider surface area.     

The Effects of Different Endodontic Access Cavity Design and Using XP-endo Finisher on the Reduction of Enterococcus faecalis in the Root Canal System

IntroductionThe aim of this study was to evaluate the effect of using the XP-endo Finisher (XPF; FKG Dentaire, La Chaux de Fonds, Switzerland) in teeth that have a traditional access cavity (TEC) and a contracted access cavity (CEC) design on the amount of decrease in the number of Enterococcus faecalis bacteria within the root canal system.MethodsEighty mandibular first molar teeth were selected and randomly divided into 2 groups: TEC and CEC (n = 40/group). After access cavity preparation in the 2 groups, 80 mesiobuccal root canals were contaminated with Enterococcus faecalis for 4 weeks. After the first sampling (S1), in order to perform root canal instrumentation, the TEC and CEC groups were further divided into 4 subgroups (10 teeth/group): Reciproc (VDW GmbH, Munich, Germany) and ProTaper Next (Dentsply Maillefer, Ballaigues, Switzerland) with or without XPF. Bacterial sampling from the root canals was performed with sterile paper points before (S1) and after (S2) instrumentation to determine the bacterial load. The bacterial reduction was counted as colony-forming units/mL and analyzed statistically by 3-factor repeated measures analysis of variance. Multiple comparisons of the main factor effect were performed using the Bonferroni correction (α < .05), all at 5% significance.ResultsThe number of E. faecalis bacteria in all the samples with different cavity designs were significantly reduced after instrumentation. The lowest value of bacterial decrease percentage was observed in the CEC-Reciproc-XPF (82.8%) group.ConclusionsThe bacterial reduction counts of E. faecalis were a similar level in the TEC and CEC cavities, and the use of XPF did not show significant differences between groups.     

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

IntroductionThis study aimed to compare the torque generated by 4 different files in root canals with 4 different curvature angles.MethodsFour brands of nickel-titanium (NiTi) endodontic files were selected: WaveOne Primary (Dentsply Sirona, Ballaigues, Switzerland), WaveOne Gold Primary (Dentsply Sirona), ProTaper Universal F2 (Dentsply Sirona), and ProTaper Next X2 (Dentsply Sirona). A tempered steel block containing artificial canals with 4 different canal curvatures (15°, 25°, 35°, and 45°) was constructed. Each file was used according to the manufacturer’s instructions in the dynamic model, with an added 15 axial up-and-down movements of 4 mm at the end of the canal. The generated torque was recorded, and the total and maximum torque values were measured. Two-way analysis of variance and the Duncan post hoc comparison test were performed at a significance level of 95%.ResultsA significant correlation between the curvature angle and the type of file system was observed (P < .05). As the degree of canal curvature increased, the generated total and maximum torque increased. At 15° and 25°, the NiTi files with reciprocating motion generated a higher total and maximum torque than files with continuous rotation. ProTaper Universal of conventional NiTi alloy showed the steepest increase in the generated total and maximum torque with the increasing curvature angle. The ProTaper Next file had the lowest torque values at the higher canal angles of 35° and 45° (P < .05).ConclusionsDespite the study limitations, it can be concluded that root canal curvature, design, and heat treatment of NiTi files and file kinematics affect the generated torque during instrumentation.     

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

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

Effect of canal taper and plugger size on warm gutta-percha obturation of lateral depressions

This study used transparent epoxy-resin root canal models to evaluate different main root canal tapers and various methods of vertical compaction for warm gutta-percha obturation of lateral depressions. The root canal models had straight main root canals with three tapers and four lateral depressions at right angles to the main root canal, 1.0 mm and 3.0 mm from the apex. Three types of experimental stainless steel pluggers with different flat-tip diameters and tapers were used to compact the warm gutta-percha. The Obtura II was used for obturation. After obturation, the depth of penetration into lateral depressions was measured under a stereoscopic microscope, and the effects of root canal taper and plugger size were analyzed by using two-way analysis of variance. The penetration of warm gutta-percha into lateral depressions using the smallest-diameter plugger decreased with increasing main root canal taper. Penetration into lateral depressions increased with the use of pluggers of the correct size. There was a close relationship between plugger size and canal taper. The results suggest that main root canal taper and plugger size should be closely matched so as to promote gutta-percha obturation of lateral depressions.     

Micro–computed Tomographic Evaluation of the Shaping Ability of 3 Reciprocating Single-File Nickel-Titanium Systems on Single- and Double-Curved Root Canals

IntroductionWe performed a micro–computed tomographic assessment of the preparation of moderately single- and double-curved root canals using 3 single-file reciprocating nickel-titanium systems: S1 Plus Standard (Sendoline, Täby, Sweden), WaveOne Gold Primary (Dentsply Sirona, Ballaigues, Switzerland), and Reciproc R25 (VDW, Munich, Germany).MethodsSeventy-five moderately curved mandibular molars with 2 separate mesial root canals were assigned to 3 experimental groups (n = 25) (ie, S1 Plus Standard, WaveOne Gold Primary, and Reciproc 25 groups) by forming matched triples according to curvature (15°–40°), radius (≤18 mm), and type of curvature (single or double curved). Teeth were scanned before and after root canal preparation with a resolution of 10.5 μm using micro–computed tomographic imaging (Bruker SkyScan 1272; Bruker microCT, Kontich, Belgium). The following parameters were assessed: changes in root canal volume and surface area, percentage of unshaped canal walls, structure model index, canal transportation, and centering ratio. Data were analyzed using 2- and 3-way analysis of variance with Tukey and Scheffé post hoc tests (significance level of 5%).ResultsNo significant differences among groups were observed concerning all parameters. The type of curvature had no significant effect on all tested parameters. Within all experimental groups, canal transportation increased significantly from the apical to the coronal region, of which the majority was directed toward the furcational area.ConclusionsPreparation with the 3 nickel-titanium systems did not result in significantly different dimensional changes, and there was no significant effect of the type of curvature on all tested parameters.     

Retreatment of Root Canals Filled with BioRoot RCS: An In Vitro Experimental Study

IntroductionThe purpose of this study was to compare the speed of removal of root canal filling material and re-establishment of apical patency in root canals filled with a tricalcium silicate–based sealer (BioRoot RCS [BRCS]; Septodont, Saint-Maur-des-Fossés, France) versus a zinc oxide–eugenol sealer (Pulp Canal Sealer [PCS]; Sybron Endo Kerr, Orange, CA) and to analyze the effect of the operator’s experience.MethodsOne hundred twenty root canals of 40 Dentalike dental simulators (Dentsply Sirona, York, PA) were shaped with a WaveOne (Dentsply Sirona) reciprocating file using short 3-mm strokes. Root canals were obturated using a single gutta-percha cone and either BRCS or PCS. Samples treated either with BRCS or PCS were equally dispatched between experienced practitioners and junior practitioners. The time required to remove root filling material and establish apical patency was recorded for each root canal. Samples were compared according to the sealer used and the practitioner’s experience (Mann-Whitney test).ResultsOne hundred fifteen root canals were successfully retreated. No differences in the time required to remove the filling material were observed between the 2 materials for mesiobuccal or distobuccal canals (P > .05). In contrast, the procedure was longer for palatal canals filled with BRCS compared with PCS (79.10 vs 182.45 seconds, P < .01). Experienced practitioners took significantly less time than junior practitioners (P < .05).ConclusionsBRCS can be successfully removed from root canals as quickly as a zinc oxide–eugenol sealer in both mesiobuccal and distobuccal canals but not in palatal ones. The duration of the procedure was affected by the operator’s experience independent of the filling material used or the canal type.     

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

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