Comparative Analysis of Surface Roughness and Plastic Deformation of Reciprocating Instruments after Clinical Use.

This study assessed the surface topography and plastic deformation (PD) of new and used contemporary reciprocating instruments. Twenty-six WaveOne Gold (WOG) and EdgeOne Fire (EO) instruments were photographed under magnification. The instruments were randomly assigned to a control group of new instruments preserved for surface roughness analysis (n = 6 each), or to an experimental group to shape the root canal system of a single molar (n = 20 each), making a total of four groups (WOGnew, EOnew, WOGused, EOused). Used instruments were also photographed after instrumentation. The presence of fractures was registered. Preoperative and postoperative images were randomly ordered for evaluation. Two blinded calibrated examiners evaluated the presence of PD. Inter-observer agreement was calculated with the Kappa coefficient (K = 0.89). 3D profilometry was also used for the surface roughness analysis of six randomly selected instruments from the WOGused and EOused groups. Chi-square and two-way ANOVA tests were used to, respectively, compare PD and changes in surface roughness among the groups. No instruments fractured; however, a significantly greater percentage of EO instruments suffered plastic deformation than WOG instruments (p < 0.001), (OR = 11.09 (CI 95% 2.6-56.3)). The overall surface roughness was higher for most parameters in the EO instruments (p < 0.05). Single uses of EO instruments produced significantly higher chances of PD and increased surface roughness values compared to WOG.

The usefulness of ultrasonography as a dynamic measurement system for visualizing root canal working length: an in vivo study.

OBJECTIVE: Although apex locators are generally effective tools for determining root canal working length, they may produce inaccurate results in some cases. The present study aimed to evaluate the efficacy of ultrasonography as an alternative method for measuring root canal length. MATERIALS AND METHODS: Forty-seven anterior teeth with apical lesions were selected for the study. Initially, an electronic apex locator was used to measure the working length. Subsequently, ultrasonography was employed to visualize the root apex and determine the working length. During ultrasound imaging, a K-file No. 15 was inserted into the root canal until its tip was visible on the ultrasound monitor. Measurements obtained from both methods were compared using an independent sample t-test. Correlations were assessed with the Pearson correlation coefficient, and agreement was determined using the Bland‒Altman plot. RESULTS: The mean working canal length was 19.9 mm for the apex locator and 20.6 mm for the ultrasonography-guided method. No significant differences were observed between the data obtained using the apex locator method and the data obtained using the ultrasonography guidance method. Furthermore, a high level of agreement was identified between the two techniques. CONCLUSION: Ultrasonography can be used to visualize the apex effectively and determine canal length, especially when canal length determination is uncertain for various reasons.

Evaluation of pulp tissue dissolution capacity through different sodium hypochlorite agitation protocols.

Aims: This ex vivo study aimed to assess the dissolving capacity of 2.5% sodium hypochlorite using eight agitation protocols within swine pulp tissue. Subjects and Methods: Twelve lower first premolars were prepared and split into the fragments with a groove housing porcine dental pulp. Groups were assigned based on agitation systems: manual, passive ultrasonic, Easy Clean and XP-Endo Finisher. Two agitation time protocols were applied: One min (3 s × 20 s cycles) and 2 min (6 s × 20 s cycles). Wilcoxon Mann-Whitney U test was used to compare the groups. Results: Both time frames demonstrated superior results compared to manual group (P > 0.5). However, in the two min groups, no significant differences were observed among the other protocols (P < 0.5). Intriguingly, increasing cycle numbers significantly improved results within each group (P > 0.5). Conclusion: Extending the chemical agitation time during final irrigation enhances tissue removal, regardless of the irrigation protocol employed.

Prevalence and Classification of C-Shaped Canal and Radix in Mandibular Molars Using Cone-Beam Computed Tomography on Mexican Population.

The diverse morphological configurations in teeth present clinical challenges in root canal treatment, complicating instrumentation and irrigation processes, which can lead to treatment failure. Understanding anatomical variations, such as C-shaped canals and radix entomolaris, enhances clinical skills and improves long-term endodontic treatment success rates. Cone-beam computed tomography (CBCT) offers superior diagnostic capabilities over conventional radiography, enabling the pre-operative detection of root configurations and canal numbers, facilitating personalized endodontic treatments. A total of 2173 teeth of a Mexican population, including 1057 first mandibular molars and 1116 s mandibular molars, were studied using only CBCT to identify C-shaped canals and radix configurations of patients who were treated from 2018 to 2023 at the Department of Radiology at the Faculty of Dentistry, Juarez University of the State of Durango, Mexico. C-shaped canals were identified in 160 teeth, with a prevalence of 0.2% in first mandibular molars and 14.1% in second mandibular molars. The highest frequency was in the left second mandibular molar (3.7) at 14.8%. Gender differences were significant, with higher prevalence in females (27.3%) compared to males (13.3%). The most common C-shaped canal configuration was type C2 (39.3%). Radix entomolaris was found in 52 teeth, with a prevalence of 3.4% in first mandibular molars and 1.4% in second mandibular molars. This research on a Mexican population using cone-beam computed tomography (CBCT) highlights significant findings in the prevalence and types of C-shaped canals and radix entomolaris in mandibular molars for this population. The left second mandibular molar (3.7) showed the highest prevalence at 14.8%, followed closely by the right second mandibular molar (4.7) at 13.5%, with a significant difference (p < 0.001). We found a significant difference in the prevalence of C-shaped canals between genders (p = 0.004, OR 1.78). Additionally, radix entomolaris (p < 0.001) was more frequently identified in first mandibular molars to a significant degree. These insights underscore the importance of CBCT in diagnosing complex root anatomies, which can greatly enhance the success rates of endodontic procedures by allowing for more tailored and precise treatments for this population.

The effect of three different primary teeth rotary instrument systems on the amount of apically extruded debris in pulpectomy of primary teeth.

Purpose: The objective of this study is to evaluate the amount of apically extruded debris and working time during root canal treatment with three different primary teeth rotary instrument systems. Materials and methods: A total of 80 extracted primary second molar teeth were randomly divided into four groups (n=20) stratified by the instruments used: AF Baby Rotary, Easyinsmile Baby Rotary, Endoart Pedo Gold, and hand files. The apical extrusion of debris was collected then dried in Eppendorf tubes that were pre-weighed with 10-4 precision micro-balance. The incubation period was set as 14 days at 37°C. The dry weight was procured by deducting the preoperative weight from the postoperative weight. The systems' working time was calculated by chronometer. Mann Whitney U test with Bonferroni correction was used for pairwise comparison following the variance analysis with Kruskal Wallis test. Wilcoxon test was used for intragroup comparison. Results: Although all instruments caused apically extruded debris (p<0.001), there was no statistically significant difference between the groups in debris extrusion. However, the longest working time was found in the manual K files, the Endoart Pedo Gold system had the shortest working time (p<0.001). Conclusion: Our results demonstrate that all instrument systems caused apical extrusion of debris. Furthermore, the rotary instrument systems designed for primary teeth exhibited significantly shorter working time.

Post-operative pain after root canal preparation with different apical finishing sizes a triple blinded split mouth clinical trial.

BACKGROUND: This is a triple-blinded, prospective split-mouth clinical trial. It is important to shed light on the effect of different apical preparation sizes regarding postoperative pain within the same patient with the same pulpal histological status. The aim is to compare and evaluate the severity of postoperative pain following apical enlargement with two different sizes after the IBF using the visual analogue scale. METHODS: Fifty "teeth" in 25 patients were assigned into two equal groups (25 per group) using E3 Azure rotary files; Group A was prepared two sizes greater than the Initial binding file (IBF) (the largest K file to bind at the actual working length) mesial canals, which were enlarged to 35#/0.04 and 40#/0.04 for the distal canals. Group B was prepared in three sizes larger than the IBF: 40#/0.04 for mesial canals and 45#/0.04 for the distal canals. On a modified VAS form, patients were questioned to indicate the degree of their pain and assisted in narrating their pain intensity during the following periods: 12, 24, and 72 h, and after a week. VAS data were non-parametric and analyzed using the signed-rank test for intergroup comparisons, Freidman's test, and the Nemenyi post hoc test for intragroup comparisons. The significance level was set at p < 0.05. RESULTS: showed that regardless of measurement time, enlargement of apical preparation was significantly associated with higher pain scores (p < 0.001). Within both groups, there was a significant reduction of measured pain score with time, with values measured after 12 and 24 h being significantly higher than values measured at other intervals (p < 0.001) and with values measured after three days being significantly higher than 1-week value (p < 0.001). CONCLUSION: The size of apical preparation had a significant effect on postoperative pain. TRIAL REGISTRATION NUMBER & DATE: NCT05847738, 08/05/2023.

Impact of Different Glidepath Techniques on the Overall Performance of WaveOne Gold in an Artificial S-Shape Canal.

OBJECTIVES: The article's aim is to test if rotary or reciprocating glide path influences the overall performance of WaveOne Gold in S-shaped canals. METHODS: Sixty endo training blocks with an S-shape curvature were divided into three groups based on the glide path method used: no glide path; glide path preparation with ProGlider; glide path preparation with WaveOne Gold Glider. All blocks were then shaped with WaveOne Gold Primary. The time for shaping, the incidence in reaching working length and the number of pecking motions were recorded. ANOVA with Turkey's test was used, and the p-value was set to 0.05. RESULTS: WaveOne Gold Primary reached working length faster in the control group when comparing total working times. No significant differences in the ability of the WaveOne Gold Primary to reach working length in all groups (p > 0.05). The mean number of pecking motions was higher in the control group compared to other groups. CONCLUSIONS: No significant differences in the time needed to achieve a glide path between Proglider and WaveOne Gold Glider. WaveOne Gold Primary can shape a double curved canal faster if a glide path is present but takes less time to reach length if it is the only file used. No difference in the ability to reach working length.

Evaluation of Minimally Invasive Preparation of Curved Mesial Canals of Mandibular Molars - An In Vitro Study.

INTRODUCTION: Curved mesial roots can be challenging for different stages of endodontic treatment. Preparation aims to enlarge, clean, and shape the root canal system, and hundreds of systems are available to carry it out. Aiming to maintain pericervical dentin, minimally invasive preparation was proposed, and with it, instruments with lower tapers emerged. This study aimed to evaluate the increase in canal volume, the centering ability of the instruments, and root canal transportation of two different rotary systems with lower tapers. METHODS: Eighteen curved mesial roots of extracted mandibular molars were scanned by micro-CT at 3 moments: initial and after the 2 stages of endodontic preparation. The canals were prepared using TruNatomy (TN) and ProDesign Logic 2 (PDL2) instruments up to sizes 25.04 and 26.04, respectively, and after 36.03 and 35.05, respectively. The data were analyzed using parametric and nonparametric tests with a significance level of 5%. RESULTS: TN and PDL2 systems showed no difference regarding the increase in the volume of the canals with the first instruments, but after preparation with a diameter size of 35 or 36, there was a difference (P < .01) between the systems in the cervical and middle thirds. CONCLUSION: Both systems shaped the mesial canals of mandibular molars while keeping low transportation and good centering ability in enlargements up to diameter size 35 or 36 with tapers of 3 or 5%.

Endodontic management of a four-canal mandibular second premolar; using an operative microscope: A case report.

Key Clinical Message: Due to the complexities and variations of the root canal system's anatomy, mandibular premolars are among the most difficult teeth for endodontic treatment. The lack of clinician knowledge ultimately leads to treatment failure. Abstract: Mandibular premolars are the most complicated teeth for endodontic treatment because of the variations in root canal anatomy. On the other hand, missing root canals can subsequently lead to failure of endodontic treatment, which causes the patient to become symptomatic. Therefore, the clinician's knowledge of the different types of root canal anatomy and the skill of using new equipment for proper root canal treatment improve the outcome. This study reported the successful endodontic treatment of a mandibular second premolar with four root canals by using an operative microscope.

The Effect of Lasers on the Healing of Periapical Lesion: A Systematic Review.

Introduction: Endodontic treatment of teeth with periapical lesions presents more clinical difficulty. Various lasers in several methods are used in endodontics, and most of them are utilized as an adjunctive protocol in order to reduce the bacterial load of the root canal system. Improved disinfection plays a crucial role in enhanced and accelerated healing of periapical lesions. This review aims to summarize studies assessing the effect of lasers on periapical lesion healing. Methods: PubMed/MEDLINE, Scopus, Embase, and Web of Science (ISI) online databases were searched, with no publication year or status restriction, for relevant articles on April 2023. Clinical studies evaluating the effect of laser application on the periapical lesion of patients using radiographic assessment were considered eligible for inclusion. Results: Eight studies were included after carefully screening the obtained articles, first by their title and abstract and then by their full texts. Diode (4), Er, Cr: YSGG (3), and Nd: YAG (1) lasers were used with output powers that varied from 0.75 to 2 watts. Photodynamic therapy was employed in two studies, and in other studies, the root canal system was directly irradiated. Irradiation of the root canal system was adjunctive to standard preparation in all studies. The healing of the teeth treated with lasers was not inferior to those conventionally treated. In all of the included studies, laser application outperformed the standard cleaning and shaping protocol; however, this improved or faster healing was not statistically significant in most studies. Conclusion: Lasers might expedite and improve the healing process of periapical lesions. Since lasers enhance the quality of cleaning of the root canal system, it is hard to point out the exact mechanism of it. Further investigations are needed to realize the effectiveness of this treatment modality and to discover the underlying biological concepts.

40-Year Outcome of Old-School, Non-Surgical Endodontic Treatment: Practice-Based Retrospective Evaluation.

(1) Background: Non-surgical endodontic treatment has been shown to be clinically successful; however, clinical long-term data are scarce. This practice-based retrospective clinical investigation evaluated endodontic outcomes over 40 years and identified relevant clinical co-factors. (2) Methods: Two experienced dental practitioners in two different private dental practices treated 174 patients with 245 teeth from 1969 to 1993. After root canal obturation, either a new direct restoration (amalgam, resin composite, or glass-ionomer cement) or the re-cementation of a pre-existing prosthetic restoration or renewal of prosthetic restoration followed. Metal posts (operator A) or metal screws (operator B) were inserted when coronal substance loss was significant. The primary outcome (i.e., tooth survival) was achieved when the endodontically treated tooth was, in situ, painless and had full function at the end of the observation period. A secondary outcome, the impact of different prognostic factors on survival rate, was evaluated. (3) Results: The overall mean survival was 56.1% of all treated teeth after 40 years of clinical service, resulting in an annual failure rate of 1.1%. Most investigated clinical co-factors (jaw, tooth position, intracanal dressings, post/screw placement, and gender) showed no significant influence on survival. (4) Conclusions: Even with materials and techniques from the 1970s and 1980s, successful root canal treatment was achievable. Except for post-endodontic restorations, most of the evaluated factors had no significant influence on the clinical long-term survival of root canal-treated teeth.

The effect of apical patency on postoperative pain following endodontic therapy: A systematic review and meta-analysis.

This systematic review and meta-analysis aimed to determine whether apical patency increases postoperative pain after endodontic therapy. This study explored the degree and incidence of postoperative pain during root canal therapy, as well as the number of required analgesic doses. We searched PubMed, Scopus, Embase, Web of Science, Cochrane Library, and gray literature from the date of database inception until May 2023. RevMan 5.4 software was used for data analysis. Twelve studies were considered eligible for meta-analysis. The mean pain scores on days 1 (mean difference [MD] = -1.69) and 2 (MD = -0.85) differed significantly between the apical patency and non-patency groups. The odds for pain after 24 h were significantly lower (OR 0.59) in the apical patency group than in the non-patency group. Furthermore, the mean number of required analgesic doses was not significantly different between the two groups. In conclusion, apical patency significantly alleviated postoperative pain (low-quality evidence) and reduced the incidence of pain (moderate evidence). However, high-quality randomized controlled trials are required to validate these findings.

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

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

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

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

Microscopic Evaluation of Dentinal Defects after Root Canal Preparation with Different Hand and Nickel-Titanium Files; An In Vitro Study.

Background: Effective endodontic instrumentation aims to remove microorganisms, debris, and tissue from the root canal while maintaining dentinal integrity. This study compares dentinal defect incidence following canal preparation with different hand files, nickel-titanium rotary files, and reciprocating files. Materials and Methods: Eighty single-rooted mandibular premolars with mature apices were collected. Four groups (n = 20) were established based on canal patency establishment, canal preparation technique, irrigation solution, and final irrigation. After root sectioning at 3 mm, 6 mm, and 9 mm from the apex, slices were examined under a stereomicroscope, and dentinal defects were recorded. A second examiner reviewed the images. Results: The results showed significant difference of P = 0.031 among Hand files vs. Rotary ProTaper files: In Hand files vs. Reciprocating WaveOne files significant difference was P = 0.048, and for rotary ProTaper files vs. Reciprocating WaveOne files: No significant difference (P = 0.643). Dentinal defect counts were similar at 3 mm, 6 mm, and 9 mm. Statistically significant variation was observed between hand files and rotary files, as well as hand files and reciprocating files. Conclusion: Both rotary and reciprocating files showed a statistically significant increase in dentinal defect incidence compared to hand files. However, clinical implications should be considered cautiously. Instrumentation technique selection should be based on clinical context, operator experience, and patient factors. Further clinical studies are needed for validation.

Compare the Centering Ability, Canal Transportation and Root Canal Area Increase of XP Endoshaper, Hyflex CM and K3 XF File System by using Cone Beam: An Original Research.

Objective: Using cone beam computed tomography (CBCT), this study compared three rotary file systems-XP Endoshaper, Hyflex CM, and K3 XF-for centering, canal transportation, and root canal area growth. Materials and Methods: The rotating file system randomly separated 60 removed human mandibular molars into three groups (n = 20). Manufacturer-recommended root canal instrumentation was done. Specialized software examined pre- and post-instrumentation CBCT scans. Centering ability was measured by canal transportation and root canal area expansion at different levels from the apex. Results: The Hyflex CM file system had the best centering and the least canal transit at all levels (P < 0.05). XP Endoshaper increased the root canal area the most (P < 0.05). The K3 XF file system had average centering and canal transfer results. Conclusion: The Hyflex CM system centered well, whereas the XP Endoshaper system increased the root canal area the most. The clinical context and therapeutic goals should determine the rotating file system.

Formation of dentinal microcracks after root canal preparation with four kinds of mechanical nickel-titanium files.

OBJECTIVES: This study aimed to compare the differences among four kinds of mechanical Ni-Ti files including T-Flex, Reciproc Blue (RB), ProTaper Gold (PTG), and ProTaper Universal (PTU) in dentinal microcrack generation after root canal preparation in vitro by using micro-computed tomography (micro-CT) analysis. METHODS: A total of 32 freshly extracted double-root-canal premolars with an angle not exceeding 10° were selected and established as root canal preparation models in vitro. Then, the specimens were randomly assigned to four experimental groups (n=8) according to the different Ni-Ti systems used for root canal preparation: group T-Flex, group RB, group PTG, and group PTU. The voxel size of the micro-CT was set at 17.18 µm. Pre- and post-operative cross-sectional images of roots (n=56 940) were scanned and analyzed to identify the presence of dentinal microcracks. The results of each group were expressed by the quantity and percentage of sectional images with microcracks. McNemar test was used to determine whether a significant difference existed in the existence of dentinal microcracks before and after instrumentation. The level of significance was set at P<0.05. RESULTS: Overall, 11.04% of the images presented dentinal defects (n=6 288). Dentinal microcracks were observed in 9.82%, 10.79%, 12.27%, and 11.25% of the post-instrumentation images from groups T-Flex, RB, PTG, and PTU, respectively. However, all these dentinal microcracks were already present in the corresponding pre-operative images. No new microcrack of premolars were generated after the root canal preparation utilizing the aforementioned systems. CONCLUSIONS: Denti-nal microcracks already existed in advance in extracted teeth before root canal preparation. Root canal preparation using the T-Flex, RB, PTG, and PTU systems did not induce the formation of new dentinal microcracks on the straight root canals of premolars.

Evaluation of apical transportation and centering ability of three single-file systems in severely curved canals using micro-computed tomography.

Background: This study aimed to compare the apical transportation and centering ability of One Curve, HyFlex EDM, and EdgeFile X1 in curved mesiobuccal and mesiolingual canals of mandibular first molars. Materials and Methods: In this in vitro experimental study, 60 mesiobuccal and mesiolingual canals of the mandibular first molars with a minimum length of 19 mm and 25°-40° curvature were randomly divided into three groups (n = 20) for root canal preparation with One Curve, HyFlex EDM, and EdgeFile X1. After access cavity preparation and confirming the glide path, the baseline micro-computed tomography (micro-CT) scans were obtained, and the root canals were instrumented with the respective systems according to the manufacturers' instructions. Apical transportation and centering ability were assessed at 1, 3, 5, and 7 mm from the apex by comparing pre- and postinstrumentation micro-CT scans. One-way ANOVA, independent t-test, and Duncan's post hoc test were used to statistically compare the groups, and data were analyzed by SPSS version 24 (alpha = 0.05). Results: The three groups were not significantly different regarding apical transportation at 5 and 7 mm from the apex (P > 0.05). At 1 mm level, One Curve caused significantly lower apical transportation; while, at 3 mm level, HyFlex EDM resulted in significantly higher apical transportation (P < 0.05). No significant difference was noted in the centering ability of the three groups at 1, 3, and 5 mm from the apex (P > 0.05). At 7 mm level, EdgeFile X1 showed significantly lower centering ability (P < 0.05). Conclusion: One Curve caused lower canal transportation in the apical third compared with EdgeFile and HyFlex EDM, but no significant difference was noted among the three in the coronal third of the roots.

In Vitro Evaluation of the Dynamic Cyclic Fatigue Resistance of a New TruNatomy Glider File after Different Cycles of Use.

INTRODUCTION: Determination of the glide path is recommended before using rotary instruments. This study aimed to evaluate the dynamic cyclic fatigue resistance of new and used glider rotary instruments in up to 6 root canals. METHODS: Seventy-two TruNatomy Glider files were used for the preparation of root canals of extracted lower molars, which were then submitted to the dynamic cyclic fatigue test carried out in a curved metallic artificial canal. The instruments were divided into 4 groups (n = 18): Control group, new instruments without any use in the root canal; Group 2U, instruments used in 2 mesial canals; Group 4U, instruments used in 4 mesial canals; Group 6U, instruments used in 6 mesial canals. The time to failure (TF) of the instrument was recorded, and the number of cycles to failure (NCF) was calculated. The data were submitted to 1-way analysis of variance and to the Games-Howell test for multiple comparisons, adopting a significance level of 5%. RESULTS: TF and NCF were significantly affected by the number of file uses. The Games-Howell test revealed that TF and NCF were significantly greater in the control group than in Group 4U. In Group 2U, TF and NCF were intermediate and not significantly different from the control group. Group 6U had significantly lower TF and NCF than all other groups. CONCLUSION: The TruNatomy Glider can be used as a glide path for up to 2 mesial canals of mandibular molars, whereas its use on 4 or 6 root canals is not suggested.

How Does Intentional Apical Foraminal Enlargement Affect the Foramen and Root Canal Morphology?

INTRODUCTION: This study assessed the effect of intentional foraminal enlargement on the foramen and the apical root canal morphology. METHOD: Sixty mesial roots of mandibular molars were scanned by micro-computed tomography. Their apical foramina were photographed with a stereomicroscope before and after preparation. Three groups were formed (n = 20) according to the working length (WL). G-1: foramen - 1 mm; G0: foramen; and G+1: foramen + 1 mm. Each group originated 2 subgroups (n = 10): G-1: Buchanan's patency (size 10 K-type file) and foraminal debridement (sizes 20, 25 and 30 K-type files); G0 and G+1: rotary foraminal enlargement (ProDesign S size 25/.08) or reciprocating foraminal enlargement (R25). The area, perimeter, transportation, and noninstrumented walls of the foramen were evaluated. The root canal transportation and the centering index of preparation at 1, 3 and 5 mm from the foramen were also assessed. Data were compared statistically (α = 5%). RESULTS: The instruments used at the foramen and 1 mm beyond promoted foraminal enlargement and transportation. Regarding NIW, there was no difference between mechanized foraminal enlargements performed at the foramen or 1 mm beyond, similar to the manual foraminal debridement group (P > .05). There was no difference in transportation and centralization at 1-, 3-, and 5-mm apical levels, regardless of the instrumentation systems. CONCLUSION: Mechanical preparation at the foramen, or 1 mm beyond, resulted in foraminal enlargement, transportation and were not able to touch all root canal walls that delimit the foramen.