Influence of bioceramic intracanal medication on the bond strength of bioceramic root canal sealer.

To investigate the influence of the remaining volume of a new intracanal medication based on bioceramic compounds on the bond strength (BS) and formation of an adhesive interface between calcium silicate-based and epoxy resin-based root canal sealers. For this purpose, the specimens were distributed according to the intracanal medication (n = 26): Bio-C Temp (BCT) and Ultracal XS (UXS). The roots were scanned in microCT, and after 7 days, the medication was removed. Then a new scan was performed to evaluate the volume of medication remaining. Subsequently, 40 specimens were redistributed into 2 subgroups (n = 10) and filled according to the sealer used: AH Plus (AHP) and Bio-C Sealer (BCS), to assess the bond strength by using the push-out test, and the adhesive interface by confocal laser fluorescence microscopy (CLSM) and scanning electron microscopy (SEM). The t test showed a smaller remainder of BCT (1.77 ± 0.86) compared with UXS (10.47 ± 5.78), irrespective of the root third evaluated. The BS showed that teeth with BCT + BCS had higher bond strength values (3.70 ± 1.22) when compared to the other groups: BCT + AHP (2.15 ± 1.07), UXS + BCS (3.18 ± 1.09) and UXS + AHP (2.11 ± 1.02) (p<0.001). The cervical third had higher BS when compared with the middle and apical thirds (p < 0.001), and higher number of adhesive failures. The adhesive interface in SEM and CLSM images showed better adaptation for the association between BCT + BCS. Intracanal medication and silicate-based endodontic sealer appeared to interact chemically by forming a biomineralizing layer, allowing for an increase in the bond strength and forming an adhesive interface between the materials, with no or less gap formation.

3D Surface Scanning-A Novel Protocol to Characterize Virtual Nickel-Titanium Endodontic Instruments.

The nickel-titanium (NiTi) instruments' geometry plays an important role in their performance and behavior. The present assessment intends to validate and test the applicability of a 3D surface scanning method using a high-resolution laboratory-based optical scanner to create reliable virtual models of NiTi instruments. Sixteen instruments were scanned using a 12-megapixel optical 3D scanner, and methodological validation was performed by comparing quantitative and qualitative measurements of specific dimensions and identifying some geometric features of the 3D models with images obtained through scanning electron microscopy. Additionally, the reproducibility of the method was assessed by calculating 2D and 3D parameters of three different instruments twice. The quality of the 3D models created by two different optical scanners and a micro-CT device was compared. The 3D surface scanning method using the high-resolution laboratory-based optical scanner allowed for the creation of reliable and precise virtual models of different NiTi instruments with discrepancies varying from 0.0002 to 0.0182 mm. The reproducibility of measurements performed with this method was high, and the acquired virtual models were adequate for use in in silico experiments, as well as for commercial or educational purposes. The quality of the 3D model obtained using the high-resolution optical scanner was superior to that acquired by micro-CT technology. The ability to superimpose virtual models of scanned instruments and apply them in Finite Element Analysis and educational purposes was also demonstrated.

Clinical Accuracy and Precision of 3 Multifrequency Electronic Apex Locators Assessed through Micro-Computed Tomographic Imaging.

INTRODUCTION: This study aimed to compare the in vivo accuracy and precision of 3 electronic apex locators (EALs) in determining the position of the major foramen using micro-computed tomographic (micro-CT) technology. METHODS: After access preparation of 23 necrotic or vital teeth from 5 patients, canals were negotiated, and hand files were used to determine the position of the foramen with 3 EALs: Propex Pixi (Dentsply Maillefer, Ballaigues, Switzerland), Woodpex III (Woodpecker Medical Instrument Co, Guilin, China), and Root ZX II (J Morita, Tokyo, Japan). After fixing the silicon stop to the file, teeth were extracted and scanned in a micro-CT device with and without the instrument inserted into the canal. Data sets were coregistered, and the accuracy and precision of the EALs were determined at a tolerance level of ±0.5 mm by measuring the distance from the tip of the instruments to a tangential line crossing the margins of the foramen. Statistical comparisons were performed using Friedman with post hoc related samples sign and Spearman tests (α = 5%). RESULTS: A significant difference was detected comparing the accuracy of Root ZX II (100%), Woodpex III (86.96%), and Propex Pixi (52.17%) (P < .05). There was a lack of significance in the relationship between the pulp status and the accuracy of the tested EALs (P > .05). Propex Pixi was significantly less precise than Root ZX II (P < .05), whereas no difference was found between Woodpex III and Root ZX II or Propex Pixi (P > .05). CONCLUSIONS: EALs presented similar precision, but Woodpex III and Root ZX II showed better accuracy to determine the position of the apical major foramen than Propex Pixi.

Taper 0.06 Versus Taper 0.04: The Impact on the Danger Zone.

INTRODUCTION: This study aimed to evaluate the effects of root canal enlargement on the danger zone (DZ) of mandibular molars. METHODS: Thirty mesial roots of mandibular first molars were scanned in micro-computed tomography (S1). Canals were sequentially enlarged with rotary instruments up to sizes 30/0.04 (S2) and 30/0.06 (S3). The dentin thickness was measured at 0.1-mm intervals after each preparation step (n = 2964 slices). Root level and position of the DZ were also recorded. Data were compared using analysis of variance with Bonferroni pairwise comparison, Cochran's Q method, and Pearson's test (α = 5%). RESULTS: Comparing the specimens before (S1) and after (S2 and S3) preparations showed a significant reduction in the thickness of the DZ (P < .05), as well as between S2 and S3 steps (P < .05). At S1, the DZ was mostly located in the middle third of the root, but after preparation, it shifted toward the coronal direction (P < .05). Both S2 (P = .004, r = 0.508) and S3 (P = .004, r = 0.506) preparation steps showed a positive correlation between canal length and the root level of the DZ. At S1, the DZ was positioned toward the distal and mesial in 73.4% (n = 22) and 26.6% (n = 8) of the specimens, respectively. After S3, the number of specimens with DZ positioned toward the mesial aspect of the root significantly reduced to 3.3% (n = 1), whereas none of the specimens with DZ positioned toward the distal changed its position after root canal enlargements (P > .05). CONCLUSION: Overall, the enlargement of mesial canals of mandibular first molars with final instruments sizes 30/0.04 and 30/0.06 affected the thickness, root level, and position of the DZ.

Influence of bioceramic intracanal medication on the bond strength of bioceramic root canal sealer

Abstract To investigate the influence of the remaining volume of a new intracanal medication based on bioceramic compounds on the bond strength (BS) and formation of an adhesive interface between calcium silicate-based and epoxy resin-based root canal sealers. For this purpose, the specimens were distributed according to the intracanal medication (n = 26): Bio-C Temp (BCT) and Ultracal XS (UXS). The roots were scanned in microCT, and after 7 days, the medication was removed. Then a new scan was performed to evaluate the volume of medication remaining. Subsequently, 40 specimens were redistributed into 2 subgroups (n = 10) and filled according to the sealer used: AH Plus (AHP) and Bio-C Sealer (BCS), to assess the bond strength by using the push-out test, and the adhesive interface by confocal laser fluorescence microscopy (CLSM) and scanning electron microscopy (SEM). The t test showed a smaller remainder of BCT (1.77 ± 0.86) compared with UXS (10.47 ± 5.78), irrespective of the root third evaluated. The BS showed that teeth with BCT + BCS had higher bond strength values (3.70 ± 1.22) when compared to the other groups: BCT + AHP (2.15 ± 1.07), UXS + BCS (3.18 ± 1.09) and UXS + AHP (2.11 ± 1.02) (p<0.001). The cervical third had higher BS when compared with the middle and apical thirds (p < 0.001), and higher number of adhesive failures. The adhesive interface in SEM and CLSM images showed better adaptation for the association between BCT + BCS. Intracanal medication and silicate-based endodontic sealer appeared to interact chemically by forming a biomineralizing layer, allowing for an increase in the bond strength and forming an adhesive interface between the materials, with no or less gap formation.

Micro-CT Study of the In Vivo Accuracy of a Wireless Electronic Apex Locator.

INTRODUCTION: This study aimed to compare the in vivo accuracy of Wirele-X and RootZX II electronic apex locators (EALs) in determining the position of the major foramen using micro-computed tomography (micro-CT) as the analytical tool. METHODS: Eleven vital teeth planned for extraction from 5 patients were used. After conventional access cavity preparation, root canals were flared and negotiated up to the apical third with sizes 08 and 10 K-files followed by irrigation with 2.5% NaOCl. K-type files were used to determine the working length of the selected canals using Root ZX II and Wirele-X apex locators until their numeric displays read "0.0." After fixing the silicon stop to the file, teeth were extracted and imaged in a micro-CT device using a double-scan protocol. Image stacks, with and without the file in the root canal, were then co-registered and the measurement error calculated as the absolute difference between the tip of the file and the major foramen. Positive and negative values were recorded when the file tip was detected beyond or short of the major foramen, respectively. Accuracy was determined on stable measurements within ± 0.5 mm when the file tip did not extend beyond the major foramen. The χ2 test was applied to compare the ability of the EALs to detect the position of the major foramen, and the t test for dependent variables was used to verify differences in the 2 measurements obtained in each tooth. Significance level was set at 5%. RESULTS: Within a tolerance level of ± 0.5 mm, no significant differences were observed between the tested EALs regarding the absolute distance values (P = .82) or in their ability to detect the position of the major foramen (χ2 = 0.2588; P = .6109). The accuracy of the Root ZX II and the Wirele-X apex locators within ± 0.5 mm were 81.8% and 90.9%, respectively. CONCLUSIONS: Root ZX II and Wirele-X performed similarly regarding the in vivo detection of the major foramen. Using strict criteria, the accuracy of the Root ZX II and the Wirele-X apex locators were 81.8% and 90.9%, respectively.

Micro-CT assessment of gap-containing areas along the gutta-percha-sealer interface in oval-shaped canals.

AIM: To assess the interfacial adaptation (gap-containing areas) of two root canal sealers (EndoSequence BC Sealer and AH Plus) to a conventional gutta-percha (GP) cone (GP-sealer interface) in oval-shaped canals filled using the single cone technique. METHODOLOGY: Sixteen teeth with oval-shaped canals were selected, scanned in a micro-computed tomographic device, and pair-matched according to the volume, aspect ratio and configuration of root canals. Root canals were then sequentially prepared with WaveOne Gold Primary and Large instruments, followed by filling with WaveOne Large GP points associated with either the premixed calcium-silicate EndoSequence BC Sealer or the epoxy resin-based AH Plus sealer (n = 8 per group) using the single cone technique. After 7 days stored in phosphate-buffered saline solution at 37°C, the specimens were rescanned and the reconstructed images segmented in order to differentiate the filling materials (sealer and GP cone) to the dentine. A total of 453 cross-sectional slices were assessed and categorized according to the presence or absence of gaps at the GP-sealer interface. Mann-Whitney U-test verified the differences between groups and were considered significant at alpha = 5%. RESULTS: Gaps were non-homogenously distributed in two-dimensional axial cross-section images and none of the specimens showed completely gap-free areas along the entire GP-sealer interface. Root canals filled with EndoSequence BC Sealer and AH Plus displayed 171 (37.75%) and 136 (30.02%) slices with gaps in the GP-sealer interface and these frequencies were statistically significant (p = .000). CONCLUSIONS: Although none of the specimens had a gap-free area along the entire GP-sealer interface, oval canals filled with AH Plus showed less gaps than the ones filled with EndoSequence BC Sealer.

A critical analysis of research methods and experimental models to study root canal fillings.

Canal filling materials and techniques have been one of the most studied topics in Endodontics. A simple search using the mesh term "root canal filling" in PubMed revealed more than 11 000 articles, an impressive number that is much higher than "root canal disinfection" (5544 articles) or even the popular "root canal preparation" (8527 articles). The overriding importance attributed to root filling procedures is not merely intuitive. It derived from the appealing relevance given by the appearance of the white lines in common radiographs grounded on retrospective clinical data that had identified the quality of a root filling as one of the major causes of treatment failure (lack of healing). Since the publication of the Washington study, impressive efforts have been made for the release of new materials and techniques, as well as, for the development of a plethora of laboratory methods to assess the quality of root filling procedures. This narrative review aims to address and discuss the most relevant laboratory methods to assess the root canal filling. As filling quality improvements have not translated into higher success rates, as reported in longitudinal clinical studies, more than to deliver a simple methodology-based review, this paper aims to present an in-depth critical view on the assessment of laboratory methods used to study the filling materials and techniques. Recent data indicate that the long-term dimensional stability/degradation over time of endodontic sealers plays a central role in the treatment outcome. In this context, laboratory methods should be developed focusing on predicting, at least to some degree, the long-term clinical behaviour of root canal fillings, rather than simply ranking different materials or techniques.

Present status and future directions - Minimal endodontic access cavities.

In the last decades, the move of medicine towards minimally invasive treatments is notorious and scientifically grounded. As dentistry naturally follows in its footsteps, minimal access preparation have also becume a trend topic in the endodontic field. This procedure aims to maximize preservation of dentine tissue backed up by the idea that this is an effective way to reduce the incidence of post-treatment tooth fracture. However, with the assessment of the body of evidence on this topic, it is possible to observe some key points (a) the demand for nomenclature standardization, (b) the requirement of specific tools such as ultra-flexible instruments, visual magnification, superior illumination, and three-dimensional imaging technology, (c) minimally invasive treatment does not seem to affect orifice location and mechanical preparation when using adequate armamentarium, but it (d) may impair adequate canal cleaning, disinfection and filling procedures, and also (e) it displays contradictory results regarding the ability to increase the tooth strengthen compared to the traditional access cavity. In spite of that, it is undeniable that methodological flaws of some benchtop studies using extracted teeth may be responsible for the conflicting data, thus triggering the need for more sophisticated devices/facilities and specifically designed research in an attempt to make clear the role of the access size/design on long-term teeth survival. Moreover, it is inevitable that a clinical approach such as minimal endodontic access cavities that demands complex tools and skilled and experienced operators bring to the fore doubts on its educational impact mainly when confronted with the conflicting scientific output, ultimately provoking a cost-benefit analysis of its implementation as a routine technique. In addition, this review discusses the ongoing scientific and clinical status of minimally invasive access cavities aiming to input an in-depth and unbiased view over the rationale behind them, uncovering not only the related conceptual and scientific flaws but also outlining future directions for research and clinical practices. The conclusions attempt to skip from passionate disputes highlighting the current body of evidence as weak and incomplete to guide decision making, demanding the development of a close-to-in situ laboratory model or a large and well-controlled clinical trial to solve this matter.

Comparison of five rotary systems regarding design, metallurgy, mechanical performance, and canal preparation-a multimethod research.

OBJECTIVES: To compare the design, metallurgy, mechanical performance, and canal preparation of 5 rotary systems. MATERIAL AND METHODS: A total of 735 25-mm NiTi instruments (sizes 0.17[0.18]/.02v, 0.20/.04v, 0.20/.07v, 0.25/.08v, 0.30/.09v) from ProTaper Gold, ProTaper Universal, Premium Taper Gold, Go-Taper Flex, and U-File systems were compared regarding overall geometry and surface finishing (stereomicroscopy and scanning electron microscopy), nickel and titanium ratio (energy-dispersive spectroscopy), phase transformation temperatures (differential scanning calorimetry), mechanical performance (torsional and bending tests), and unprepared canal surface (micro-CT). One-way ANOVA and Mood's median tests were used for statistical comparisons with a significance level set at 5%. RESULTS: Stereomicroscopic analysis showed more spirals and high helical angles in the Premium Taper Gold system. All sets of instruments had symmetrical spirals, no radial lands, no major defects, and an almost equiatomic ratio between nickel and titanium elements, while differences were observed in their tips' geometry and surface finishing. At room temperature (20 °C), DSC test revealed martensitic characteristics for ProTaper Gold and Go-Taper Flex, and mixed austenite plus R-phase for the Premium Taper Gold, while ProTaper Universal and U-Files had full austenitic characteristics. Overall, larger instruments had higher torque resistance and bending load values than smaller ones, while a lack of consistency and mixed values were observed in the angle of rotation. The 0.25/.08v and 0.30/.09v instruments of ProTaper Universal and U-File had the highest maximum torques, the lowest angles of rotation, and the highest bending loads than other tested systems (P < .05). No significant difference was noted regarding the untouched root canal walls after preparation with the tested systems (P > .05). CONCLUSIONS: Although differences observed in the overall geometry and phase transformation temperatures have influenced the results of mechanical tests, unprepared canal surface areas were equivalent among systems. CLINICAL RELEVANCE: Root canal preparation systems with similar geometries might present different mechanical behaviors but equivalent shaping ability.

Methodological proposal for evaluation of adhesion of root canal sealers to gutta-percha.

AIM: To compare the bond strength of an epoxy resin-based sealer and two calcium silicate-based sealers (CSS) to gutta-percha discs using a new method. METHODOLOGY: Round discs of gutta-percha (n = 60), measuring 10 mm in diameter and 2 mm in thickness, were placed on a glass plate and a drop of each sealer (AH Plus, EndoSequence BC Sealer and EndoSeal MTA) was placed on their surface. Another identical disc was placed onto the first one and a standardized weight (0.0981 N) applied over them using a specially developed apparatus. Ten samples prepared for each sealer were submitted to a microshear bond strength test accomplished by a specially designed set-up coupled to a universal testing machine. The Kruskal-Wallis test followed by a post hoc procedure was used to compare groups considering the preliminary analysis of the raw data had indicated the nonadherence to a Gaussian distribution (Shapiro-Wilk, p < .05). Alpha error was set at 5%. RESULTS: Overall, no premature failure occurred. All sealers had some degree of adhesiveness to gutta-percha discs but with a significant difference amongst them (Kruskal-Wallis, p = .019). The epoxy resin-based sealer (AH Plus) had significantly higher median shear bond strength values (1.43 MPa; 1.40-1.83) compared to EndoSeal MTA (0.53 MPa; 0.46-0.73) (p = .021) and EndoSequence BC Sealer (0.45 MPa; 0.34-0.46) (p = .023), whilst the lowest median value was observed with EndoSequence BC Sealer (0.45 MPa; 0.34-0.46) (p < .05). CONCLUSIONS: CSS sealers had weaker bonding to gutta-percha when compared to the epoxy resin-based AH Plus sealer. The proposed methodology is an innovative and reproducible method for testing the bond strength of root canal sealers to gutta-percha.

Glide Path with Reciprocating Driven Pathfinding Instrument: Performance and Fracture Rate.

INTRODUCTION: This study assessed the number of mesial and distal canals of mandibular molars in which the R-Pilot pathfinding reciprocating instrument reached the working length (WL) during macro glide path procedure. Fracture and deformation rates were also evaluated. METHODS: One hundred fifty-six root canals of 52 teeth were scouted to the length of the apical foramen. Then the R-Pilot instrument was positioned at the canal orifice and activated. The instrument was moved by using a pecking motion and light apical pressure. This procedure was repeated in an attempt to reach the WL. The type of fracture and/or instrument deformation was assessed by scanning electron microscopy, whereas the roots with fractured instruments were scanned through micro-computed tomography. The percentage frequency distribution of fractures, deformations, and root canals in which the R-Pilot reached the WL were recorded and statistically compared by using the Pearson's χ2 test with α = 5%. RESULTS: R-Pilot instruments reached the WL in 139 root canals (89.10%), and χ2 test showed a significant difference between the observed frequencies and the expected frequencies (χ2 = 95.41, P = .000). The observed frequencies of fractures (2.56%) and deformations (1.92%) were also significantly lower than the expected (fracture: χ2 = 140.41, P = .000; deformation: χ2 = 144.23, P = .000). Fractures occurred mostly at the apical and curved parts of the root canals. CONCLUSIONS: R-Pilot reached the WL in 89.10% of the root canals of mandibular molars with fracture and deformation rates of 2.56% and 1.92%, respectively.

Root groove depth and inter-orifice canal distance as anatomical predictive factors for danger zone in the mesial root of mandibular first molars.

OBJECTIVES: This study evaluated the danger zone (DZ) in mesial roots of mandibular molars and the correlation between anatomical references of the DZ and some anatomical landmarks including tooth/root length, depth of mesial and distal grooves, and inter-canal orifices distance. MATERIAL AND METHODS: Twenty-eight mesial roots of mandibular molars with 2 independent canals were scanned and divided into 2 groups according to root length. The anatomical landmarks were correlated (Pearson or Spearman coefficients) with root level, thickness, and position of the DZ and also compared (independent samples t or Mann-Whitney tests) between the 2 groups at α = 5%. RESULTS: No statistical difference was observed between groups regarding DZ parameters and depth of mesial and distal grooves (P > 0.05). Orifice distance in group 2 (4.49 ± 0.75 mm) was significantly greater than group 1 (3.76 ± 0.89 mm) (P < 0.05). Significant correlations (P < 0.05) were found between (i) DZ level and root/tooth length (r = 0.54 and 0.49, respectively), (ii) DZ thickness and distal groove depth (r = - 0.45), and orifice distance (r = 0.38), and (iii) DZ position and depth of mesial (r = 0.39) and distal (r = 0.40) grooves. Other variables such as root length and distal groove depth (r = 0.28), and orifice distance and mesial groove depth (r = 0.36) were also correlated (P < 0.05). CONCLUSIONS: The length of tooth/root, the distance of canal orifices, and the depth of mesial/distal grooves of mesial roots of mandibular molars might be predictive factors for the root level, position, and thickness of the DZ. CLINICAL RELEVANCE: The length, distance of mesial canal orifices, and the depth of mesial and distal grooves of the mesial roots of mandibular molars might be moderate predictive factors for the root level, position, and thickness of the DZ.

3-dimensional Ability Assessment in Removing Root Filling Material from Pair-matched Oval-shaped Canals Using Thermal-treated Instruments.

INTRODUCTION: The purpose of this study was to evaluate the ability of the XP-endo Shaper instrument (FKG Dentaire, La Chaux-de-Fonds, Switzerland) during the removal of root fillings from oval-shaped canals. M-Wire Reciproc and Reciproc Blue systems (VDW, Munich, Germany) were used as reference instruments for comparison, and micro-computed technology was used as an analytical tool. METHODS: Thirty mandibular incisors with oval-shaped canals were matched based on similar anatomic features of the canal (eg, volume, aspect ratio, and 3-dimensional configuration) after scanning procedures. The canals were prepared with M-Wire Reciproc R25 instruments and filled with gutta-percha and AH Plus sealer (Dentsply DeTrey, Konstanz, Germany) using the continuous wave of condensation technique. Then, the sample was allocated into 3 experimental groups (n = 10) according to the retreatment protocol used: M-Wire Reciproc, Reciproc Blue, and XP-endo Shaper. M-Wire Reciproc R25, Reciproc Blue R25, and XP-endo Shaper instruments were used to remove the root fillings. Apical enlargement was performed with M-Wire Reciproc R40, Reciproc Blue R40, and BioRace BR5 (FKG Dentaire) instruments. Each sample was scanned after each endodontic procedure. The volume of remaining root filling material was quantified before and after apical enlargement. The percentage volumes of root filling reduction in relation to the instrumented canals at both time points (before and after apical enlargement) were calculated and considered for statistical analysis. Data were analyzed statistically with a significance level of 5%. RESULTS: Reciproc Blue presented significantly lower removal of filling material compared with the XP-endo Shaper (Tukey test, P < .05). No difference was detected either between M-Wire Reciproc and Reciproc Blue (Tukey test, P > .05) or M-Wire Reciproc and XP-endo Shaper (Tukey, P > .05). The increase of apical enlargement significantly improved the removal of root fillings from the root canals (P < .05); this effect was similar for all systems (time point × file system, P > .05). CONCLUSIONS: The XP-endo Shaper instrument showed a higher percentage of root filling removal, but no differences were observed comparing M-Wire Reciproc with the XP-endo Shaper or Reciproc Blue. The increase of apical enlargement improved the removal of root fillings in all groups. None of them was able to render root canals completely free from root fillings.

Performance of Reciproc Blue R25 Instruments in Shaping the Canal Space without Glide Path.

INTRODUCTION: This study assessed the frequency in which Reciproc Blue R25 instruments (VDW, Munich, Germany) reached the full working length (WL) of mandibular molar canals without a glide path. The influence of the type of electric motor (ie, conventional corded or cordless) on the instrument's performance was also assessed. METHODS: One hundred mandibular molars with slight to moderate root canals were selected and randomly assigned into 1 of 2 experimental groups according to the type of electric motor used: conventional corded (VDW Silver, VDW) or cordless motors (VDW.CONNECT Drive, VDW). Therefore, 50 molars and 154 root canals were selected for each motor. Reciproc Blue R25 instruments were used until reaching two thirds of the estimated WL. Then, a size 10 K-file was passively inserted to determine the full WL. No active instrumentation movement was performed with a size 10 K-file. Independently, whether a size 10 K-file reached the apex or not, Reciproc Blue R25 instruments were used to complete canal preparation. When the Reciproc Blue R25 instrument was able to reach the full WL, the case was classified as "reaching the full working length" (RFWL). If the instrument was not able to reach the full WL, the case was classified as "not reaching the full working length" (NRFWL). The chi-square test of goodness of fit was used to verify whether the observed frequencies of RFWL and NRFWL adhered to the expected ones. A 5% cutoff level of significance was considered for statistical assumptions. RESULTS: Reciproc Blue R25 instruments were able to reach the full WL in 304 root canals (98.70%). The chi-square test revealed the observed frequencies of RFWL and NRFWL to be significantly different from the expected frequencies (χ2 = 292,208, P = .000). The frequency of RFWL and NRFWL was exactly the same for both types of electric motors. No instrument fractured, and a single file deformed. In 50 of 308 root canals, a size 10 K-file was unable to passively reach the full WL. From these 50 canals, Reciproc Blue R25 instruments were able to reach the full WL in 47 of them. CONCLUSIONS: Reciproc Blue R25 instruments were able to reach the full WL in a high frequency of cases. The type of electric motor used did not interfere in the frequency of RFWL cases. No instrument fractured, and a single file deformed.