Present Status and Future Directions - Canal Shaping

Root Canal Instrumentation: Current Trends and Future Perspectives

The evolution of root canal instrumentation techniques has significantly impacted the field of endodontics, enhancing both the efficiency and outcomes of treatments. This review outlines the transition from manual to mechanical and rotary instruments, highlighting the role of nickel-titanium (NiTi) alloys and smart technologies in advancing procedural precision and reducing patient discomfort. Key historical developments and technological innovations, such as digital imaging and navigation systems, are explored for their contributions to improved clinical outcomes and patient satisfaction. Additionally, the review addresses the challenges presented by the complex anatomy of the root canal system and the advent of current instrumentation techniques. The potential of emerging trends, including artificial intelligence and advances in materials science, is discussed in the context of future endodontic practices. Despite the progress, challenges related to using advanced instrumentation methods, ethical considerations, and the cost factor of new technologies persist. The present review underscores the ongoing need for research and development to further refine root canal instrumentation techniques, ensuring that advancements in endodontic care remain patient-centered and accessible.

Syringe irrigation in confluent canals: A sequential computational fluid dynamics assessment

This study aims to assess the influence of root canal preparation, irrigation needle design and its placement depth in the irrigation flow of confluent canals during syringe irrigation. A mandibular molar presenting two confluent canals in its mesial root was sequentially prepared and scanned by micro-computed tomography after mechanical preparation up to ProTaper Next system sizes X2 (25/.06v), X3 (30/.07v) and X4 (40/.06v). In each of the root canal preparation models, a side-vented and an open-ended needle at 5, 3 and 2 mm from the working length were included, and irrigation flow was assessed by a validated computational fluid dynamics model. The results revealed that the irrigant flowed out of the confluent canals mainly through the canal that did not have the needle. Apical penetration and renewal of the irrigant were most efficiently achieved with the use of a 30G open-ended needle and a 30/.07v preparation.

Expert consensus on irrigation and intracanal medication in root canal therapy

Chemical cleaning and disinfection are crucial steps for eliminating infection in root canal treatment. However, irrigant selection or irrigation procedures are far from clear. The vapor lock effect in the apical region has yet to be solved, impeding irrigation efficacy and resulting in residual infections and compromised treatment outcomes. Additionally, ambiguous clinical indications for root canal medication and non-standardized dressing protocols must be clarified. Inappropriate intracanal medication may present side effects and jeopardize the therapeutic outcomes. Indeed, clinicians have been aware of these concerns for years. Based on the current evidence of studies, this article reviews the properties of various irrigants and intracanal medicaments and elucidates their effectiveness and interactions. The evolution of different kinetic irrigation methods, their effects, limitations, the paradigm shift, current indications, and effective operational procedures regarding intracanal medication are also discussed. This expert consensus aims to establish the clinical operation guidelines for root canal irrigation and a position statement on intracanal medication, thus facilitating a better understanding of infection control, standardizing clinical practice, and ultimately improving the success of endodontic therapy.

Cleaning and disinfection of the root canal system provided by four active supplementary irrigation methods

This in vitro study evaluated the bacterial reduction provided by the EndoActivator (EA), Easy Clean (EC), passive ultrasonic irrigation (PUI), and XP-Endo Finisher. Eight-four mesial roots of mandibular first molars were instrumented, inoculated with Enterococcus faecalis, and divided into four groups (n. 20). Bacterial reduction in the main canals and dentinal tubules were respectively determined by MTT assays and Live/Dead BackLight technique through confocal laser scanning microscopy (CLSM) at 50, 100, and 150 µm in-depth (n. 10 per group). Statistical analyses were conducted following a significance level of 95% (P < 0.05). A significant statistical difference was just identified between XPF and EC in the main canals. In the dentinal tubules from the main root canals, at 100 and 150 µm in-depths, significant statistical differences were only observed between XPF and EC (P = 0.027) for the former and between XPF and EC (P = 0.011) and XPF and PUI (P = 0.021) for the latter. In the dentinal tubules from the isthmus, at 100 µm in-depth, statistically relevant differences did occur between XPF and EC (P = 0.038) and EC and EA (P = 0.029). At 150 µm in-depth, these differences were only significant by comparing XPF and PUI (P = 0.025) and XPF and EC (P = 0.036). Although no irrigation method could thoroughly disinfect the RCS, bacterial reduction indexes were generally better after using XPF.

Risk factors associated with the survival of endodontically treated teeth: A retrospective chart review

BACKGROUND

Studies on risk factors affecting tooth retention after endodontic treatment in dental school settings are limited. Understanding these factors is crucial for preserving teeth. The aim of this retrospective study was to evaluate patient- and tooth-level risk factors associated with the survival of endodontically treated teeth.

METHODS

Electronic health records of patients who underwent endodontic treatment at the School of Dental Medicine at the University of Pennsylvania from 2017 through 2020 were analyzed. Patient-level factors included age, sex, American Society of Anesthesiologists Physical Status Classification, smoking history, diabetes status, and amoxicillin allergy. Tooth-level factors included position, presence of restorations, and periodontal conditions with preprosthetic treatments.

RESULTS

The results of this study indicate that the patient-level factors significantly associated with tooth retention included age, sex, American Society of Anesthesiologists Physical Classification Status, and amoxicillin allergy. Tooth-level factors such as core buildup, full-coverage crown, healthy periodontium, and scaling and root planing were also associated with higher survival rates. Mandibular premolars had higher survival rates than mandibular molars.

CONCLUSIONS

This investigation revealed that the tooth retention rate of endodontically treated teeth was 96.2% after initial root canal treatment, 92.4% for nonsurgical re-treatment, and 97.8% for surgical re-treatment.

PRACTICAL IMPLICATIONS

The tooth retention of the endodontic treatment was associated with healthy periodontium, tooth structure, tooth position, tooth restoration, and the patient's overall health.

The Effect of Combined Ultrasonic Tip and Mechanized Instrumentation on the Reduction of the Percentage of Non-Instrumented Surfaces in Oval/Flat Root Canals: A Systematic Review and Meta-Analysis

This systematic review and meta-analysis aimed to evaluate the effectiveness of the ultrasonic tip associated with mechanized instrumentation in reducing the percentage of non-instrumented surfaces of human teeth with oval or flattened root canals. The study followed the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) guidelines. Pubmed/MEDLINE (Medical Literature Analysis and Retrieval System Online), Scopus, Embase, Web of Science, and Cochrane Library were searched for literature published till October 2022. Only in vitrostudies were included, which compared conventional mechanized endodontic treatment alone against conventional endodontic treatment in association with ultrasonic tips, evaluating the reduction in the percentage of non-instrumented walls (computed microtomography). Four studies were eligible for qualitative and quantitative analysis. The majority of the studies scored low for risk of bias. The meta-analysis comparing protocols demonstrated a reduced percentage of non-instrumented walls in groups using ultrasonic tips after the conventional mechanized technique (p<0.01) with a confidence interval of 1.04 (95%CI: 0.59, 1.50). The ultrasonic tip associated with mechanized instrumentation demonstrates a significant reduction in the percentage of non-instrumented surfaces in oval or flattened canals.

To flat or not to flat? Exploring the impact of flat-side design on rotary instruments using a comprehensive multimethod investigation

AIM

To assess the influence of a flat-side design on the geometry, metallurgy, mechanical performance and shaping ability of a novel nickel-titanium rotary instrument.

METHODOLOGY

Sixty-five new 25-mm flat-side rotary instruments (size 25, taper 0.04) and their nonflat-side prototypes (n = 65) were assessed for major deformations and examined regarding macroscopic and microscopic design, determination of nickel and titanium elements ratio, measurement of phase transformation temperature and evaluation of mechanical performance parameters including time/cycles to fracture, maximum torque, angle of rotation, maximum bending and buckling strengths and cutting ability. Additionally, unprepared canal areas, volume of hard tissue debris and percentage reduction of dentine thickness were calculated for each tested instrument after preparing mesial canals of mandibular molars (n = 12), using micro-CT imaging. Statistical analyses were performed using the U-Mann-Whitney test and independent Student t-test (α = 5%).

RESULTS

The number of spirals (n = 8) and blade direction (clockwise) were similar between both flat and nonflat instruments, whilst the helical angles were equivalent (⁓25°). Flat-instruments showed inconsistencies in the homogeneity of the gold colour on the flat-side surface, blade discontinuity, and incomplete and variable S-shaped cross-sections. The titanium-to-nickel ratios were equivalent, but significant differences in the R-phase finish and austenitic start phase transformation temperatures were observed between the flat and nonflat-side instruments. The flat-side instruments demonstrated superior cutting ability compared to the nonflat instruments, as well as, significantly lower values for time to fracture, rotation to fracture and maximum torque to fracture (p < .001). No statistical difference was observed between tested instruments regarding angle of rotation (p = .437), maximum bending (p = .152) and buckling load (p = .411). Preparation protocols using flat and nonflat instruments did not show any statistically significant differences (p > .05). All flat-side instruments exhibited deformation after shaping procedures.

CONCLUSIONS

The flat-side instrument showcased enhanced cutting ability compared to its nonflat counterpart. However, it exhibited inferior performance in terms of time, rotation and maximum torque to fracture, along with distinct phase transformation temperatures. No differences were observed in the titanium-to-nickel ratios, angle of rotation, maximum bending, buckling load, preparation time, percentage of untouched canal walls, volume of hard tissue debris and percentage reduction of dentine thickness.

Effectiveness of root canal instrumentation for the treatment of apical periodontitis: A systematic review and meta-analysis

BACKGROUND

The development of endodontic instruments has rapidly advanced, but their impact on endodontic outcome parameters remains unclear.

OBJECTIVES

This systematic review aimed to answer the following PICOT questions: In patients with apical periodontitis (P) what is the effectiveness of root canal instrumentation ([Q1] performed with contemporary techniques [I] in comparison with 'traditional' techniques [C]] and ([Q2] performed with contemporary engine-driven NiTi instruments [I] compared with other types of contemporary engine-driven NiTi instruments [with different design and/or technology] [C]) in terms of clinical and patient-related outcomes (O)?

METHODS

After PROSPERO protocol registration, a literature search was conducted using Clarivate Analytics' Web of Science, Scopus, PubMed and Cochrane Central Register of Controlled Trials. Grey literature and major journal contents were examined. Two independent reviewers performed the study selection, data extraction and appraisal of included studies. A quantitative meta-analysis was considered, and statistical heterogeneity and overall quality of evidence were assessed.

RESULTS

Nine studies were identified showing substantial methodological differences. Five studies addressed PICOT 1 and three PICOT 2, whereas one study aimed both. A random-effects meta-analysis model was considered for the outcome 'radiographic evidence of normal periodontal ligament space or reduction of apical lesion size' (PICOT 1) based on three studies with 332 evaluable participants and showed that contemporary instrumentation was associated with a more favourable outcome (p = .005) compared with root canal preparation with stainless steel instruments (odds ratio = 2.07 [95%-confidence interval = 1.25-3.44]) with no evidence of statistical heterogeneity (I2  = 0%) but low quality of evidence.

DISCUSSION

Albeit a few studies fulfilled eligible criteria, no study had a low risk of bias. Compelling evidence indicating significantly different outcome rates using different endodontic instruments when treating teeth with apical periodontitis is lacking.

CONCLUSIONS

In terms of healing, the results of the meta-analysis determined the higher effectiveness of root canal instrumentation performed with contemporary techniques in comparison with conventional stainless steel instruments in patients with apical periodontitis followed for a minimum of 1 year with low quality of evidence. No differences could be demonstrated between preparations with traditional stainless steel and contemporary NiTi instruments for other clinical and patient-related outcomes.

REGISTRATION

PROSPERO (CRD42021274642).

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

BACKGROUND

Rotary nickel-titanium (NiTi) instruments are made to exacting standards and are costly to manufacture, and quality control is paramount. Consequently, unauthorized factories make counterfeit instruments that are less expensive and may therefore be attractive to dentists. Little information exists about the metallurgy and manufacturing quality of such instruments. There is the potential for counterfeit instruments to be at higher risk of fracture during treatment, thereby compromising clinical outcomes. The aim of this study was to evaluate physical and manufacturing properties of genuine and counterfeit ProTaper Next™ and Mtwo® rotary NiTi instruments.

METHODS

This study investigated the metallurgical properties, manufacturing quality, microhardness and number of cycles to failure of two commonly used rotary NiTi systems and compared them with counterfeit products purporting to be genuine articles.

RESULTS

Counterfeit instruments were found to be inferior in manufacturing standards and were less resistant to cyclic fatigue when compared to genuine instruments.

CONCLUSIONS

Counterfeit rotary NiTi instruments may be less efficient at preparing root canals and may be at higher risk of fracture during endodontic treatment. Dentists must be aware that, although less expensive, counterfeit instruments may be of dubious manufacturing quality and at higher risk of fracture if used in patients. © 2023 Australian Dental Association.

Middle mesial canal in mandibular first molar: A narrative review

Purpose

This review aimed to assess the incidence, anatomical characteristics, identification, and clinical management using conventional techniques and advanced tools to manage MMCs successfully.

Methods

Medline/PubMed and Scopus databases were searched using "Middle mesial canal," "Middle mesial root canal," OR "Accessory mesial canal" keywords from 1 January 1970 and 1 February 2023. The most pertinent articles were chosen for the review from the retrieved articles. In addition, relevant articles were added by manually searching the list of references.

Results

The incidence of MMC is noticeable in younger people, and the confluent canal is the most common type. The majority of MMCs merged with mesiobuccal (MB) canals rather than mesiolingual (ML) canals. Clinical management could be employed using the standard endodontics protocol, and recent radiography technologies, magnification, rotary, and obturation materials can facilitate the procedures.

Conclusion

The possibility of the incidence of MMC is not unusual. Detection and thorough debridement followed by obturation of the canal could increase the success rate of clinical outcomes.

Evaluation of apical extrusion of debris and centering ability in different nickel-titanium files during curved root canal preparation

BACKGROUND

Curved root canals lead to difficulties in cleaning, shaping and filling the root canal system. Apical extrusion of debris and root canal transportation are important factors causing postoperative complications. In clinical practice, commonly selected instruments include multifile NiTi systems, such as M3-Pro PLUS (M3-PRO), Orodeka Plex 2.0 (ODP), Rotate (ROT), and Protaper Gold (PTG), as well as single-file NiTi systems, such as M3-L Platinum 2019 (M3L), Waveone Gold (WOG), and Reciproc Blue (RCB). This study aimed to comprehensively evaluate the differences in the apical extrusion of debris and centering ability of the above NiTi files.

METHODS

Seventy 3D-printed resin teeth were used (n = 10). The apically extruded debris was collected in a preweighed centrifuge tube. The resin teeth with or without root canal preparation were cut into separate cross sections at 1 mm, 3 mm, 5 mm, and 7 mm away from the root apex, and then the root canal transportation and centering ratio of each cross section were calculated.

RESULTS

Apical extrusion of debris was highest in RCB but lowest in OD-P (P < 0.05). Root call deviation was lowest in ROT at the 3 mm level, in PTG at the 5 mm level, and in PTG and ROT at the 7 mm level (P < 0.05). The centering ratio of NiTi files was highest in the RCB group at the 3 mm level, in the PTG group at the 5 mm level, in the ROT group at the 7 mm level (P < 0.05).

CONCLUSIONS

For NiTi files with the same system, the cross-sectional design is the greatest factor affecting the extrusion of debris, and motion mode is the second. In addition, the multifile system could reduce the degree of root canal transportation.

Anatomical complexities affecting root canal preparation: a narrative review

A fundamental aspect of the Endodontic field is the knowledge of root canal anatomy. Using a variety of techniques, the internal and external anatomy of teeth have been extensively investigated throughout the past century. Recent improvements in three-dimensional computed tomography have enabled more detailed evaluations of root canal morphology in both clinical and laboratory settings. Essentially, researches have unveiled that the root canal constitutes a complex system, comprising not only the main root canal but also lateral components, including isthmuses, fins, accessory canals and apical ramifications. Undoubtedly, this intricate morphology poses a significant challenge when it comes to the process of shaping, cleaning and disinfecting the root canal system. This article aims to explore the anatomical aspects of the root canal system that impact the chemomechanical procedures.

A review of the latest developments in rotary NiTi technology and root canal preparation

The introduction of nickel-titanium (NiTi) mechanical instruments dramatically changed clinical endodontics over the last few decades. Before NiTi, it was necessary to use more instruments to create an ideal root canal shape, and many approaches, sequences and techniques were developed over the years. Recently, NiTi endodontic instruments have undergone a series of changes brought about by modifications in design, surface treatments, and thermal treatments to improve their root canal preparation outcomes and reduce associated canal preparation risks during root canal treatment. Heat treatment is one of the most fundamental approaches to improving the fatigue resistance and flexibility of NiTi endodontic instruments. In addition, new kinematics have been developed to offer greater safety and efficiency. This narrative review describes the general properties and manufacturing of NiTi instruments, and the mechanical system evolution of NiTi instruments.

Advancing Nitinol: From heat treatment to surface functionalization for nickel–titanium (NiTi) instruments in endodontics

Nickel-titanium (NiTi) alloy has been extensively researched in endodontics, particularly in cleaning and shaping the root canal system. Research advances have primarily focused on the design, shape, and geometry of the NiTi files as well as metallurgy and mechanical properties. So far, extensive investigations have been made surrounding surface and thermomechanical treatments, however, limited work has been done in the realm of surface functionalization to augment its performance in endodontics. This review summarizes the unique characteristics, current use, and latest developments in thermomechanically treated NiTi endodontic files. It discusses recent improvements in nano-engineering and the possibility of customizing the NiTi file surface for added functionalization. Whilst clinical translation of this technology has yet to be fully realized, future research direction will lie in the use of nanotechnology.

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Nitinol (Nickel Titanium alloy) is widely used to clean/shape root canal system in endodontics.

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To enhance its performance, various thermo-mechanical and nano-engineering modifications have been performed.

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This comprehensive review summarizes the latest advances and future trends relating to functionalized NiTi endodontic files.

Shaping ability of WaveOne Gold and OneReci by using two apical sizes: a micro-computed tomographic assessment

Backround

OneReci (MicroMega, Besançon, France) is a recently introduced single-file reciprocating system with scarce information revealed on its shaping ability. This study aimed to compare the shaping abilities of OneReci and a well-documented single-file reciprocating system WaveOne Gold (WOG; Dentsply Maillefer, Ballaigues, Switzerland) and evaluate the effect of increased apical enlargement on the preparation quality, using micro-computed tomography (micro-CT).

Methods

After an initial micro-CT scanning, twenty mesial root canals of mandibular molars were anatomically matched. The canals were assigned to two experimental groups (n = 10), using OneReci or WOG in different canals of the same root. The glide paths were created, and root canals were prepared twice, using size 25 and 35 instruments of the systems, respectively. The specimens were scanned with micro-CT after each preparation. The increase in canal volume, amount of dentin removal, unprepared root canal surface, canal transportation, centering ratio and preparation times were assessed. The data were analysed with independent sample t-tests, variance analyses, Friedman and Mann-Whitney U tests. The significance level was set at 5%.

Results

Each preparation increased the canal volume and dentin removal while decreasing the unprepared root surface. The difference between the systems became significant after preparation with size 35 instruments (p < 0.05). Regarding canal transportation and centering ratio, the difference was insignificant (p > 0.05). The first preparation step (glide path + size 25 instrument) was significantly faster in the OneReci group (p < 0.05).

Conclusions

Preparation with size 25 instruments of the systems appeared to be safe with similar shaping performances. Larger apical preparation promoted significantly higher dentin removal, volume increase, and prepared surface area in WOG.

A Comparative Evaluation of the Apically Extruded Debris from Root Canals Prepared by R-Motion NiTi File System

Background

Apically extruded debris (AED) is an inherent concern during root canal treatment for both endodontists and general practitioners. The present study investigates the AED of the novel R-Motion single-file reciprocating system compared to standard single reciprocating and multifile rotary systems.

Materials and Methods

Fifty-six moderately curved palatal roots of upper maxillary first molars were selected for the present study. The samples were then divided randomly into four groups (n = 14)- Group I: R-motion (RM), Group II: WaveOne Gold (WOG), Group III: ProTaper Next (PTN), and Group IV: HyFlex EDM (HFEDM). The researcher has modified Myers and Montgomery's method to simulate human body temperature. Vials were used to collect debris and weighted using a 0.00001 sensitive balance before and after instrumentation. The instrumentation of all experimented groups was done at 37°C, terminated at master apical file #25. An auto syringe with a side vented needle was used to deliver 8 ml of deionized water for irrigation of each sample during preparation. Vials were stored in a dry sealed desiccator which contained CaSO₄ crystals, for 24 hr before weighing. The weight of the collected debris was obtained by subtracting the preinstrumentation weight from the postinstrumentation weight for each vial. The Kruskal-Wallis and Mann-Whitney U tests were performed to analyse the statistical difference in the amount of debris between the tested groups at a 0.05 significance level.

Results

The RM system produced less debris extrusion than all tested groups, with a significant difference between the former and the WOG and the PTN systems. However, WOG, PTN, and HFEDM showed no statistically significant difference in the amount of AED.

Conclusion

All tested groups produced apical debris in different amounts. The RM produced substantially less AED than WOG and PTN. Meanwhile, WOG, PTN, and HFEDM caused a comparable amount of AED.

Mechanical Properties and Root Canal Shaping Ability of a Nickel-Titanium Rotary System for Minimally Invasive Endodontic Treatment: A Comparative In Vitro Study

Selection of an appropriate nickel−titanium (NiTi) rotary system is important for minimally invasive endodontic treatment, which aims to preserve as much root canal dentin as possible. This study aimed to evaluate selected mechanical properties and the root canal shaping ability of TruNatomy (TRN), a NiTi rotary system designed for minimally invasive endodontic shaping, in comparison with existing instruments: HyFlex EDM (HEDM), ProTaper Next (PTN), and WaveOne Gold (WOG). Load values measured with a cantilever bending test were ranked as TRN < HEDM < WOG < PTN (p < 0.05). A dynamic cyclic fatigue test revealed that the number of cycles to fracture was ranked as HEDM > WOG > TRN > PTN (p < 0.05). Torque and vertical force generated during instrumentation of J-shaped artificial resin canals were measured using an automated instrumentation device connected to a torque and vertical force measuring system; TRN exhibited smaller torque and vertical force values in most comparisons with the other instruments. The canal centering ratio for TRN was smaller than or comparable to that for the other instruments except for WOG at the apex level. Under the present experimental conditions, TRN showed higher flexibility and lower torque and vertical force values than the other instruments.

Shaping ability of new reciprocating or rotary instruments with two cross-sectional designs: an ex vivo study

AIM

This study compared the shaping ability of four new reciprocating and rotary nickel-titanium instruments, with triangular or S-shaped cross-section, in the mesial canals of mandibular molars using micro-computed tomographic (micro-CT) evaluation.

METHODOLOGY

Twenty-four extracted mandibular molars with Vertucci's class IV configuration in the mesial root were selected for this study. The teeth were matched in fours according to anatomic similarities as revealed by micro-CT and then distributed into four groups of 12 mesial canals each according to the instrumentation technique: Reciproc Blue, R-motion, VDW.Rotate, and RaCe EVO. The final apical size of instrumentation was 30/.04 for 3 systems and 25/08 for the Reciproc Blue instrument. Micro-CT scans were taken before and after preparation to evaluate the canal volume, area and unprepared surface areas, as well as the centering ability, and the canal:root width ratio.

RESULTS

Preparation with all systems significantly increased the volume and area of the canals (P < .05). There were no significant differences between groups regarding the amount of unprepared areas in both the apical and full canal lengths (P > .05). Variation in the centre of gravity showed no significant difference between groups either (P > .05). The canal:root width ratio at levels 0 and 4 mm apically to the coronal canal opening was significantly increased by all systems (P < .01), with no significant differences between groups (P > .05). The canal width never exceeded 40% of the root width.

CONCLUSIONS

Reciprocating or rotary instruments, with a triangular or an S-shaped cross-section, performed equally in shaping Vertucci's class IV mesial canals of mandibular molars.

A Multimethod Assessment of a New Customized Heat-Treated Nickel-Titanium Rotary File System

This study aimed to compare three endodontic rotary systems. The new Genius Proflex (25/0.04), Vortex Blue (25/0.04), and TruNatomy (26/0.04v) instruments (n = 41 per group) were analyzed regarding design, metallurgy, and mechanical performance, while shaping ability (untouched canal walls, volume of removed dentin and hard tissue debris) was tested in 36 anatomically matched root canals of mandibular molars. The results were compared using one-way ANOVA, post hoc Tukey, and Kruskal−Wallis tests, with a significance level set at 5%. All instruments showed symmetrical cross-sections, with asymmetrical blades, no radial lands, no major defects, and almost equiatomic nickel−titanium ratios. Differences were noted in the number of blades, helical angles, cross-sectional design, and tip geometry. The Genius Proflex and the TruNatomy instruments had the highest and lowest R-phase start and finish temperatures, as well as the highest and lowest time and cycles to fracture (p < 0.05), respectively. The TruNatomy had the highest flexibility (p < 0.05), while no differences were observed between the Genius Proflex and the Vortex Blue (p > 0.05). No differences among tested systems were observed regarding the maximum torque, angle of rotation prior to fracture, and shaping ability (p > 0.05). The instruments showed similarities and differences in their design, metallurgy, and mechanical properties. However, their shaping ability was similar, without any clinically significant errors. Understanding these characteristics may help clinicians to make decisions regarding which instrument to choose for a particular clinical situation.

The Novel Role of Solvents in Non-Surgical Endodontic Retreatment

Non-surgical endodontic retreatment is a reliable conservative option for managing post-treatment apical periodontitis. However, effective microbial control, based on the maximization of filling removal and disinfection protocols, is not yet predictable. Traditional gutta-percha solvents, which are indistinctively used for both the core and sealer filling materials, became obsolete due to unprecedented advances in endodontic technology. Nonetheless, microtomography, scanning electronic microscopy findings, and histobacteriological analysis tend to confirm the persistence of filling materials and the lack of association between root canal enlargement and superior disinfection. There is a controversy regarding the most suitable clinical protocols surrounding the shaping procedures and the supplementary disinfection steps. Based on the literature and the previous work of the team, the authors aimed to summarize the current knowledge regarding specific solvent formulations that target filling materials. Additionally, the advantage of an additional irrigation step to optimize disinfection was highlighted. This adjunctive procedure serves a dual role in the dissolution of filling materials, and in conferring an antibiofilm effect. Further research is needed to understand the novel contribution of these strategies upon clinical practice outcomes.