Management of intracanal separated instruments

Correlation Between Fibrous Area Ratio and Numbers of Cycles to Fracture Resistances of Nickel-Titanium Files

INTRODUCTION

This study aimed to evaluate the correlation between the fibrous area ratio and the number of cycles to failure (NCF) in terms of fatigue fracture resistance of nickel-titaniumrotary files.

METHODS

ProTaper Universal (PTU) and ProTaper Gold (PTG) files of size F2 (25 mm) were tested to make cyclic fatigue fracture using a custom-made device simulating a 35° canal curvature (n = 24). Using the fractured fragments, scanning electron microscopy was taken to analyze the fracture surfaces, focusing on fibrous areas on the cross-sections. Fibrous area ratios were calculated using ImageJ software, and NCF was determined by multiplying the time to fracture by rotational speed. Statistical analysis was performed to evaluate differences between groups and assess the correlation between fibrous area ratio and NCF (P < .05).

RESULTS

Scanning electron microscopy analysis revealed a higher fibrous area ratio in PTU files (P < .05). The correlation analysis indicated a weak relationship between fibrous area ratio and NCF in both groups. PTG files demonstrated significantly higher NCF compared to PTU files (P < .05). PTG group had a significantly lower fibrous area ratio than the PTU group (P < .05).

CONCLUSIONS

While PTG files show improved cyclic fatigue resistance due to thermal processing, the fibrous area ratio is not a strong representing factor or predictor of NCF. Heat treatment influences the property of fracture resistance more significantly than propagation process of cyclic fatigue fracture.

Effect of Cross-sectional Designs on Torsional Resistance of Endodontic Nickel-Titanium Files: A Finite Element Study

OBJECTIVES

 This study aimed to assess the influence of two key design parameters on the torsional resistance of endodontic rotary files: the ratio of the equivalent radius (re ) to the polar moment of inertia (J), or re /J ratio, and the percentage of the inner core area. Understanding these factors can guide the development of files with improved performance during root canal procedures.

MATERIALS AND METHODS

 Finite element analysis was employed to simulate the behavior of rotary files under torsional loading conditions. This method allowed for the investigation of maximum shear stress across various cross-sections (D4-D16) of the files. The relationship between the re /J ratio and the maximum shear stress was also evaluated. To assess the impact of cross-sectional design modifications on stress distribution, the study analyzed files with progressively changing configurations.

RESULTS

 Regions situated outside the inner core circle experienced lower shear stress compared with a circular shaft. Furthermore, a strong linear correlation was observed between the maximum shear stress experienced by the file, the applied torque during operation, and the re /J ratio. Significantly, the study established a connection between the percentage of the inner core area and the torsional resistance of the file. Files with a larger inner core area exhibited a lower coefficient (C) within a newly derived torsional formula. This lower C value directly translated to a reduction in the maximum shear stress experienced by the file. In essence, files with a higher percentage of inner core area demonstrated enhanced torsional resistance, allowing them to withstand higher torsional loads encountered during root canal procedures.

CONCLUSION

 This study identified the re /J ratio and the percentage of inner core area as the most critical design factors influencing the torsional resistance of rotary files. Files with a lower re /J ratio and a larger inner core area experienced lower shear stress, resulting in enhanced torsional resistance and potentially reducing the risk of torsional fracture during use. These findings offer valuable insights for both clinicians selecting rotary files and manufacturers designing future iterations, ultimately contributing to improved safety and efficacy during root canal treatments.

Phase Transformation and Mechanical Behaviour of Different Heat-Treated Nickel-Titanium Rotary Instruments

OBJECTIVES

This study evaluated the phase composition, phase transformation behaviour, and mechanical properties of five heat-treated NiTi instruments.

METHODS

ProTaper NEXT (M-wire, PTN), ProTaper Gold (Gold-wire, PTG), One Curve (C-wire, OC), EdgeTaper Platinum (Fire-wire, ETP), NeoNiTi (electrical discharge machining-wire, NNA), and ProTaper Universal (conventional wire, PTU, control) with #25-tip size were tested (n = 12/group) for cyclic fatigue resistance (number of cycles to failure; NCF) and torsional resistance (angle of rotation to fracture and maximum torque at fracture [ultimate torsional strength]). The geometry and fracture surfaces of the tested instruments were examined by scanning electron microscopy. The phase transformation temperature and phase composition of the instruments were evaluated using differential scanning calorimetry and X-ray diffraction. Data were statistically analysed using one-way ANOVA and Tukey's post hoc test, with the significance level set at 5%.

RESULTS

PTG showed the highest NCF (P < .05) at 37°C, while ETP exhibited the highest angle of rotation to fracture, ultimate torsional strength, and stiffness (P < .05). Scanning electron microscopy demonstrated typical clusters of fatigue striations and numerous cracks after cyclic fatigue fracture, whereas there was a concentric abrasion pattern with a dimple and microvoids at the centre after torsional fracture. In differential scanning calorimetry curves, austenite-finishing temperatures of heat-treated instruments were higher than 37°C, whereas that of PTU was lower than 37°C. PTU showed strong peaks of austenite at 25 and 37°C, whereas ETP showed a strong peak of R-phase at 25°C, but mostly austenite phase at 37°C in X-ray diffraction.

CONCLUSIONS

Geometry, alloy type, and phase transformation temperatures of NiTi instruments affected their mechanical behaviour.

CLINICAL RELEVANCE

PTG showed the highest NCF, suitable for markedly curved canals. ETP had the highest torsional resistance, appropriate for narrow and constricted canals.

Endoscope-assisted retrieval of separated instruments: An ex vivo comparative study of Masserann, microsonic, and loop techniques

Instrument separation during root canal treatment can hinder effective cleaning and shaping, making reliable retrieval techniques essential. Endoscopic visualization might aid in instrument removal procedures offering direct magnification of root canal anatomy. This ex vivo study evaluated the success rate and procedure time of three instrument retrieval techniques - Masserann, microsonic, and loop techniques - under the visualization of dental operation microscope (DOM) assisted by an endoscope. Sixty extracted human mandibular single-rooted teeth with simulated fractures were assigned to the Masserann, microsonic, or ultrasonic with loop techniques (n = 20/group), each performed under endoscopic visualization alongside DOM. The success rate of instrument removal and procedure time were recorded. Complications, such as root perforation, apical extrusion and secondary fracture, were recorded. Statistical analysis was conducted using Pearson χ2 and Kruskal-Wallis tests with 5% significance threshold. Success rates for the microsonic, Masserann, and ultrasonic with loop techniques were 80%, 70%, and 80%, respectively (p > 0.05). The average procedure times were 13.02 min for the microsonic technique, 17.25 min for the Masserann technique, and 17 min for the ultrasonic with loop technique (p > 0.05). The Masserann technique demonstrated a higher complication rate, with two cases each of perforation and apical extrusion, whereas no secondary fractures occurred in any group. Conclusively, the microsonic technique showed the highest success rate with the shortest retrieval time, indicating its efficiency and suitability for instrument removal from root canals, particularly when combined with enhanced visualization through endoscopy.

A novel methodology for detecting separated endodontic instruments using a combination of algorithms in post-processing CBCT software

Separated endodontics instruments and high-density obturating materials produce metal artifacts on cone-beam computed tomography (CBCT) scans. This study evaluated a novel methodology to detect separated instruments using artifact suppression and color map algorithms with CBCT post-processing software and compared with periapical radiographs (PRs). Endodontic instruments were incorporated into 168 root canals filled with four sealers. Additionally, 40 root canals were only filled, serving as control. CBCT scans were acquired in PreXion-3D-Elite, and digital PRs were taken in distoradial, mesioradial, orthoradial, and proximal directions. The treated teeth were analyzed using an artifact suppression algorithm combined with a color map algorithm. The separated instruments appear in the color map with larger expansion in red to allow identification. This map provides valuable information by showing dynamic visualization toward the point of expansion of the high-density object, hence suggesting a separated instrument. The chi-square test was used to compare the separated instruments among the imaging methods. Bonferroni correction was used for multiple comparisons. Statistical significance was considered P < 0.05. Overall, CBCT performed significantly better than PRs (P < 0.001) in detecting separated instruments. PR was influenced by all the variables studied (P < 0.05). The artifact suppression and color map algorithms, combined with dynamic navigation, effectively identified separated instrument fragments in all the root canal fillings, regardless of filling material, image view, or root canal. Only 32.3% of the root canal fillings viewed by PR detected separated instrument fragments. This method seems to be useful in the resolution of the problem of viewing separated instruments with CBCT post-processing software.

Assessment of the bypass of obturation materials beyond fractured instruments after using different obturation techniques in simulated curved canals (An in-vitro study)

This study evaluated the extent to which obturation materials bypass fractured endodontic instruments positioned in the middle and apical thirds of severely curved simulated root canals using different obturation techniques. Sixty resin blocks with simulated root canals were used, each with a 50° curvature, a 6.5 mm radius of curvature, and a length of 16.5 mm, prepared to an ISO #15 diameter and taper. Canals were shaped using ProTaper Universal files (Dentsply Maillefer) attached to an X-smart Plus endo motor (Dentsply), set at 3.5 Ncm torque and 250 rpm, up to size S2 at working length. To simulate fractures, F2 and F3 files were weakened 3 mm from the tip, then twisted to break in the apical and middle sections of the canal, respectively. All samples were sealed with GuttaFlow 2 and divided into three groups (n = 20/group) according to obturation technique: A) single cone, B) lateral condensation with a rotary spreader, and C) softcore obturators. Each group was then divided into two subgroups (n = 10) based on the instrument fracture location (1 = apical, 2 = middle). The linear intrusion of obturation materials through the fractured instruments was measured using ImageJ software and analyzed statistically with ANOVA, Tukey tests, and independent t-tests, with significance set at p<0.05. Material bypass in group B1 (3.27 ± 0.63 mm) was significantly greater than in group A1 (2.39 ± 0.44 mm) and group C1 (2.91 ± 0.77 mm). In group C2, bypass (5.76 ± 0.64 mm) was significantly higher than in group A2 (3.82 ± 0.2 mm) and group B2 (2.27 ± 0.96 mm). Additionally, bypass in group A2 was greater than in group B2, and group B1 had more bypass than B2, while group C2 exceeded C1. The lateral condensation technique with a rotary spreader and softcore obturators increased the bypass of obturation materials through fractured instruments in simulated curved canals. These techniques may thus enhance material flow in endodontic procedures involving instrument fractures.

Impact of anatomical and clinical variables on the success of endodontic instrument fragment retrieval

PURPOSE

Separation of instrument fragments can impede the progress of endodontic treatment, and effective management of this complication is crucial for treatment success. This study examined the factors that impact the success of retrieval of separated instrument fragments by postgraduate endodontic residents.

METHODS

A retrospective analysis was conducted on a total of 224 teeth associated with instrument fragment separation that were managed by postgraduate residents specializing in endodontics between January 2020 and March 2024. Data were extracted from patient records, periapical radiographs, and clinical notes. Chi-squared test and t-test were employed to identify factors significantly influencing retrieval success. Associations between successful retrieval and variables were assessed using binary logistic regression models.

RESULTS

Fragment retrieval was successful in 32% of the examined cases. Retrieval was more likely to be successful for anterior teeth than for premolars and molars (P = 0.003). Fragment separation in the coronal third of the canal had a higher retrieval success rate (P < 0.001). Longer separated fragments were also associated with increased retrieval success (t = 3.035, P = 0.003).

CONCLUSION

The study revealed that factors critically influencing the successful retrieval of separated instrument fragments included the tooth type, the level of separation within the canal, and the fragment length. These findings highlight the importance of careful case selection in order to optimize management outcomes.

Removal of a fractured file beyond the apical foramen using robot-assisted endodontic microsurgery: a clinical report

BACKGROUND

Endodontic file fractures are common complications of root canal treatment, and requires removal via specialized techniques such as endodontic microsurgery when the file beyond the apical foramen. It is often challenging to precisely and minimally remove a fractured file. Recently the use of dental autonomous robotic system (ATR) has shown promise in precisely and minimally in dental surgery. Therefore, this case details a technique for using the ATR system to precisely and minimally guide the removal of a fractured file beyond the apical foramen.

CASE PRESENTATION

A 48-year-old male patient, with no evidence of bone defects, was diagnosed with a file fractured completely beyond the apical foramen during root canal treatment of the right maxillary lateral incisor. Patient information was used to incorporate a digital model into preoperative planning software to develop a surgical strategy. The ATR system employs spatial alignment methods for registration, directing the robotic arm to independently locate the fractured file in accordance with the surgical plan. To maximize minimally invasive surgery, the long fractured file was removed in two stages. After removing the bone and fracture file, the clinician performed suturing under a microscope. No complications were observed during the surgery, and the treatment appeared to be successful based on the 9-month follow-up evaluation.

CONCLUSIONS

The ATR system enables precise localization of the fractured file beyond the apical foramen with intact cortical plates. This technology has the potential to improve positioning accuracy, minimize the need for invasive bone removal, reduce intraoperative time, and facilitate successful endodontic microsurgical procedures.

Predictive factors in the retrieval of endodontic instruments: the relationship between the fragment length and location

Objectives

This study aimed to relate the file fragment length and location in the root canal to the retrieval chances, the clinical time required and the occurrence of secondary fractures.

Materials and Methods

Sixty clinical cases of fractured instruments were included in this study. They were classified according to the instrument length and the location of the root canal. In each group, the success rate in the instrument retrieval, the clinical time required and the occurrence of secondary fractures were evaluated. The collected data were analyzed using the Kruskal-Wallis test on the basis of a 0.05 significance level.

Results

The fragment length showed no significant influence on the assessed variables (p > 0.05). The root third where the instrument was located resulted in an increased clinical time, with statistically significant differences (p < 0.05). However, the procedure success rate and the occurrence of secondary fractures showed no association with these variables.

Conclusions

In accordance with the findings of this study, the fractured fragment length did not influence any of the variables assessed, but it is suggested to focus on the fragment location inside the root canal to decide the retrieval of a fractured instrument.

Microhardness and energy dispersive X-ray evaluation of dentinal walls following chemical and electrochemical dissolution of fractured nickel-titanium file: An in vitro study

Purpose

Chemical dissolution of nickel-titanium (NiTi) files involves the application of a fluoride solution in direct contact with a damaged instrument, whereas electrochemical dissolution involves the application of an electrical current to the electrolyte, which accelerates fragment dissolution. This study aimed to determine the hardness and concentration of calcium and phosphorus (Ca and P) ions in dentinal walls following chemical and electrochemical dissolution of fractured ProTaper F2 files with a novel chemical solution. Materials & Methods : Thirty human maxillary first molar palatal roots with fractured ProTaper F2 files in the middle third (length, 2.5 mm were divided into three groups according to the treatment techniques used with a novel solution (NaF 12 g/L + NaCl2 60 g/L + MgCl2 60 g/L + CaCl2 60 g/L) at pH 5: Group 1: distilled water (control group), Group 2: electrochemical dissolution, and Group 3: chemical dissolution using the novel solution. The novel solution was placed for 10 min using an electrochemical technique, and for 30 min in contact with the separated instrument in the chemical group. The Vickers microhardness test was performed in three areas: at 3, 6, and 9 mm from the apex, and an energy-dispersive X-ray test for both Ca and P ions was performed. The analysis of variance (ANOVA) and Tukey's tests were used for statistical analysis.

Results

According to the one-way ANOVA analysis, no difference was observed between the tested approaches (P > 0.05) in the three areas evaluated (3, 6, and 9 mm), with no difference in the Ca/P ratio between the tested groups.

Conclusion

Compared to the control group, the use of chemical and electrochemical dissolution methods with the novel solution did not affect dentin hardness or dentinal structure in terms of the Ca/P ratio, thereby indicating promising results while saving time.

Analysis of Endodontic Successes and Failures in the Removal of Fractured Endodontic Instruments during Retreatment: A Systematic Review, Meta-Analysis, and Trial Sequential Analysis

This study presents a systematic review with meta-analysis to evaluate the success rates of endodontic retreatments in teeth where separated instruments are located within the roots. The search and selection of studies were conducted across two databases, SCOPUS and PubMed, as well as the Cochrane Library registry, yielding a total of 1620 records. Following the selection process, 11 studies were included in the systematic review. Overall, out of 1133 retreated teeth, there were 172 failures in instrument removal and 55 perforations. The meta-analysis results indicate that failures are more frequent when instruments are located in the apical third, with a failure rate of 21%, compared to an 8.8% failure rate in the middle/coronal third. The anatomy of the root canals, particularly the location of the separated instruments, significantly influences the success rates.

Finite element evaluation of dentin stress changes following different endodontic surgical approaches

The aim was to compare the effect of different endodontic surgical treatments on the stress distributions in dentin of a simulated first mandibular molar tooth using the finite element analysis method. Three surgical endodontic procedures (apical resection, root amputation, and hemisection) were simulated in a first mandibular molar. Biodentine or mineral-trioxide-aggregate was used to repair the surgery site in apical resection and root amputation models; the remaining root canal spaces were filled with gutta-percha. Access cavities were restored using resin composite. In hemisection model, root canal was filled with gutta-percha, and coronal restoration was finished with a monolithic zirconia crown. A sound tooth model was created as a control model. An oblique force of 300 N angled at 45° to the occlusal plane was simulated. Maximum von Mises stresses were evaluated in dentin near the surgery regions and the entire tooth. Apical resection/Biodentine and apical resection/mineral-trioxide-aggregate models generated maximum von Mises stresses of 39.001 MPa and 39.106 MPa, respectively. The recorded maximum von Mises stresses in root amputation models were 66.491 MPa for root amputation/Biodentine and 73.063 MPa for root amputation/mineral-trioxide-aggregate models. The highest maximum von Mises stress value among all models was observed in the hemisection model, measuring 138.87 MPa. Hemisection induced the highest von Mises stresses in dentin, followed by root amputation and apical resection. In apical resection, Biodentine and mineral-trioxide-aggregate did not show a significant difference in stress distribution. Biodentine in root amputation may lead to lower stresses compared to mineral-trioxide-aggregate.

Broken Instrument Removal Methods with a Minireview of the Literature

Instrument fracture in the root canal system is an unpleasant incident that may occur during root canal treatment. Comprehensive cleaning of the root canal system is often impossible in the presence of a broken instrument. Therefore, it is often imperative to remove the broken fragment from the root canal system. To date, various methods have been proposed for the removal of broken instruments from the root canal system. However, no consensus has been reached on a safe technique with a high success rate for broken instrument removal. This case series reports six cases of successful removal of broken instruments using different methods including the ultrasonic, tube-and-glue, tube-and-wire, tube-and-internal shaft, and the forceps techniques and also provides a brief review of the relevant literature.

Comparative evaluation of increase in temperature on the external root surface of teeth during retrieval of broken NiTi instrument using two ultrasonic tips and two power settings: An in vitro study

Context

An unfavorable event that can hinder endodontic treatment and affect the outcome of root canal treatment is the separation of endodontic instruments. Endodontic instrument separation can occur due to clinical or metallurgical factors. Friction between the ultrasonic tip and the remaining dentin generates heat, which is subsequently transferred to the external root surface. Elevated temperatures exceeding 10°C above body temperature for more than a minute may result in injury to periodontal or bone tissue.

Aim

The aim of this study was to evaluate and compare temperature rise on the external root surface of teeth during retrieval of broken NiTi instrument using two different ultrasonic tips and two power settings.

Materials and Methods

In each group, a sample size of 8 was sufficient to attain a statistical power exceeding 90%, enabling the detection of a minimum mean difference of 0.9204 (delta) through a one-way ANOVA test at a 95% confidence level (alpha 0.05). After access opening and working length determination, samples were randomly distributed into two groups - Group 1 (A and B) - ProUltra tip at high and low power settings and Group 2 (A and B) - Cric Dental IR3 at high and low power settings. The temperature rise was measured using K-type thermocouple thermometer. The comparisons were analyzed using the Kruskal-Wallis test with pairwise comparisons using the Dunn's test.

Results

Group 1A and Group 1B resulted in lower heat generation compared to Group 2A and 2B and its difference was statistically significant (P < 0.05). Minimum temperature rise is seen in the ProUltra group at lower power settings (Group 1A) at the apical level and maximum temperature rise is seen in the Cric Dental IR3 group at higher power settings (Group 2B) at the middle third level.

Conclusion

It was found that there is a significant temperature rise seen when ultrasonic tips are used for the retrieval of separated files, especially at higher power settings. The ProUltra tip demonstrated the lowest temperature rise at lower power settings, particularly at the apical level, whereas the IR3 Cric Dental tip exhibited the highest temperature rise, notably at higher power settings and the middle third level.

Assessment of Incidence, Management and Contributory Factors of Root Canal Instrument Separation in an Endodontics Post- Graduate Program: A Retrospective Clinical Study

BACKGROUND

The successful outcome of nonsurgical root canal treatment (NS-RCT) is largely dependent on the technical quality of the procedure.

OBJECTIVE

To investigate the incidence of separated instruments in endodontic postgraduate clinics between January 2018 and December 2021, and to determine the potential contributory factors that increase the risk of instrument separation.

MATERIALS AND METHODS

A retrospective observational study was conducted in the Department of Endodontics, Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia. Data was collected to determine the incidence of separated instruments and their associated variables. Seven variables were analyzed separately: nonsurgical initial or retreatment case, tooth type, tooth arch, tooth location, canal type, root curvature, level of fracture, and file type.

RESULTS

A total of 3150 cases were treated, of which 108 cases had separated instruments. The overall incidence of instrument separation was 3.4% while 53.7% of separated instruments occurred in the mandibular molars, followed by 42.6% in the maxillary molars. The highest frequency of instrument separation was recorded in the mesiobuccal canal (35.2%). The level of separation was found to be statistically significant in relation to the management (P < .001).

CONCLUSION

Nickel-titanium instruments tend to separate more inside the root canal system than stainless steel instruments. However, under the limitation of this study, the incidence of instrument separation is still quite low, even with postgraduate endodontic residents with limited experience.

A Novel Approach for Orthodontic Extrusion Prior to Intentional Replantation: A Case Report

AIM

This case report aimed to present a novel surgical technique involving orthodontics luxation of the offended tooth using miniscrew prior to performing intentional replantation (IR) to remove an extruded separated instrument that injured the inferior alveolar nerve (IAN).

BACKGROUND

Intentional replantation is a dental procedure that involves extracting a tooth, managing the root canal, and then reinserting the tooth back into its socket. This procedure is typically used as a last resort when other treatment options have failed or are not possible. Intentional replantation can be successful in preserving the tooth and preventing tooth loss, but it is important to note that there are risks involved. Maintaining the viability of the periodontal ligament (PDL) is a pivotal step to achieve a favorable outcome.

CASE DESCRIPTION

A 15-year-old female patient came to the clinic complaining of electric-like pain in the left mandibular posterior area that radiated to the left ear and sometimes caused a headache. Upon clinical and radiographic evaluation, extruded endodontic file from the mesial root of the left first molar that penetrated the IAN canal was noticed. Nonsurgical root canal retreatment was performed, which failed to retrieve the separated file. Orthodontics luxation of the offended tooth was done 2 weeks before the surgical intervention using a miniscrew to induce PDL inflammation, which increased the tooth mobility and PDL volume, facilitating the atraumatic extraction and reduced the risk of complications, such as root resorption and ankylosis. Then, IR was performed, and the extruded file was successfully retrieved. Three months follow-up showed complete recovery of the endodontics-related IAN injury symptoms. Preapical radiographic evaluation and cone-beam computed tomography scan showed complete healing of the periapical radiolucency/area of low density and complete formation of the PDL space and lamina dura around the resected roots.

CONCLUSION

This novel approach using a miniscrew suggests a noninvasive technique that minimizes the damage to the offended tooth surrounding tissues as well as minimizing the morbidity of the adjacent teeth and the vital anatomical structures.

CLINICAL SIGNIFICANCE

Multidisciplinary comprehensive preplanning of complicated cases is essential to maximize treatment efficiency. The orthodontic extrusion facilitates the extraction process that helps in preserving the PDL, and ultimately increases the survivability of the teeth. How to cite this article: Alharbi MA, Alghamdi BA, Alswajy WA, et al. A Novel Approach for Orthodontic Extrusion Prior to Intentional Replantation: A Case Report. J Contemp Dent Pract 2023;24(11):895-901.

Evaluation of a broken instrument removal training course for general dentistry residents

INTRODUCTION

To help general dentistry residents better manage the intracanal broken instrument situation, we introduced a hands-on training course into the endodontic curriculum of a general dentistry residency programme.

MATERIALS AND METHODS

Thirty general dentistry residents and 30 residents with endodontic specialty training background in a general hospital served as the experimental group and reference group, respectively. The experimental group underwent a training course including a 30-min lecture and two hands-on sessions (2 h each). After the course, residents from both groups were asked to perform the instrument removal procedure on simulated root canals. Success rate, procedure time and canal volume change were compared between groups. Questionnaire results were also analysed.

RESULTS

All residents successfully managed to remove the broken instruments in the test. Procedure time was significantly longer for general dentistry residents (15.8 ± 5.7 min vs 13.7 ± 4.5 min, Mann-Whitney U test, p = .038). Canal volume change was significantly greater for general dentistry residents (8.53 ± 3.82 μl vs 5.94 ± 2.73 μl, independent-samples t-test, p = .004). In the questionnaires, trainees gave overall positive ratings for the course. The marginal homogeneity test on before and after scores of the questionnaire items showed the training helped the trainees to reduce the stress level associated with instrument breakage (p < .001). It also motivated the trainees to remove the broken instrument in some straightforward cases (p < .001).

CONCLUSION

The broken instrument removal training course could help the general dentistry residents better manage the intracanal broken instrument situation.

Endodontic Orthograde Retreatments: Challenges and Solutions

Endodontic orthograde retreatments are considered one of the possible treatment options in case of post-treatment diseases considering the promising results present in the literature. Despite this, a plethora of articles have been published on this topic, and drawing conclusions could be challenging. For this reason, this review aims to summarize the crucial points on each aspect of non-surgical endodontic retreatments, discussing and comparing the current protocols, techniques, materials, and indications. Taking into consideration data from the literature, in terms of diagnosis, CBCT should be considered the first choice, since it can thoroughly affect the diagnosis and treatment plan. Regarding the procedural phases, some conclusions can be drawn: when present, coronal restoration materials such as crowns, partial prostheses, post, and core should be removed; the use of magnification devices, ultrasonic instruments, and an in-depth interpretation of radiographic images with both 2D and 3D images are strongly recommended during the orifice location; additional protocols such as irrigants activation, ultrasonic cleaning, and rotary or reciprocating instrumentation of treated canals are strongly recommended for filling materials removal and to achieve a high-quality chemo-mechanical disinfection; perforations should be treated as soon as possible, and the material of choice to treat them is the MTA or other calcium-silicate-based repair materials; the presence of ledges does not intrinsically reduce the success rate of RCRts if properly managed; in case of instrument fragments, their removal should be considered as the first treatment option, however many variables should be considered to select the proper technique or consider the option of bypassing.

Efficacy of the HBW Ultrasonic Ring for retrieval of fragmented manual or rotatory instruments

A study was conducted to evaluate the success rates of bypassing or removing fragments of instruments that had fractured within the roots of mandibular molars using a HBW Ultrasonic Ring. Forty extracted first permanent mandibular molars with root canal curvature were included. The teeth were distributed randomly into four groups according to the type of instrument and the root canal third where they had fractured. The success rate for removal of instrument fragments was 100% for both of two stainless steel groups, 90% for a nitinol middle third group, and 80% for a nitinol apical third group. The mean time required for instrument removal was around 40 min. The HBW Ultrasonic Ring showed acceptable experimental results for retrieval of broken instrument fragments.

Nickel ion release and surface analyses on instrument fragments fractured beyond the apex: a laboratory investigation

BACKGROUND

To analyse the changes in surface and nickel ion release characteristics of fractured root canal shaping instruments in a simulated body fluid environment.

METHODS

A total of 54 new instruments were studied. The instrument groups consisted of five different NiTi alloys and a stainless-steel alloy. To standardize instrument fracture, a torsional type of failure was created on each instrument. The fractured specimens of each instrument group were randomly divided into three static immersion subgroups of 1 h, 7-day, and 30-day (n = 3). Simulated body fluid (SBF) was prepared to mimic human blood plasma by Kokubo&Takadama protocol for ex situ static immersions at 37ºC. The surfaces were examined via scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. To determine the quantitative ion release, the retrieved SBFs were analyzed using inductively coupled plasma mass spectrometry. Two-way ANOVA and Tukey post hoc tests sought the statistical significance of the nickel ion values(p < 0.05).

RESULTS

In 1 h of immersion, the newly formed structures, exhibiting mostly oxygen signals, were widespread and evident on NiTi surfaces. In contrast, fewer structures were detected on the SS surface in that subgroup. In 7 days of immersion, a tendency for a decrease in the density of the new structures was revealed in NiTi groups. The oxygen signals on NiTi group surfaces significantly increased, contrary to their decrease in SS. Signals of sodium, chlorine, and calcium were detected, indicating salt precipitates in groups. In 30 days of immersion, salt precipitates continued to form. The Ni-ion release values in all instrument groups presented significant differences in comparison to the SBF control in all immersion periods(p < 0.001). No significant differences were observed in immersion time periods or instrument groups(p > 0.05).

CONCLUSIONS

Within the limitations of the presented study, it was concluded that the fractured SS and NiTi root canal instruments release Ni ions in contact with body fluid. However, the Ni ion release values determined during the observation periods are lower than the critical toxic or allergic thresholds defined for the human body. This was due to the ionic dissolution cycle reaching a stable state from 1-hour to 30-day exposure to the body fluid of fractured instruments.

Comparative Evaluation of a Dynamic Navigation System versus a Three-dimensional Microscope in Retrieving Separated Endodontic Files: An In Vitro Study

INTRODUCTION

This study aimed to compare the effectiveness of a dynamic navigation system and a three-dimensional microscope in retrieving broken rotary Nickel-Titanium files when using trepan burs and the extractor system.

MATERIALS AND METHODS

Thirty maxillary first bicuspids with 60 separate roots were split into 2 comparable groups based on a comprehensive cone beam computed tomography analysis of the root length and curvature. After standardized access opening, glide paths, and patency attainment with the K file (sizes 10 and 15), the teeth were arranged on 3D models (three per quadrant, six per model). Subsequently, controlled-memory heat-treated Nickel-Titanium rotary files (#25/0.04) were notched 4 mm from the tips and fractured at the apical third of the roots. The C-FR1 Endo file removal system was employed under both guidance to retrieve the fragments, and the success rate, canal aberration, treatment time, and volumetric changes were measured. The statistical analysis was performed using IBM SPSS software at a significance level of 0.05.

RESULTS

The microscope-guided group had a higher success rate than the dynamic navigation system guidance, but the difference was insignificant (P > .05). In addition, the microscope-guided drills resulted in a substantially lower proportion of canal aberration, shorter time to retrieve the fragments and less change in the root canal volume (P < .05).

CONCLUSION

Although dynamically guided trephining with the extractor can retrieve separated instruments, it is inferior to three-dimensional microscope guidance regarding treatment time, procedural errors, and volume change.

Removal of separated instruments from unfavourable locations: Case reports using the HBW ultrasonic ring or a surgical approach

Two patients were admitted to the dental clinic to evaluate two right mandibular first molars (both FDI no. 46). In Case 1, there was an accidental instrument separation, which was thought to have been bypassed; however, the instrument was located beyond the apical foramen, in the alveolar bone. The 1-week follow-up revealed that the fragment was close to the inferior alveolar nerve, thus allowing surgical removal to be performed. In Case 2, two separated instruments located in the apical third of the mesiobuccal and mesiolingual canals were removed using the HBW ultrasonic ring coupled to ISO 10 and 15 hand instruments. The 3-month and 1-year follow-ups (Case 1), and the 2-year and 3-year follow-ups (Case 2) showed a favourable evolution in both cases. It can be concluded that both the surgical approach and the HBW ultrasonic ring are viable options for the removal of separated instruments in unfavourable locations.

Endodontic Clinical Outcome after Separated Instrument Removal Using a Spinal Needle Technique: A Retrospective Study of Thirty Years of Clinical Experience

INTRODUCTION

Current methods for the removal of separated endodontic instruments (RSI) are not predictable.

METHODS

The primary outcome of this retrospective study was to assess the clinical and radiographic success (CRS) of teeth in case of RSI after a 5-year follow-up. Secondary outcomes were to evaluate (1) the effectiveness in RSI and (2) the risk of root fracture after RSI. The study protocol was registered at ClinicalTrials.gov (ID: NCT05128266). The patients were treated by the same endodontist between January 1991 and December 2019. The RSI was performed under the operative microscope as follows: first, the dentine surrounding the coronal part of the broken instrument was selectively removed by using a small ultrasonic tip to loosen the fragment; then, a modified spinal needle was used to catch and remove the instrument. The 1-, 3-, 5-, and >5-year CRS were recorded. Logistic regression analysis was performed to determine independent predictors of failure (ie, tooth number, type of root canal, shape of the root canal, type of broken instrument, apicocoronal level of the separated instrument, presence of periapical lesions, and root perforations).

RESULTS

A total of 158 teeth were included in this study. Finally, 131 instruments underwent RSI (82.9%). RSI was an independent predictor of CRS after 1-year of treatment (odds ratio: 58.3; 95% confidence interval: 27.42-95.73, P < .05). At the 5-year follow-up, only 10 of 131 teeth (7.6%) failed. All failures were caused by root fracture (10/10) (χ2 test, P < .05). Separated instruments located in the apical third of the root were more difficult to remove (13/49 cases, 26.5%; χ2 test, P < .05).

CONCLUSIONS

The proposed technique can achieve excellent effectiveness in RSI, can achieve a high CRS rate when a periapical lesion is present, is not associated to a significant increase in root fracture incidence, and should be performed with the help of an operative microscope.

Removing Fractured Endodontic Files with a Tube Technique-The Strength of the Glued Joint: Tube-Endodontic File Setup

One recommended technique for removing broken root canal instruments is to glue the fragment into a cannula adapted to it (i.e., the tube technique). The aim of the study was to determine the influence of the adhesive kind and length of the joint on the breaking force. During the investigation, 120 files (60 H-files and 60 K-files) and 120 injection needles were used. Fragments of broken files were glued into the cannula using one of three materials: cyanoacrylate adhesive, composite prosthetic cement, or glass ionomer cement. The lengths of the glued joints were 2 and 4 mm. After the polymerization of adhesives, a tensile test was carried out to find a breaking force. The results were statistically analyzed (p < 0.05). For 4 mm lengths of glued joints, the breaking force was higher than for 2 mm for both file types (K and H). In the case of K-type files, the breaking force was higher for cyanoacrylate and composite adhesives than glass ionomer cement. For H-type files, no significant difference in joint strength was found between binders at 4 mm, while at 2 mm, a much better connection was obtained for cyanoacrylate glue than prosthetic cements.

Retrieval of Separated Intracanal Endodontic Instruments: A Series of Four Case Reports

The separation of an endodontic instrument during a root canal procedure is one of the most common endodontic mishaps. Separation of endodontic instruments may block access to the apical portion of the root and hamper the disinfection process. It obstructs the appropriate debridement of the canal apical to the fragment, jeopardizing the treatment's outcome. However, due to the advancements in the methods and armamentarium, the effective retrieval of a separated instrument (SI) from the root canal has become possible. This paper includes a case series of management of separated instruments whereby SI was successfully removed in four cases. The instruments were separated intracanal at various levels in the middle and apical third of maxillary and mandibular molar teeth. The level of separation was located, staging performed, and SI was removed using an ultrasonic device under magnification. Removal of the SI was followed by obturation till the entire working length and subsequent post-endodontic restoration. Patient satisfaction with treatment outcomes in all cases was good. Case evaluation, good armamentarium, adequate knowledge along with good clinical skills and experience aid in the successful retrieval of separated instruments. Removal of the instrument without further damage to radicular dentin is important to maintain the integrity of the tooth.

Factors that affect the outcomes of root canal treatment and retreatment-A reframing of the principles

This paper undertakes a broad and comprehensive synthesis of relevant clinical, biological, biomechanical, technical and healthcare services data to understand the factors affecting outcomes of periapical healing after root canal (re)treatment. The medical and dental evidence-based era (1980-present) is contextualized with the earlier evidence drive in endodontics (1911-1940) triggered by the focal infection era. The current evidence-based approach has a sharper focus on evidence quality and derivation of practice guidelines. Contrary views question whether guideline-driven, or expertise-development-driven endeavours would best serve outcome improvement in society. The endodontic discipline functions in a broad healthcare framework and sustains industrial, economic and trend pressures that may be deemed to influence outcomes. The nature of root canal treatment and the challenges in determining the factors that affect its outcomes is discussed. The factors potentially affecting periapical healing after root canal treatment are classified into pre-operative, intra-operative and postoperative groups. These categories subsume multiple elements with interactive influences, creating a complex picture, further confounded by some apparently surprising, counter-intuitive and contradictory findings. The technical versus biological conundrum in root canal treatment continues to cause cognitive dissonance. However, due reflection and cross-discipline-synthesis resolve the apparent data conflicts into a very simple, consistent and plausible picture of how root canal treatment works and the key factors that affect periapical healing. Root canal retreatment is considered mainly in the context of its differences from primary treatment as the majority of factors influencing outcomes are common to both. The exceptional difference is that retreatments have a proportionately reduced probability of healing by virtue of compromised apical root canal ramification access or modified host/infection interactions. Root canal (re)treatment outcomes are dominantly influenced by the nature of prior dynamic host/infection interaction (pre-operative patient factors) and how the direction of this dynamic is influenced by two factors: (1) the active efficacy of the operators' root canal treatment protocol to sustain a microbial ecological shift (intra-operative treatment factors) and dampen periapical inflammation; and (2) the passive ability of the functional tooth (and its restoration margin) to maintain its integrity to resist infection reversal (postoperative restorative factors).

Perception of Dental House Officers regarding Endodontic File Separation during Endodontic Treatment

Background

Despite of having improved endodontic file designs as well as the reinforced metal alloy file structure, intracanal endodontic file separation (EFS) is still a very problematic and worrisome dental incident, which usually occurs without any visible signs of permanent deformation. Further, there have been conflicting reports regarding the clinical significance of leaving separated files within root canals.

Aims

The aim of this study was to look into the current perceptions and awareness about file separation during endodontic treatment among the dental house officers (DHOs).

Materials and Methods

A novel validated questionnaire comprising of 15 close-ended questions was distributed anonymously via Google Forms through email to 1100 DHOs across Pakistan. The questionnaire consisted of two parts: the first component (Section I) collected demographic data and the second component (Section II) investigated the causes of EFS during root canal treatment. Following the completion of socioeconomic information, including age and gender, the DHOs were asked to answer a few questions about the various reasons for endodontic instrument fracture.

Results

A total of 800 responses were recorded, with an effective rate of 72.8%. The majority of the DHOs (p value < 0.001) perceived that endodontic instrument fracture occurred in the posterior (61.5%) and apical third of the canal (50.5%) and in older permanent dentition (67.3%), possibly due to patient anxiety (62%). Better choice of instrument (61.15%), operators' experience (95.3%), knowledge (87.5%), and proper root canal cleaning (91.1%) are believed to be the vital steps in reducing endodontic file separation/fracture. Furthermore, majority of them (p value < 0.001) perceived that stainless steel was a superior alloy for filing instruments. Manual files tend to be more prone to fractures due to repeated use than rotary files.

Conclusion

This study demonstrated that young DHOs had adequate knowledge and awareness regarding the potential predisposing factors and handling techniques for EFS. This study thereby provides an evaluating tool to access the insights of the current perceptions and awareness of DHOs concerning EFS.

MAGNIFICATION, ULTRASONICS AND BIOCERAMICS - THE IDEAL TRIO FOR FILE RETRIEVAL: A CASE REPORT

During routine endodontic therapy, a clinician may encounter many procedural errors which alter the course and outcome of the treatment. Instrument separation is one of the most common types of procedural error, resulting in metallic obstruction in the canal and impeding efficient cleaning and shaping of the root canal. The clinician has to evaluate the options of attempting retrieval, bypassing or leaving the fragment as it is. When an attempt such a fragment becomes difficult, it should be retrieved with the help of ultrasonics under magnification and the canals should with bioceramic sealer to improve the tooths prognosis.

Demystifying Failures Behind Separated Instruments: A Review

Instrument separation is one of the most routinely encountered mishaps occurring in the arena of endodontics. Separation occurs unknowingly most times and we are left to ponder as to where to head next. It is majorly the lack of knowledge and skill that makes us panic in these times. The objective still remains to effectively clean as well as shape the root canal so that it can best receive the obturating material. Thus sudden breakage of a file during this critical phase leaves the clinician in an absolute dilemma. This review thereby throws light onto the various factors that remain in the hand of the clinician before proceeding for biomechanical preparation of the root canal so as to prevent instrument fracture. The correct application and knowledge of these techniques will prevent procedural mishaps from occurring and further enhance the quality of the treatment.

The Efficiency of the BTR-Pen System in Removing Different Types of Broken Instruments from Root Canals and Its Effect on the Fracture Resistance of Roots

The study aimed to evaluate the efficiency of the BTR-Pen system in removing different types of instrument fragments from root canals and to assess its effect on fracture resistance of the roots after the removal of the instruments. One hundred thirty human teeth were divided into 10 groups (2 control groups and 8 study groups) according to the localization and type of the fractured fragment as well as the retrieval techniques. Broken instruments were extracted either with BTR-Pen system loops or removed using solely ultrasonic tips. The success rate of instrument removal and consumed time were recorded. All the teeth were subjected to a load at a 1 mm/min rate in a universal testing machine for mechanical testing. The success of removing broken instruments using the BTR-Pen and ultrasonic was 86.7% and 83.3%, respectively (p > 0.05). When the time is compared, the BTR-Pen system (23.97 ± 8.35 min) showed similar results to that of the ultrasonic technique (24.1 ± 8.28 min) (p > 0.05). The BTR-Pen group required less force to fracture than the ultrasonic group (p = 0.024). In conclusion, the BTR-Pen and ultrasonic groups showed no significant difference in terms of the success rate and removal time. The roots that underwent instrument removal using the BTR-Pen system had less fracture resistance.

The Effect of Cone-Beam Computed Tomography (CBCT) Evaluation on Treatment Planning after Endodontic Instrument Fracture

Intracanal instrument fracture is a procedural iatrogenic event during endodontic treatment that may affect treatment planning and eventually treatment outcome. Cone Beam Computed Tomography (CBCT) has offered several advantages, especially in endodontic cases in which information from conventional periapical radiograph may not be adequate to allow a precise treatment planning decision and a subsequent appropriate management of the cases. The present study was firstly conducted to assess the effect of CBCT evaluation on the decision-making process after instrument fracture; secondly, to introduce a new clinical approach in cases with fractured instruments located in the mesial roots of mandibular and maxillary molars. The study design was observational. The sample comprised all cases of mandibular and maxillary molars where an instrument fracture had occurred in the mesial roots. Two qualified (National and Kapodistrian University of Athens, Greece) and experienced (more than fifteen years of daily practicing) endodontists evaluated all the cases. The initial treatment plan made by evaluating periapical radiographs of each case was compared to the final plan set after CBCT evaluation. A marginal homogeneity test for paired data was conducted to test the concordance of treatment planning with periapical radiographs versus CBCT. Multivariable logistic regression was structured to identify predictors of modification in treatment planning following CBCT assessment, and to record estimators for decision to remove, bypass or retain the fragment. The level of statistical significance was pre-specified at p < 0.05. Of a total 52 cases evaluated, change in treatment planning with conventional periapical radiograph as a reference, following evaluation of CBCT, was observed in more than half of the teeth. The difference was statistically significant (p < 0.001). Apical location of the fragment was more likely to induce a perceived change in treatment planning after CBCT evaluation (p < 0.01). Canal merging induced 95% lower odds (p = 0.01) for taking a decision to remove or bypass, revealing that retaining the fragment was by far a more likely decision. A significant impact of CBCT preoperative evaluation on treatment planning for the management of such cases was demonstrated. Apical location of the fragment and canal merging seem to influence the decision-making process.

Robotic and Microrobotic Tools for Dental Therapy

Robotic and microrobotic tools such as dental operating microscopes and dental endoscopes are being used extensively in dental therapy, which have a significant impact on dental therapy and education. Herein, this paper reviews the state of the art of robotic and microrobotic tools for dental therapy. This article starts with a brief introduction of current robotic and microrobotic tools for dental therapy and then displays their applications in various dental problems; strengths and weaknesses are also surveyed. Lastly, the conclusion and outlook are discussed, referring to the emerging dental clinic problems and demands. This review is expected to provide guidelines for the therapeutic application of robotic and microrobotic tools and to promote the development of robots in dentistry.

Management of a radiopaque foreign body associated with a lower first premolar: A case report

Operator mishaps significantly affects root canal treatment outcome. However, several factors affect root canal anatomy of teeth. Therefore, knowledge of teeth anatomy and the use of advanced technologies like cone-beam computed tomography (CBCT), magnification, and illumination are crucial for better diagnostic purposes and to avoid any procedural errors. In this case report, we present a case of a 32-year-old male patient with a radiopaque foreign body associated with a lower first premolar tooth and how do the use of advanced technologies could affect the treatment outcome.

Cyclic and spontaneous movement of a fractured and extruded instrument back into the root canal: A rare case report

Retreatment of endodontically involved teeth may require the removal of obstruction from root canal space. Instrument fracture is an undesirable and stressful incident which can negatively affect the prognosis of the tooth. Any corrective step taken should be performed with utmost care to prevent extrusion of the fragment into periapex. This case report describes a rare occurrence of movement of a fractured instrument during inter-appointment period. A previously treated left mandibular first molar with a fractured instrument was taken up for retreatment. During the course of treatment, the fractured fragment which was previously located in the apical third of the distal canal was dislodged into the periapical region. However, it was found that fragment moved back inside the canal after the inter-appointment period. The same sequence of events repeated before the instrument could be retrieved. Hydrostatic and vascular pressure build due to periapical inflammation could be cited reasons for such a movement.

Techniques to address fractured instruments in the middle or apical third of the root canal in human permanent teeth: a systematic review of the in vitro studies

OBJECTIVE

The objective of this study is to investigate techniques for approaching fractured instruments in the root canal and to present possible outcomes in relation to dentin thickness, fracture resistance, technique success, and clinical time.

MATERIALS AND METHODS

The bibliographic research was carried out in PubMed, Cochrane, Lilacs, Web of Science, Scopus, grey literature, and manual search. Following the inclusion and exclusion criteria, the titles and abstracts of 506 articles were read. Of these, 60 articles were selected and read in full. Fourteen articles were included in this systematic review.

RESULTS

The most studied technique was the ultrasonic technique and obtained good general results. The more apically the instrument is located, the more difficult it is to remove, the more dentin is removed, and the lower the fracture resistance of the tooth. When removal is not possible, the bypass technique can be performed (bypassing), and on weakened teeth or with little dental remnants, the GentleWave System technique can be used.

CONCLUSION

This systematic review shows the evidence from laboratory studies that the curvature and the root third in which the fracture of instruments occurred is relevant to fracture resistance and success. The ultrasonic technique got the best results. Well-conducted clinical studies should be performed for clinical practice.

CLINICAL RELEVANCE

The approach of fractured instruments in the root canal is efficient with the use of ultrasound, bypass technique, and Gentle Wave System.

Effect of Core Mass and Alloy on Cyclic Fatigue Resistance of Different Nickel-Titanium Endodontic Instruments in Matching Artificial Canals

Instrument failure during root canal preparation is still a concern among endodontists. However, it remains unclear whether the use of more martensitic alloys or the cross-sectional design parameters (i.e., core mass) significantly improve fracture resistance. The aim of the study was to evaluate the impact of core mass and alloy on dynamic cyclic fatigue resistance of nickel-titanium endodontic instruments in matching artificial canals at body temperature. Two groups were tested. (A) taper 0.04: F360 (Komet, Lemgo, Germany), Twisted file (Sybron Endo, Glendora, CA, USA) (=TF), JIZAI (Mani, Tochigi, Japan) (=J_04) (all size #25) and the variable tapered TruNatomy (Dentsply, Ballaigues, Switzerland) (size #26) (=TN). (B) size #25; taper 0.06: (Mtwo (VDW, Munich, Germany), JIZAI (Mani) (=J_06), and variable tapered Hyflex EDM OneFile (Coltene Whaledent, Altstätten, Switzerland) (=HF). Time, number of cycles to fracture (NCF), and number and length of fractured fragments were recorded and statistically analysed using ANOVA Student-Newman-Keuls, Kruskal–Wallis or Chi-square test (significance level = 0.05). (A) TN showed the significantly shortest time until fracture, followed by TF, F360 and J_04 which also differed significantly, while NCF showed the following order: F360 < TN < TF < J_04 (p < 0.05). Only one J_04 but all instruments of the other groups fractured within the test-limit of 10 min. (B) Mtwo was significantly inferior concerning time until fracture and NCF, compared to J_06 and HF (p < 0.05), which did not differ significantly (p > 0.05). While all Mtwo instruments fractured, only four instruments failed in the other groups (p < 0.05). Within the limitations of this study, alloy and cross-sectional design (i.e., core mass) were critical factors regarding instrument failure, but none of these factors could be determined as a main parameter for increased or decreased time, and cycles to fracture. Rather, it seemed to be the interaction of multiple factors (e.g., longitudinal and cross-sectional design, alloy, and rotational speed) that was responsible for differences in the time and cycles to fracture. Nonetheless, all instruments had lifetimes that allow safe clinical use. However, the superiority or inferiority of an instrument with regard to cyclic fatigue based on laboratory results—even when identical trajectories are guaranteed—may be considered questionable, as the characteristics and design parameters of the instruments vary considerably, and the experimental setups lack additional clinical parameters and thus clinical relevance.

A Novel Surgical Approach for the Successful Removal of Overextruded Separated Endodontic Instruments

Endodontic procedures can result in various complications. Separation of the endodontic instrument is a common complication of incorrect use or overuse of the instrument. However, a separated endodontic instrument may hinder cleaning and shaping during endodontic treatment procedures, which can potentially impact prognosis. Therefore, it is necessary to manage this complication by removal of the separated instruments from inside the root canal. Although several devices are used, nonsurgical removal for retreatment remains difficult. We report the case of a failed attempt to manage a separated endodontic instrument nonsurgically by a private dentist, which resulted in extrusion of the instrument beyond the root apex and its migration into the mandible. We describe a novel surgical approach involving intentional tooth replantation combined with alveolar osteotomy. There have been few reports on the management of separated endodontic instruments that were pushed out beyond the root apex. Our novel surgical approach suggests a technique for the potential removal of a separated endodontic instrument extruded beyond the root apex.

A Modified Partial Platform Technique to Retrieve Instrument Fragments from Curved and Narrow Canals: A Report of 2 Cases

Two cases are reported to present the "Burrow platform" (BP) technique. The BP technique uses a partial platform for retrieving instrument fragments, thereby reducing the loss of radicular dentin.The BP technique is a microscope-aided approach implementing coated ultrasonic tips to create an access to instrument fragments in the middle and apical thirds of the root canal. The technique consists of 4 steps: (1) coronal access, (2) radicular access, (3) partial platform, and (4) exposure of the fragment and retrieval. A precise, angulated access pathway is specific to the BP technique. In the coronal half, the radicular access pathway extends toward the outer wall of the curvature. In the apical half, the radicular access pathway is oriented toward the inside of the curvature. One and 4 instrument fragments were successfully retrieved in the respective cases. At follow-up, all teeth were asymptomatic and had responded favorably to the treatment.The BP technique may present a suitable alternative to fragment removal from curved canals and slender roots to avoid ledge formation, transportation, and perforation. Instrument retrieval using the BP technique can be performed using commonly available armamentarium.

Angle of Insertion and Torsional Resistance of Nickel-Titanium Rotary Instruments

Previously published studies have investigated the influence of instrument access on cyclic fatigue resistance. However, no studies have evaluated the relationship between angulated access and torsional resistance. The aim of this study was to investigate the influence of the angle of access on the torsional resistance of endodontic instruments. One hundred and eighty instruments were selected: 90 F-One Blue 25/04 and 90 HeroShaper 25/04 instruments. Three subgroups (n = 30) for each instrument type (A and B) were established according to the angle of insertion of the instruments inside the artificial canal (0°, 10° and 20°). The tests were performed using a custom-made device consisting of the following: a motor that can record torque values of 0.1 s; interchangeable stainless-steel canals with different curvature (0°, 10° and 20°) that allow the instrument’s angulated insertion and keep it flexed during testing procedures; and a vise used to secure the instrument at 3 mm from the tip. Torque limit was set to 5.5 Ncm, and each instrument was rotated at 500 rpm until fracture occurred. Torque to fracture (TtF) was registered by the endodontic motor, and the fragment length (FL) was measured with a digital caliper. Fractographic analysis was performed using a scanning electron microscopy (SEM) evaluation to confirm the cause of failure. TtF values and fragment length (FL) values were statistically analyzed using one-way analysis of variance (ANOVA) test and the Bonferroni correction for multiple comparisons across the groups with significance set to a 95% confidence level. Regarding the F-One Blue instruments, the results showed a higher TtF for group A3 (20°) than for group A1 (0°) and group A2 (10°), with a statistically significant difference between group A3 and the other two groups (p < 0.05), whereas no statistically significant difference was found between group A1 and group A2 (p > 0.05). Regarding the HeroShaper instrument, the results showed the highest TtF for group B3, with a statistically significant difference between the three subgroups B1, B2 and B3 (p < 0.05). The results showed that the torsional resistance increases as the angle of instrument access increases with a varying intensity, according to the crystallographic phase of the instrument selected.

A Paradigm Shift for Torsional Stiffness of Nickel-Titanium Rotary Instruments: A Finite Element Analysis

INTRODUCTION

The aim of this study was to investigate the influence of mass and the polar moment of inertia on the torsional behavior of nickel-titanium rotary instruments to understand which parameter of cross-sectional design had a key role in terms of torsional resistance.

METHODS

Four different instrument models were designed and meshed using computer-aided engineering software (SolidWorks; Dassault Systems, Waltham, MA). Instrument models shared the same characteristics, except for cross-sectional design; triangle, rectangle, square, and hollow square geometry was selected. Finite element analysis was performed simulating a static torsional test using the FEEPlus internal solver (Solid Works). Von Mises stress and torsional load at fracture were calculated by the software. Linear regression analysis was performed to investigate the relationship of the polar moment of inertia, cross-sectional area, inner core radius, and mass per volume on the torsional resistance of nickel-titanium rotary instruments.

RESULTS

The polar moment of inertia positively affected the maximum torsional load with the highest level of correlation (R² = 0.917). It could be stated that the higher the polar moment of inertia is, the more maximum torsional load at fracture is present. Mass and cross-sectional area had a lower level of correlation compared with the polar moment of inertia (R² = 0.5533). According to this, 2 instruments with the same mass/mm and/or cross-sectional area could have different torsional resistance.

CONCLUSIONS

The polar moment of inertia can be considered as the most important cross-sectional factor in determining the torsional resistance of rotary instruments over metal mass and cross-sectional area.

Preventing nickel-titanium rotary instrument from breakage by continuous irrigation with different fluids during root canal preparation

To study the effect of continuous irrigation of rotating nickel-titanium instrument with several common clinical fluids on the diameter, breaking length and breaking position of nickel-titanium instrument, so as to provide some reference and theoretical basis for clinical operation and instrument improvement.A standardized curved root canal model was established, and ProTaper Universal (PTU) F1 instrument was selected for root canal preparation. The nickel-titanium F1 instrument was flushed with distilled water, 0.9% NaCl, 0.2% chlorhexidine, 1% sodium hypochlorite and 5% sodium hypochlorite, and the diameter, length and position of the instrument before and after breakage were recorded.Only 5% sodium hypochlorite influenced the diameter of 6 mm marker points under different irrigation conditions (P < .05). There was no statistical difference in the length of broken instruments among all the groups, and torsional deformation mainly occurred at the end of broken instruments. The broken positions of instruments in all the groups were located at the bending segment of the root canal. The breaking frequency of the 5% sodium hypochlorite group was the highest in the area 3-5.5 mm away from apical foramen, while the other 4 groups had the highest breaking frequency in the area 0 to 1.5 mm away from apical foramen.External irrigation with different fluids did not influence the breaking length of instruments. The closer to the apical foramen was, the higher the breaking frequency of instruments was. However, only 5% sodium hypochlorite can affect the diameter of rotary nickel-titanium instruments, and may lead to early breakage of the instrument, indicating that the use of disinfectants, except 5% sodium hypochlorite, cannot reduce breakage resistance of nickel-titanium instrument compared with distilled water flushing. Furthermore, 5% hypochlorite could not be recommended for irrigation in clinical practice.

Management of an over-extruded fragment in a C-shaped root canal configuration: A case report and literature review

Separation of root canal instruments is a common incident during root canal treatments' procedures. The complex configuration of root canal systems is one of the most influencing factors, not only during the occurrence of instrument separation but also during the management of such unpleasant incidents. There are few reports on the management of fractured instruments located in the apical third of the root canals apical, especially those extruded beyond the apex. A 37-year-old woman was referred to an endodontic specialist to complete a root canal treatment after the separation of an endodontic file in the middle-third of the C-shaped root canal configuration (Vertucci type II) of the mandibular second molar. A failed attempt at managing the fragment by the dentist resulted in the backward placement of the fragment, which was more apically, and partial extrusion beyond the root apex. The fractured instrument was successfully and safely retrieved using different procedures and techniques including bypassing the fragment, loosening the fragment using ultrasonics and then removing it by the crab-claw shaped tweezers (Zumax broken instruments removal kit). This case report demonstrates the importance of high magnification provided by the dental operating microscopes and sound clinical skills and judgment, especially in assessing the difficulty of cases that is necessary for various treatment approaches. In addition, the availability of different armamentaria to manage separated instruments is essential. Finally, this case report proposes and advocates the idea of removing fractured instruments extruding beyond the apex without surgery.

Ethical Aspects concerning Instrument Separation and Perforations during Endodontic Treatment: A Cross-Sectional Study

Aim

During endodontic treatment, dentists may face various unwanted procedural accidents, at any stage of the treatment that might compromise endodontic treatment outcome and bring obstacles to dentists as well. This study aimed to address and analyze several ethical concerns relating to the behavioural conduct of dentists towards endodontic instrument separation as well as perforation of the crown and/or root during root canal treatment in Riyadh, Saudi Arabia.

Method

Hundred and eleven questionnaires were distributed among dentists working in Riyadh in university clinics and government and private sectors. Data were collected, reviewed, and statistically analyzed by Fisher's exact and chi-square tests at a 5% significance level, using SPSS software.

Results

54.5% of the respondents have encountered instrument separation. 53.2% stated that they would inform the patient about the instrument separation. 43.6% of the respondents had experienced perforation during root canal treatment, and 54.9% reported that they would inform the patient of the accident.

Conclusion

Within the limitation of this survey, we concluded that most of the dental professionals did not hesitate to adhere to the correct ethical conduct, and they would inform the patient if an incident occurred.

Electrochemical dissolution of nickel-titanium instrument fragments in root canals of extracted human maxillary molars using a small reservoir of electrolyte

AIM

To evaluate the viability of the electrochemical dissolution of fragments of fractured NiTi instruments in root canals of extracted human maxillary molars, using two electrodes and the solution restricted to a small reservoir coupled to the pulp chamber. The primary hypothesis was that this method enables the reduction of fragment volume and re-establishment of the root canal path with a size 08 K-file, both in simulated canals and in extracted human maxillary molars.

METHODOLOGY

Fragments of F1 ProTaper instruments were polarized in simulated root canals and in distobuccal root canals of extracted maxillary molars using a new method, with the solution restricted to a small acrylic microcell coupled to each resin block or pulp chamber. Two electrodes were used, where one was kept in contact with the intracanal fragment and another was positioned in the solution present in the acrylic microcell. After the tests, a size 08 K-file was used passively to verify the possibility of bypassing the fragment, which was also confirmed by radiographic analysis. Micro-CT analysis of the teeth was used before and after fragment dissolution to evaluate the volume, length and porosity of the fragments. The D'Agostino-Pearson normality test was used to verify the distribution of the data. A paired t-test (P < 0.05) was used to compare the volume, length and porosity of the fragments before and after the dissolution tests.

RESULTS

After dissolution, all fragments could be bypassed with a size 08 K-file in both simulated canals and in extracted teeth. The dissolution process did not result in significant reduction of neither the fragment length nor the fragment porosity. However, it resulted in a significant reduction of fragment volume (paired t-test, P < 0.05).

CONCLUSION

The electrochemical dissolution of fragments of NiTi files in root canals of extracted human maxillary molars using two electrodes, and the solution restricted to a small reservoir coupled to the pulp chamber resulted in a significant reduction of fragment volume. The re-establishment of the root canal path with the passive insertion of size 08 K-files was possible in all samples after the tests, both in simulated canals and in extracted teeth.

Effect of different irrigation methods in the presence of a separated instrument: an in vitro study

Objective: The aim of this study was to evaluate the effect of different irrigation methods on sodium hypochlorite (NaOCl)/debris extrusion and dentinal tubule penetration of 2.5% NaOCl in the presence of an apically separated instrument.Materials and methods: Sixty root canals of freshly extracted mandibular single-rooted premolars were chemomechanically prepared up to ProTaper F2. Manual needle irrigation (30-gauge/side-vented) with 2.5% NaOCl was performed between files and a smear layer was removed with 17% ethylenediaminetetraacetic acid. Three mm of notched ProTaper F3 files were separated in the apical third of the roots. Samples were then randomly divided according to the final irrigation systems as follows: EndoActivator, EndoVac, manual needle irrigation, passive ultrasonic activation, and RinsEndo. Samples were mounted to Eppendorf tubes and root canals were irrigated with 3-mL Rhodamine B-labelled 2.5% NaOCl, which was applied using one of the above-mentioned methods. The extruded NaOCl/debris weight was calculated by extracting pre-irrigation weights of tubes from post-irrigation ones. Samples embedded in acrylic resin were sectioned transversely in 1-mm thicknesses at apical 1- and 3-mm levels. NaOCl's penetration depth and percentage into the dentinal tubules were evaluated with the aid of a confocal laser scanning microscope. Data were analysed statistically with Kruskal-Wallis and post hoc Siegel-Castellan tests (p < .05).Results: EndoVac significantly decreased the extruded NaOCl/debris compared to RinsEndo, passive ultrasonic activation, and EndoActivator in the presence of a separated instrument (p < .05). The penetrability of NaOCl significantly increased with the use of RinsEndo and EndoVac compared to the remaining groups (p < .05).Conclusion: In the presence of an irretrievable separated instrument, it could be suggested that devices with apical negative pressure such as EndoVac may improve the penetrability of irrigation solutions to the apical part of the root while preserving periapical tissues from NaOCl/debris extrusion.

Sealer penetration: effect of separated file's cross-section, taper and motion characteristics

OBJECTIVES

The separated root canal instruments may affect the quality of root canal filling, hence the success of endodontic treatment. The aim of this study was to evaluate the effects of separated file fragments of nickel-titanium rotary systems with different cross-section, taper and motion characteristics on the apical sealer penetration in oval-shaped root canals via confocal laser scanning microscope (CLSM).

MATERIALS AND METHODS

Distal roots of 60 mandibular molars with oval-shaped root canals were randomly divided into 4 groups as follows: group 1, FlexMaster Nickel Titanium Rotary File System (NTRFS) (separated instrument: 30/.06); group 2, ProTaper Next NTRFS (X3); group 3, ProTaper Universal NTRFS (F3); group 4, Revo-S NTRFS (AS30/.06). Root canals were filled with gutta-percha and AH plus labelled with 0.1% rhodamine B using a warm vertical compaction technique. Each specimen was horizontally sectioned at 1st, 3rd and 5th mm from apical foramen. Amount of maximum and average penetration depths, penetration percentage and sealer penetrated area were measured and analysed with one-way repeated measures of ANOVA and the Bonferroni post hoc tests. p < 0.05 was considered significant.

RESULTS

The penetration depth, percentage and penetrated area of the sealer increased from apical to coronal in all systems. The maximum and average penetration depths and penetration areas were higher in FlexMaster and Revo-S groups at the 3rd mm (p < 0.05). At the 5th mm, the Revo-S group had a higher penetration percentage, when compared with ProTaper Next and ProTaper Universal groups (p < 0.05).

CONCLUSIONS

In the 1st mm, separated fragments of any system did not allow the penetration of the sealer, while it was observed that the files with constant taper showed more positive results in terms of sealer penetration at apical 3rd and 5th mm.

CLINICAL RELEVANCE

In the presence of a separated file, the taper of the file might significantly affect the amount of penetrated sealer into the dentinal tubules as compared with the cross-section and motion characteristics of the file.

Removing Fractured Endodontic NiTi Instruments with a Tube Technique: Influence of Pre-Treatment with Various Agents on Adhesive Forces In Vitro

The aim of the study was to evaluate the adhesive forces for removing iatrogenically fractured endodontic nickel-titanium instruments using a modified tube technique with various pre-treatment agents in combination with a light-curing composite. 120 Nickel-Titanium-Mtwo instruments were cut at its parallel shaft and fixed in a vise with an overlap of 2 mm. The surfaces were treated with different agents: A) GC Metalprimer; B) Prime and Bond active; C) NaOCl (3%); D) citric acid (15%); E) phosphoric acid (37%) and group (F) was not pretreated (control). One end of a matching microtube, filled with light-curing composite, was placed over the instrument and a transmitting glass fiber inserted from the opposite side guaranteed polymerization. Pull-out tests (1 mm/min) were performed and failure load was measured digitally. Data were statistically analyzed using the ANOVA and Student–Newman–Keuls tests. Interfaces were subjected to SEM analysis. Prime and Bond active created significant higher pull-out values (mean 30.5 N) compared to all other groups (p < 0.001) and Metalprimer (18.5 N) was significantly superior to the untreated (12.6 N) and NaOCl (11.7 N) group (p < 0.05). No significant differences were obtained between the other groups (p > 0.05). Thus, adhesives improved bonding to fractured NiTi instruments.