Instrument separation is a critical complication during root canal therapy, impacting treatment success and long-term tooth preservation. The etiology of instrument separation is multifactorial, involving the intricate anatomy of the root canal system, instrument-related factors, and instrumentation techniques. Instrument separation can hinder thorough cleaning, shaping, and obturation of the root canal, posing challenges to successful treatment outcomes. Although retrieval of separated instrument is often feasible, it carries risks including perforation, excessive removal of tooth structure and root fractures. Effective management of separated instruments requires a comprehensive understanding of the contributing factors, meticulous preoperative assessment, and precise evaluation of the retrieval difficulty. The application of appropriate retrieval techniques is essential to minimize complications and optimize clinical outcomes. The current manuscript provides a framework for understanding the causes, risk factors, and clinical management principles of instrument separation. By integrating effective strategies, endodontists can enhance decision-making, improve endodontic treatment success and ensure the preservation of natural dentition.
Humans ; Root Canal Therapy/adverse effects* ; Consensus ; Root Canal Preparation/adverse effects*

OBJECTIVES: This study aimed to compare the effectiveness of ultrasound and acoustic and laser cleaning of curved root canals. METHODS: A total of 92 molars with independent root canals with a curvature of 20°-40° were prepared and standardized at 04 25# and stained with gentian violet solution for 72 h. Among them, 52 were randomly divi-ded into four groups for final rinsing (n=13): NI group, PUI group, EDDY group, and PIPS group. Ten samples in each group were cut horizontally along the long axis perpendicular to the root and divided into curved upper, curved, and apical segments. Images were taken with a stereomicroscope and Image J measurements were taken to calculate the depth of rinse penetration. The remaining three samples from each group were split along the long axis of the dentin, photographed by scanning electron microscope to record the dentin tubule exposure and staining layer, and scored for staining layer by double-blind method. SPSS 26.0 software was used to perform statistical analysis and select the best flushing method. An extra 40 samples were randomly divided into four groups for detection of flushing fluid penetration depth (n=10): 10, 20, 30, and 40 s. RESULTS: In the upper part, the mean depth of infiltration was not significantly different between the experimental and control groups (P>0.05). The PIPS group had a significantly lower smear layer score than the control group and the EDDY group (P<0.01). In the curved segment, the mean depth of infiltration was significantly greater in the PUI group than in the control group (P<0.05); the tarnish layer score was lower in each experimental group than in the control group. At the top, the mean depth of infiltration was greater in the PUI and PIPS groups than in the control group (P<0.05), and the smear layer score was lower in the PIPS group than in the other groups (P<0.05). After the time was changed, the depth of infiltration of PUI increased only in the apical segment as the flushing time increased. CONCLUSIONS The PUI and PIPS methods facilitate the penetration of irrigation solution into the dentin canal in curved root canals, especially in the apical segment. The PIPS technique is effective in removing the smear layer in curved root canals.
Humans ; Dental Pulp Cavity ; Microscopy, Electron, Scanning ; Root Canal Irrigants ; Root Canal Preparation/methods* ; Smear Layer ; Sodium Hypochlorite ; Therapeutic Irrigation/methods* ; Double-Blind Method

Root canal therapy is the common treatment for endodontic infections. Successful root canal therapy depends on favorable root canal preparation, root canal medication and three-dimensional obturation of the root canal system. The key to successful root canal therapy is to prevent re-infection of the highly complex root canal systems by removing infecious biofilms and bacterial toxins in the root canal system. The present paper reviews the pathogenic mechanism of the Enterococcus faecalis in the harsh environment of root canal system, the inflammation and immunity of refractory periapical periodontitis and the progress of infection control methods.
Dental Pulp Cavity ; Enterococcus faecalis ; Humans ; Periapical Periodontitis/therapy* ; Persistent Infection ; Root Canal Irrigants ; Root Canal Preparation ; Root Canal Therapy

Objectives: To evaluate the diagnostic consistency of working lengths by observing endodontic files in root canals and periapical subtle structures in digital intraoral radiographs presented in two smartphones, a tablet and a laptop computer. Methods: A dried human skull embedded in an acrylic compound was used for exposing radiographs of the upper and lower second premolars and first molars with two endodontic files (Kerr files size 10 and 15) positioned to the full length of the roots or 1.5 mm short of apexes. A total of 100 radiographs were taken for each of the file sizes. Five observers were asked to assess all the 200 digital radiographs according to a 5-category scale in smartphone A (HUAWEI P9 Plus), smartphjone B (Apple iPhone 7), tablet (Apple iPad 2018) and laptop computer (Lenovo Thinkpad E480), respectively. The gold standard for receiver operating characteristic curve (ROC) analysis was determined with the endodontic Kerr file size 20. A total of 150 roots with files were radiographed, 75 of which with files reaching the radiographic apexes of the respective roots and 75 of which with files 1.5 mm short of the radiographic apexes for each endodontic file size. Results from ROC analysis was analyzed with one-way ANOVA and independent sample t test. Results: For the Kerr file size 10, the area under the ROC curve for laptop, tablet and two smartphones were 0.891±0.037, 0.869±0.037, 0.870±0.017 and 0.849±0.037, while for the Kerr file size 15 the ROC values were 0.957±0.02, 0.961±0.02, 0.961±0.01 and 0.961±0.02, respectively. There were no significant differences for diagnostic accuracy for observing endodontic file positions among digital radiographs presented in the two smartphones, one tablet and one laptop devices (endodontic file size 10: F=1.39, P=0.281; endodontic file size 15: F=0.05, P=0.985). A significant difference was found in the diagnostic accuracy of endodontic file positions between size 10 and 15 files in different display devices (t=-10.65, P<0.001). Conclusions: There was a high diagnostic consistency in the determination of working length and periapical subtle structures of roots by observing digital radiographs displayed on smartphones, tablet and laptop computer.
Dental Instruments ; Dental Pulp Cavity/diagnostic imaging* ; Electronics ; Humans ; Molar ; Observer Variation ; Root Canal Preparation

OBJECTIVE: To evaluate the clinical effect of root canal obturation therapy using cold flowable gutta-percha on young permanent teeth after apexification. METHODS: Ninety cases of young permanent teeth with pulp necrosis or periapical periodontitis treated by apexification were randomly divided into two groups. The cases in each group were divided into single root canal and multiple root canal according to the number of the root canal, and divided into classifications Ⅰ, and Ⅱ/Ⅲ/Ⅳ according to Frank's classification of root development after apexification. Cold flowable gutta-percha and warm gutta-percha obturation techniques were used for root canal obturation of the two groups. The operation time was recorded, and the patients' therapy pain degree was evaluated by visual analog scale (VAS) immediately after operation. Periapical X-ray was performed after operation to evaluate the effect of the root canal filling. The total length of the root was divided into equal three parts on the X-ray film, and three-dimensional tightness of the apical, middle, and coronal region of the root canals were statistically analyzed respectively. Clinical examinations and X-ray examination were performed 6 and 12 months after the operation to evaluate the treatment success rate. RESULTS: The operation time of cold flowable gutta-percha group was significantly lower than that of the control group, which were 51 s and 74 s (P < 0.05); The percentages of pain and discomfort in the two groups were 26.67% and 40.00%, respectively. There were two cases of underfilling and no overfilling in both groups. The percentages of proper filling and tight three-dimensional obturation in the experimental and control groups were 71.11% and 60.00% respectively; and the percentages of tight three-dimensional obturation in the apical third areas were 86.67% and 66.67%, the difference was significant (P < 0.05). There was no significant difference in the three-dimensional tightness between the two groups in the middle and coronal third areas. The percentages of tight three-dimensional obturation in classification Ⅰ groups were 86.67%, 83.33%, 93.33% and 76.67%, 90.00%, 96.67% in experimental and control group, respectively; The percentages of classification Ⅱ/Ⅲ/Ⅳ groups were 86.67%, 86.67%, 100.00% and 46.67%, 86.67%, 100.00%, respectively, and the difference was significant (P < 0.05). There were no apical lesions that occurred in either group during the one-year review period. CONCLUSION The application of cold flowable gutta-percha on young permanent teeth root canal obturation after apexification can achieve good obturation effect. The root obturation effect in the apical third area is significantly better than that of warm gutta-percha obturation techniques. Cold flowable gutta-percha can shorten the clinical treatment time and ameliorate the patients' therapy comfort.
Apexification ; Dental Pulp Cavity ; Gutta-Percha ; Humans ; Radiography ; Root Canal Filling Materials ; Root Canal Obturation ; Root Canal Preparation

OBJECTIVES: This study aimed to evaluate the efficacy of three methods in root canal retreatment to remove the filling material in the root canals. METHODS: Ninety tooth roots filled by gutta percha or plasticized material (n=45, each) were randomly divided into three groups (n=15). WaveOne (WaveOne group), 1^#P drill+WaveOne (1^#P+WaveOne group), and ultrasound P5 working end ET25+ProTaper Universal (P5+ProTaper Universal group) were used to remove the root canal filling material and prepare for root canal. The operating time of each canal was recorded and the percentage of residual filling material area was measured on the root canal wall of the mesial and distal dissected root section. The degree of deviation of the root canal after operation was measured for the root samples filled by gutta percha. RESULTS: The type of root filling material and the method of root canal retreatment had no significant effect on the percentage of residual area of the filling material (P>0.05). However, the remaining filling material area of apical 1/3 of the root canal was significantly higher than that of cervical 1/3 of the root canal (P<0.05). The average operating times for removing gutta-percha or plasticized material in the W and 1^#P+WaveOne groups were significantly less than that in the P5+ProTaper Universal group (P=0.000). The root canal retreatment methods had no significant effect on the curvature of the root canal (P=0.650). CONCLUSIONS WaveOne single file's cleaning ability and center positioning ability were similar to those of ProTaper Universal. Moreover, WaveOne can be independently used for most root canals without a pathway when removing the root canal fillings, thereby simplifying the process of root canal retreatment.
Equipment Design ; Gutta-Percha ; Nickel ; Root Canal Filling Materials ; Root Canal Preparation/methods* ; Titanium

Various engine-driven NiTi endodontic files have been indispensable and efficient tools in cleaning and shaping of root canals for practitioners. In this review, we introduce the relative terms and conceptions of NiTi file, including crystal phase composition, the design of the cutting part, types of separation. This review also analysis the main improvement and evolution of different generations of engine-driven nickel-titanium instruments in the past 20 years in the geometric design, manufacturing surface treatment such as electropolishing, thermal treatment, metallurgy. And the variety of motion modes of NiTi files to improve resistance to torsional failure were also discussed. Continuous advancements by the designers, provide better balance between shaping efficiency and resistance to of NiTi systems. In clinical practice an appropriate system should be selected based on the anatomy of the root canal, instrument characteristics, and operators' experience.
Dental Alloys/chemistry* ; Dental Instruments ; Equipment Design ; Nickel/chemistry* ; Root Canal Preparation ; Titanium/chemistry*

The aim of this study was to compare the efficiency of four final irrigation protocols in smear layer removal and bacterial inhibition in root canal systems. Thirty roots inoculated with Enterococcus faecalis were prepared with ProTaper Universal files. The teeth were disinfected by conventional needle irrigation, sonic agitation using the EndoActivator device, passive ultrasonic irrigation, or an M3 Max file. Teeth with no root canal preparation served as blank controls for the establishment of the infection baseline. Teeth with preparation but no final irrigation served as a post-instrumentation baseline. After the final irrigation, the teeth were sectioned in half. One half of each tooth was examined by scanning electron microscopy (SEM) to assess smear layer removal using a five-point scale. The other half was examined by confocal laser scanning microscopy (CLSM) using the LIVE/DEAD BackLight bacterial viability kit to evaluate the depth of bacterial survival in dentinal tubules. SEM analysis revealed no significant difference in smear layer removal throughout the whole canal among the EA, PUI, and M3 Max groups (P > 0.05). CLSM revealed that PUI achieved the greatest bacterial inhibition depth in the coronal ((174.27 ± 31.63) μm), middle ((160.94 ± 37.77) μm), and apical ((119.53 ± 28.49) μm) thirds of the canal (all P < 0.05 vs. other groups). According to this comprehensive SEM and CLSM evaluation, PUI appears to have the best infection control ability in root canal systems.
Dental Pulp Cavity ; Edetic Acid ; Humans ; Microscopy, Electron, Scanning ; Root Canal Irrigants ; Root Canal Preparation ; Smear Layer ; Sodium Hypochlorite

OBJECTIVE: To construct a model for a controlled memory (CM) nickel-titanium (NiTi) file and another M-wire NiTi file with the same geometry by using finite element analysis. To evaluate the flexibility of a CM NiTi file by using three dimensional finite element method and to compare its mechanical responses with that M-wire NiTi. METHODS: Based on the reverse engineering, the 21 mm long, 25#/08 taper Hyflex NT NiTi file and Hyflex CM NiTi file were fixed by the cantilever bending model at a distance of 9.5 mm from the tip of the file. The mechanical tester's indenter was loaded/unloaded at a distance of 3 mm from the tip of the file. The maximum displacement was 3 mm, the load displacement curve was obtained. Subsequently, by using a micro-CT to scan (layer spacing of 8 μm) NiTi files, and ABAQUS (6.10) was introduced to construct a geometric model. Hyflex NT was considered as a shapememory alloy constitutive model, Hyflex CM was considered as a power-hardening plastic constitutive model, respectively. Comparing the load-displacement curve of cantilever bending in the three-dimensional finite element model with the load-displacement curve in the experiment. RESULTS: Two tetrahedral element models were constructed, the total number of nodes was 99 353 and the total number of cells was 63 744. When the loading displacement was 1 mm, the stress distribution of the cross section at 6.1 mm from the tip of the file was observed. The upper and lower surfaces were subjected to the maximum bending stress and entered the phase transformation yield stage. The finite element simulation could clearly show the deformation of the file. Various information such as deformation characteristics and stress distribution in the process were well fitted to the actual experimental curve. CONCLUSION The constitutive behavior of the material has a significant effect on the mechanical behavior of NiTi file. The finite element model established for the NiTi file of the CM wire can accurately capture the characteristics of various deformation processes of the NiTi root canal file, and it has a good fit with the actual experimental curve. The finite element model can be used for study on bending properties of CM wire.
Dental Alloys ; Equipment Design ; Finite Element Analysis ; Materials Testing ; Nickel ; Root Canal Preparation ; Stress, Mechanical ; Titanium

OBJECTIVE: To set up near-field microwave detection system, to evaluate the accuracy of measuring water and to compare the effects of different methods on drying root canal. METHODS: Known and quantitative distilled water in Eppendorf tube and root canal was detected by near-field microwave detection system which was set up first. The microwave reflection coefficient was recorded so as to evaluate the accuracy of the measuring water. 12 single-rooted mandibular premolar teeth with apical matureness and a curvature less than 10° were decoronated, leaving roots 14 mm in length. After instrumentation to F3, the root canals were air-dried and injected with 10 μL distilled water each. Then all the root canals were assigned to 4 groups (n=12) according to different methods on root canal drying. Near-field microwave detection system was used to detect the change of water after air-drying and root canal drying so as to evaluate the effects of different root canal drying methods: (1) negative control group, the canals were injected with 10 μL distilled water and no root canal drying method was performed; (2) paper points drying experimental group, four #60 paper points were used to blot-dry the middle and upper part of the canal, followed by #40 paper points blot-drying the apical area. The above step was repeated with the tip of paper point that appeared with no water under microscope as finished; (3) 95% (volume fraction) ethanol drying experimental group, after the distilled water was removed with paper points (similar to paper points experimental group), 10 μL 95% ethanol was injected into the canal and was left in place for 10 s, then paper points were used to dry the canal; (4) 70% (volume fraction) isopropyl alcohol drying experimental group, after the distilled water was removed with paper points (similar to paper points experimental group), 10 μL 70% isopropyl alcohol was injected into the canal and was left in place for 10 s, then paper points were used to dry the canal. The linear correlation analysis was used to test the accuracy of the measuring water by near-field microwave detection method and physical measurement. The Pearson correlation coefficient was calculated based on the data. The effects of different methods on drying root canal were analyzed by Chi square test. RESULTS: The R2 for the microwave reflection coefficient and the physical measurement of the water in Eppendorf tube and root canal were 0.991 and 0.970. The microwave reflection coefficient in all the experimental groups showed significant difference (P<0.05). After drying with paper points, the residual water was the most, and the microwave reflection coefficient was the highest: 0.023. While after 70% isopropyl alcohol drying root canal, the residual water was the least with the microwave reflection coefficient 0.006, showing that the effect of drying was the best. CONCLUSION Near-field microwave detection system could detect the change of water in root canal. The effect of root canal drying by 70% isopropyl alcohol was superior to 95% ethanol and paper points.
Dental Pulp Cavity ; Desiccation ; Microwaves ; Root Canal Preparation ; Root Canal Therapy ; Tooth Root