Roots Of Molars Research Articles

Management of additional roots in mandibular molars: report of radix entomolaris and radix paramolaris cases

Achieving a favorable outcome after endodontic treatment depends on a clear understanding of tooth anatomy, identification of variations, and precise root canal location. Multi-rooted mandibular molars often deviate from the expected configuration, sometimes featuring additional roots, such as radix entomolaris (RE) and radix paramolaris (RP), posing challenges during treatment. Detecting these variations is challenging due to their proximity to the distal root, and overlooking them can lead to complications. This study presents three cases involving RE and RP and offers insights into their clinical management, encompassing thorough clinical assessment, diagnosis, and root canal treatment. At follow-up examinations, patients were asymptomatic with no radiographic evidence of persistent infection. Therefore, clinicians must be aware and informed about the potential presence of additional roots in mandibular molars during root canal procedures, as understanding and addressing anatomical variations like RE and RP is crucial for achieving favorable outcomes in root canal treatments.

Enhancing orthodontic treatment control with fish scale-derived hydroxyapatite nanoparticles: Insights from an animal model study

ObjectivesThis study investigates the impact of injected fish-scale-derived hydroxyapatite nanoparticles (FsHA-NPs) on orthodontic tooth movement (OTM) and the width of the periodontal ligament (PDL) space. Materials and MethodsTwenty-six Wistar rats underwent mesial orthodontic traction with a force of 50 g for 21 days. Following the application of the orthodontic appliance, the rats were randomly divided into two groups: a control group, which received a 0.3 µg saline injection, and the experimental FsHA group, which received 100 mg/0.3 ml of FsHA-NPs after thorough characterisation. Injections were administered immediately after appliance application and repeated at 7 and 14 days. Statistical analysis was conducted with a significance level of P ≤ 0.05. ResultThe experimental group exhibited a significant reduction in OTM at 7-, 14-, and 21-day post-force application. Additionally, a reduction in PDL width was observed in the mesiocervical and disto-apical regions of the mesial and distal roots of the first molar. ConclusionFsHA-NPs derived from biowaste fish scales exhibit promising potential as biomaterials for enhancing control over OTM. This study underscores the viability, accessibility, and safety of FsHA-NPs as a locally injectable material for orthodontic applications.

Morphological study of distal furcation in mandibular first molars based on cone beam computed tomography images in Beijing population.

This retrospective study explored the incidence of independent distal-lingual root (DLR) in mandibular first molars and the morphologic features of distal furcations through cone beam computed tomography (CBCT) in Beijing population. A total of 401 CBCT images of both mandibular first molars existed were included. The sex of the patients, the incidence of DLR, the distal root trunk length (DRT), the locations of distal furcation entrance (DFE), and the separation angle of distal furcation (ADF) were recorded. The incidence rates of DLR were 33.2% on the subject level and 26.8% on the tooth level. The incidence of DLR was not different between genders but was higher on the right sides. The DRT values were 4.15 mm±1.02 mm. The ADF was 65.56°±11.56°. The DFE was located lingually, and 97.2% DFE was located more apically than buccal/lingual furcations. A high incidence of DLR was found in the Beijing population. The DRT was longer than buccal and lingual sites. The DFE was located lingually with a wide separation. Understanding the morphological features of distal furcation can help clinicians to make proper treatment plans.

Exploring morphometric transformations in temperature-sensitive NiTi instruments alongside real-time intracanal temperature dynamics.

This study was twofold: (i) it aimed to investigate the morphometric changes of three temperature-sensitive nickel-titanium (NiTi) instruments at different temperatures, and (ii) to conduct an invivo real-time analysis of intracanal temperature changes. Changes in the shape and length of XP-Endo Shaper, XP-Endo Finisher, and XP-Endo Finisher-R were evaluated in real time whilst heated in a temperature-controlled water bath from 22 to 45°C. Instruments were fixed to a laminated water-resistant 1 mm graph paper attached to a stone block. Instruments were imaged whilst subjected to increasing temperature using a digital camera attached to an operating microscope. From recorded videos, still frames were extracted at 10-s intervals and changes in the length and shape of each instrument were measured and changes were plotted against time. Moreover, the intracanal temperature of distal roots of lower molars was measured invivo for patients attending the clinic for non-surgical root canal treatments. The temperature was measured using a K-type thermocouple probe inserted into the mid-root level after irrigating the canal with a solution set at room temperature (22°C) or heated to 45°C. The intraoral and intracanal temperatures were recorded using a video camera for 180 s at 5-s intervals to plot the change in the intraoral and intracanal temperature, after both irrigation solution temperatures, with time. The shape transformation of XP-Endo Shaper began at 31.5 ± 2.0°C and reached its optimal transformation at 35.1 ± 1.0°C. For the Finisher and Finisher-R, shape transformations began at 29.2 ± 1.9 and 26.9 ± 2.2°C reaching the optimal transformation at 33.9 ± 1.4 and 32.7 ± 1.7°C, respectively. The average decreases in lengths of XP-Endo Shaper, Finisher, and Finisher-R after full transformation were 0.43 ± 0.23, 1.07 ± 0.22, and 1.15 ± 0.22 mm, respectively. The intracanal temperature reached 32.9 ± 0.8 and 33.2 ± 1.0°C after 3 min of application of irrigation solutions set at 22 or 45°C, respectively. The tested instruments exhibited diverse changes in their shapes and lengths at varying temperatures. Despite the temperature of the irrigation solution, the intracanal temperature consistently remained lower than the intracanal temperature once equilibrium was reached. This highlights the importance of considering the temperature of irrigation solution during invitro testing of endodontic instruments.

Prognostic risk factors for apical root resorption in orthodontic patients – Are the Kjær’s morphologic characteristics of clinical relevance?

BackgroundPatients undergoing orthodontic treatment (OT) face an increased risk of developing external apical root resorption (EARR). A prognostic risk assessment prior to OT can potentially be conducted through anatomical features in panoramic radiography. This retrospective study aimed to assess the significance of Kjær's morphological characteristics in analyzing the risk of EARR. MethodsPanoramic radiographs of 1,156 patients (624 females, 532 males) were retrospectively analyzed. Anamnestic and treatment-related data were extracted from patient records. The mean age at the start of OT was 12.8 ± 2.2 years (min. 6.4 years, max. 22.3 years) and at the end of OT 15.9 years (min. 8.5 years, max. 24.1 years). The mean treatment duration was 3.1 ± 1.6 years. Panoramic radiographs with a minimum of two per patient were examined for the presence of Kjær’s characteristics. The degree of EARR was registered defining resorption in four degrees of severity. Bivariate analysis and multivariate Poisson regression were performed to assess the association between Kjær’s characteristics and EARR patient- and tooth- related (α = 0.05). ResultsIn total, 72.8% of the patients showed EARR at the end of OT with lateral maxillary incisors most frequently affected. Short roots (p < 0.001) were significantly associated with EARR in patients. Tooth-related microdontia (#12, #22, lower second premolars), narrow crowns (#11, #21, lower incisors), short roots (upper incisors, lower first molars) and ectopia (#11, #21, #13), such as shorter distal roots of the mandibular first molar showed a significant association with EARR depending on severity degree. The type of orthodontic appliance (fixed: p < 0.001, fixed and removeable: p = 0.008), as well as treatment duration (p < 0.001) were also identified as risk factors for EARR. ConclusionsAlthough the risk assessment for EARR development through panoramic radiography analysis is limited, predisposition appears to be present in specific dental characteristics and treatment-related factors.

Biomechanical impact of different isthmus positions in mandibular first molar root canals: a finite element analysis.

This study used image-based finite element analysis (FEA) to assess the biomechanical changes in mandibular first molars resulting from alterations in the position of the root canal isthmus. A healthy mandibular first molar, characterized by two intact root canals and a cavity-free surface, was selected as the subject. A three-dimensional model for the molar was established using scanned images of the patient's mandibular teeth. Subsequently, four distinct finite element models were created, each representing varied root canal morphologies: non-isthmus (Group A), isthmus located at the upper 1/3 of the root (Group B), middle 1/3 of the root (Group C), and lower 1/3 of the root (Group D). A static load of 200 N was applied along the tooth's longitudinal axis on the occlusal surface to simulate regular chewing forces. The biomechanical assessment was conducted regarding the mechanical stress profile within the root dentin. The equivalent stress (Von Mises stress) was used to assess the biomechanical features of mandibular teeth under mechanical loading. In Group A (without an isthmus), the maximum stress was 22.2MPa, while experimental groups with an isthmus exhibited higher stresses, reaching up to 29.4MPa. All maximum stresses were concentrated near the apical foramen. The presence of the isthmus modified the stress distribution in the dentin wall of the tooth canal. Notably, dentin stresses at specific locations demonstrated differences: at 8mm from the root tip, Group B: 13.6MPa vs. Group A: 11.4MPa; at 3mm from the root tip, Group C: 14.2MPa vs. Group A: 4.5MPa; at 1mm from the root tip, Group D: 25.1MPa vs. Group A: 10.3MPa. The maximum stress in the root canal dentin within the isthmus region was located either at the top or bottom of the isthmus. A root canal isthmus modifies the stress profile within the dentin. The maximum stress occurs near the apical foramen and significantly increases when the isthmus is located closer to the apical foramina.

Clinical, radiographic features and prognosis of cemental tear: A retrospective study of 63 teeth

Cemental tears are often misdiagnosed due to their scarcity. In this study, we reported the second largest cohort of cemental tears thus far. By reviewing the radiographic data and medical records of 63 cemental tear teeth, we found that periapical periodontitis was the most frequent diagnosis, followed by cracked tooth/root fracture and periodontitis. Most of the cemental tear teeth that did not have root canal treatment had vital pulp. The apical third of the root was the most prominent site of cemental tears. Cemental tears occurred more frequently in the palatal root of the maxillary molars and in the mesial root of the two-root mandibular molars. Uncontrollable bone loss and tooth mobility were the two main reasons for the extraction of teeth with cemental tears. We suggest that cemental tears should be included in the differential diagnosis of periapical periodontitis, cracked tooth, vertical root fracture and periodontitis, especially for teeth with periapical radiolucency and vital pulp. We believe our study could provide more insights into cemental tears, which will aid clinicians in the early diagnosis and proper treatment of cemental tears.

Effect of Multiple Glide Path Files on Apical Debris Extrusion in Severely Curved Mesial Roots of Mandibular Molars: An In Vitro Study

Effect of Multiple Glide Path Files on Apical Debris Extrusion in Severely Curved Mesial Roots of Mandibular Molars: An In Vitro Study

Influence of root shape on canal complexity at the mandibular molar apical surgical resection level: A micro-CT study

ObjectivesThis study aimed to investigate the relationship between the aspect ratios of mandibular molar roots at the apical 3-mm level and their root canal complexity. DesignThis study used micro-CT imaging to analyze 163 two-rooted mandibular molars. The aspect ratios of the roots at the apical 3-mm level were categorized as "< 2.75" or "≥ 2.75" (mesial) and "< 1.75" or "≥ 1.75" (distal). A two-dimensional (2D) analysis focused on four apical axial cross-section levels to determine the presence of main and accessory canals and isthmus. Additionally, a three-dimensional (3D) assessment of the apical 4-mm of both roots examined main and accessory canals, apical foramina, apical deltas, and middle mesial canals. ResultsMesial roots with aspect ratios ≥ 2.75 showed a higher number of main canals at all levels compared to those with aspect ratios < 2.75 at the 3-mm level. Additionally, the ≥ 2.75 group exhibited more accessory canals and a higher average number of accessory canals. The 3D assessment confirmed significantly more accessory canals and apical foramina in the ≥ 2.75 group. The prevalence of roots with apical deltas was nearly double in the ≥ 2.75 group, and middle mesial canals were exclusively found in this group. In the distal root, the ≥ 1.75 group showed a significantly higher number of main canals at all axial levels. No significant differences were observed between groups in terms of accessory canals, apical foramina, or deltas. ConclusionsA higher root aspect ratio is related to higher anatomical complexity.

Elimination of E. faecalis with NaOCl versus chlorhexidine gluconate from primary molar root canal systems: an ex vivo model study

ObjectivesThis ex vivo human study aimed to evaluate the efficacy of NaOCl and chlorhexidine gluconate (CHG) irrigations in eliminating Enterococcus faecalis from the RCS of primary molars.Materials and methodsDisinfected extracted primary molars were inoculated with E. faecalis for 24 h. Then, the RCS samples were then irrigated with either 2.5% NaOCl, 0.2% and 2% CHG, or sham saline. The samples were collected immediately after irrigation; and 24 h later, the bacterial viability and counts were measured using blood agar and qRT-PCR, respectively. Histological sections were used to measure E. faecalis penetration and viability in dentin tubules using fluorescence microscopy.ResultsThe recovery of viable E. faecalis after the irrigation of the primary molars showed more significant bactericidal effects of NaOCl and 0.2% and 2% CHG than of saline. Immediately after the irrigation, the NaOCl group showed the greatest reduction in E. faecalis; and 24 h later, all the groups had lower viable E. faecalis than the saline control. The bacterial penetration was also lowest in the NaOCl group, although there was no difference in bacterial viability in the tubules between the groups.ConclusionIn primary teeth, NaOCl and CHG showed similar degrees of bacterial elimination efficacy in terms of E.faecalis.Clinical relevanceWithin the limitations of this study, NaOCl and CHG have the similar ability to perform endodontic irrigation of primary ex vivo teeth regarding the elimination of E.faecalis, but NaOCl penetrates dentin tubules better.

Molar root canal treatment performed by undergraduate dental students; an observational study of procedural errors and student perception

BackgroundMolar root canal treatment (RCT) is challenging and requires training and specific skills. Rotary instrumentation (RI) reduces the time needed for instrumentation but may increase the risk of certain procedural errors. The aims of this study were to evaluate the quality of molar RCTs provided by undergraduate students, to compare the prevalence of procedural errors following manual and RI, and to assess the students’ self-perceived confidence to perform molar RCT without supervision and their preference for either manual or RI.MethodsMolar RCTs performed by the final year students were evaluated radiographically according to predefined criteria (Appendix 1). The procedural errors, treatment details, and the students’ self-perceived confidence to perform molar RCT and their preference for either manual or RI were recorded. Descriptive statistics were performed, and the Chi-squared test was used to detect any statistically significant differences.Results60.4% of RCTs were insufficient. RI resulted in more sufficient treatments compared with MI (49% vs. 30.3% respectively. X2: 7.39, p = 0.007), required fewer visits to complete (2.9 vs. 4.6 respectively. X2: 67.23, p < 0.001) and was the preferred technique by 93.1% of students. The most common procedural errors were underextension of the root canal obturation (48.4%), insufficient obturation (45.5%), and improper coronal seal (35.2%) without a significant difference between the two techniques. 26.4% of the participating students reported that they did not feel confident to perform molar RCT without supervision.ConclusionThe quality of molar RCT provided by UG students was generally insufficient. RI partially improved the technical quality of RCT compared with MI. UG students need further endodontic training and experience before they can safely and confidently practise molar RCT.

Comparative Morphology of the Carnassial Teeth Root Canals in Mixed-Breed Dogs and German Shepherds.

Root canal treatment of carnassial teeth in dogs is a common endodontic technique which aims to re-establish or maintain the health of the periapical tissues. In total, 43 dogs were used in this study. Root canal morphology was evaluated in 86 superior fourth premolars and 86 inferior first molars. Apical delta was present in 247 roots, while obliteration of the root canal was found in 11 roots. The most common type of apical delta of the roots of superior fourth premolars was type II, with up to 10 apical ramifications, while type IIIA, with 10-20 apical ramifications, was most commonly present in the roots of inferior first molars. Considering that knowledge of the morphology of root canals is essential for a successful endodontic procedure, the aim of this study was to analyze and compare the morphology of root canals in the carnassial teeth of German shepherds and mixed-breed dogs. Apical resection for the purpose of endodontic therapy of the superior fourth premolar and the inferior first molar is indicated at a length of 4 to 6 mm from the anatomical tip of the roots, which would completely remove the apical delta of these two teeth.

A new dryolestid fossil from the Late Jurassic illuminates molar root structure of dryolestids

ABSTRACT We report a micro-CT study of a new specimen of Dryolestes priscus (Dryolestidae, Cladotheria) from the Upper Jurassic Morrison Formation of Wyoming. The fossil (KUVP 134101) is an incomplete lower jaw preserving eight intact teeth, including two premolars (p3, p4) and six molars (m1–6), along with double-alveoli for m7 and a single alveolus for m8. Its preserved teeth and molar alveoli are consistent with the dental formula in more complete jaws of this species (i4.c1.p4.m8–m9). Here we have newly characterized diagnostic features on the molar trigonid of Dryolestes priscus and other species of Dryolestidae. Our analysis places this specimen close to Dryolestes priscus in terms of phylogeny. CT scans and visualization made it possible to illustrate the distinctive root structures of lower molars of dryolestid species. The two-rooted lower molars of D. priscus show a hypertrophied anterior root that is spatulate and much broader and longer than the simpler posterior root of the same molar. The disparate shape and size of the two molar roots are a highly derived pattern of dryolestids, which is absent in closely related genera formerly assigned to “paurodontids.” It is also unique among all mammaliaforms with typically two-rooted molars. The hypertrophied anterior root corresponds to most of the molar crown, and likely provided better support for occlusal forces acting on the large trigonid of the molar.

Morphometric analysis of the relationship between maxillary posterior teeth and maxillary sinus floor in central Indian population: A cone-beam computed tomography study.

The relationship between the maxillary sinus (MS) and the root apices of posterior teeth is of significant clinical relevance as it influences the diagnosis and treatment planning when operating in the posterior areas of the maxilla. The aim of this study, therefore, is to assess this anatomic relationship and evaluate the propensity of roots of posterior maxillary teeth to be intruded into the MS space using cone-beam computed tomography (CBCT) scanning. One thousand CBCT scans of patients, aged 20 years or above, were analyzed in the study. The distance from the MS floor to the root apices of the posterior teeth was measured and the relationship between the MS and the posterior teeth roots were recorded, based on Kwak's and Didilescu's classification. Based on Kwak's classification, type I configuration was frequently observed in the maxillary posterior teeth, followed by type II. Based on Didilescu's classification, the longest distance, among premolars, was observed between the palatal root of the left 1st premolar and MS, i.e., 8.2467 mm. Among molars, the longest distance was observed between mesiobuccal root of the right first molar and MS, i.e., 5.8966 mm. The shortest distance, among premolars, was observed between the buccal root of the left second premolar and MS, i.e., 3.5500 mm, and among molars, the shortest distance was between the mesiobuccal root of the left second molar and MS, i.e., 1.3556 mm. From the present study, it may be concluded that, among the central Indian population, mesiobuccal root of the second molars and buccal root of the second premolars show the closest proximity to the MS floor. Therefore, any surgical or endodontic intervention in the vicinity of these roots must be performed with utmost care.

Radiographic Assessment Regarding the Pattern of Third Molar Impaction and its Association with Gender in the Population of Islamabad

Abstract &#x0D; Objective: To analyze and document the gender-specific incidence of impacted third molars and elucidate the specific patterns associated with impacted third molars.&#x0D; Methodology: This retrospective cross-sectional study analyzed orthopantomograms (OPG) data from 278 patients, covering a total of 445 impacted third molars. A convenient sampling technique was used and the study was completed in three months from September 2023 and December 2023, Inclusion criteria: OPGs of individuals aged 25 years or older with fully formed third molar roots, Exclusion criteria: OPGs of individuals younger than 25, with craniofacial anomalies, prior orthodontic treatment, erupted third molars, or incomplete root formation in third molars.&#x0D; Results: Both males and females were almost equal in number. The majority 73.2% of OPG showed mandibular third molar impaction while 26.8% showed maxillary third molar impaction. In the maxillary arch, the distoangular type of impaction was observed in the majority, accounting for 48.7%. In the mandibular arch, mesioangular impaction prevailed, comprising 41.7%. In the maxillary arch, a statistically significant correlation (p=0.006) was found between gender and impaction type, with females exhibiting a distinct and more prevalent impaction pattern than males. In the mandibular arch, there was no statistically significant association between gender and impaction type (p=0.23).&#x0D; Conclusion: In conclusion, our study reveals noteworthy gender variations in the prevalence and types of third molar impactions. Mandibular third molars exhibit a higher prevalence than maxillary counterparts, with mesioangular impaction prevailing in the mandibular arch and distoangular impaction in the maxillary arch.

Microbial composition and diversity in intraradicular biofilm formed in situ: New concepts based on next-generation sequencing.

This study aimed to characterize the taxonomic composition of intraradicular multispecies biofilms (IMB) formed in situ in a model to reproduce clinical conditions. Twelve palatal roots of maxillary molars had its canals prepared. Two roots were randomly selected to sterility control. Ten intraoral prosthetic appliances with lateral slots were fabricated. The roots were positioned in the slots with the canal access open to the oral cavity. Eight volunteers wore the appliance for 21 days, and two wore it at two different time points. One root from each appliance was removed and stored at -20°C until DNA extraction and sequencing (n=10). Biofilm was analyzed using next-generation sequencing and bioinformatics. The V4 hyper-variable region of the 16SrRNA gene was amplified and sequenced. For data analyses, the mothur pipeline was used for 16SrRNA processing, and subsequent analyses of the sequence dataset were performed in R using the Microbiome Analyst R package. The taxonomy-based analysis of bacterial communities identified 562 operational taxonomic units (OTUs), which belonged to 93 genera, 44 families, and 8 phyla. Bacterial colonization was different for each biofilm, and samples did not have the same group of bacteria. Alpha and beta diversity analysis revealed some general patterns of sample clustering. A core microbiome of prevalent OTUs and genera was identified. IMBs were heterogeneous when analyzed individually, but some diversity patterns were found after sample clustering. The experimental model seemed to reproduce the actual biofilm composition in endodontic infections, which suggests that it may be used to evaluate disinfection protocols.

Microbial composition and diversity in intraradicular biofilm formed in situ: New concepts based on next-generation sequencing.

This study aimed to characterize the taxonomic composition of intraradicular multispecies biofilms (IMBs) formed in situ in a model to reproduce clinical conditions. Twelve palatal roots of maxillary molars had its canals prepared. Two roots were randomly selected to sterility control. Ten intraoral prosthetic appliances with lateral slots were fabricated. The roots were positioned in the slots with the canal access open to the oral cavity. Eight volunteers wore the appliance for 21 days, and two wore it at two different time points. One root from each appliance was removed and stored at -20°C until DNA extraction and sequencing (n=10). Biofilm was analyzed using next-generation sequencing and bioinformatics. The V4 hyper-variable region of the 16SrRNA gene was amplified and sequenced. For data analyses, the mothur pipeline was used for 16SrRNA processing, and subsequent analyses of the sequence dataset were performed in R using the MicrobiomeAnalyst R package. The taxonomy-based analysis of bacterial communities identified 562 operational taxonomic units (OTUs), which belonged to 93 genera, 44 families, and 8 phyla. Bacterial colonization was different for each biofilm, and samples did not have the same group of bacteria. Alpha and beta diversity analysis revealed some general patterns of sample clustering. A core microbiome of prevalent OTUs and genera was identified. IMBs were heterogeneous when analyzed individually, but some diversity patterns were found after sample clustering. The experimental model seemed to reproduce the actual biofilm composition in endodontic infections, which suggests that it may be used to evaluate disinfection protocols.

Evaluation of maxillary sinus changes following molar distalization using clear aligners: A three-dimensional study

ObjectiveTo evaluate the impact of molar distalization with clear aligners (CAs) on maxillary sinus parameters and its proximity to the root apices of maxillary molars using Cone Beam Computed Tomography (CBCT). MethodsThe study involved pre- and post-treatment CBCT images of 27 adult patients. MIMICS 21.0 software was used to measure maxillary sinus volume and surface area, while Invivo Dental 6.0 program was used to measure the sinus diameters and proximity of the maxillary molar root apices to the sinus floor. ResultsPost-treatment, there was a marked increase in the average volume and surface area of the maxillary sinus on both sides; however, changes in dimensions were not statistically significant. Sinus proximity to the root apices of the maxillary molars showed statistically significant differences, particularly on the left side for all roots. Gender and age impacted the outcomes, with males and younger individuals showing more pronounced changes. No significant differences were observed between the left and right sinuses in all parameters. ConclusionMolar distalization with CAs increases maxillary sinus parameters, more notably in younger and male patients. All molar teeth roots moved toward the sinus, particularly the mesiobuccal root of the maxillary second molar protruded to the sinus.

Effect of Radiotherapy and Taper of Root Canal Preparation on the Biomechanical Behavior of Mesial Roots of Mandibular Molars

IntroductionThis study aimed to investigate the effect of radiotherapy and taper of root canal preparation on the biomechanical behavior of mesial roots of mandibular molars. MethodsEighty mandibular molars with 2 canals in the mesial root were randomly allocated into 2 groups (n = 40): one group underwent irradiation (60 Gy), while the other did not. Subsequently, the mesial roots were sectioned and each group was subdivided into 5 subgroups (n = 8), according to the preparation taper: no preparation (control); 25.03; 25.04; 25.06; and 25.08. All groups were considered homogeneous regarding their dimensions, weight, and morphology. The prepared specimens were embedded in cylindrical plastic molds and subjected to a cyclic fatigue test. A failure analysis was performed according to the extension and course of the fractures. Two-way ANOVA, Tukey's post-hoc, Fisher's exact, and Kaplan–Meier tests were conducted to evaluate the obtained data (α = 5%). ResultsFatigue resistance decreased as the taper of the preparation increased (P < .05). Preparation 25.03 presented significantly higher values only than 25.08 (P < .05), while 25.04, 25.06, and 25.08 were considered similar (P > .05). Irradiation significantly reduced the biomechanical performance (P < .05). Survival analysis corroborated these findings. There were no differences in the distribution of fracture types among the groups (P > .05). ConclusionThe biomechanical behavior of the mesial roots of the mandibular molars decreased significantly in the face of irradiation and as the taper of the preparation increased.

Root canal dentin wear during final irrigation in endodontic retreatment with passive ultrasonic irrigation and easy clean instruments.

Complementary procedures have been proposed to improve the endodontic retreatments. The aim of this study was to evaluate, by microcomputed tomography (micro-CT), the dentin wear caused by passive ultrasonic irrigation (PUI) and easy clean (EC) instruments, when used for the final removal of filling material during endodontic retreatment. Thirty-six mesial roots of the lower first molars were divided into four groups (n = 9), according to the final irrigation and sealer: PUI/AH Plus, EC/AH Plus, PUI/Total Fill (TF), and EC/TF. Canal volume was evaluated, both before and after the final irrigation, by micro-CT analysis. The Kruskal-Wallis test was used to compare the volumes among groups and the paired Wilcoxon test was used to compare the volume values before and after the final irrigation within each group. Both complementary cleaning procedures promoted dentin wear that was observed only when the volume was analyzed for each third of the root canal. In the apical third, both instruments showed significant wear, where the use of the EC instrument resulted in greater wear than the PUI, in teeth filled with both AH Plus and TF BC Sealers (P < 0.05). Both complementary cleaning procedures promoted dentin wear and must be used cautiously.