Evaluation of dentine thickness of middle mesial canals of mandibular molars prepared with rotary instruments: a micro‐CT study

Tip and taper compatibility of accessory gutta-percha points with rotary and reciprocating instruments

Objectives

This study was conducted to evaluate and compare the tip and taper compatibility of accessory gutta-percha points (AGPs) with various rotary and reciprocating instruments.

Materials and Methods

Using a profile analyzer, tip and taper measurements were taken of 10 AGPs of each of the 14 models available from Odous de Deus and the 4 models available from Dentsply-Maillefer. Diameter measurements were taken at 1-mm intervals, from 3 mm from the tip (D3) to 16 mm.

Results

Based on the mean values obtained, 3-dimensional (3D) models of the AGPs were drawn in Autodesk Fusion 360 and superimposed on 3D models of each instrument selected (Mtwo, Reciproc, RaCe, K3, and ProDesign Logic) to determine the compatibility between the instrument and the AGP. Data corresponding to the tips and tapers of the various AGPs, as well as the tip and taper differences between the AGPs and the instruments, were analyzed using descriptive statistics. The tapers of the AGPs were subject to the American National Standards Institute/American Dental Association No. 57 standard. The Odous de Deus extra-long medium and extra-long extra-medium AGPs were shown to be compatible with Mtwo, K3, and ProDesign Logic instruments with taper 0.06 and tip sizes 25 and 30, while the Dentsply fine and fine medium cones were compatible with Mtwo, RaCe, and K3 instruments with conicity of 0.04 and tip sizes 35 and 40.

Conclusions

Both the Odous de Deus and Dentsply commercial brands included 2 AGP models with tip (D3) and taper compatibility with Mtwo, RaCe, K3, and/or Prodesign Logic instruments.

Anatomical complexities affecting root canal preparation: a narrative review

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

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

INTRODUCTION

This study aimed to evaluate the effects of root canal enlargement on the danger zone (DZ) of mandibular molars.

METHODS

Thirty mesial roots of mandibular first molars were scanned in micro-computed tomography (S1). Canals were sequentially enlarged with rotary instruments up to sizes 30/0.04 (S2) and 30/0.06 (S3). The dentin thickness was measured at 0.1-mm intervals after each preparation step (n = 2964 slices). Root level and position of the DZ were also recorded. Data were compared using analysis of variance with Bonferroni pairwise comparison, Cochran's Q method, and Pearson's test (α = 5%).

RESULTS

Comparing the specimens before (S1) and after (S2 and S3) preparations showed a significant reduction in the thickness of the DZ (P < .05), as well as between S2 and S3 steps (P < .05). At S1, the DZ was mostly located in the middle third of the root, but after preparation, it shifted toward the coronal direction (P < .05). Both S2 (P = .004, r = 0.508) and S3 (P = .004, r = 0.506) preparation steps showed a positive correlation between canal length and the root level of the DZ. At S1, the DZ was positioned toward the distal and mesial in 73.4% (n = 22) and 26.6% (n = 8) of the specimens, respectively. After S3, the number of specimens with DZ positioned toward the mesial aspect of the root significantly reduced to 3.3% (n = 1), whereas none of the specimens with DZ positioned toward the distal changed its position after root canal enlargements (P > .05).

CONCLUSION

Overall, the enlargement of mesial canals of mandibular first molars with final instruments sizes 30/0.04 and 30/0.06 affected the thickness, root level, and position of the DZ.

A micro-CT analysis of radicular dentine thickness in mandibular first premolars presenting C-shaped root canals: Identification of potential danger zones

AIM

To describe the radicular dentine thickness in mandibular first premolars presenting C-shaped root canals, in order to identify the canal walls with less thickness as potential danger zones. In addition, to describe the internal and external anatomical characteristics of these teeth and to associate them to the dentine thickness.

METHODOLOGY

A total of 70 mandibular first premolars presenting C-shaped root canals were examined. Their internal morphology was analyzed using Vertucci´s and Fan´s criteria, and their external morphology was analyzed using the ASUDAS score. Besides, the dentine thickness around the root canals was two/three-dimensionally determined at five root planes and quantified in the distal and the mesial aspects.

RESULTS

According to Fan´s, ASUDAS, and Vertucci´s classifications, the most common canal configurations were category C3, grade 3, and type V, respectively. In Vertucci's type III anatomy, the mesial root wall of the lingual canal showed significantly less dentine thickness than the distal wall in the middle plane (p = 0.031). Similarly, in Vertucci's type V anatomy, significantly less dentine thickness was observed in the mesial root wall of the buccal and lingual canals in the middle plane (p < 0.001) and the buccal canal in the middle-apical plane (p = 0.014) than the distal root wall of these canals. In teeth with ASUDAS grade 3 and 4 scores, significantly less dentine thickness was observed in the mesial in comparison with the distal root wall of these canals. These differences were demonstrated in the middle and middle-apical planes (p < 0.001) of grade 3 teeth and the middle-apical plane (p < 0.001) of grade 4 teeth. In these root planes, the Ver1-AS3 and VerV-AS3 combinations presented a 4-times greater risk of presenting walls with a critical dentine thickness of 0.6 mm (OR=4, p = 0.025) than the combinations Ver1-AS2, VerV-AS2, VerV-AS4, and VerIII-AS3.

CONCLUSIONS

The root canal system configuration of mandibular first premolars with C-shaped canals showed a wide range of anatomical variations. The lowest dentine thickness was located in the mesial wall of the canals in the middle and apical root thirds of Vertucci´s type III and V anatomies and in teeth with deep radicular grooves scored as ASUDAS grade 3 and 4. In the middle and middle-apical planes, the presence of the combinations Ver1-AS3 and VerV-AS3 showed a high risk of presenting a critical dentine thickness of 0.6 mm. Therefore, these root canal walls with less dentine thickness represent potential instrumentation danger zones in mandibular first premolars with C-shaped canals.

Influence of access cavity preparation on the dentine thickness of mesial canals of mandibular molars prepared with reciprocating instruments

AIM

To evaluate the influence of traditional and conservative access cavity preparations on the remaining dentine thickness in the coronal third of mesial canals of extracted mandibular molars prepared with reciprocating instruments using micro-computed tomography as the analytical tool.

METHODOLOGY

Seventy extracted mandibular molars were scanned at a pixel size of 19 μm. From this initial sample, 20 teeth were selected, pair-matched and distributed into two groups (n = 10) according to the access cavity preparation: traditional (TradAC) or conservative (ConsAC). The root canals were sequentially enlarged with Reciproc Blue R25 (size 25, 0.08v taper) and R40 (size 40, 0.06v taper) instruments. A new scan was performed and the postoperative stacks were coregistered with their respective preoperative datasets. A colour-coded cross sections of the roots were created and used to identify and measure the smallest dentine thickness related to both MB and ML canals at 1.0-mm intervals from the furcation level of up to 5 mm in the apical direction, in both mesial and distal aspects of the roots, before and after preparation. The statistical analyses were performed with paired-samples t-test, independent-samples Student T-test and Chi-Square test with a significance level of 5%.

RESULTS

At all levels of both groups, dentine thickness before preparation was greater than after preparation (p < .05). No difference in the percentage of dentine reduction was observed between TradAC and ConsAC groups (p > .05), but a significantly greater reduction was observed to the distal aspect of the roots (p < .05). After root canal preparation, dentine thinner than 0.5 mm was observed mostly along the distal aspect of the root (10% to 15%) of the MB and ML canals, with no influence of the access cavity type on its incidence to either mesial (X²  = 1.66; p = .2) or distal (X²  = 0.40; p = .5) directions. In the TradAC group, dentine thickness in most slices was greater than 1.0 mm after preparation (n = 124) whilst, in the ConsAC, it ranged from 0.5 to 1.0 mm (n = 136).

CONCLUSION

Traditional or conservative access cavity preparation in extracted mandibular molars did not influence the remaining dentine thickness in the coronal third of mesial canals enlarged with thermomechanically treated nickel-titanium reciprocating instruments.

The Effect of Root Canal Preparation Size and Taper of Middle Mesial Canals on Fracture Resistance of the Mandibular Molar Teeth: An In Vitro Study

INTRODUCTION

The aim of the present study was to investigate the influence of root canal preparation size and taper of middle mesial (MM) canals on fracture resistance of mandibular molars.

METHODS

Fifty-five mandibular molar teeth having an MM canal were selected based on the cone-beam computed tomographic analysis. After the decoronation and distal root separation procedure, the lengths of the mesial roots were standardized to 13 mm. The specimens were randomly distributed into 5 groups (n = 11). Mesiobuccal and mesiolingual canals were prepared up to size 30.06 using VDW.ROTATE rotary files (VDW, Munich, Germany). The MM canal was prepared up to size 25.04, 25.06, 30.04, and 30.06, respectively. No preparation was done in the MM canal in the control group. After the irrigation protocol, the canals were obturated with the single-cone technique. A thin layer of silicone-coated specimens was embedded in acrylic resin and subjected to a fracture strength test by a universal testing machine. A vertical force was applied to the roots until they fracture. Statistical analysis was performed with 1-way analysis of variance and post hoc Duncan tests (P = .05).

RESULTS

There was no significant difference between group 25.04 and the control group, but the fracture strengths of these groups were found to be significantly higher than that of groups 25.06, 30.04, and 30.06 (P < .05).

CONCLUSIONS

Within the limitations of this study, we concluded that increasing the apical diameter and taper in the MM canal reduces the fracture strength of mandibular molar teeth. Among the tested instrumentation sizes, fracture strength decreased significantly when greater than 25.04 instrumentation sizes were chosen.

Effect of canal preparation with XP-endo Shaper and ProTaper Next on root canal geometry and dentin thickness of mandibular premolars with radicular grooves and two canals: a micro-CT study

OBJECTIVES

This study aimed to evaluate the effects of different shaping protocols on the root canal geometry and remaining dentin thickness of mandibular premolars with radicular grooves (RG) and two canals by means of micro-CT.

MATERIALS AND METHODS

Mandibular premolars with RG and two canals were matched based on their similar morphological dimensions and assigned to 2 experimental groups according to the canal preparation (n=8): XP-endo Shaper (XPS) and ProTaper Next (PTN) systems. Before and after preparation, morphometric measurements of the volume, surface area, structure model index, area, perimeter, roundness, major and minor diameters, as well as untouched canal walls, canal transportation, and dentin wall thickness were evaluated. Data were statistically compared within and between groups using the independent sample t test (α=5%).

RESULTS

XPS revealed less changes in volume, surface area, area, perimeter, and major and minor diameters (P<0.05). There was no significant difference in structure model index (SMI), roundness, and percentage of untouched canal walls between groups (P>0.05). XPS resulted in less apical canal transportation and a higher remaining dentin thickness toward the RG compared to PTN in lingual canals (P<0.05).

CONCLUSIONS

XPS revealed fewer changes in root canal geometry as well as lower transportation and a greater remaining dentin thickness in the lingual canals toward the RG compared to PTN.

CLINICAL RELEVANCE

Internal and external anatomical characteristics of mandibular premolars might have an influence on biomechanical preparation. Considering the risk of perforation, the canal preparation using XPS appears to be more conservative compared to PTN.

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

OBJECTIVES

This study evaluated the danger zone (DZ) in mesial roots of mandibular molars and the correlation between anatomical references of the DZ and some anatomical landmarks including tooth/root length, depth of mesial and distal grooves, and inter-canal orifices distance.

MATERIAL AND METHODS

Twenty-eight mesial roots of mandibular molars with 2 independent canals were scanned and divided into 2 groups according to root length. The anatomical landmarks were correlated (Pearson or Spearman coefficients) with root level, thickness, and position of the DZ and also compared (independent samples t or Mann-Whitney tests) between the 2 groups at α = 5%.

RESULTS

No statistical difference was observed between groups regarding DZ parameters and depth of mesial and distal grooves (P > 0.05). Orifice distance in group 2 (4.49 ± 0.75 mm) was significantly greater than group 1 (3.76 ± 0.89 mm) (P < 0.05). Significant correlations (P < 0.05) were found between (i) DZ level and root/tooth length (r = 0.54 and 0.49, respectively), (ii) DZ thickness and distal groove depth (r = - 0.45), and orifice distance (r = 0.38), and (iii) DZ position and depth of mesial (r = 0.39) and distal (r = 0.40) grooves. Other variables such as root length and distal groove depth (r = 0.28), and orifice distance and mesial groove depth (r = 0.36) were also correlated (P < 0.05).

CONCLUSIONS

The length of tooth/root, the distance of canal orifices, and the depth of mesial/distal grooves of mesial roots of mandibular molars might be predictive factors for the root level, position, and thickness of the DZ.

CLINICAL RELEVANCE

The length, distance of mesial canal orifices, and the depth of mesial and distal grooves of the mesial roots of mandibular molars might be moderate predictive factors for the root level, position, and thickness of the DZ.

Publication trends in micro-CT endodontic research: a bibliometric analysis over a 25-year period

AIM

To conduct a bibliographic analysis of the research studies published in Endodontics using micro-computed tomography (micro-CT) as an analytical tool over a 25-year period.

METHODOLOGY

The Web of Science electronic database was accessed, and an advanced search using strict criteria was undertaken from January 1995 to June 2020 for studies in the field of Endodontics that used micro-CT as an analytical tool. A further search was conducted between January and August of 2020 for a combination of specific terms and descriptors. For each selected article, the following parameters were recorded: field of the study, analysed specimen, publication title and year, authorship, journal of publication, institution and country of origin, collaborating institutions and countries, and number of citations. The acquired data were analysed using descriptive statistics and graphical mappings.

RESULTS

The screening process identified 877 relevant articles that were classified into 30 thematic categories. The main fields of research were root canal preparation (23.8%), root canal anatomy (17.4%), canal filling (9.2%) and root canal retreatment (7.0%). The most productive half-decade comprised the period of 2015-2019 (n = 513; 58.5%), with the highest number of articles published in 2019 (n = 146; 16.6%). The authors who lead the list as first authors were G De-Deus, A Keleş, F Paqué, MA Versiani and Y Gu, respectively, whilst Versiani was the most productive (n = 51). The leading countries regarding the number of studies were Brazil, China and Turkey with 236, 130 and 65 publications, respectively. The University of São Paulo (n = 90; 10.3%) followed by Wuhan University (n = 37; 4.2%) and the University of Zurich (n = 18; 2.1%) were the prominent contributors by producing the largest number of articles, whilst the University of Zurich was the most-cited institution. The selected studies were published in 140 scientific journals, but the Journal of Endodontics and International Endodontic Journal accounted for almost 50% of the publications.

CONCLUSION

This bibliometric analysis portrayed an original and comprehensive view on the progress and trends of the use of micro-CT technology in endodontic research, and enabled a deep understanding of the development process in this field over the last 25 years.

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.

Accuracy of an endoscope to detect root canal anastomoses in mandibular molar teeth: a comparative study with micro-computed tomography

Objective: The aim of this study was to investigate the accuracy of endoscopic visualization to detect root canal anastomoses at the coronal half of the mesial root canals of mandibular molars using micro-computed tomographic (micro-CT) images as reference.Material and methods: Seventy-four mesial roots of mandibular first molars with (n = 47) or without (n = 27) intercanal anastomosis were selected based on the micro-CT scans of 269 mandibular first molars at a pixel size of 10 µm. The specimens were mounted on the mannequins and their root canals were evaluated using dental operating microscope (DOM) and endoscope. The endoscopic probe was inserted into the main mesial root canals and 2 blinded observers evaluated the presence of a divergence point of anastomosis (where the branching occurs) as 'present' or 'absent'. The scorings were compared with the three-dimensional reconstructed images of the specimens and recorded as 'correct' or 'incorrect' evaluation. Degree of agreement between evaluators was assessed with Kappa test and the accuracy of endoscopic visualization according to the presence and location of anastomosis was compared using Fisher exact tests with a significance threshold at 5%.Results: High inter-examiner reliability was reported (0.91). None of the divergence points were identified using DOM whereas 11 divergence points were detected using endoscope, corresponding the 23.4% of the intercanal anastomoses. The endoscope also showed the absence of an intercanal anastomosis correctly in all of the specimens without an anastomosis. Detectability of a divergence point using endoscope was not affected by its location within the coronal half of root canal (p > .05).Conclusions: The endoscopes were able to visualize the divergence points of 23.4% of the intercanal anastomoses located at the coronal halves of root canals.

Root dentine thickness of danger zone in mesial roots of mandibular first molars

BACKGROUND

Better understanding of the danger zone anatomy in mesial roots (MRs) of mandibular first molars (MFMs) may serve to decrease the risk of mishaps. This study aimed to measure the minimal distal dentine thicknesses of danger zone in MRs of MFMs in a native Chinese population using cone-beam computed tomography (CBCT).

METHODS

CBCT images of 1792 MFMs from 898 Chinese patients were analyzed. The minimal distal dentine thicknesses of the mesiobuccal (MB) and mesiolingual (ML) canals below the furcation 1, 2, 3, 4, 5 mm were measured. The association between the minimal distal dentine thicknesses and the root lengths, patient's age and gender, side were assessed.

RESULTS

The minimal distal dentine thicknesses of MB and ML canals are located 3 ∼ 4 mm below the furcation for both men and women. There are no differences between MB and ML canals, while the minimal distal dentine thicknesses of MB and ML canals were higher in men than women (P < 0.05), except at 1 and 3 mm of ML canals (P > 0.05). The minimal distal dentine thicknesses of MB and ML canals increased with age in both men and women at each location (P < 0.05). The minimum distal dentine thickness at every location were significantly different between long teeth and short teeth both in men and women (P < 0.05), with short teeth having the smallest mean values. There are no significant differences between two sides (P > 0.05).

CONCLUSIONS

The minimal distal dentine thicknesses of MRs in MSMs have close correlation with root length, patient's age and gender.