The Effect of Larger Apical Preparations in the Danger Zone of Lower Molars Prepared Using the Mtwo and Reciproc Systems

Shaping Efficiency of Rotary and Reciprocating Kinematics of Engine-driven Nickel-Titanium Instruments in Moderate and Severely curved Root Canals Using Microcomputed Tomography: A Systematic Review of Ex Vivo Studies

INTRODUCTION

This systematic review aimed to compare reciprocating with continuous rotary instrumentation kinematics, by means of microcomputed tomography evaluations, in extracted human permanent teeth with moderate and severe canal curvatures.

METHODS

The research protocol was registered in the International Prospective Register of Systematic Reviews and given the reference number CRD42023404035. An electronic search was undertaken in MEDLINE (PubMed), EBSCO, Scopus, Web of Science databases until December 2021. Manual screening of issues in endodontic journals and references of relevant articles were assessed individually. The risk of bias (RoB) of the included articles was evaluated with the QUIN tool (Quality Assessment Tool for In Vitro Studies).

RESULTS

Among 1640 retrieved articles, 49 were included in the qualitative synthesis. Fifteen articles had low RoB, 33 articles had medium RoB, and only 1 study was at high RoB. Continuous rotary systems had better centering ability in both moderate and severe canal curvatures and resulted in less apical transportation in severely curved root canals. None of the kinematic systems was capable of instrumenting the entire canal surface area. Reciprocating kinematics systems tended to provide higher increase in surface area of severely curved canals and produced fewer dentinal microcracks in moderately curved canals.

CONCLUSIONS

The evidence presented in this review suggests that continuous rotary system seems to be better than reciprocating system in solving the major issues encountered during root canal instrumentation of extracted teeth with moderate and severe curvatures.

Apical transportation using Mtwo or Reciproc retreatment systems in severely curved canals: a micro-computed tomographic study

OBJECTIVE

To assess apical root canal transportation using Mtwo or Reciproc during retreatment of severely curved canals, using a multi-analytical approach.

METHODS

Forty mesial canals from mandibular molars (Vertucci type IV) were evaluated before and after endodontic retreatment to compare apical transportation with Mtwo retreatment or Reciproc. The systems were used on the same root but alternating the mesial canals. The analyses were performed by micro-computed tomography. Four evaluations were performed: (a) longitudinal transportation, (b) horizontal transportation, (c) variation in the angle of curvature of the canal, and (d) canal-root width ratio. Horizontal transportation and canal-root width ratio were evaluated in 1-, 3-, and 5-mm levels.

RESULTS

Longitudinal transportation occurred in all samples, with a mean of 0.13 mm for Mtwo and 0.17 mm for Reciproc. Horizontal transportation increased as distant from the apex was the evaluated level, in mean. However, the transport was not observed in all samples. The mean angle of curvature was 4.16 for Mtwo and 3.03 for Reciproc. Canal-root width decreased as distant from the apex was the evaluated level. No significant differences were observed considering all tested variables, independently of the retreatment system or evaluated level (p > 0.05).

CONCLUSION

Mtwo retreatment and Reciproc presented similar apical transportation (horizontal or vertical).

CLINICAL RELEVANCE

Both Mtwo retreatment and Reciproc systems could be considered safe regarding apical transportation.

Evaluation in the danger zone of mandibular molars after root canal preparation using novel CBCT software

This study measured the thickness of cementum/dentin in the danger zone of the mandibular molars after root canal preparation using novel cone-beam computed tomography (CBCT) software. Eighty-four teeth were distributed into four groups: ProTaper Next, BioRace, Reciproc Blue, and WaveOne Gold. E-Vol DX® CBCT software was used to measure initial and final remaining cementum-dentin thicknesses after root canal preparation of the mesial root of mandibular molars at 1 and 3 mm from the furcation. The Kolmogorov-Smirnov test was used to test variable symmetry. The variables were described as mean and standard deviations, compared among the groups using analysis of variance (ANOVA), and within the groups using the Student t test. A generalized estimating equation model was used to compare the variation before and after root canal preparation. The level of significance was set at 5%. Differences between mean initial and final thicknesses of the mesiobuccal (MB) and mesiolingual (ML) canals were not statistically significant. The mean initial thickness was 3 mm (0.900 mm ± 0.191), considering that a mean lower than 1 mm (1.035 mm ± 0.184) indicates the danger zone. Although cementum/dentin is thinner at 3 mm from the furcation (0.715±0.186) after root canal preparation, the greatest amount of dentin removed was found at 1 mm (0.734 ± 0.191). The cementum-dentin remaining after preparation was thicker than 0.715 mm in root canals prepared using #35 (WaveOne Gold®) and #40 (ProTaper Next®, BioRace® and Reciproc Blue®) instruments. This confirms the safety of canal preparation in the danger zone using these systems.

Impact of Endodontic Kinematics on Stress Distribution During Root Canal Treatment: Analysis of Photoelastic Stress

INTRODUCTION

Structural defects created by endodontic treatment are the most common cause of major dental failures. This study analyzed levels of stress produced by endodontic instruments during the root canal treatment by photoelastic analysis of stress.

METHODS

Twenty-four human premolars were randomly divided into 4 groups (n = 6) according to instrumentation protocol: ProTaper Next (GPT), One Shape (GOS), Wave One Gold (GWO), and TF Adaptive (GTF). The evaluation of the photoelastic model was performed at 4 dental zones: dental-crown region, cervical third of root, middle third of root, and apical third of root. Silicone molds were prepared (2 × 15 mm), and pinjets were used inside the root canals to fixate teeth. Photoelastic resin (2:1 ratio) was poured into the silicone molds to form photoelastic models. A transmission polariscope was used to analyze the positions of interest and recorded with a digital camera. Tardy's method was used to quantify the fringe order (n) and calculate the maximum stress value (τ) at each selected point. Data were analyzed with two-way analysis of variance, Tukey test (P < .05), fringe descriptive analysis.

RESULTS

All groups showed a significant increase in the level of stress created during biomechanical preparation of the root canals. In the quantitative analysis, there was no statistically significant difference among the groups (P > .05). In the qualitative analysis, GPT and GTF instruments achieved greater levels of stresses compared with GWO and GOS instruments. At the beginning of instrumentation, stresses were concentrated at the coronary level and the end of instrumentation at the middle and apical root level.

CONCLUSIONS

All endodontic systems resulted in accumulation of stress along the dental structure. Stress was found in different concentrations along the tooth and at different levels.

Residual Dentin Thickness in Bifurcated Maxillary Premolars after Cervical Preflaring Preparation: A CBCT Analysis

Objective:

This study evaluated the residual dentin thickness (RDT) of maxillary premolars after the use of different cervical preflaring (PF) drills by using cone-beam computed tomography (CBCT).

Methods:

Eighty bifurcated maxillary premolars were accessed and randomly divided into 5 groups (n=16). PF was performed with Gates-Glidden #1, #2, and #3 (group 1), Largo #1 and #2 (group 2), and LA Axxess #20/.06 (group 3), #35/.06 (group 4), and #45/.06 (group 5). CBCT images were acquired before (preoperative) and after (postoperative) PF. Initial and final cervical dentin thickness was measured at the buccal, palatal, mesial, and distal aspects, 0.5 mm coronally to the furcation, on both buccal and palatal roots, using CBCT’s image analysis software. The percentage of removed dentin after PF preparation was also calculated. Data were analyzed using ANOVA followed by Tukey’s test at a significance level of P < 0.05.

Results:

No statistically significant differences were found among the groups for preoperative or postoperative RDT (P > 0.05). LA Axxess #20/.06 (group 3) removed significantly less cervical dentin at all root canal aspects on both buccal and palatal roots. The mesial aspect of the buccal root and distal aspect of the palatal root were significantly reduced after the use of LA Axxess #45/.06 (group 5) and Largo #1 and #2 drills (group 2), respectively (P < 0.05).

Conclusion:

PF in bifurcated maxillary premolars should be performed with LA Axxess instrument #20/.06. The use of Gates-Glidden #1, #2, and #3, Largo #1 and #2, and LA Axxess #45/.06 drills should be done with caution.

Analysis of Instrumentation Protocols Regarding the Quality of Mesial Canal Preparation in Mandibular Molars: A Micro-computed Tomographic Study

INTRODUCTION

This study aimed to use micro-computed tomographic imaging to analyze the quality of the endodontic preparation of mesial canals in mandibular molars provided by 3 instrumentation protocols.

METHODS

Forty-five extracted mandibular molars with 2 independent mesial canals were selected, and the initial micro-computed tomographic imaging was performed. The initial volume values of the canals were submitted to statistical analysis for paired division. The groups were determined according to the final enlargement of the canal and the working length adopted (ie, G25.06/+1 mm, G35.05/foramen, and G50.01/-1 mm). At the end of each instrumentation sequence, the root canals were scanned and analyzed with regard to the increase in the total and apical volume, centralization, and preparation transportation and the percentage of the total and apical uninstrumented walls.

RESULTS

For the intragroup comparison, the Wilcoxon test was used, and for the intergroup analysis, the Kruskal-Wallis and Dunn tests were used (P < .05). In the analysis of the canal total volume, a statistical difference was found between G25.06/+1 mm and the remaining groups (P < .05). In the apical third, a statistical difference was observed between G25.06/+1 mm and G50.01/-1 mm (P < .05). No statistical difference was found between the groups in terms of centralization and transportation of the preparation or in terms of the percentage of the total or apical uninstrumented walls.

CONCLUSIONS

The preparation of the mesial canals of mandibular molars up to larger tip files but with a lower taper at 1 mm before the foramen resulted in a larger volume of apical preparation, kept the preparation centralized, and provided safe apical dentin wear without excessive cervical wear.

Root canal shaping of curved canals by Reciproc Blue system and Pro Taper Gold: A micro-computed tomographic study

Background

This study aimed to evaluate the centralization and transportation of ProTaper Gold (PTG) rotary system and Reciproc Blue (RB) reciprocating system in curved canals, by using micro-CT.

Material and Methods

Twenty extracted mandibular molars were previously scanned by using the SkyScan 1174 microtomograph to select the Vertucci IV anatomic type. The specimens were divided into two groups (n=10) according to the mechanized system used to prepare the root canals. The teeth were scanned by micro-CT to calculate the increase volume, percentage of dentin removed, remaining dentin thickness, structure model index (SMI), degree of transportation and centering ability of root canals. The Student's t test was used to evaluate differences between PTG and RB in each measurement evaluated.

Results

No significant differences were found between the groups in the increase of the total root canal and apical volume; percentage of dentin removed after preparation; SMI of the mesiolingual canal; degree of transportation of the canal and centering ability of the cervical and middle thirds (P>0.05). There were significant differences in the mesiobuccal canal in SMI and in the centering ability of the apical third (P<0.05). Concerning the remaining dentin thickness, there was also no significant diferences between the groups, except for some regions were RB was observed to have a superior cutting capacity (P<0.05).

Conclusions

Both systems were efficient and safe for performing preparation of the moderately curved root canals of mandibular molars. RB instruments produced more circular and better centralized canals in the apical third of the mesiobuccal canal, with superior cutting action when compared with PTG instruments. Key words:Nickel-titanium instrument, heat treatment, micro-computed tomography, canal transportation.

Safety of large preparation with different instruments in the buccal canals of maxillary molars

This study aimed to evaluate the influence of large apical preparations with Reciproc (REC), Hyflex CM (HCM) and Twisted File Adaptive (TFA) systems using micro-computed tomography (MCT). Ninety mesiobuccal (MB) and distobuccal (DB) root canals of maxillary molars (n = 45) were scanned using MCT before and after the shaping procedures. The root canals (n = 15) were prepared until REC 40.06, HCM 40.04 and TFA 35.04. The root canal transportation (RCT), centring ability (CA), change in volume of the root canal and at different levels (VC), remaining dentine thickness (RDT), removal of dentine wall (RDW) and working time (WT) were evaluated. Data were analysed using the Kruskal-Wallis and Dunn tests, and the one-way ANOVA and Tukey tests with a level of significance set at 5%. No significant difference among the instruments was found regarding the RCT, CA, RDT, RDW and WT (P > 0.05), in larger apical preparations in curved MB and straight DB canals of maxillary molars.

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.

Root Canal Preparation and Enlargement Using Thermally Treated Nickel-Titanium Rotary Systems in Curved Canals

INTRODUCTION

The purpose of this study was to evaluate root canal preparation and apical enlargement of curved canals using rotary heat-treated and heat/surface-treated systems by micro-computed tomographic imaging.

METHODS

Curved mesial root canals (n = 48) of mandibular molars (20°-40°) were prepared using ProDesign Logic (PDL; Easy Equipamentos Odontológicos, Belo Horizonte, MG, Brazil) 25/.01 and 25/.06 or HyFlex EDM (HFEDM) 10/.05, HyFlex CM 20/.04, and HFEDM 25/.08. Apical enlargement was performed using PDL 40/.05 or HFEDM 40/.04. Scanning (9 μm) was performed before and after preparation and after apical enlargement using micro-computed tomographic imaging. Volume, percentage of volume increase, debris, untouched root canal surface, and centering ability were analyzed. Statistical analysis was performed using Mann-Whitney, Wilcoxon, and unpaired t tests (α = .05).

RESULTS

HFEDM promoted a higher volume increase of the root canals than PDL after preparation and after apical enlargement (P < .05). The apical enlargement promoted a significant decrease in debris and untouched surface in both groups (P < .05). The percentage of debris and untouched surface were similar between HFEDM and PDL after preparation and after apical enlargement (P > .05). Both systems promoted centered canals (P > .05).

CONCLUSIONS

HFEDM instruments promoted greater volume of the root canal than PDL. However, the cleaning ability of the instruments was similar. The apical increase up to size 40 with both instruments provided less debris and untouched surfaces and allowed centralization of the curved root canals.

Evaluation of smear layer and debris removal by stepwise intraoperative activation (SIA) of sodium hypochlorite

OBJECTIVES

To evaluate the efficacy of a stepwise intraoperative activation (SIA) of irrigants during and after the instrumentation compared with that of a conventional activation (CA) performed only after the instrumentation to remove smear layer and debris using different activation devices.

MATERIALS AND METHODS

A total of 70 single-rooted teeth were divided into a control group (no activation, n = 10) and two different experimental groups according to the irrigant activation protocol used: group 1 (CA), in which sodium hypochlorite was activated only after the use of the last mechanical file, and group 2 (SIA), in which activation was performed during and after the instrumentation. The two groups were divided into 3 subgroups according to the activation device used (n = 10): passive ultrasonic irrigation (PUI, subgroup a), EndoActivator (EA, subgroup b), and EDDY (subgroup c). The roots were split longitudinally and observed using scanning electron microscopy (SEM) to evaluate the presence of debris and smear layer, and the results were statistically analyzed.

RESULTS

All activation protocols and devices were more effective than control group in removing smear layer and debris from all root canal thirds (P < 0.05), except for CA-EA (group 1b) in the apical third. In the apical third, SIA was found to be more effective than CA (P < 0.05) to remove smear layer and residual debris when PUI was used, to remove the smear layer when EA was used (P < 0.05), and to remove residual debris when EDDY was used (P < 0.05). PUI and EDDY removed statistically more smear layer and debris than EA in the apical third (P < 0.05).

CONCLUSIONS

The SIA technique improved the smear layer and debris removal from the apical third and debris removal from the coronal third, and PUI and EDDY were more effective than EA in the apical third.

CLINICAL RELEVANCE

The stepwise intraoperative activation (SIA) technique may increase smear layer and debris removal.

The influence of kinematics of engine-driven nickel-titanium instruments on root canal shape assessed by micro-computed tomography: a systematic review

AIM

To evaluate if the kinematics of engine-driven instruments affect the root canal shape.

METHOD

The systematic review was registered in PROSPERO (CRD 42017077043). A broad search was performed for articles published before 26 September 2018 in the electronic databases: pubmed, scopus, web of science and Lilacs using MeSH and free terms. Only in vitro studies with human teeth that evaluated root canal shape by volume, surface area and unprepared surface area using reciprocating and rotary system assessed by micro-computed tomography were included. A modified checklist for randomized controlled trials from the Joanna Briggs Institute was used to assess the risk of bias.

RESULTS

Twenty-one articles were selected. According to quality assessment, all studies were considered 'moderate methodological quality'. Eighteen articles analysed volume increase, only four studies showed statistically significant difference, three indicating that the reciprocating movement obtained a greater increase in volume than the rotary system and one rotary system obtained a greater increase. Twelve studies analysed surface area, only three studies showed statistically significant difference, two presented a reciprocating system revealing greater amount of surface area and one showed a rotary system obtained a greater amount of surface area. Ten articles evaluated unprepared surface area, two studies that analysed total length, one study presented that the rotary system revealed lower unprepared surface area while another study showed reciprocating with less unprepared area. One study analysed middle and apical third, and observed that the rotary system presented lower unprepared surface area in the middle third.

CONCLUSIONS

Both the rotary and reciprocating kinematics produce changes in volume and surface area and leave unprepared areas in the root canal, however reciprocating system showed greater increase of volume and surface area, while the rotary system maintains less unprepared surface area.

Comparisons by microcomputed tomography of the efficiency of different irrigation techniques for removing dentinal debris from artificial grooves

AIM

The aim of this study was compare the capacity of different irrigation protocols for debris removal from artificial grooves and assess the effectiveness of Easy Clean used in different kinematics by means of micro-CT.

METHODOLOGY

Fifty acrylic prototyped maxillary incisors were instrumented and included in a muffle. The specimens were longitudinally sectioned, and a longitudinal groove was made on the inner surface of the root canal in one of hemisections, and the dentin debris was inserted into the grooves. The specimens were divided into five groups (n = 10): G1: Conventional with open-ended needle; G2: Conventional with double side-vented needle; G3: Easy Clean in reciprocating movement; G4: Easy clean in continuous rotation (ECCR); and G5: Passive ultrasonic irrigation (PUI). All specimens were scanned using microcomputed tomography before and after the irrigation technique and calculated the volume (mm3) of dentin debris. The paired t-test and post hoc Tukey test were the statistical tests used, with significance set at 5%.

RESULTS

There were no significant difference (P > 0.05) between PUI and ECCR. ECCR was significantly (P < 0.05) more effective than the groups of conventional irrigation techniques.

CONCLUSIONS

PUI and ECCR favored the removal of a larger volume of dentin debris from the groove.

Transportation Assessment in Simulated Curved Canals after preparation with Twisted File Adaptive and BT-Race instruments

Background

This study compared the incidence of deviation along curved canals after preparation with two nickel-titanium (NiTi) rotary systems, Twisted File Adaptive and BT-RaCe.

Material and Methods

Forty resin training blocks with curved canals were filled with ink and divided into two groups according to the instrumentation technique. Preinstrumentation images were acquired by using a stereomicroscope. The canals were up to an instrument #35/0.04. Postinstrumentation images were captured using the same conditions, and the images were superimposed. The amount of resin removed was measured at 8 different points, beginning at the apical terminus of the canal. Differences in the mesial and distal aspects were measured to evaluate the occurrence of deviation. The Student’s-t test was used for comparison of the intragroup deviation. Intergroup analysis was performed by using one-way ANOVA for each level. For multiple comparisons, the Bonferroni test was used and a cutoff for significance was set at 5%.

Results

Intragroup analysis showed that both instrumentation techniques promoted some deviation at all levels. BT-RaCe showed significantly lower deviation at 0 and 4-mm levels than Group Twisted File Adaptive (p<0.05). On the other hand BT-RaCe showed worse performance at level 6.

Conclusions

The results of this study demonstrated that none of the NiTi tested systems was able to instrument curved canals simulated in resin blocks without some deviation during the preparation. There is still need for improvement in the instruments manufacturing aiming the better performance of endodontic files in curved root canals.

Key words:BT-RaCe, Curved root canals, Deviation, Twisted File Adaptive.

Influence of NiTi alloy on the root canal shaping capabilities of the ProTaper Universal and ProTaper Gold rotary instrument systems

Objective

This study aimed to evaluate the influence of the NiTi wire in Conventional NiTi (ProTaper Universal PTU) and Controlled Memory NiTi (ProTaper Gold PTG) instrument systems on the quality of root canal preparation.

Material and Methods

Twelve mandibular molars with separate mesial canals were scanned using a high-definition microcomputed tomography system. The PTU and PTG instruments were used to shape twelve mesial canals each. The canals were scanned after preparation with F2 and F3 instruments of the PTU and PTG systems. The analyzed parameters included the remaining dentin thickness at the apical and cervical levels, root canal volume and untouched canal walls. Data was analyzed for statistical significance by the Friedman and Dunn's tests. For the comparison of data between groups, the Mann-Whitney test was used.

Results

In the pre-operative analysis, there were no statistically significant differences between the groups in terms of the area and volume of root canals (P>.05). There was also no statistically significant difference between the systems with respect to root canal volume after use of the F2 and F3 instruments. There was no statistical difference in the dentin thickness at the first apical level between, before and after instrumentation for both systems. At the 3 cervical levels, the PTG maintained centralization of the preparation on the transition between the F2 and F3 instruments, which did not occur with the PTU. Conclusion The Conventional NiTi (PTU) and Controlled Memory NiTi (PTG) instruments displayed comparable capabilities for shaping the straight mesial root canals of mandibular molars, although the PTG was better than the PTU at maintaining the centralization of the shape in the cervical portion.

The dentin thickness remaining in the risk zone of mandibular molars after cervical preflaring with four methods

Abstract Introduction Cervical preflaring is an important step of the canal system instrumentation, but can lead to excessive enlargement or root perforation. Objective Evaluate the remaining dentin thickness in the mandibular molars of mesial roots using cone beam computed tomography: Gates-Glidden (crown-down); Gates-Glidden (step-back); LA Axxess and Easy Pro-Design. Material and method Were selected 40 lower molars mesial roots, which were scanned in a cone beam CT scanner before and after preparation. Were obtained five sections of the CT images with an interval of 1 mm from the furcation, and measured the thickness variation between the root canal to the root external portion in analysis software. Result The evaluation of the different levels showed no significance within the same group for the Gates-Glidden group. On the other hand, were observed difference for LA Axxess (p=0.002) and Easy Pro-Design (p=0.005). In the intergroup analysis, were observed difference in all levels, especially for Gates-Glidden in the ascendant order (ANOVA and Tukey). Conclusion Within the limitations of these study, is possible to conclude that the protocol with greater wear in the cervical risk area was the Gates-Glidden in step-back sequence, as the other groups were equivalent (p>0.05).