Dynamic Photoelastic Analysis of Stress Distribution in Simulated Canals Using Rotary Instruments with Varied Tip and Taper Sizes: A Quasi-3D Approach.

INTRODUCTION: To compare the stress produced on the walls of simulated canals by rotary instruments with varied tip and taper sizes. METHODS: Ninety isotropic transparent blocks, each containing a 60-degree curved canal, were distributed into 18 groups (n = 5) based on the instrument tip (sizes 10, 15, 20, 25, 30, and 35) and taper (sizes 0.02, 0.04, and 0.06). The blocks were fixed in a circular polariscope setup for dark field analysis. A digital camera was employed to capture the real-time birefringence patterns generated by each instrument. Digital image frames, corresponding to the instrument reaching the end of each canal third, were extracted and evaluated by 2 independent observers for the stress generation on canal walls. The data analysis employed a semi-quantitative scale ranging from 0 to 5. Cohen's Kappa coefficient test was used to determine the inter-observer agreement while the results were compared using Kruskal-Wallis test followed by an all-pairwise posthoc procedure (α = 5%). RESULTS: Inter-observer agreement was 0.95. A significant influence of the tip size on stress was observed across the coronal (P = .011), middle (P = .006), and apical (P = .026) thirds. In contrast, taper size did not affect the stress induced at the coronal (P = .509), middle (P = .958), or apical (P = .493) thirds. The variations in tip and taper sizes did not result in a significant stress differences among the thirds (P = .181). CONCLUSIONS: The stress significantly increased across all canal thirds with larger tip sizes of rotary instruments, whereas the taper sizes did not influence the stress when compared to the canal thirds.

Impact of access cavities on root canal preparation, restorative protocol quality, and fracture resistance of teeth.

The survival of endodontically treated teeth depends on the remaining tooth structure. The aim of this study was to evaluate the impact of different access cavities on root canal preparation, restorative protocol, and fracture resistance of endodontically treated teeth. Fifty-six mandibular molars were divided into control (n=8) and experimental (n=16) groups according to access cavity: Traditional, Conservative, and Truss; and redistributed (n=8) according to instrumentation protocols: Reciproc Blue and R-motion. After, teeth were scanned in micro-CT and then filled and redistributed according to composite resin restoration (n=8): Filtek One BulkFill and Filtek Z350. A new micro-CT scan was performed to analyze the restorative material. Then, samples were submitted to fracture resistance testing and the failure pattern was determined. Data were analyzed using paired T-test, ANOVA, Tukey, and chi-square tests (α=0.05). In Truss, R-Motion promoted less transportation in different thirds of root canals. Higher percentages of voids (5.05%) and filling material (11.7%) were observed in Truss. Fracture resistance values were higher for the control group, followed by Truss, Conservative, and Traditional. The predominant failure pattern was type-II. In Truss, reciprocating instruments with smaller taper showed less canal transportation. Also, Truss provided higher values of fracture resistance, although it presented a higher percentage of voids and remaining filling material. Thus, in Truss, reciprocating files with smaller taper showed less canal transportation, and these cavities provided higher values of fracture resistance, although it presented a higher percentage of voids and remaining filling material.

Quasi-3D dynamic photoelastic analysis of stress distribution during preparation of simulated canals with 13 mechanical preparation systems.

AIM: The aim of this study is to compare the stress produced on the internal walls of simulated canals by nine rotary and four reciprocating systems. METHODOLOGY: Sixty-five isotropic transparent blocks containing a 60° curved and tapered simulated canal were selected and distributed into 13 groups (n = 5) according to the preparation system: BioRace, HyFlex EDM, iRaCe, Mtwo, One RECI, ProTaper Next, RaCe EVO, Reciproc, Reciproc Blue, R-Motion, VDW.ROTATE, XP-Endo Rise Shaper, and XP-Endo Shaper. Each resin block was mounted in a vice and a digital camera recorded the entire sequence of each preparation system through a circular polariscope set for dark field analysis. The video frames when each instrument reached the end of the coronal, middle, and apical thirds of the canal were extracted from the recordings and analysed by two independent observers regarding the stress generated on the canal walls using a semi-quantitative evaluation on a 0-5 scale. Intra- and inter-observer agreement were subjected to the Cohen's Kappa coefficient test, whilst the experimental results were compared using Kruskal-Wallis test post hoc pairwise comparisons with Bonferroni correction (α = 5%). RESULTS: The inter- and intra-observer agreement were 0.98 and 1, respectively. Most instruments demonstrated acceptable performance (scores ≤ 2) in all thirds. Other instruments, such as the HyFlex EDM 25.12 (coronal and middle thirds), Reciproc Blue R25 and Reciproc R25 (coronal and apical thirds), R-Motion 30.04 (apical third), and VDW.ROTATE 20.05 (apical third) showed scores higher than 3. Statistical analysis revealed a significant difference amongst the tested systems at the coronal, middle, and apical thirds (p < .05). CONCLUSION: None of the canal instrumentation protocols were stress-free, showing varying levels of stress concentrations. Various factors seemed to influence the magnitude of stress and its distribution pattern on the canal walls. Overall, instruments characterized by a larger taper, lower speed, reciprocating motion, and made of heat-treated NiTi alloy exhibited higher patterns of stress distribution.

Evaluation of rotary instruments with whipping motion in the biomechanical preparation of large root canals of young permanent teeth.

Shaping ability evaluation of taper ./01 instruments in large root canals, by microcomputed tomography (micro-CT) and scanning electron microscopy (SEM). Maxillary central incisors with large diameter root canals were divided into two groups (n = 10): XP-Endo Shaper (FKG-Dentaire, Switzerland) and manual instrumentation (FKG-Dentaire). Two- and three-dimensional parameters from cervical to apical root thirds were evaluated by micro-CT. Apical stop was evaluated by SEM images. Data were analysed by ANOVA and Tukey tests (α = 5%). XP-Endo Shaper allowed a regular biomechanical preparation with less dentinal wear compared with manual instrumentation, which showed excessive wear of the thin root canal walls (p < 0.05). Roundness and SMI showed similarity between both protocols (p > 0.05). XP-Endo Shaper SEM showed a regular and well-defined shape of the apical foramen suggesting the formation of the apical stop. Reduced diameter and taper instruments promoted a conservative wear and a well-defined apical stop formation in large root canals.

Impact of access cavities on root canal preparation, restorative protocol quality, and fracture resistance of teeth

Abstract The survival of endodontically treated teeth depends on the remaining tooth structure. The aim of this study was to evaluate the impact of different access cavities on root canal preparation, restorative protocol, and fracture resistance of endodontically treated teeth. Fifty-six mandibular molars were divided into control (n=8) and experimental (n=16) groups according to access cavity: Traditional, Conservative, and Truss; and redistributed (n=8) according to instrumentation protocols: Reciproc Blue and R-motion. After, teeth were scanned in micro-CT and then filled and redistributed according to composite resin restoration (n=8): Filtek One BulkFill and Filtek Z350. A new micro-CT scan was performed to analyze the restorative material. Then, samples were submitted to fracture resistance testing and the failure pattern was determined. Data were analyzed using paired T-test, ANOVA, Tukey, and chi-square tests (α=0.05). In Truss, R-Motion promoted less transportation in different thirds of root canals. Higher percentages of voids (5.05%) and filling material (11.7%) were observed in Truss. Fracture resistance values were higher for the control group, followed by Truss, Conservative, and Traditional. The predominant failure pattern was type-II. In Truss, reciprocating instruments with smaller taper showed less canal transportation. Also, Truss provided higher values of fracture resistance, although it presented a higher percentage of voids and remaining filling material. Thus, in Truss, reciprocating files with smaller taper showed less canal transportation, and these cavities provided higher values of fracture resistance, although it presented a higher percentage of voids and remaining filling material.

Heat-treated NiTi instruments and final irrigation protocols for biomechanical preparation of flattened canals.

This study evaluate shaping ability of heat-treated NiTi-alloy instruments associated with different final irrigation protocols in flattened root canals. Thirty human mandibular incisors with flattened root canals were divided into 5 groups (n = 10): (XP) Original Protocol XP-endo Shaper; (XP-WT) Original Protocol XP-endo Shaper with working time variation; (XP-K) XP-endo Shaper with kinematics variation; (XP-WTK) XP-endo Shaper with kinematics and working time variations; (Hyflex) Hyflex CM. For the variation in working time protocols the same sample of the XP-endo Shaper groups with and without kinematic variation were used. To evaluate final irrigation protocols, groups 1, 3 and 5 were submitted to 3 protocols: (NI) No irrigation (n = 2); (CI) conventional irrigation (n = 4), and (EndoVac) irrigation (n = 4). The samples were scanned by microcomputed tomography and prepared for scanning electron microscopy evaluation. Quantitative data were evaluated using the parametric ANOVA test, with statistical significance level set at 5%, and qualitative data obtained were compared to establish the agreement between examiners through the Kappa test. It was observed that in the analysis of XP-endo Shaper protocols, the additional working time did not cause difference in any of parameters evaluated (p > 0.05) in relation to time recommended by manufacturer. Compared to Hyflex, XP-K showed highest mean volume increase (p < 0.05) and lowest percentage of untouched walls (p < 0.05). In the qualitative evaluation, final irrigation protocol with EndoVac provided the best cleaning results when associated with XP-K and with Hyflex. Thus, supplementary techniques are effective tools to enhance cleaning and to promote higher touch of walls during root canal preparation.

Impact of several NiTi-thermally treated instrumentation systems on biomechanical preparation of curved root canals in extracted mandibular molars.

AIM: To evaluate the shaping ability of several heat-treated nickel-titanium systems used to prepare root canals with moderate and severe curvature, in extracted mandibular molars, by micro-computed tomography, considering their variation in kinematics and design. METHODOLOGY: Curved-mesial roots of mandibular molars were randomly selected and assigned into 4 balanced experimental groups (n = 10), established by determining homogeneous 3D parameters of volume and surface area: R-Motion (RM) size 30, 0.04 taper (RM; FKG Dentaire), Reciproc Blue (RCB) size 25, 0.08 taper (RCB; VDW GmbH), HyFlex CM (HFX) size 30, 0.04 taper (HFX; Coltène Whaledent) and XP-endo Shaper size (XPS) 30, 0.01 taper (XPS; FKG Dentaire). The volume of irrigation was established at 10 ml of 2.5% NaOCl. Throughout the entire root canal preparation procedures, the samples were fixed in a vice submerged in a container with water monitored at 37°C. Dimensional cross-sectional measures of area, perimeter, roundness, major/minor diameters and 3-dimensional (volume, surface area, structure model index - SMI) parameters as well as the smallest dentine thickness along the cervical and middle root thirds were evaluated by micro-CT. Data were analysed using analysis of variance and post hoc Tukey tests (α = 5%). RESULTS: Reciproc Blue and XPS had significantly greater mean increases in cross-sectional area measurements, only in the middle third, when compared with RM and HFX (p < .05). RM, RCB and XPS had a similar increase in measurements of length and width of perimeter (p > .05), and HFX had significantly lower mean increases in perimeter values only when compared with XPS (p < .05). RCB and XPS had significantly greater mean increases in volume when compared with RM and HFX (p < .05). RM had a significantly lower difference in SMI after preparation, compared with RCB, HFX and XPS (p < .05). The smallest dentine thickness was observed after the use of RCB (p < .05), in the danger and safety zones. CONCLUSIONS: XP-endo Shaper and RM had a shaping ability similar to that of instruments with larger tapers, achieved with less dentine removal in danger and safe zones in curved-mesial canals of extracted molar teeth treated on a laboratory benchtop.

Heat-treated NiTi instruments and final irrigation protocols for biomechanical preparation of flattened canals

Abstract This study evaluate shaping ability of heat-treated NiTi-alloy instruments associated with different final irrigation protocols in flattened root canals. Thirty human mandibular incisors with flattened root canals were divided into 5 groups (n = 10): (XP) Original Protocol XP-endo Shaper; (XP-WT) Original Protocol XP-endo Shaper with working time variation; (XP-K) XP-endo Shaper with kinematics variation; (XP-WTK) XP-endo Shaper with kinematics and working time variations; (Hyflex) Hyflex CM. For the variation in working time protocols the same sample of the XP-endo Shaper groups with and without kinematic variation were used. To evaluate final irrigation protocols, groups 1, 3 and 5 were submitted to 3 protocols: (NI) No irrigation (n = 2); (CI) conventional irrigation (n = 4), and (EndoVac) irrigation (n = 4). The samples were scanned by microcomputed tomography and prepared for scanning electron microscopy evaluation. Quantitative data were evaluated using the parametric ANOVA test, with statistical significance level set at 5%, and qualitative data obtained were compared to establish the agreement between examiners through the Kappa test. It was observed that in the analysis of XP-endo Shaper protocols, the additional working time did not cause difference in any of parameters evaluated (p > 0.05) in relation to time recommended by manufacturer. Compared to Hyflex, XP-K showed highest mean volume increase (p < 0.05) and lowest percentage of untouched walls (p < 0.05). In the qualitative evaluation, final irrigation protocol with EndoVac provided the best cleaning results when associated with XP-K and with Hyflex. Thus, supplementary techniques are effective tools to enhance cleaning and to promote higher touch of walls during root canal preparation.

Analysis of the physicochemical properties, cytotoxicity and volumetric changes of AH Plus, MTA Fillapex and TotalFill BC Sealer.

BACKGROUND: To evaluate the physicochemical properties and cytotoxicity of AH Plus, MTA Fillapex and TotalFill BC Sealer. Volumetric changes were also evaluating using micro-computed tomography (micro-CT). MATERIAL AND METHODS: Radiopacity and flow were evaluated in accordance with the ISO 6876, while setting time was evaluated in accordance with the ASTM- C266-08 specifications. The release of Ca2+ ions and pH were measured with spectrophotometer and pH meter, respectively, after different time intervals (1h, 3h, 24h, 72h, 168h, and 360h). Cytotoxicity was evaluated by MTT reduction assay to check 3T3 cells viability at 24, 48 and 72 hours. Volumetric change was evaluated by micro-CT, by using 30 acrylic teeth, filled with gutta-percha cones and the tested root canal sealer. The samples were evaluated after 168h, 360h and 720h of immersion in distilled water. Data were statistically analyzed by one-way ANOVA and Tukey test or by Kruskal-Wallis and Dunn tests (P<0.05). RESULTS: MTA Fillapex and TotalFill BC Sealer showed lower radiopacity than AH Plus (P<0.05). The MTA Fillapex showed the highest flow, while AH Plus showed the lowest flow (P<0.05). The initial and final setting time of AH Plus were lower than MTA Fillapex and TotalFill BC Sealer (P<0.05). In general, TotalFill BC Sealer presented higher Ca2+ ion release and pH than the other tested sealers. TotalFill BC Sealer also showed overall lower cytotoxicity when compared to the other sealers. Volumetric change of AH Plus and TotalFill BC Sealer was lower than MTA Fillapex (P<0.05). CONCLUSIONS: AH Plus, MTA Fillapex and TotalFill BC Sealer showed slight differences in the physicochemical properties and cytotoxicity, but all suitable for an endodontic sealer. However, AH Plus and TotalFill BC Sealer showed low volumetric changes when compared to MTA Fillapex. Key words:Calcium silicate, cytotoxicity, physicochemical properties, micro computed tomography.

Root canal preparation using micro-computed tomography analysis: a literature review.

This literature review has critically analyzed the published research related to the biomechanical preparation of root canals with three-dimensional analysis using micro-computed tomography (micro-CT). In December 2017, six databases (PubMed, Cochrane, Web of Science, Embase, Scopus, and Science Direct) were accessed using keywords to find articles including the use of the micro-CT analysis in biomechanical root canal preparation. There were 60 full articles that were selected, which were screened and read by two authors. The research that was reviewed and analyzed included root canal anatomy and sample selection, changes in canal shape and untouched canal areas, canal transportation and centering ability, and kinematics (motion). Of the studies selected, 49.18% discussed anatomical characteristics, with 54.1% of these studies describing mesial roots of mandibular molars with moderate curvature. Only 35% used a stratified distribution based on root canal system morphology and quantitative data obtained by micro-CT. The analysis of canal transportation and centering ability showed that transport values in the apical third exceeded the critical limit of 0.3 mm in mesial roots of mandibular molars with moderate curvature, especially in the groups in which a reciprocating system was used. In relation to kinematics, 91.70% of the reviewed studies evaluated continuous rotating instruments, followed by reciprocating rotation (38.33%), vibratory (15%), and the adaptive kinematics, which was in only 8.33%. The reciprocating kinematics was associated with higher canal decentralization and transportation indexes, as well as a greater capacity for dentin removal and debris accumulation. This literature review showed that the anatomy, the type of design and kinematics of instruments, and the experimental design are factors that directly influence the quality of biomechanical preparation of root canals analyzed in a qualitative and quantitative manner by micro-CT.

Avanço tecnológico no tratamento de canais radiculares de molares: apresentação de técnica / Technological advance in the treatment of root canals of molars – presentation of a technique

Nos últimos 20 anos, considerados como “época contemporânea da Endodontia”2, ocorreu uma evolução técnica nessa especialidade de intensa magnitude que está atingindo patamares não observados em toda a sua história. Os sistemas rotatórios3 que utilizam instrumentos de níquel/titânio acionados por diferentes e sofisticados motores elétricos representam um dos avanços mais significativos dessa especialidade. Na presente apresentação de técnica, o tratamento (biopulpectomia) foi realizado em primeiro molar inferior esquerdo (36) com diagnóstico clínico de pulpite aguda irreversível. Utilizando-se o motor Dentaport ZX e instrumentos do sistema FKG RaCe, os canais radiculares foram instrumentados, proporcionando ao profissional maior ergonomia, melhor qualidade no tratamento, maior ganho de tempo e, principalmente, maior conforto para o paciente