Fluctuations in local shear-fault energy produce unique and dominating strengthening in metastable complex concentrated alloys.

Local chemical short-range ordering (SRO) and spatial fluctuations of planar fault energy are important features of multi-element and metastable complex concentrated alloys (CCAs). Arising from them, dislocations in such alloys are distinctively wavy in both static and migrating conditions; yet, such effects on strength have remained unknown. In this work, molecular dynamics simulations are used to show that the wavy configurations of dislocations and their jumpy motion in a prototypic CCA of NiCoCr are due to the local fluctuations of the energy of SRO shear-faulting that accompanies dislocation motion, with the dislocation getting pinned at sites of hard atomic motifs (HAMs) associated with high local shear-fault energies. Unlike the global averaged shear-fault energy which in general will subdue on successive dislocation passes, the local fluctuations in the fault energy always remain in a CCA, thus offering a strength contribution that is unique in such alloys. Analysis of the magnitude of this form of dislocation resistance shows that this is dominating over contributions due to elastic misfit of alloying elements and is in good agreement with strengths predicted from molecular dynamics simulations and experiments. This work has unfolded the physical basis of strength in CCAs, which is important for the development of these alloys into useful structural materials.

The effect of different chelators on the dislodgement resistance of MTA Repair HP, MTA Angelus, and MTA Flow.

The aim of this study was to investigate the influence of various irrigants on the dislodgement resistance of MTA Repair HP, MTA Angelus, and MTA Flow to root dentin. Three slices (1.0 ± 0.1 mm) were prepared from the middle third of 20 human maxillary anterior teeth. On each dentin disc, three perpendicular simulated perforation holes with a standardized 0.8 mm diameter were created. The sections from the same root were distributed arbitrarily into three groups (n = 20) for smear layer removal procedure: ethylenediaminetetraacetic acid (EDTA), chitosan-based silver nanoparticles (AgNPs-chitosan), and maleic acid (MA). Afterwards, the holes were randomly filled with one of the three investigated cements. The samples were submitted to the push-out test using a universal measuring system. Kruskal-Wallis and Mann-Whitney U tests were used to assess statistical differences among the groups. When the results were evaluated, it was found that the types of cement and chelating agents significantly affected the dislocation resistance (P < 0.05). EDTA provided a higher dislocation resistance with the investigated cements in comparison to MA and AgNPs-chitosan (P < 0.05). Furthermore, it was observed that MTA Flow and MTA Angelus presented improved dislocation resistance values than the MTA Repair HP when used with EDTA (P < 0.05). The findings indicated that EDTA increased the dislodgement resistance of the investigated cements. In conclusion, when EDTA used, MTA Flow, and MTA Angelus showed higher dislocation resistance values.

A chitosan-based irrigant improves the dislocation resistance of a mineral trioxide aggregate-resin hybrid root canal sealer.

OBJECTIVES: To investigate the effectiveness of root canal irrigation with chitosan on the dislocation resistance of a root canal sealer (MTA Fillapex) in vitro, measured by the push-out bond strength test. MATERIALS AND METHODS: Root canals of mandibular premolars (n = 57) were prepared using rotary files with 5.25% sodium hypochlorite as the irrigant during instrumentation. Following this, the specimens were randomly divided into three groups (n = 19) based on the final irrigant: group 1, 0.2% chitosan solution; group 2, 17% EDTA solution; group 3, saline. Three specimens from each group were analyzed using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The remaining specimens of each group were divided into two subgroups (n = 8) based on the method of agitation of the final irrigants (chitosan/EDTA/saline): subgroup A, sonic (Endoactivator, Dentsply Maillefer); subgroup B, no activation (control). After irrigation, all specimens obturated with a commercial mineral trioxide aggregate-resin hybrid sealer (MTA Fillapex, Angelus, Londrina, Brazil). Dislocation resistance was measured using the push-out bond strength test after 3 weeks. The data were analyzed using Kruskal-Wallis test (P = 0.05). RESULTS: Immaterial of the irrigant agitation, groups irrigated with chitosan showed significantly higher bond strength values than those irrigated with EDTA (P < 0.05). Groups irrigated with saline showed the least bond strength values (P < 0.05). When EDTA was used, sonic agitation significantly improved the bond strength of the sealer, compared to the control (P < 0.05). There was no significant difference between sonic agitation and the control when chitosan solution was used as the final irrigant (P > 0.05). The nitrogen/carbon ratio was significantly higher in chitosan groups compared to the control group (P < 0.05). CONCLUSION: This study provides the first evidence that chitosan irrigation improves the dislocation resistance of MTA-resin hybrid root canal sealer, compared to EDTA and saline irrigation. CLINICAL RELEVANCE: Chitosan-based irrigation has been previously shown to demonstrate anti-biofilm properties in the root canal. The present study demonstrates that chitosan can improve the bond strength of a root filling material, which may contribute to better sealing of the root canal system.

Effect of root canal irrigation protocols on the dislocation resistance of mineral trioxide aggregate-based materials: A systematic review of laboratory studies.

The aim of this systematic review was to address the question: Do different irrigating protocols have an impact on the dislocation resistance of mineral trioxide aggregate (MTA)-based materials? The review was performed using a well-defined search strategy in three databases (PubMed, Scopus, Web of Science) to include laboratory studies performed between January 1995 and May 2017, in accordance with PRISMA guidelines. Two reviewers analysed the papers, assessed the risk of bias and extracted data on teeth used, sample size, size of root canal preparation, type of MTA-based material, irrigants, canal filling method, storage method and duration, region of roots and the parameters of push-out testing (slice thickness, plunger dimensions and plunger loading direction), the main results and dislocation resistance values (in MPa). From 255 studies, 27 were included for full-text analysis. Eight papers that met the inclusion criteria were included in this review. There was a wide variation in dislocation resistance due to differences in irrigation sequence, time and concentration of irrigants, storage method and duration, and the parameters of push-out bond strength testing. A meta-analysis was not done but qualitative synthesis of the included studies was performed. No definitive conclusion could be drawn to evaluate the effect of irrigation protocols on dislocation resistance of MTA-based materials. Recommendations have been provided for standardized testing methods and reporting of future studies, so as to obtain clinically relevant information and to understand the effects of irrigating protocols on root canal sealers and their interactions with the dentine walls of root canals.

The correlation between fluid transport and push-out strength in root canals filled with a methacrylate-based filling material.

AIM: To investigate the correlation between fluid transport and dislocation resistance in canals filled with a methacrylate-based filling material. METHODOLOGY: The root canals in sixty-five single-rooted human teeth were prepared to size 40, 0.06 taper. Sixty roots were filled with a single-cone technique using RealSeal SE sealer and divided into 3 groups, whilst five roots served as fluid transport positive control. Group 1 (n = 20): correlation group. Specimens were consecutively tested with fluid transport for 90 min and thereafter with the push-out test at coronal and apical root levels. Group 2 (n = 20): push-out control. Specimens were only subjected to the push-out test at coronal and apical root levels. Group 3 (n = 20): fluid transport negative control. Specimens were totally covered with nail varnish. The correlation between fluid transport and dislocation resistance was assessed by Kendall's tau-b coefficient. The Mann-Whitney U-test was used to compare dislocation resistance between groups 1 and 2 and fluid transport between groups 1 and 3. Significance level was set at P < 0.05. RESULTS: Kendall's tau-b correlation coefficients between fluid transport and dislocation resistance were weak, being coronally 0.139 (P = 0.444) and apically -0.080 (P = 0.658). No significant difference in dislocation resistance could be detected between groups 1 and 2 at both root levels (P = 0.052 and P = 0.336, respectively). CONCLUSION: No significant correlation could be identified between fluid transport and dislocation resistance, meaning that the corono-apical sealing ability of a methacrylate-based root canal filling is independent of its adhesive properties as indicated by its dislocation resistance.

Influence of the use of chelating agents as final irrigant on the push-out bond strength of epoxy resin-based root canal sealers: A systematic review.

This systematic review (PROSPERO - CRD42020150722) was performed to answer the following question: Does the use of chelating agents affect the dislodgment resistance of epoxy resin-based root canal sealers? A search was conducted in PubMed, EMBASE, Scopus, LILACS and Web of Science, hand searching of two endodontic journals and grey literature until September 2020. Extracted data included: teeth used, sample size, root canal preparation, irrigant, chelating solution, neutralisation solution, type of resin-based sealer and obturation approach, storage method and duration, root third and slice thickness, plunger dimension and loading direction and the push-out testing parameters and values. The search retrieved a total of 2.389 studies. After analysis, 12 studies fulfilled the eligibility criteria and were included. Most of the final irrigation protocols with chelating agents had a positive impact and promoted an improvement in the dislodgment resistance of epoxy resin-based sealers to the root dentin.

Effects of radiation therapy on the dislocation resistance of root canal sealers applied to dentin and the sealer-dentin interface: a pilot study.

OBJECTIVES: This study evaluated and compared the effects of radiation therapy on the dislocation resistance of AH Plus and BioRoot RCS applied to dentin and the sealer-dentin interface. MATERIALS AND METHODS: Thirty single-rooted teeth were randomly assigned to 2 groups (n = 15 each): AH Plus (Dentsply DeTrey) and BioRoot RCS (Septodont). Each group was subdivided into control and experimental groups. The experimental group was subjected to a total radiation dose of 60 Gy. The root canals of all samples were cleaned, shaped, and obturated using the single-cone technique. Dentin slices (1 mm) were sectioned from each root third for the push-out test and scanning electron microscopy (SEM) was done to examine the sealer-dentin interface. The failure mode was determined using stereomicroscopy. Bond strength data were analyzed by the independent t-test, 1-way analysis of variance, and the Tukey post hoc test (α = 0.05). RESULTS: Significantly lower bond strength was observed in irradiated teeth than non-irradiated teeth in the AH Plus group (p < 0.05). The BioRoot RCS group showed no significant reduction in bond strength after irradiation (p > 0.05) and showed a higher post-irradiation bond strength (209.92 ± 172.26 MPa) than the AH Plus group. SEM revealed slightly larger gap-containing regions in irradiated specimens from both groups. CONCLUSIONS: The dislocation resistance of BioRoot RCS was not significantly changed by irradiation and was higher than that of AH Plus. BioRoot RCS may be the sealer of choice for root canal treatment in patients undergoing radiation therapy.

Dentin moisture conditions strongly influence its interactions with bioactive root canal sealers.

OBJECTIVES: It is known that bioactive materials interact with the dentin to undergo biomineralization. The exact role of moisture in this interaction is unknown. Here, we investigate the effects of dentin moisture conditions on the dislocation resistance of two bioactive root canal sealers (MTA Fillapex [Angelus Solucoes Odontologicas] and GuttaFlow BioSeal [Colténe/Whaledent AG]) at 3 weeks and 3 months after obturation. MATERIALS AND METHODS: Mandibular premolars (n = 120) were prepared and randomly divided into 3 groups based on the dentin condition: group 1, dry dentin; group 2, moist dentin; group 3, wet dentin. Each group was divided into 2 subgroups for root canal filling: MTA Fillapex and GuttaFlow BioSeal. Dislocation resistance was evaluated by measuring the push-out bond strength at 3 weeks and 3 months. Failure modes were examined under a stereomicroscope. Data were statistically analyzed by Kruskal-Wallis test with a significance level of 5%. RESULTS: Moist dentin resulted in higher bond strength values for both materials at both time points. This was significantly higher than wet and dry dentin for both the sealers at the 3 months (p < 0.05), while at 3 weeks it was significant only for GuttaFlow Bioseal. The different moisture conditions demonstrated similar trends in their effects on the dislocation resistance of the 2 root canal sealers. CONCLUSIONS: The dentin moisture conditions had a significant impact on its interaction with the bioactive materials tested. Maintaining moist dentin, but not dry or wet dentin, may be advantageous before the filling root canals with bioactive sealers.

Design Variability of the Push-out Bond Test in Endodontic Research: A Systematic Review.

INTRODUCTION: There is limited literature on the impact of testing variables on the push-out bond test (POBT). This review identified designs of the POBT used in the endodontic literature and aimed to determine which experimental variables may influence the push-out bond strength (POBS). METHODS: A systematic review based on PRISMA guidelines was performed by searching the PubMed, SCOPUS, and Cochrane library databases using terms including push-out and dislocation resistance and descriptions of endodontic materials. Test variables assessed included method of root preparation, timing of sectioning compared with filling, thickness, diameter and taper of sections, and plunger size and velocity. The POBS of 3 common materials (gutta-percha and AH Plus, mineral trioxide aggregate, and Biodentine) were collected from investigations, and a comparison was attempted. RESULTS: One hundred thirty-three studies assessed the POBS of root-filling materials, 68 assessed root repair cements/root-end filling materials, and 16 assessed orifice barrier materials other than mineral trioxide aggregate. There was significant variation in all of the assessed variables, resulting in a large range of reported values for the POBS of the various materials. Because of this heterogeneity in study design, no further statistical analysis of the impact of the test variables on POBS was possible. CONCLUSIONS: There was considerable variation in the POBT design used in endodontic research. Greater standardization is required for future research as well as accurate reporting for all test variables to assess the impact of specific design variables on POBS.

Influence of Irrigation Sequence on the Adhesion of Root Canal Sealers to Dentin: A Fourier Transform Infrared Spectroscopy and Push-out Bond Strength Analysis.

INTRODUCTION: There is a lack of evidence on the chemical interaction between sealers and dentin. The influence of irrigation on the chemical interaction between root canal sealers and dentin was analyzed by using Fourier transform infrared spectroscopy (FTIRS) and measurement of dislocation resistance. METHODS: Single-rooted teeth (n = 120) were instrumented with 3% NaOCl as the irrigant and divided into 4 groups (n = 30) on the basis of irrigation protocol: group 1, 3% NaOCl, 17% EDTA, water; group 2, 17% EDTA, 3% NaOCl, water; group 3, 3% NaOCl, QMix, water; group 4, 3% NaOCl, water. Each group was divided into 3 subgroups (n = 10) on the basis of the root canal sealer: A, epoxy resin (AH Plus); B, silicone (RoekoSeal); C, calcium hydroxide (Sealapex). The dislocation resistance was assessed by using push-out bond strength test. The data were statistically analyzed by three-way analysis of variance and Holm-Sidak tests (P = .05). Dentin powder treated as per the conditioning protocols mentioned was mixed with the sealers and analyzed by FTIRS. RESULTS: A significant interaction was observed between irrigation protocol, type of sealer, and root segment (P < .001) for AH Plus but not for RoekoSeal and Sealapex (P > .05). AH Plus showed the highest bond strength (P < .05). FTIRS showed chemical bonding between AH Plus and dentinal collagen. In groups 2 and 4, no chemical bonding was observed. CONCLUSIONS: Bond strength of sealers is differentially affected by the irrigation protocol. The epoxy resin sealer AH Plus chemically bonds to dentinal collagen. This interaction is influenced by the irrigation protocols.

The effect of medicaments used in endodontic regeneration technique on the dislocation resistance of mineral trioxide aggregate to root canal dentin.

INTRODUCTION: The aim of this study was to evaluate the effect of calcium hydroxide (CH) and antibiotic pastes, including a mixture of metronidazole and ciprofloxacin, with and without minocycline or cefaclor, on the dislocation resistance of mineral trioxide aggregate (MTA) to root dentin. METHODS: Eighty single-rooted human mandibular premolars were selected. The teeth were prepared by using the ProTaper system. The prepared teeth were then instrumented to a #6 Peeso reamer to obtain a standard internal diameter of 1.5 mm. The reamers were passed 1 mm beyond apex to simulate immature teeth. The specimens were then randomly divided into a control group (no intracanal medicament was used) and 4 experimental groups that were treated with an intracanal medicament: CH, double antibiotic paste (DAP) with metronidazole and ciprofloxacin, triple antibiotic paste (TAP) with minocycline, or TAP with cefaclor (n = 16). After 3 weeks, the medicaments were removed, and approximately 3 mm of MTA was placed in the coronal third of the canals. A push-out test was used to measure the dislocation resistance between the root dentin and MTA. Data were analyzed by using one-way analysis of variance and Tukey post hoc tests. RESULTS: The dislocation resistance values of the CH, TAP with minocycline, and TAP with cefaclor groups were similar to those of the control group (P > .05), whereas the DAP group had the lowest dislocation resistance when compared with the other groups (P < .05). Overall, there was a predominance of cohesive failures between root dentin and MTA. CONCLUSIONS: The results of this study indicate that the application of DAP as an intracanal medicament reduced the dislocation resistance of MTA to root dentin.