Fracture Resistance Of Roots Research Articles

Vertical root fracture resistance and dentinal crack formation of root canal-treated teeth instrumented with different nickel-titanium rotary systems: an in-vitro study.

To compare the vertical root fracture (VRF) resistance of root canal-treated teeth instrumented with four different nickel-titanium (NiTi) rotary file systems and examine the dentinal crack pattern and direction using a new classification. Eighty mature mandibular premolars were selected and decoronated, leaving 13mm of the root. The root samples were mounted in acrylic resin and divided randomly into five groups of different NiTi file systems: Group 1-control, Group 2-T-Pro, Group 3-HyFlex CM, Group 4-TG6 and lastly Group 5-ZenFlex. Samples in Group 2 and Group 3 were instrumented up to size 25/0.04, whereas Group 4 and Group 5 were instrumented up to size 25/0.06. Obturation was performed with AH Plus sealer and gutta-percha using single cone technique. Subsequently, all samples were subjected to occlusal compressive force until they were fractured. The force (N) needed to cause root fracture was recorded. The crack patterns and directions were also inspected under magnification and classified using a new and simple classification. The highest (VRF) resistance was noted in the control group (453.15 ± 92.23N), followed by T-Pro (387.43 ± 76.81N), HyFlex CM (381.88 ± 52.73N), ZenFlex (369.15 ± 89.41N) and finally TG6 (346.05 ± 72.08N), but there was no significant difference between T-Pro and HyFlex (P = 0.438). A significantly higher prevalence (P = 0.001) of Type 1 crack pattern was observed, especially in samples instrumented with TG6. Majority of the cracks ran buccolingually except in some samples instrumented with ZenFlex (P = 0.898). Smaller file taper increased the VRF resistance of root canal-treated teeth. Majority of the dentinal crack exhibited Type 1 pattern and ran buccolingually.

The effect of calcium hydroxide on dentine composition and root fracture resistance of human teeth: An in vitro study.

The purpose of this study was to evaluate the effect of calcium hydroxide [Ca(OH)2 ] on dentine composition and root fracture resistance. Root canals of fifty extracted mandibular premolars were prepared and divided into five groups (N=10). Canals were filled with non-setting Ca(OH)2 or left empty and were subsequently stored in phosphate buffered saline for 7, 14, 30, or 90days, respectively. Ca(OH)2 was then washed out, and roots were separated from the crowns and subjected to fracture strength test. Fractured fragments were examined by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The results showed a significant and progressive reduction in fracture resistance the longer the duration of exposure to Ca(OH)2 , and the fracture resistance in teeth exposed for 90days was significantly lower than in any other group. SEM revealed cracks in the dentine surfaces that had been exposed to Ca(OH)2 . FTIR showed a significantly lower mineral to matrix ratio in roots exposed to Ca(OH)2 for 30 and 90days than seen in roots exposed for a shorter duration. XRD analysis revealed a reduction in dentine crystallinity. It was concluded that Ca(OH)2 significantly reduced the fracture resistance of the roots overtime. Exposure to Ca(OH)2 reduced the mineral to matrix ratio and crystallinity of the dentine.

The effect of diabetes on Fracture Resistance of Teeth: An invitro study.

The root fracture resistance (RFR) of premolars extracted from diabetic patients and the effect of biomaterials: white mineral trioxide aggregate (WMTA) and WMTA+Na2 HPO4 as an additive, on enhancing RFR were evaluated. Diabetic and non-diabetic teeth were divided into 4 subgroups (n = 5): root canals were obturated with WMTA, WMTA+Na2 HPO4 , gutta-percha and one unfilled (control). A plunger (1 mm diameter) applied a downward compressive load with crosshead speed of 1 mm min-1 on the specimens mounted on resin blocks, and the ultimate force to fracture was measured. The mean RFR values of diabetic specimens were significantly lower. The lowest and highest means of RFR were recorded in the control and WMTA, in normal group and the control and WMTA+Na2 HPO4 in the diabetic group, respectively. The RFR in diabetic patients was significantly lower, indicating their higher susceptibility to fracture under vertical forces. The use of WMTA (with or without Na2 HPO4 ) for obturation enhances the RFR.

Effect of final irrigation protocols on the fracture resistance of roots with varying dentine thickness.

This study evaluated the effects of 9% etidronic acid (HEBP) and 17% ethylenediaminetetraacetic acid (EDTA) used either with conventional syringe irrigation (CSI) or passive ultrasonic irrigation (PUI) on the fracture resistance of roots with different dentine thickness. The root canals of 120 extracted teeth were widened, leaving dentinal walls with different thicknesses of either 0.75mm, 1.50mm, or 2.25mm with 40 teeth in each group. Within each of these groups, four subgroups (n=10) were formed according to the final irrigation regimens applied: 2.5% NaOCl-17% EDTA with CSI; 2.5% NaOCl-17% EDTA with PUI; 2.5% NaOCl+9% HEBP with CSI; 2.5% NaOCl+9% HEBP with PUI. The irrigated root canals were obturated with AH Plus sealer and gutta-percha cones. A compressive vertical loading was applied to the samples and the force at fracture was recorded. Data were statistically analysed using a multiple linear regression analysis. The most influencing factor for the fracture strength of roots was the remaining dentine thickness, followed by the irrigation method, and then the irrigation solution. The samples irrigated using PUI were statistically significantly more resistant to fracture than those using CSI (mean difference=116.3N; 95% CI=[53.9, 178.6] N). The application of HEBP was associated with higher resistance to fracture than the application of EDTA (mean difference=71.0N; 95% CI=[8.6, 133.3] N).

Influence of Various Irrigation Protocols on Resistance to Vertical Root Fracture in Root Canal Treated Teeth

Introduction: This study compared influence of various irrigation protocols on vertical root fracture resistance of root canal treated teeth. Methods: Forty-eight extracted mandibular premolars were included in the study. The root canals of teeth were instrumented and specimens were allocated into 4 (n = 12) groups according to the irrigation solutions: Group 1: 5% EDTA, 2.5% NaOCl and DW; Group 2: 5% EDTA, 2.5% NaOCl, DW and 2% CHX; Group 3: 5% EDTA, 2.5% NaOCl and 5% Na2S2O3; Group 4: 5% EDTA, 2.5% NaOCl, 5% Na2S2O3 and 2% CHX. Root canals were filled and a load in a vertical direction was applied a week later to specimens. The data were analysed using two-way ANOVA test (P < 0.05). Results: Interaction between using DW or Na2S2O3 and using or not using CHX had a significant effect on fracture resistance to vertical forces (P < 0.001). Irrigation with Na2S2O3 improves fracture resistance to vertical forces when compared to irrigation with DW (P < 0.001). Irrigation with CHX did not affect fracture resistance to vertical forces (P = 0.759). Conclusion: The irrigation solutions statistically affect resistance of root canal treated teeth to vertical fracture forces.

Evaluation of Fracture Resistance of Mandibular Premolar Canals Filled with Four Different Obturation Techniques- An In vitro Study

Introduction: To prevent the ingress of microorganisms and their byproducts into root canal space is the primary goal of obturation. Endodontically treated teeth are weak and more susceptible to fracture than vital teeth. Therefore, to increase the strength of the root canal and increase root fracture resistance by adhesion and mechanically interlocking root canal filling material with radicular dentin is also one of the goal of obturation. Aim: To evaluate and compare the fracture resistance of mandibular premolar canals filled with four different obturation techniques. Materials and Methods: The in vitro study was conducted in Department of Conservative Dentistry and Endodontics, Krishna Institute of Medical Sciences (Deemed To Be University), Karad, Maharshtra, India, from August 2020 to December 2020. A total of 100 extracted human mandibular premolars with single canals were collected for the study and sectioned horizontally to obtain a standardised length of 14 mm. With the help of 15 K-file (Dentsply) working length was determined and root canals were prepared to an International Organisation for Standardisation (ISO) size 45 file at the apex and flared using a #4 Gates-Glidden drill (Mani, Japan). The teeth were then randomly divided into four experimental groups, Group I-Lateral condensation, Group II-ROEKO GuttaFlow® bioseal, Group III- Guttacore, Group IV-Thermoplasticised gutta percha (System B) and two control groups, they were Group V-(Negative control), instrumentation was done, but no obturation, Group VI-(Positive control), teeth were neither instrumented nor obturated. All the experimental teeth were filled as per the obturation technique. A universal testing machine was used for evaluating fracture resistance. The results were analysed using the One-way ANOVA test. The significance between the groups was tested with Scheffe’s post hoc test. Results: There were statistically significant difference among six group for mean fracture load (N) with p-value &lt;0.001. furthermore, pair wise comparison of fracture load (N) showed that the mean difference is significant at p-value &lt;0.05. The mean difference between Group IV and V was not significant (p-value=0.935) Conclusion: Under the limitation of this study, it was concluded that the resistance of the root to vertical fracture amongst the experimental group was maximum in Group III (Guttacore) and minimum in Group IV (Thermoplasticised gutta-percha, System B).

The effect of taper and apical preparation size on fracture resistance of roots.

This study investigated the effect of taper and apical preparation size on the fracture resistance of roots. 84 mandibular incisor teeth were selected. Groups (n=12): uninstrumented (control group), 25/0.04, 25/0.06, 25/0.08, 30/0.04, 30/0.06 and 30/0.08. K3XF files (Kerr Endodontics, Orange, CA) were used for canal preparation. Fracture resistance was tested using a Universal test machine. For statistical analysis, the level of significance was P≤0.05, and one-way anova and post hoc LSD tests were used. The control group showed the highest fracture resistance (P<0.05). No significant difference was found between 25/0.04 and 25/0.06; 25/0.06 and 25/0.08; 30/0.04 and 30/0.06; 30/0.06 and 30/0.08; 25/0.04 and 30/0.04; 25/0.06 and 30/0.06; and 25/0.08 and 30/0.08 (P>0.05). Significant differences were found between 25/0.04 and 25/0.08; 30/0.04 and 30/0.08; and 25/0.08 and 30/0.04 (P<0.05). In conclusion, the clinical selection of larger tapers can cause a higher risk of fracture.

Fracture resistance of human roots filled with mineral trioxide aggregate mixed with phosphate-buffered saline, with and without calcium hydroxide pre-medication.

To compare the fracture strength of extracted human roots with apical plugs of mineral trioxide aggregate (MTA) mixed with either Ca- and Mg-free phosphate-buffered saline (PBS) or water, with and without calcium hydroxide (CH) canal pre-medication. A total of 180 single-rooted human teeth were prepared to resemble immature roots and divided into groups (n=20). The negative control received canal irrigation only, and the positive control received intracanal treatment with CH for either two or twelve weeks. MTA mixed with water was used in Group 1: (i) without CH pre-medication - MTA(W); (ii) after 2weeks CH pre-medication - 2/52CH+MTA(W); and (iii) after 12-week CH pre-medication - 12/52 CH+MTA(W). MTA mixed with PBS was used in Group 2: (i) without CH pre-medication - MTA(PBS); (ii) after 2-week CH pre-medication - 2/52CH+MTA(PBS); and (iii) after 12-week CH pre-medication - 12/52 CH+MTA(PBS). A compressive force was applied to each root until the point of fracture. The results were analysed by the Kruskal-Wallis and Dunn's multiple comparisons tests (P<0.05). There was no significant difference between groups MTA(W), MTA(PBS) and 2/52CH+MTA(PBS), and all three groups were significantly (P<0.01, P<0.05 and P<0.05, respectively) more resistant to fracture than the negative control. Within Group 1, the samples that received two- (P<0.01) and twelve-week (P<0.001) CH pre-treatment were more prone to fracture than those which did not. No difference was found amongst the control groups. The roots of the MTA(PBS) group had a higher dependability (P<0.05) than the MTA(W) group when compared by the Weibull modulus. The difference was also present when a 2-week CH pre-medication was used. Mineral trioxide aggregate mixed with Ca- and Mg-free phosphate-buffered saline had a significant strengthening effect on the fracture resistance of structurally weak roots, even when short-term calcium hydroxide pre-medication had been used. MTA mixed with water lost its strengthening effect on human roots when 2- or 12-week CH pre-treatment had been used. Use of CH dressing for up to 12weeks had no negative effect on fracture resistance of human roots.

Do pre-existing microcracks play a role in the fracture resistance of roots in a laboratory setting?

To investigate a potential cause-effect relationship between dentinal microcracks and fracture resistance of mandibular incisors that had not been endodontically treated. Sixty mandibular incisors with circular-shaped canals were selected based on micro-computed tomographic scans to create a homogeneous sample. The cross-sectional images of the specimens were screened to identify and quantify the presence of dentinal microcracks. Then, teeth were embedded in polystyrene resin and subjected to axial compressive loading using a universal testing machine. After fracture, the roots were re-scanned and fractography analysis was performed by inspection of 3D models to verify crack propagation. Spearman's rank correlation was used to assess the correlation between the number of microcracks and force required to fracture. Dentinal microcracks were detected in 79% of the specimens (n=44). The incidence of microcracks varied between teeth from 6% to 42% of the total slices per sample (average of 14±17%). The number of microcracks per sample varied from 0 to 1605, with an average of 412±484 (median=221 and IQR 25%=15/75%=658). The load at failure values varied from 227 to 924N, with an average of 560.3±168.1N (median=561 and IQR 25%=458/75%=694). The Spearman correlation coefficient (rho) equalled 0.065. There was no cause-effect relationship between the number of dentinal microcracks and the fracture resistance of nonendodontically treated mandibular incisors. The presence and quantity of microcracks did not make these roots more prone to fracture.

Current status on minimal access cavity preparations: a critical analysis and a proposal for a universal nomenclature.

In the last decade, several access cavity designs involveing minimal removal of tooth tissue have been described for gaining entry to pulp chambers during root canal treatment. The premise behind this concept assumes that maximum preservation of as much of the pulp chamber roof as possible during access preparation would maintain the fracture resistance of teeth following root canal treatment. However, the smaller the access cavity, the more difficult it may be to visualize and debride the pulp chamber as well as locate, shape, clean and fill the canals. At the same time, a small access cavity may increase the risk of iatrogenic complications as a result of poor visibility, which may have an impact on treatment outcome. This study aimed to critically analyse the literature on minimal access cavity preparations, propose new nomenclature based on self-explanatory abbreviations and highlight the areas in which more research is required. The search was conducted without restrictions using specifics terms and descriptors in four databases. A complementary screening of the references within the selected studies, as well as a manual search in the highest impact journals in endodontics, namely International Endodontic Journal and Journal of Endodontics, was also performed. The initial search retrieved 1831 publications. The titles and abstracts of these papers were reviewed, and the full text of 94 studies was assessed. Finally, a total of 28 studies were identified as evaluating the influence of minimally invasive access cavity designs on the fracture resistance of teeth and on the different stages of root canal treatment (orifice location, canal shaping, canal cleaning, canal filling and retreatment). Overall, the studies had major methodological drawbacks and reported inadequate and/or inconclusive results on the utility of minimally invasive access preparations. Furthermore, they offered limited scientific evidence to support the use of minimally invasive access cavities to improve the outcome of root canal treatment and retreatment; they also provided little evidence that they preserved the fracture resistance of root filled teeth to a greater extent than traditional access cavity preparations. It was concluded that at present, there is a lack of supporting evidence for the introduction of minimally invasive access cavity preparation into routine clinical practice and/or training of undergraduate and postgraduate students.

Middle Mesial Canal Preparation Enhances the Risk of Fracture in Mesial Root of Mandibular Molars

IntroductionThe aim of this investigation was to evaluate the effect of the presence and preparation of middle mesial (MM) canals on the fracture resistance of the mesial root of mandibular molars. MethodsForty intact mesial roots of mandibular first molars having 2 (n = 20) or 3 (n = 20) independent canals from the furcation level for up to at least 5 mm apically were selected based on preoperative micro–computed tomographic scanning. The selected roots were then distributed into 2 experimental (n = 10) and 2 control groups (n = 10) according to the root length, canal configuration (2 or 3 independent canals), and root thickness at the furcation level. In the experimental groups 1 (2 independent canals) and 3 (3 independent canals), root canals were enlarged up to the ProTaper Next X3 rotary instrument (Dentsply Sirona, Ballaigues, Switzerland), whereas in groups 2 (2 independent canals) and 4 (3 independent canals) root canals were not prepared. The specimens were embedded in acrylic resin after their surfaces were coated with a thin layer of silicone and subjected to a fracture strength using a universal testing machine. The types of fracture extension and course were recorded and statistically compared with the chi-square test, whereas fracture strength was analyzed using 1-way analysis of variance and post hoc Tukey tests (α = 5%). ResultsNo statistical difference in fracture strength was observed between nonprepared roots with 2 (group 2, 696.1 ± 186.3 N) or 3 (group 4, 558.4 ± 154.6 N) independent canals (P > .05), whereas the lowest values were obtained in the prepared roots with an MM canal (groups 3, 377.1 ± 77.2 N) (P < .05). The mean fracture strength observed in the prepared roots with 2 canals (group 1, 528.4 ± 134.3 N) showed no statistically significant difference compared with nonprepared roots with 3 canals (group 4, 558.4 ± 154.6 N) (P > .05). The chi-square test revealed no significant differences in fracture extent, types, and courses among groups (P > .05). Fracture extensions in all groups were mostly central and buccal-central types, whereas the highest frequency of fracture course was the curved and zigzag types. ConclusionsThe fracture resistance of the mesial roots of the mandibular molars decreased after the preparation of mesial canals with large-tapered instruments. Preparation of the MM canal further diminished the fracture resistance of the mesial roots. The resultant fracture displayed a distinct pattern in the buccolingual plane.

Could calcium hypochlorite and grape seed extract keep the mechanical properties of root dentin and fracture resistance of weakened roots?

ObjectivesTo evaluate the effect of different endodontic irrigation protocols on dentin mechanical properties and fracture resistance of roots with 0.5 mm (weakened roots) and 1.5 mm of thickness. MethodIrrigation protocols were the following: Distilled water (DW) + Ethylenediamine tetraacetic acid (EDTA); grape seed extract (GSE) + EDTA; sodium hypochlorite (NaOCl) + EDTA; NaOCl + EDTA + GSE; calcium hypochlorite (Ca(ClO)2) + EDTA; Ca(ClO)2 + EDTA + GSE; chlorhexidine (CHX) + EDTA; CHX + EDTA + GSE. The samples were prepared and the values of microhardness, ultimate tensile strength (UTS), and flexural strength were obtained. Further, fracture resistance of roots with dentin thickness of 0.5 mm and 1.5 mm, and restored with fiberglass post relined with composite resin and metal crowns, were evaluated with same irrigation protocols previously described; the failure mode was evaluated as well. All tests presented normality in data distribution (Kolmogorov-Smirnov), and Analysis of Variance and Bonferroni test (α = 0.05) were performed. ResultsHigher reduction of dentin microhardness was observed in the NaOCl and NaOCl + EDTA + GSE groups (p < 0.0001). An increased in the UTS values was obtained in the CHX groups (p < 0.0001), while similar values were observed between the control and other groups (p > 0.05). The reduction of dentin flexural strength was observed in the NaOCl groups (p < 0.0001), while no significant changes were observed in the other groups (p > 0.05). With regard to fracture resistance, no statistical difference was obtained among the irrigation's protocols (p > 0.05), except for CHX (p = 0.0031) and CHX + GSE (p = 0.0001) that showed increased in fracture resistance values in roots with 1.5-mm thickness. An increased rate of irreparable failure was obtained in the NaOCl groups, whereas there was a predominance of repairable failure in the other groups. ConclusionsThe endodontic irrigation protocol has a significant impact on the dentin mechanical properties; on the other hand, do not reduce the fracture resistance of root with 0.5 mm and 1.5 mm of thickness.

Comparative evaluation of macro-form and nano-form of bioactive glass and triple antibiotic paste on fracture resistance of root dentin

IntroductionThe aim of this study was to compare the effect of using nanoparticle and macroparticles of bioactive glass (BAG) and triple antibiotic paste (TAP) as intracanal medicaments on the fracture resistance of root dentin.Materials and methodsAfter root canal preparation, one hundred single-rooted premolars were randomly assigned into five groups according to the applied intracanal medicaments (n = 20): BAG, bioactive glass nano-form (BAG-N), TAP, triple antibiotic paste nano-form (TAP-N), and a control group where only irrigation with 5% NaOCl was done. After mounting roots in a universal testing machine, the force required to break each tooth was recorded in Newtons. Data analysis was performed using Kruskal–Wallis test to determine the level of significance among all groups P less than 0.05, and Mann–Whiteny test was used to compare paired independent samples.ResultsFracture resistance values of BAG either macro or nano-form were significantly higher than those of TAP macro and nano-forms. Roots treated with nano-form medicament either BAG or TAP showed lower fracture resistance values than those treated with macro form but this difference was statistically insignificant. Roots treated with TAP-nano-form showed the lowest fracture resistance values among all groups.ConclusionUsing nano-form medicaments as intracanal dressing did not enhance fracture resistance of endodontically treated teeth.

Etidronic acid and ethylenediaminetetraacetic acid associated with sodium hypochlorite have limited effect on the compressive fracture resistance of roots ex vivo.

Aims:To assess the effect of etidronic acid (EA) mixed with sodium hypochlorite (NaOCl) and two ethylenediaminetetraacetic acid-containing preparations (EDTA and SmearClear) alternated with NaOCl, as a final rinse, on root fracture resistance to a compressive force.Materials and Methods:Seventy-two premolar roots were randomly allocated to the following groups according to the irrigant solutions. For the EA group, 9% EA + 2.5% NaOCl were used throughout the assays (n = 21). The remaining groups received 2.5% NaOCl during and immediately after chemo-mechanical instrumentation. Intermediately, the roots received 17% EDTA (n = 19), or SmearClear (n = 16), or no irrigation (control) (n = 16) plus a final rinse with 2.5% NaOCl. The specimens were subjected to a vertical compressive force loaded at a crosshead speed of 0.02 mm/s parallel to the long axis of the root until fracture occurred. The results were compared statistically using the one-way analysis of variance for intergroup comparisons.Results:The negative control presented with the highest values, whereas the SmearClear presented with the lowest values, though no significant differences were found when comparing the different groups (P = 0.82).Conclusions:The use of EA + NaOCl or two EDTA formulations in association with NaOCl does not affect the fracture resistance of previously chemo-mechanically prepared roots.

Fracture resistance of roots obturated with bio-ceramic and epoxy resin-based sealers: In vitro study

Objective:This study aimed to assess the resistance of roots to fracture after being root canal filled with two types of endodontic sealers; bio-ceramic based sealer (TotalFill) and epoxy-resin based sealer (AH Plus).Methods:Fifty-nine single canal mandibular premolars were instrumented. Group I (n=14, negative control): root canals were left without instrumentation and unfilled, group II (n=15, positive control): root canals were instrumented only and left unfilled, group III and IV (n=15 each): root canals were instrumented and filled with either gutta-percha/TotalFill or gutta-percha/AH Plus, respectively. The resistance of the roots to fracture was measured with a universal testing machine “Instron Corp” through recording the maximum force in Newton (N) needed to fracture each root. To analyze the data Kruskal–Wallis test was utilized, followed by Dunn’s Bonferroni post hoc test for multiple comparisons. The level of significance was set at 0.05 (P≤0.05).Results:TotalFill group showed slightly better fracture resistance (734.62 N) than AH Plus group (728.29 N). However, no statistical significant difference was found between the two groups (P>0.05). The greatest mean fracture force was shown in the negative control group (913.915 N) with statistical significant difference between the other three groups (P<0.05).Conclusion:Gutta-percha/TotalFill and gutta-percha/AH Plus did not reinforce the root canal treated teeth.

Effect of Glass Fiber Post Diameter on Fracture Resistance of Endodontically Treated Teeth

Objective: To determine the fracture resistance of endodontically treated teeth restored with three different diameters of glass fiber posts and metal-ceramic crowns. Material and Methods: Thirty human maxillary canines were selected and subjected to root canal therapy. The teeth were randomly divided into three groups of glass fiber posts with 1.4 mm diameter (Group I), 1.6 mm diameter (Group II), and 2.0 mm diameter (Group III). The teeth were restored with metal-ceramic crowns and subjected to the compressive load applied at 45° angle to the longitudinal axis until fracture. The mode of failure was determined. Data were analyzed using ANOVA, followed by Tukey's post hoc multiple comparisons test (p<0.05) . Results: The mean fracture resistance of groups I, II and III was 574 ± 91.2 N, 617 ± 85.21 N and 467 ± 99.43 N, respectively. No significant difference was noted between groups I and II, while the fracture resistance was significantly different between groups I and III (p<0.05) and groups II and III (p<0.05). No case of post fracture alone occurred in any group . Conclusion: The diameter of glass fiber posts can affect the fracture resistance of teeth. Based on the results, increasing the diameter of the post up to 1.6 mm may increase the fracture resistance of root, although excessive diameters are not recommended.

Root Fracture Resistance of Maxillary Premolars Obturated with Three Root Canal Sealers after Passive Utrasonic Irrigation: An in Vitro study.

Maxillary premolars, may be more susceptible to fracture due to their anatomy; especially when there is loss of tooth structure. Therefore, it is necessary to evaluate materials and techniques that may increase fracture resistance during and post root canal treatment. This in vitro study aimed to evaluate root fracture resistance of maxillary premolars when filled with three root canal sealers as well as whether this resistance would be increased by passive ultrasonic irrigation (PUI). Sixty-four maxillary premolars with two roots were randomly divided into one negative control group (intact canals; n = 8), one positive control group (instrumented, unsealed canals; n = 8), and six experimental groups (n = 8), which were instrumented with ProTaper Next rotary system up to X2 file and subdivided according to final irrigation (with or without PUI) and type of sealer used (AH-Plus [AH], MTA Fillapex [MTA], or EndoSequence BC Sealer [ES]). The specimens were subjected to fracture strength test in a universal testing machine at a speed of 1 mm/min until fracture. The maximum force required to induce fracture was recorded (N). The Kruskal-Wallis test and DUNN test were used for analysis. The lowest force required to cause root fracture was observed in the positive control group (310.48 ± 54.08 N); this was significantly different from the other groups (P < 0.05). There was no significant difference between experimental groups obturated with the same sealer, whether with or without PUI (AH with PUI: 558.80 ± 87.12 N; AH without PUI: 508.75 ± 97.55 N; MTA with PUI: 507.27 ± 174.55 N; MTA without PUI: 516.69 ± 96.56 N; ES with PUI: 526.76 ± 143.97 N; ES without PUI: 628.40 ± 94.74 N) (P > 0.05). There was also no significant difference between the experimental groups and the negative control group (P > 0.05). In this in vitro study PUI did not increase the fracture resistance of maxillary premolars, while AH Plus, MTA Fillapex, EndoSequence sealers increased fracture resistance of instrumented root canals.

Evaluating Fracture Resistance And Failure Modes Of Root Filled Teeth Restored With CAD/CAM-Fabricated Post And Core.

ObjectiveThe aim of this study was to measure the fracture resistance and failure modes of root-filled teeth restored with three different computer-aided design/computer-aided manufacturing (CAD/CAM)-fabricated post and core assemblies.MethodsThirty extracted intact maxillary central incisors were used in the study, and the teeth were endodontically treated and sectioned to a root length of 16 mm. The samples were divided into three groups (n = 10) according to the mean of the dimensions at the cervical portion of the root. The posts and cores were fabricated with CAD/CAM technology using metal, zirconia, and polymer-infiltrated ceramic network (PICN) material. The posts were luted using resin cement, and then, metal crowns were fabricated, cemented, and then subjected to a compression to determine the fracture resistance force. Fracture of the post and core or fracture of the root above the level of the acrylic resin was considered as a favorable fracture, while nonfavorable fractures were those where the root fracture occurred below the level of the acrylic resin. Statistical analysis was carried out using SPSS software, and one-way analysis of variance was used to analyze root fracture resistance in Newton. The number of failure modes, post–core fractures and/or root fractures was calculated. The differences between study groups were revealed using the chi-square test.ResultsThe results of ANOVA revealed a nonsignificant difference in the resistance to fracture among the study groups (P = 0.114). The failure modes were nonfavorable for all metal and zirconia samples and seven PICN samples. However, three PICN samples exhibited a favorable represented by core fracture without root fracture.ConclusionThere was no significant difference between metal and zirconia samples in terms of nonfavorable fracture, while few PICN samples exhibited a favorable fracture. PICN material can be used in the fabrication of post and core assemblies using CAD/CAM.

Does ultraconservative access affect the efficacy of root canal treatment and the fracture resistance of two-rooted maxillary premolars?

To evaluate the influence of ultraconservative endodontic cavities (UEC) on canal shaping and filling ability, cleaning of the pulp chamber, time required to perform root canal treatment and fracture resistance of 2-rooted maxillary premolars in comparison with traditional endodontic access cavities (TEC) in extracted teeth placed in a phantom head to simulate clinical conditions. Twenty extracted intact 2-rooted maxillary premolars were scanned in a micro-computed tomographic device, matched based on similar anatomical features of the canals and assigned to UEC or TEC groups (n=10). Then, teeth were mounted on a mannequin head and their pulp chamber accessed. After canal preparation, filling and cavity restoration, the time required to perform root canal treatment was recorded and the specimens were loaded to fracture in a universal testing machine. The maximum load at fracture was recorded. The sample was scanned after root canal instrumentation, filling and restoration procedures. Untouched canal areas, accumulation of hard-tissue debris (AHTD), voids in root fillings and cleaning of the pulp chamber were analysed. Data were analysed statistically using Shapiro-Wilk and Student's t-tests with a significance level of 5%. The percentage of untouched canal area did not differ significantly between UEC and TEC groups (P>0.05). However, UECs were associated with a greater percentage of AHTD after canal preparation (P<0.05). No differences were observed in terms of voids in root fillings between the groups (P>0.05). Nonetheless, UEC had a greater percentage of root filling remnants in the pulp chamber after cleaning procedures (P<0.05). The time required to perform root canal treatment was significantly longer in the UEC group (P<0.05). There was no difference regarding the mean load at fracture between the groups (P>0.05). Unrestorable fractures were observed in all specimens of both groups. There was no true benefit associated with ultraconservative endodontic cavities. UEC resulted in more AHTD remaining inside the root canals. UEC did not influence the quality of root fillings; however, UEC made the cleaning procedure of the pulp chamber more difficult, thus increasing the total time required to perform root canal treatment. Moreover, UEC were not associated with an increase in fracture resistance of root filled 2-rooted maxillary premolars.

Effects of Ultrasonic Removal of Fractured Files from the Middle Third of Root Canals on the Resistance to Vertical Root Fracture

IntroductionThis study aimed to analyze the effects of ultrasonic removal of fractured files from the middle third of root canals on the vertical root fracture resistance. MethodsThis study was an extension of a previous study assessing the effects of fractured file removal on dentinal microcracks. It included 18 bilaterally matched pairs of human mandibular incisors prepared and analyzed in the previous study. Briefly, 1 member of each pair was assigned to an ultrasonic or a control group. In the ultrasonic group, K-files were fractured in the middle third of canals followed by ultrasonic file removal and canal preparation. In the control group, the root canals were simply prepared. Micro–computed tomographic imaging was performed before and after treatment, and the cross-sectional root images were screened for microcracks. For the present study, 3-dimensional reconstruction was performed for volumetric assessments. The fracture resistance was measured using a universal testing machine. All data were statistically analyzed. ResultsFracture loads were significantly smaller in the ultrasonic group (P < .05). The percentage increase in the canal volume significantly influenced the root fracture resistance (P < .05), whereas microcracks had no significant effect (P > .05). ConclusionsUltrasonic removal of fractured instruments from the middle third of root canals lowers the vertical root fracture resistance, with increased dentin removal being the primary cause.