Contracted Endodontic Cavities Research Articles

Impact of Contracted Endodontic Access Cavities on the Fracture Resistance of Endodontically Treated Teeth After Mechanical Aging by Simulated Chewing Forces

IntroductionThis in vitro study aimed to comparatively evaluate the fracture resistance of contracted endodontic cavities (CECs) versus traditional endodontic cavities (TECs) in mandibular molars after subjecting the samples to a chewing simulator. MethodsA total of 24 freshly extracted human mandibular molars were included in the study. Teeth with intact crowns and mature root apices that were devoid of caries, attrition, restorations, and cracks were selected and randomly assigned to 3 groups (n = 8) as follows: Group 1: TECs, Group 2: CECs, and Group 3: intact teeth (control group). After endodontic treatment, the teeth were restored with EverX bulk-fill composite and layered occlusally with nanohybrid composite SolareX and subjected to a chewing simulator where 240,000 masticatory cycles were simulated, which translates to 1 year of clinical function. The teeth were then subjected to static loading in a universal testing machine and the maximum load to fracture and the pattern of failure (restorable/unrestorable) were recorded. Data were evaluated with analysis of variance and the Tukey post hoc test for multiple comparisons. ResultsThe CEC group had higher fracture resistance when compared with the TEC group; however, the difference was not statistically significant. The fracture resistance of the samples in the control group was statistically higher than those in the experimental groups (P < .005). ConclusionsThere was no difference observed in the fracture resistance of mandibular molars with TECs and CECs subjected to masticatory loading.

Effect access cavity preparation and taper instrumentation on upper premolar fracture

Background : Fractures are the most undesirable thing in endodontically treated teeth. The main reason in endodontically treated teeth has a considerable risk for fractures is the loss of tooth structure. Objective : This study aims to determine the effect of access cavity preparation and instrument taper percentage on upper premolar fractures. Material and Methods : Twenty-four upper premolar samples were stored in sterile saline solution. The sample was divided into 2 large groups which were then divided into two groups for each group by random allocation. Twelve contracted endodontic cavity (CEC) preparations and the remaining twelve samples using traditional endodontic cavity (TEC) techniques. Each group was prepared with 6 samples 4% taper instrumentation and 6 samples 8% taper instrumentation. Each sample was irrigated with 5 ml of NaOCl. After that, the sample is tested using a universal testing machine. Result : The CEC group showed a significant reduction in fracture rates compared to the TEC group (p &lt;0.05), but there was no significant difference in the fracture in the tapering instrumentation (p&gt; 0.05). Conclusion : Preparation with the concept of minimally invasive CEC provides better resistance to fractures in the upper premolar while tapering instrumentation does not affect the fracture of the upper premolars.

Effect of access cavities on the biomechanics of mandibular molars: a finite element analysis

IntroductionThis study aimed to predict the fracture resistance of a mandibular first molar (MFM) with diverse endodontic cavities using finite element analysis (FEA).MethodsFive experimental finite element models representing a natural tooth (NT) and 4 endodontically treated MFMs were generated. Treated MFM models were with a traditional endodontic cavity (TEC) and minimally invasive endodontic (MIE) cavities, including guided endodontic cavity (GEC), contracted endodontic cavity (CEC) and truss endodontic cavity (TREC). Three loads were applied, simulating a maximum bite force of 600 N (N) vertically and a normal masticatory force of 225 N vertically and laterally. The distributions of von Mises (VM) stress and maximum VM stress were calculated.ResultsThe maximum VM stresses of the NT model were the lowest under normal masticatory forces. In endodontically treated models, the distribution of VM stress in GEC model was the most similar to NT model. The maximum VM stresses of the GEC and CEC models under different forces were lower than those of TREC and TEC models. Under vertical loads, the maximum VM stresses of the TREC model were the highest, while under the lateral load, the maximum VM stress of the TEC model was the highest.ConclusionThe stress distribution of tooth with GEC was most like NT. Compared with TECs, GECs and CECs may better maintain fracture resistance, TRECs, however, may have a limited effect on maintenance of the tooth resistance.

Apically extruded debris, canal transportation, and shaping ability of nickel-titanium instruments on contracted endodontic cavities in molar teeth.

Apically extruded debris, canal transportation and shaping ability were compared between contracted endodontic cavities (CECs) and traditional endodontic cavities (TECs) after instrumentation with XP-endo Shaper (XPS), ProTaper Gold (PTG), ProTaper for hand-use (HPT) and Hero Shaper. The CECs or TECs groups were sub-divided into 24 groups according to root canal morphology and nickel-titanium (Ni-Ti) instruments. The weight of apically extruded debris was calculated using the Myers and Montgomery model. Pre- and postoperative images of teeth were scanned using micro-CT and the three-dimensional models were constructed and compared. Under CECs or TECs, XPS and PTG produced less apical debris and formed less canal transportation than HPT and Hero Shaper (P < 0.05). XPS group under CECs extruded less apical debris than that under TCEs for round canals with curvature of 20°-35° (P < 0.05). The centering ratios of four tested instruments were higher under TECs than those under CECs (P < 0.05). The HPT and Hero Shaper had more transportation under CECs than that under TCEs (P < 0.05). No statistical difference was found regarding shaping ability among all the groups. Under CECs, XPS preserves the original root canal anatomy, meanwhile it produces less apical debris than the other instruments.

File Breakage in Conventional Versus Contracted Endodontic Cavities.

To compare rotations to failure and tip separation length of a nickel-titanium (Ni-Ti) rotary in- strument within a simulated mesio-buccal canal of a mandibular molar with a conventional or contracted endodontic cavity. Two identical lithium disilicate #30 crowns were milled. A conventional or contracted endodontic cavity was prepared. A custom glass tube was fabricated with taper and length replicating a mesio-buccal canal, including buccal and lingual curvature, and placed at the mesio-buccal orifice of each crown, held in a silicone mold. Instrumentation was simulated using 30/.04 Ni-Ti rotary files following manufacturer recommended 1.8 Nm torque and 500 RPM (n=20 per access type). Instrumentation was video recorded to determine time (sec- onds) and rotations to failure. The length of broken tips was measured. The experimental data were compared using a t-test (significance level 0.05). Stresses in the instruments were examined using finite element analysis. Number of rotations to failure (mean±standard deviation) was 599±126 for conventional and 465±65 and for contracted access; tip separation lengths (mean±standard deviation) were 3.99±0.29 for conventional and 4.90±1.02 mm for contracted access. Number of rotations to failure and tip separation lengths were signifi- cantly different between the two access openings (p<0.001). Finite element analysis confirmed higher file curva- ture and accompanying higher stress levels with contracted access and the maximum stress further from the tip. Within the limitations of this study, the contracted access caused earlier failure of the Ni-Ti in- strument with longer tip separation lengths than the conventional access due to higher stresses towards the middle section of the instrument. (EEJ-2022-11-143).

Minimally invasive endodontics, an overview and current update

Introduction: The small access cavities could make it more difficult to visualize the pulp chamber as well as to locate, shape, clean and fill the canals. At the same time, increase the risk of iatrogenic complications. (Silva et al., 2020) Objective: To analyze the literature concerning the influence of minimally invasive endodontic access in pulp therapy, in relation to the degree of disinfection, degree of conformation, quality of obturation and resistance to the fracture. Methodology: By searching in electronic databases such as PubMed, using keywords: “minimally invasive endodontics”, “degree of disinfection”, “shaping”, “obturation” and “resistance to fracture”. Results: A true compromise of the degree of conformation of the canal is not demonstrated, although neither a benefit, when performing a contracted endodontic cavity (CEC). It is not possible to reach an adequate conclusion about the degree of disinfection in a CEC; priority should be given to a traditional endodontic cavity (TEC). Efficient canal obturation in CEC is limited to a single obturation technique, but if it is not intended to work under this protocol, the use of a TEC is suggested. No noticeable change in fracture strength is demonstrated in a CEC over a TEC.Conclusions: Success of endodontic treatment is represented by each of the stages that make up the procedure. CECs are an alteration to the traditional protocol and with it to the rest of the treatment stages.

Impact of contracted endodontic cavity on shaping ability of protaper next files system by using cone beam computed tomography: an ex-vivo study

Impact of contracted endodontic cavity on shaping ability of protaper next files system by using cone beam computed tomography: an ex-vivo study

Effect of Access Cavity Preparation on Dentin Preservation, Biomechanical Property, and Instrumentation Efficacy: A Micro–Computed Tomographic Study

IntroductionThe purpose of this study was to evaluate the influence of a contracted endodontic cavity (CEC) on dentin preservation, biomechanical property, and instrumentation efficacy of first permanent molars in comparison with a traditional endodontic cavity (TEC). MethodsForty-eight extracted intact maxillary and mandibular first molars were selected and scanned by micro–computed tomographic (micro-CT) imaging. Each tooth type was anatomically matched and assigned to the CEC group or the TEC group (n = 12). After root canal instrumentation with the ProGlider (Dentsply Maillefer, Ballaigues, Switzerland) and WaveOne Gold (Dentsply Maillefer), the specimens were scanned by micro-CT again. Pre- and postpreparation micro-CT imaging was used to evaluate the dentin preservation and instrumentation efficacy. The results on volume and thickness reduction in the coronal dentin and pericervical dentin (PCD), root canal volume and surface area, percentage of unprepared surface area, canal transportation and centering ratio, and canal wall thickness in the “danger zone” were measured and analyzed with the Shapiro-Wilk and independent sample t tests. Based on micro-CT imaging of maxillary and mandibular first molars, CEC and TEC models were constructed on the intact tooth, and 2 different static loads were applied to the occlusal load points. The stress distribution patterns and von Mises stress on the occlusal surface and cervical region were assessed by 3-dimensional finite element analysis. ResultsThe CEC had a significantly lower volume and thickness reduction of coronal dentin and PCD above the alveolar crest compared with the TEC group (P < .05), whereas no difference was observed in PCD below the alveolar crest between the 2 groups (P > .05). There was no difference regarding all instrumentation efficacy outcomes (root canal volume and surface area, percentage of unprepared surface area, canal transportation and centering ratio, and canal wall thickness) in the danger zone between the 2 groups (P > .05). The CEC effectively reduced the maximum von Mises stress and stress concentration area on the occlusal surface and cervical region compared with the TEC. ConclusionsThe CEC preserved more coronal dentin and PCD above the alveolar crest and thus reduced stress concentration on the occlusal surface and cervical region. The CEC had no significant adverse effects on the instrumentation efficacy compared with the TEC given that the instrumentation procedures were performed with ProGlider and WaveOne Gold files.

Antibacterial efficacy of sodium hypochlorite versus apple cider vinegar against Enterococcus faecalis in contracted endodontic cavity: An in vitro study

Antibacterial efficacy of sodium hypochlorite versus apple cider vinegar against Enterococcus faecalis in contracted endodontic cavity: An in vitro study

Impact of Contracted Endodontic Access Cavity on Shaping Ability of Hyflex Electrical Discharge Machining Single File Using Cone Beam Computed Tomography: An Ex Vivo Study

AIM: The aim of the study was to evaluate and compare the effect of different access cavity designs, using cone-beam computed tomography (CBCT), on root canal transportation, and centralization performed on two rooted maxillary premolars. METHODS: Twenty maxillary premolars were randomly divided into two groups. In Group 1, traditional endodontic cavities (TECs) were prepared. In Group 2, contracted endodontic cavities (CECs) were prepared. Mechanical preparation was done by HyFlex electrical discharge machining (EDM) single file in both groups. CBCT imaging was performed pre- and post-root canal preparation for calculations of root canal transportation and centering ability. RESULTS: Data were analyzed using Mann–Whitney U test and Kruskal–Wallis test. For transportation, teeth with CECs showed the statistically significantly highest median amount of transportation, while as for centering ability, results showed no significant difference between both groups. CONCLUSION: Under the conditions of this study, HyFlex EDM prepared canals with different access cavity designs without significant shaping errors. TEC showed less transportation than CEC, while both TEC and CEC had no effect on the file centering ability.

Impacts of contracted endodontic cavities compared to traditional endodontic cavities in premolars

BackgroundThis study aims to compare the percentage of dentin removed, instrumentation efficacy, root canal filling and load at fracture between contracted endodontic cavities, and traditional endodontic cavities on root canal therapy in premolars.MethodsForty extracted intact human first premolars were imaged with micro-CT and randomly assigned to the contracted endodontic cavity (CEC) or traditional endodontic cavity (TEC) groups. CEC was prepared with the aid of a 3D-printed template, canals were prepared with a 0.04 taper M-Two rotary instrument, and cavities were restored with resin. Specimens were loaded to fracture in an Instron Universal Testing Machine after a fatigue phase. The data were analyzed by the independent samples T test and Mann-Whitney U test, appropriate post hoc tests.ResultsIn the premolars tested in vitro, the percentage of dentin removed in the premolars with two dental roots in the CEC group (3.85% ± 0.42%) was significantly smaller (P < 0.05) than in the TEC group (4.94% ± 0.5%). The untouched canal wall (UCW) after instrumentation for TECs (16.43% ± 6.56%) was significantly lower (P < .05) than the UCW (24.42% ± 9.19%) for CECs in single-rooted premolars. No significant differences were observed in the increased canal volume and surface areas in premolars between the TEC and CEC groups (P > 0.05). CECs conserved coronal dentin in premolars with two dental roots but no impact on the instrument efficacy.There were no differences between the CEC groups and the TEC groups in the percentage of filling material and voids (P > 0.05). In addition, the mean load at failure of premolars did not significantly differ between the CEC and TEC groups and there was no significant difference in the type of fracture (P > 0.05).ConclusionThe results of this study suggest that CEC could not improve the fracture resistance of the endodontically treated premolars. The instrumentation efficacy and the percentage of filling material did not significantly differ between CECs and TECs in premolars.

Impact of Contracted Endodontic Cavities on Root Canal Disinfection and Shaping

IntroductionThe impact of minimally invasive endodontic procedures on root canal disinfection has not been determined. This ex vivo study compared root canal disinfection and shaping in teeth with contracted or conventional endodontic cavities. MethodsMandibular incisors with oval-shaped canals were selected and anatomically matched based on micro–computed tomographic (micro-CT) analysis and distributed into 2 groups. Conservative and conventional access cavities were prepared, and the canals were contaminated with a pure culture of Enterococcus faecalis for 30 days. Root canal preparation in both groups was performed using the XP-endo Shaper instrument (FKG Dentaire, La Chaux-de-Fonds, Switzerland) and 2.5% sodium hypochlorite irrigation. Intracanal bacteriologic samples were taken before and after preparation, and DNA was extracted and subjected to quantitative polymerase chain reaction. Micro-CT scans taken before and after preparation were used for shaping evaluation. Bacteriologic data were analyzed by the Poisson regression model and the chi-square test with Yates correction. Micro-CT data were analyzed by the Wilcoxon, Mann-Whitney, and Student t tests with the significance level set at 5%. ResultsAll initial samples were positive for E. faecalis. After preparation, the number of bacteria-positive samples was significantly higher in the contracted cavity group (25/29, 86%) than in the conventional cavity group (14/28, 50%) (P < .01). Intergroup quantitative comparison showed that the reduction in bacterial counts was also significantly higher in the group of conventional cavities (P < .01). Micro-CT data revealed no significant difference in the amount of unprepared areas between groups. ConclusionsOur findings showed that although shaping using an adjustable instrument was similar between groups, disinfection was significantly compromised after root canal preparation of teeth with contracted endodontic cavities.

Effects of the endodontic access cavity on apical debris extrusion during root canal preparation using different single-file systems.

ObjectivesThis study was conducted to evaluate the effects of traditional and contracted endodontic cavity (TEC and CEC) preparation with the use of Reciproc Blue (RPC B) and One Curve (OC) single-file systems on the amount of apical debris extrusion in mandibular first molar root canals.Materials and MethodsEighty extracted mandibular first molar teeth were randomly assigned to 4 groups (n = 20) according to the endodontic access cavity shape and the single file system used for root canal preparation (reciprocating motion with the RCP B and rotary motion with the OC): TEC-RPC B, TEC-OC, CEC-RPC B, and CEC-OC. The apically extruded debris during preparation was collected in Eppendorf tubes. The amount of extruded debris was quantified by subtracting the weight of the empty tubes from the weight of the Eppendorf tubes containing the debris. Data were analyzed using 1-way analysis of variance with the Tukey post hoc test. The level of significance was set at p < 0.05.ResultsThe CEC-RPC B group showed more apical debris extrusion than the TEC-OC and CEC-OC groups (p < 0.05). There were no statistically significant differences in the amount of apical debris extrusion among the TEC-OC, CEC-OC, and TEC-RPC B groups.ConclusionsRPC B caused more apical debris extrusion in the CEC groups than did the OC single-file system. Therefore, it is suggested that the RPC B file should be used carefully in teeth with a CEC.

Impacts of Contracted Endodontic Cavities on Primary Root Canal Curvature Parameters in Mandibular Molars

IntroductionThe purpose of this study was to provide information regarding the debate on contracted endodontic cavities (CECs); their impacts on angle, location, and radius of the primary canal curvature (PCC) were assessed in type IV mesial root canals of mandibular molars at different stages of instrumentation. Impacts on treatment time were also assessed. MethodsTwenty-four teeth were matched by radiographic and micro–computed tomographic criteria and accessed via CECs (CEC, n = 12) or nonextended traditional endodontic cavities (TECs, n = 12). PCC parameters were radiographically determined using a repositioning apparatus before glide path preparation (PI), after glide path preparation, and after final instrumentation (FI). Instrumentation was performed with PathFiles (13/.02, 16/.02; Dentsply Maillefer, Ballaigues, Switzerland) and ProFile Vortex files (Dentsply Tulsa Dental Specialties, Tulsa, OK) to size 30/.04 at the working length under copious irrigation. Changes in PCC were measured with ImageJ (National Institutes of Health, Bethesda, MD). The instrumentation time was recorded. Data were analyzed with 2-way repeated measures analysis of variance (α < .05) and Tukey honest significant difference tests. ResultsA significant (P < .001) decrease in the mean angle and increase in the mean radius were detected at each instrumentation stage for both CECs (angle: PI = 42.57°± 8.00°, FI = 32.61°± 5.17°; radius: PI = 6.48 ± 1.81 mm, FI = 10.55 ± 1.48 mm) and TECs (angle: PI = 38.80°± 7.15°, FI = 30.08°± 6.99°; radius: PI = 6.97 ± 2.31 mm, FI = 11.01 ± 2.20 mm). PCC location shifted apically (P < .001). Changes in PCC parameters did not differ significantly between CECs and TECs (P > .05). The treatment time was significantly (P < .0001) longer for CECs (83.17 ± 6.71 minutes) than for TECs (33.18 ± 9.20 minutes). ConclusionsInstrumentation of curved mesial canals reduced the severity and abruptness of PCC and shifted the PCC location apically similarly in mandibular molars with CECs and those with nonextended TECs. The extended treatment time with CEC merits consideration when debating CECs versus TECs.

Influence of Contracted Endodontic Access on Root Canal Geometry: An In Vitro Study

IntroductionContracted endodontic cavities (CECs) have developed from the concept of minimally invasive dentistry and provide an alternative to traditional endodontic cavities (TECs). They have been designed in an effort to preserve the mechanical stability of teeth. The contracted cavity design preserves more of the dentin but may influence the geometric shaping parameters. The aim of this micro–computed tomographic study was to evaluate the influence of contracted endodontic cavities on the preservation of the original root canal anatomy after shaping with nickel-titanium rotary instruments. MethodsThirty extracted human mandibular molars with fully formed apices and independent mesial canals were randomly assigned to group 1 (TEC) and group 2 (CEC). Each group was shaped using ProGlider (Dentsply Maillefer, Ballaigues, Switzerland) and WaveOne Gold (Dentsply Maillefer). Irrigation was performed with 10% EDTA and 5% sodium hypochlorite. Samples were scanned before and after canal shaping to match canal volumes (SkyScan; Bruker microCT, Kontich, Belgium [100 kV, 100 μA, and 15-μm resolution]), and images were analyzed to evaluate canal volumes, surface areas, and centroid shift on cross sections at −1 mm and −3 mm from the apex. ResultsTECs showed a greater preservation of the original root canal anatomy with less apical transportation than CECs, possibly because of the absence of coronal interferences and, therefore, fewer pecking motions required to complete instrumentation. ConclusionsWithin the limitations of this study, TECs may lead to a better preservation of the original canal anatomy during shaping compared with CECs, particularly at the apical level.

Efficacy of rotary and reciprocating single-file systems on different access outlines for gutta-percha removal in retreatment: An in vitro study.

Introduction:The aim of this study is to compare the effectiveness of reciprocating and continuous rotary nickel-titanium instruments during retreatment performed through two different access outlines.Methodology:A total of 48 freshly extracted mandibular first and second premolars with single root and canal were selected. Initial root canal treatment was completed through a contracted endodontic cavity (CEC) design. Canals were instrumented with F2 ProTaper instrument, obturated with warm lateral condensation of gutta-percha with AH Plus sealer, and allowed to set for 30 days at 37°C and 100% humidity. For retreatment, specimens were divided into two groups (n = 24) on the basis of access outline, CEC or traditional endodontic cavity. Retreatment was initiated using ProTaper Retreatment instruments (D1–D3). Specimens were further divided (n = 12) and reinstrumented up to Neoniti 25/0.08 or WaveOne 25/0.08. Irrigation was performed using 3% sodium hypochlorite and 17% ethylene diamine tetraacetic acid. Retreatment time was recorded. Teeth were sectioned and photographed, and the percentage of remaining obturation material was measured.Results:Data were collected, and statistical analysis was performed using one-way analysis of variance and Tukey honestly significant difference multiple post hoc procedures (P < 0.05).Conclusion:None of the systems completely removed the root filling material from root canals. However, ProTaper/Neoniti instruments removed more GP when compared to Protaper/WaveOne instruments with both the access outlines. Both the instruments with traditional access outline required less time for removal of obturating material when compared to CEC.

Impact of contracted endodontic cavities on fracture resistance of endodontically treated teeth: a systematic review of in vitro studies.

This systematic review was performed to answer the following question: do contracted endodontic cavities (CECs) increase resistance to fracture in extracted human teeth compared to traditional endodontic cavities (TECs)? A literature search without restrictions was carried out in PubMed, Science Direct, Scopus, Web of Science, and Open Grey databases. Articles were selected by two independent reviewers. In addition, a reference and hand search was also fulfilled. All included in vitro studies evaluated the influence of CECs on strength to fracture in extracted human teeth and compared to TECs. The quality of the selected studies was evaluated and they were classified as having a low, moderate or high risk of bias. A total of 810 articles were obtained in the electronic search. After the application of the eligibility criteria, reference and hand search, and duplicate removal, six studies were included in this systematic review. All included studies evaluated the influence of CECs on strength to fracture in extracted human teeth and compared to TECs. Characteristics investigated in the selected articles included the sample size and tooth type, access cavity design, filling and restoration procedures, load at fracture test characteristics, and results. The studies demonstrated large variability among the fracture resistance values and standard deviations and low power. Three of the reviewed studies presented low risk of bias and the other three showed medium risk of bias. Overall, this systematic review of in vitro studies showed that there is no evidence that supports the use of CECs over TECs for the increase of fracture resistance in human teeth. Recently, CECs have gained attention in endodontics due to maximum tooth structure preservation including the pericervical dentin, which could improve the strength to fracture of endodontically treated teeth. However, the influence of access cavity design on fracture resistance remains limited and controversial.

Effect of access design on intracoronal bleaching of endodontically treated teeth: An ex vivo study.

To determine the effect of access design on intracoronal bleaching with 35% carbamide peroxide on discolored teeth. Forty-two intact maxillary central incisors were selected, sectioned and artificially stained using whole blood. Color measurements were performed with a spectrophotometer: before staining (T1), after staining (T2), at 7 (T3), and 14 (T4)days postbleaching. After T1, specimens were stratified and divided randomly into two groups according to access design (N=20): G1: contracted endodontic cavity (CEC) access performed with a #848-010M bur and G2: traditional endodontic cavity (TEC) access done with a #1157bur. Canals were obturated, a cervical barrier was placed and 35% carbamide peroxide was sealed in the chamber for 7days and replaced at 7days for an additional 7days. Data were collected based on CIELAB-CIE1976 (L* a* b* ) system. Repeated measures SNK anova was used to evaluate the effects of access design and time on color change (ΔE* ) and luminosity (L* ) (α<0.05). For CEC, L* was significantly different at all times points (P<.05). For TEC, L* values were significantly different at all time points (P<.05) except for T0 and T4, which were similar (P>.05). There was no statistical difference for ΔE* between CEC and TEC designs at any time point (P>.05). In general, teeth accessed with CEC or TEC designs showed statistically similar bleaching when using 35% carbamide peroxide. However, lightness values were only reestablished with bleaching through a TEC access design. Despite the current trend to conserve tooth structure when performing endodontic access cavities, the use of conservative access designs for bleaching discolored maxillary central incisors affected the acceptability threshold when compared with a traditional access design. These smaller accesses might not be an alternative treatment option when internal bleaching in the esthetic zone is anticipated.

Influence of Access Cavity Design on Root Canal Detection, Instrumentation Efficacy, and Fracture Resistance Assessed in Maxillary Molars

IntroductionThe aim of this study was to assess the influence of contracted endodontic cavities (CECs) on root canal detection, instrumentation efficacy, and fracture resistance assessed in maxillary molars. Traditional endodontic cavities (TECs) were used as a reference for comparison. MethodsThirty extracted intact maxillary first molars were scanned with micro–computed tomographic imaging at a resolution of 21 μm, assigned to the CEC or TEC group (n = 15/group), and accessed accordingly. Root canal detection was performed in 3 stages:(1) no magnification,(2) under an operating microscope (OM), and(3) under an OM and ultrasonic troughing. After root canal preparation with Reciproc instruments (VDW GmbH, Munich, Germany), the specimens were scanned again. The noninstrumented canal area, hard tissue debris accumulation, canal transportation, and centering ratio were analyzed. After root canal filling and cavity restoration, the sample was submitted to the fracture resistance test. Data were analyzed using the Fisher exact, Shapiro-Wilk, and t tests (α = 0.05). ResultsIt was possible to locate more root canals in the TEC group in stages 1 and 2 (P < .05), whereas no differences were observed after stage 3 (P > .05). The percentage of noninstrumented canal areas did not differ significantly between the CEC (25.8% ± 9.7%) and TEC (27.4% ± 8.5%) groups. No significant differences were observed in the percentage of accumulated hard tissue debris after preparation (CEC: 0.9% ± 0.6% and TEC: 1.3% ± 1.4%). Canal transportation was significantly higher for the CEC group in the palatal canal at 7 mm from the apical end (P < .05). Canal preparation was more centralized in the palatal canal of the TEC group at 5 and 7 mm from the apical end (P < .05) and in the distobuccal canal of the CEC group at 5 mm from the apical end (P < .05). There was no difference regarding fracture resistance among the CEC (996.30 ± 490.78 N) and TEC (937.55 ± 347.25 N) groups (P > .05). ConclusionsThe current results did not show benefits associated with CECs. This access modality in maxillary molars resulted in less root canal detection when no ultrasonic troughing associated to an OM was used and did not increase fracture resistance.

Impacts of Contracted Endodontic Cavities on Instrumentation Efficacy and Biomechanical Responses in Maxillary Molars

IntroductionRecently, we reported that in mandibular molars contracted endodontic cavities (CECs) improved fracture strength compared with traditional endodontic cavities (TECs) but compromised instrumentation efficacy in distal canals. This study assessed the impacts of CECs on instrumentation efficacy and axial strain responses in maxillary molars. MethodsEighteen extracted intact maxillary molars were imaged with micro–computed tomographic imaging (12-μm voxel), assigned to CEC or TEC groups (n = 9/group), and accessed accordingly. Canals were instrumented (V-Taper2H; SSWhite Dental, Lakewood, NJ) with 2.5% sodium hypochlorite irrigation, reimaged, and the proportion of the modified canal wall determined. Cavities were restored with bonded composite resin (TPH-Spectra-LV; Dentsply International, York, PA). Another 28 similar molars (n = 14/group) with linear strain gauges (Showa Measuring Instruments, Tokyo, Japan) attached to mesiobuccal and palatal roots were subjected to load cycles (50–150 N) in the Instron Universal Testing machine (Instron, Canton, MA), and the axial microstrain was recorded before access and after restoration. These 28 molars and additional 11 intact molars (control) were cyclically fatigued (1 million cycles, 5–50 N, 15 Hz) and subsequently loaded to failure. Data were analyzed by the Wilcoxon rank sum and Kruskal-Wallis tests (α = 0.05). ResultsThe overall mean proportion of the modified canal wall did not differ significantly between CECs (49.7% ± 12.0%) and TECs (44.7% ± 9.0%). Relative changes in axial microstrain responses to load varied in both groups. The mean load at failure for CECs (1703 ± 558 N) did not differ significantly from TECs (1384 ± 377 N) and was significantly lower (P < .005) for both groups compared with intact molars (2457 ± 941 N). ConclusionsIn maxillary molars tested in vitro, CECs did not impact instrumentation efficacy and biomechanical responses compared with TECs.