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AIM: To compare the effects of Cervical Access Cavity (CervAC) and Traditional Access Cavity (TradAC) on root canal preparation, root canal filling, and fracture resistance in mandibular incisors. METHODOLOGY: Twenty recently extracted and intact mandibular incisors were initially scanned using a micro-CT device. The specimens were anatomically matched to create two groups (n = 10). A wedge-shaped non-carious cervical lesion (NCCL) was created on the buccal aspect of all teeth using a double-faced segmented diamond disc. In group 1, a TradAC was prepared, whilst in group 2, access was created through the simulated NCCL using a round diamond bur 1012. After root canal preparation with Rotate instruments sizes 15/0.04, 20/0.04, and 25/0.04, the teeth were scanned again and evaluated for root canal volume and surface area, static voxels, volume of removed dental tissue, and dentine thickness. After that, the root canals were filled using the single-cone technique, teeth were restored with composite resin, and subsequently rescanned to calculate the volume of filling materials and voids. Then, the restored teeth were subjected to fracture resistance tests using a universal testing machine. Statistical comparisons between groups were performed with the Mann-Whitney test or the Student's t-test, with a statistical significance level of 5%. RESULTS: Statistical comparisons indicated no significant differences between groups in terms of root canal volume, surface area, static voxels, removed root dentine, root canal filling volume, percentage of voids, or fracture resistance load (p > .05). Conversely, teeth prepared with TradAC showed a significantly higher percentage of dental tissue removed from the crown (p = .001) and a greater volume of filling material remnants in the pulp chamber (p < .001) compared to the CervAC group. A significantly lower percentage reduction in dentine thickness was observed only on the mesial aspect of root at Level 1 in TradAC group (p = .008). CONCLUSIONS: CervAC can be considered a viable alternative approach in the presence of NCCL in mandibular incisors.

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Background: Several designs of access cavity have been evolved in the recent past with the concept of minimal tooth tissue removal which would improve the root canal treated teeth fracture resistance. Aim: To investigate the effect of conservative design access cavity during the instrumentation of maxillary molar root canals. Materials and Methods: Eighty noncarious maxillary molars were assigned to the traditional and conservative access groups (n = 40 each). After designated access preparations, the teeth were immersed in Lugols's solution for staining the pulp tissue. Root canal instrumentation was performed with TruNatomy file system. Pre- and postinstrumentation nano-computed tomography (CT) images were taken and reconstructed using CT-An software. Root canals volumetric analysis was done with CT-Vol software. The analysis of the data was dealt with Shapiro-Wilk test and independent t-test. Results: The volume of pulp canal space before and after instrumentation changed significantly between the traditional and conservative access design groups, according to an independent t-test. In comparison, the mean volume of dentin removed was much larger in the TAC group (P = 0.0016). The independent t-test manifests difference significantly between traditional endodontic access cavity (TAC) and conservative access cavity (CAC) with percentage of unprepared canal walls. The mean percentage of unprepared area was significantly lesser in TAC group as compared to CAC group (P = 0.0022). Conclusion: The volume of dentin removed was greater in TAC than with the CAC design. The amount of untouched canal wall area was significantly higher in conservative access design than with the traditional access design group.

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INTRODUCTION: This study aimed to assess the fracture resistance of mandibular first molars after preparation with 3 different access cavity designs and 2 rotary systems using finite element analysis. METHODS: Six 3-dimensionally printed mandibular first molars simulating natural teeth received traditional, conservative, and ultraconservative (truss) access cavity preparations. The root canals in each group were instrumented with either XP-Endo Shaper (FKG Dentaire, La Chaux-de-Fonds, Switzerland) or TruNatomy (Dentsply Sirona, Ballaigues, Switzerland) rotary files. The models were individually digitized, and micro-computed tomographic scans were transferred to Mimics software (Materialise NV, Leuven, Belgium) to create a geometric model of the tooth. The designed model was exported to 3-matic software (Materialise NV), and STL files were transferred to Geomagic Design X (3D Systems, Rock Hill, SC). Point cloud data were used for surfacing and transferred to ANSYS software (Ansys, Canonsburg, PA). A 200-N superficial force was applied vertically to the buccal cusps and central fossa, and the maximum and minimum equivalent von Mises stress values were calculated and reported. RESULTS: The traditional and ultraconservative access cavity designs yielded the highest and the lowest von Mises stress values, respectively. In the ultraconservative cavity design, the stress values in pericervical dentin were lower in canal preparation with TruNatomy compared with XP-Endo Shaper. In the traditional and conservative cavity designs, stress was lower in the first 2 mm from the cementoenamel junction in the XP-Endo Shaper group and in the next 3 mm in the TruNatomy group. CONCLUSIONS: Stress was lower in the ultraconservative and conservative cavity designs compared with the traditional design. Also, root canal preparation with TruNatomy yielded lower stress values in general compared with XP-Endo Shaper.

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INTRODUCTION: This 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. METHODS: A 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. RESULTS: The 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). CONCLUSIONS: There was no difference observed in the fracture resistance of mandibular molars with TECs and CECs subjected to masticatory loading.

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Background: Guided conservative endodontic access is a novel technique and the influence of such access cavities on apical debris extrusion (ADE) can have a significant effect on postoperative pain. Objective: This study compared ADE and preparation time (PT) in the mesial canals of the mandibular first permanent molars in different access cavity designs and the amount of sodium hypochlorite in the extruded debris using attenuated total reflection-Fourier transform infrared spectrometer (ATR-FTIR). Materials and Methods: Human mandibular first permanent molars (N = 72) were selected and randomly divided into six groups (n = 12) based on type of cavity design and files used: Group 1, Conservative Access Cavity [ConsAC])-WaveOne Gold; Group 2, ConsAC-Mtwo; Group 3, ConsAC-XP-endo shaper; Group 4, Traditional Access Cavity [TradAC])-WaveOne; Group 5, TradAC-Mtwo; and Group 6, TradAC-XP-endo shaper. All the ConsAC were prepared with a customized template fabricated using cone beam computed tomography. ADE evaluation was done using the Myers and Montgomery set up. All the instruments were used according to the manufacturers' instructions, followed by a final irrigation using Endoactivator. The time taken for preparation was calculated using a digital watch. Five samples in each group was taken and subjected to ATR-FTIR analysis. Results: There was no significant difference between the groups with respect to ADE (P > 0.05). Whereas, a statistically significant difference was seen in PT between the TradAC and ConsAC (P < 0.05). Using ATR-FTIR, it was found that all the samples of extruded debris had the presence of sodium hypochlorite. Conclusions: All instrumentation systems produced ADE irrespective of access cavity design. The time taken for preparation of canals in ConsAC was significantly longer compared to TradAC. Clinical Relevance: ADE can translate clinically as postoperative pain. Assessing the ADE in ConsAC could shed light on the type of file systems that can be used in such cavities in order to minimize postoperative pain clinically.

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AIM: This in vitro study aimed to determine the influence of access cavity design and residual tooth structure and to compare the fracture resistance of the teeth post endodontically restored with short fiber-reinforced composite (GC everX Posterior; GC, India) and conventional posterior high-strength GIC (Glass Ionomer Cement) (GC Gold Label IX; GC, India). METHODS: Ninety extracted human mandibular molars were classified into five groups, i.e., one control group (n = 10) and four test groups based on the access cavity design (n = 20): Traditional access cavity (TAC), Conservative access cavity (CAC), Ninja access cavity (NAC), and Truss access cavity (TRAC). Then 80 teeth in test groups were endodontically treated and further subdivided (n = 10) based on post-endodontic restorative materials, i.e., short fiber-reinforced composite (SFC) and Type 9 GIC. Samples were then subjected to fracture resistance under a universal testing machine and fracture loads were compared statistically. RESULTS: The fracture resistance of various access cavity designs (TAC, CAC, NAC, and TRAC) varied significantly (P < .05). Regardless of access cavity design, teeth restored with SFC had higher fracture resistance than teeth restored with high strength posterior GIC (P = .001). CONCLUSION: Using newer access cavity designs like (CAC, NAC, and TRAC) and reinforcing the teeth with a post-endodontic restoration such as SFC, fracture resistance of endodontically treated teeth can be improved notably.

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INTRODUCTION: The aim was to compare the glide path and final preparation times of WaveOne Gold and TruNatomy in conjunction with two different endodontic access cavity designs in extracted human molar teeth. METHODS: 60 extracted human mandibular molars with mesiobuccal canals were selected and randomly divided into two different access cavity design preparation groups (n = 30). Traditional access cavities (TAC) and conservative access cavities (CAC). Within each cavity design group, the 30 teeth were divided in to two instrumentation groups (WaveOne Gold Primary (n = 15) and TruNatomy Prime (n = 15)). Group 1: TAC, #10 stainless steel manual K-file followed by WaveOne Gold Glider and WaveOne Gold Primary. Group 2: CAC, #10 stainless steel manual K-file followed by WaveOne Gold Glider and WaveOne Gold Primary. Group 3: TAC, #10 stainless steel manual K-file followed by TruNatomy Orifice Modifier and Glider and TruNatomy Prime. Group 4: CAC, #10 stainless steel manual K-file followed by TruNatomy Glider and TruNatomy Prime. Glide path and final preparation times were recorded. RESULTS: Shaping time with TruNatomy Glider in combination with TruNatomy Prime instruments were faster compared to the WaveOne Gold Glider/ WaveOne Gold Primary instruments regardless of the type of access cavity preparation. TAC design yielded faster preparation time (38.2 ± 4.57 seconds) compared to the CAC (55.6 ± 6.91 seconds) in the WaveOne Gold Glider/ WaveOne Gold Primary instrumentation group. No difference was found between the different access cavity design groups in combination with TruNatomy Glider/TruNatomy Prime preparation. CONCLUSION: Preparation time with TruNatomy Glider and Prime instruments was significantly faster than WaveOne Gold Glider/WaveOne Gold Primary, regardless of the access cavity design. TAC design in combination with WaveOne Gold Glider/ WaveOne Gold Primary instrumentation resulted in faster preparation time compared to WaveOne Gold Glider/WaveOne Gold in combination with the CAC design.

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AIM: To evaluate the influence of traditional and conservative access cavity preparations on the remaining dentine thickness in the coronal third of mesial canals of extracted mandibular molars prepared with reciprocating instruments using micro-computed tomography as the analytical tool. METHODOLOGY: Seventy extracted mandibular molars were scanned at a pixel size of 19 µm. From this initial sample, 20 teeth were selected, pair-matched and distributed into two groups (n = 10) according to the access cavity preparation: traditional (TradAC) or conservative (ConsAC). The root canals were sequentially enlarged with Reciproc Blue R25 (size 25, 0.08v taper) and R40 (size 40, 0.06v taper) instruments. A new scan was performed and the postoperative stacks were coregistered with their respective preoperative datasets. A colour-coded cross sections of the roots were created and used to identify and measure the smallest dentine thickness related to both MB and ML canals at 1.0-mm intervals from the furcation level of up to 5 mm in the apical direction, in both mesial and distal aspects of the roots, before and after preparation. The statistical analyses were performed with paired-samples t-test, independent-samples Student T-test and Chi-Square test with a significance level of 5%. RESULTS: At all levels of both groups, dentine thickness before preparation was greater than after preparation (p < .05). No difference in the percentage of dentine reduction was observed between TradAC and ConsAC groups (p > .05), but a significantly greater reduction was observed to the distal aspect of the roots (p < .05). After root canal preparation, dentine thinner than 0.5 mm was observed mostly along the distal aspect of the root (10% to 15%) of the MB and ML canals, with no influence of the access cavity type on its incidence to either mesial (X2  = 1.66; p = .2) or distal (X2  = 0.40; p = .5) directions. In the TradAC group, dentine thickness in most slices was greater than 1.0 mm after preparation (n = 124) whilst, in the ConsAC, it ranged from 0.5 to 1.0 mm (n = 136). CONCLUSION: Traditional or conservative access cavity preparation in extracted mandibular molars did not influence the remaining dentine thickness in the coronal third of mesial canals enlarged with thermomechanically treated nickel-titanium reciprocating instruments.

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OBJECTIVES: To assess related studies and discuss the clinical implications of endodontic access cavity (AC) designs. MATERIALS AND METHODS: A systematic review of studies comparing the fracture resistance and/or endodontic outcomes between different AC designs was conducted in two electronic search databases (PubMed and Web of Science) following the PRISMA guidelines. Study selection, data extraction, and quality assessment were performed. Meta-analyses were undertaken for fracture resistance and root canal detection, with the level of significance set at 0.05 (P = 0.05). RESULTS: A total of 33 articles were included in this systematic review. The global evaluation of the risk of bias in the included studies was assessed as moderate, and the level of evidence was rated as low. Four types of AC designs were categorized: traditional (TradAC), conservative (ConsAC), ultraconservative (UltraAC), and truss (TrussAC). Their impact on fracture resistance, cleaning/disinfection, procedural errors, root canal detection, treatment time, apical debris extrusion, and root canal filling was discussed. Meta-analysis showed that compared to TradAC, (i) there is a significant higher fracture resistance of teeth with ConsAC, TrussAC, or ConsAC/TrussAC when all marginal ridges are preserved (P < 0.05), (ii) there is no significant effect of the type of AC on the fracture resistance of teeth when one or two marginal ridges are lost (P > 0.05), and (iii) there is a significantly higher risk of undetected canals with ConsAC if not assisted by dental operating microscope and ultrasonic troughing (P < 0.05). CONCLUSIONS: Decreasing the AC extent does not necessarily present mechanical and biological advantages especially when one or more surfaces of the tooth structure are lost. To date, the evidence available does not support the application of TrussAC. UltraAC might be applied in limited occasions. CLINICAL RELEVANCE: Maintaining the extent of AC design as small as practical without jeopardizing the root canal treatment quality remains a pragmatic recommendation. Different criteria can guide the practitioner for the optimal extent of AC outline form which varies from case to case.

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INTRODUCTION: The aim of this study was to investigate the fracture resistance of endodontically treated and restored permanent mandibular molars with minimally invasive access cavities subjected to thermocycling and dynamic loading. METHODS: Forty first and second mandibular molars were randomly assigned to 4 groups (n = 10/group) as follows: group 1, control (intact teeth); group 2, traditional access cavity (TradAC); group 3, conservative access cavity (ConsAC); and group 4, truss access cavity (TrecAC). After endodontic treatment, teeth were restored with SDR core (Dentsply Caulk, Milford, DE) and subjected to thermocycling followed by dynamic and static loading with a multiaxial fatigue testing machine (Instron, Canton, MA). The maximum load to fracture and pattern of failure (restorable/unrestorable) were recorded. Data were evaluated with analysis of variance and the Tukey post hoc test for multiple comparisons. RESULTS: Fracture resistance of the samples in the control group were higher than those in the experimental groups (P < .005). TradAC exhibited the least resistance to fracture (P < .005). There was no statistically significant difference in the fracture resistance of ConsAC and TrecAC (P = .361) Unrestorable fractures were more frequent in the TradAC group compared with all other groups. CONCLUSIONS: Mandibular molars with ConsAC and TrecAC exhibited superior fracture resistance compared with TradAC. TradAC had the highest number of unrestorable fractures.

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INTRODUCTION: Several endodontic access cavity designs have been proposed in the past decade to access the root canal space in a minimally invasive manner. The rationale for this approach was derived from the assumption that preserving more tooth structure during access preparation will improve the tooth's resistance to fracture and its long-term survivability. However, is this assumption valid? Also, can this approach compromise other treatment-related aspects? METHODS: We conducted a literature review using 4 online databases and classified the access cavity designs presented in each article according to our proposed classification. RESULTS: Through the literature search, we identified 49 articles that evaluated the effect of the access cavity design on 11 different treatment parameters. The majority of the studies failed to demonstrate clear benefits of the minimally invasive access designs, whereas others raised concerns regarding the ability to adequately disinfect, fill, and restore teeth with a minimally invasive access cavity design. CONCLUSION: Minimally invasive access cavity designs present more risk than benefit on the outcome of endodontic treatment. Clinicians should reconsider the application of a minimally invasive access cavity for routine endodontics and cautiously apply it in selected cases when the proper armamentarium is available.

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OBJECTIVE: The main aim of this present systematic review is to ascertain whether a conservative endodontic cavity (ConsAC) has a better fracture resistance than a traditional access cavity (TradAC) in endodontically treated molars. MATERIALS AND METHODS: Three independent reviewers researched without limits in multiple engines: PubMed, ScienceDirect, Scopus, ResearchGate, EBSCOhost, Wiley Online Library, and Google Scholar, in addition to reference and hand search. Articles were chosen according to a certain inclusion and exclusion criteria, which, in brief, are in vitro studies assessing the fracture resistance difference between ConsAC and TradAC performed on extracted sound human molar teeth. A quality assessment criteria was produced to evaluate the chosen articles and categorized them according to their risk of bias into low, moderate and high. RESULTS: Out of a total of 105 studies, which were obtained from seven different search engines, only eight in vitro studies were included after eliminating the duplicates followed by the application of the eligibility criteria. Five of the articles showed low risk of bias while the others revealed a moderate risk of bias. CONCLUSION: To sum up, there is insufficient evidence to give a final decision whether ConsAC is more advantageous than TradAC in terms of fracture resistance and further studies regarding this topic are needed.

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INTRODUCTION: The purpose of this study was to evaluate the tooth structure theoretically required to be removed in the coronal and cervical regions to accomplish 3 different endodontic access preparations in a novel digital model. The deviation of the center of access cavity from the central fossa will also be measured and compared among the 3 endodontic cavity designs, which in turn may serve as suggested points of entry for different access openings. METHODS: Twenty-one maxillary molars and 15 mandibular molars were selected and 3-dimensionally imaged with cone-beam computed tomographic imaging. Three-dimensional (3D) volume reconstructions were made and converted into stereolithography files. Digital access cavity preparation was performed on each 3D reconstruction model with the 3 most commonly used endodontic access preparations: minimally invasive (MI), modified straight-line (MS), and traditional straight-line (TS) techniques. After the access cavity outlines were determined, digital sectioning of each reconstructed 3D tooth model was performed orthogonal to the long axis of the tooth at 3 levels: (1) passing through the central fossa, (2) 1.5 mm apical to the central fossa, and (3) 2 mm apical to the cementoenamel junction. The linear distance from the centroid of the access opening to the central fossa was measured to calculate the point of entry, and the amount of tooth structure removal at the pericervical area was measured to calculate the theoretically minimum amount of linear dentin removal required. Two-way repeated measures analysis of variance was performed for the interactions between different access designs and the amount of cervical dentin removal. Other data were statistically analyzed with 1-way repeated measures analysis of variance. The Tukey post hoc test was used for multiple comparisons. Significance was set at .05. RESULTS: The amount of deviation of the center of the access cavity from the central fossa in all test groups was less than 1 mm. The dimensions of access openings differed significantly among the 3 access forms (TS > MS > MI, P < .0001). The amount of required cervical dentin removal was the greatest in the TS method followed by the MS and MI methods (P < .0001). CONCLUSIONS: The central fossa could serve as good starting points in all access preparations in both maxillary and mandibular molars. Dentin removal in the coronal and cervical regions was the greatest in the TS design followed by the MS and MI designs. When comparing different canals in the same access form, less cervical dentin was sacrificed in the palatal canals of maxillary molars and the distal canals of mandibular molars.

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INTRODUCTION: This study evaluated the effects of traditional and truss access cavity preparations in addition to artificial truss restoration on the fracture resistance of endodontically treated mandibular molars. METHODS: A total of 66 recently extracted, intact mandibular first molars were collected from patients between 20 and 45 years of age. After the preparation of a mesio-occluso-distal cavity in all teeth, the teeth were randomly grouped into the following 4 groups according to the access cavity design: traditional access cavity, artificial truss restoration, truss access cavity, and control groups. Endodontic access cavities were performed in the experimental groups according to each treatment modality followed by instrumentation, irrigation, and obturation. After composite restoration, the teeth were subjected to a vertical occlusal force until fracture occurred. The data were statistically analyzed, and the fracture patterns were evaluated. RESULTS: First, a 1-way analysis of variance test analysis of the fracture resistance of the experimental groups showed nonsignificant differences among groups (P > .05). Second, the data were statistically analyzed using the Student t test to compare the fracture resistance of each experimental group with that in the control group. The control group had statistically significantly higher mean values for fracture resistance than the traditional access group and the artificial truss restoration group (P < .05). No statistically significant difference was recorded in the fracture resistance between the control group and the truss access cavity group (P > .05). CONCLUSIONS: The truss access cavity preparation improved the fracture resistance of endodontically treated teeth with mesio-occluso-distal cavities, whereas the artificial truss restoration did not improve it.

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INTRODUCTION: The purpose of this study was to assess the impact of access cavity preparation and the remaining tooth substance on the fracture strength of endodontically treated teeth. METHODS: One hundred sound mandibular first and second molar teeth were selected and divided into 1 control and 9 test groups (n = 10/group) as follows: control group, intact teeth; group 1, teeth prepared with traditional endodontic access cavity (TEC); group 2, teeth prepared with conservative endodontic access cavity (CEC); group 3, teeth prepared with truss endodontic access cavity (TREC); group 4, TEC + 3 residual walls; group 5, CEC + 3 residual walls; group 6, TREC + 3 residual walls; group 7, TEC + 2 residual walls; group 8, CEC + 2 residual walls; and group 9, TREC + 2 residual walls. After access cavity preparation, all test teeth were endodontically treated and restored. The specimens were then loaded to fracture in a universal loading machine (Triaxial Tester T400 Digital; Controls srl, Cernusco, Italy), and fracture values were recorded in newtons. The data were analyzed with 2-way analysis of variance and Tukey post hoc analysis for multiple comparisons (P < .05). RESULTS: Intact teeth were more resistant to fracture than the teeth in all the test groups. No statistically significant differences were found between the 3 tested access cavities (P > .05). Significant differences were observed between the different number of residual walls (P < .05). CONCLUSIONS: TRECs do not increase the fracture strength of endodontically treated teeth in comparison with CECs and TECs. Moreover, the loss of mesial and distal ridges reduced the fracture strength of teeth significantly.

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AIM: The present study aimed to compare the remaining dentin thickness (RDT) and fracture resistance of conventional and conservative access and biomechanical preparation in molars using cone-beam computed tomography (CBCT). METHODOLOGY: A total of 60 freshly extracted human molars were selected and were randomly divided into two groups of conventional and conservative access preparation group (n = 30). Samples were subjected to pre-CBCT scan at the pericervical region for the measurement of total dentin thickness. For the conventional group, samples were accessed and biomechanical preparation was done using K3 XF file. For conservative group, samples were accessed using CK microendodontic burs using a dental operating microscope and biomechanical preparation was done using self-adjusting file. After obturation and postobturation with nanohybrid composite restoration, samples of both groups were subjected to post-CBCT scan at pericervical region for the measurement of RDT. The samples were then loaded to fracture in the Instron Universal Testing Machine, and the data were analyzed using paired sample t-test and independent sample t-test. RESULTS: The mean RDT was less in conventional group than conservative group. Pericervical dentin was preserved more in conservative group. The statistical difference among both the experimental group was highly significant (<0.001). The mean load at fracture was less in conventional group than conservative group (<0.001). CONCLUSION: Coronal dentin was conserved in molars when accessed through conservative than through conventional. The dentin conservation afforded an increased resistance to fracture in conservative group which is doubled the fracture resistance in conventional group.

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INTRODUCTION: The aim of this study was to compare the fracture strengths of mandibular molar teeth prepared using traditional endodontic cavity (TEC) and conservative endodontic cavity (CEC) methods and restored using SDR (Dentsply Caulk, Milford, DE) and EverX Posterior (GC Dental, Tokyo, Japan) base composite materials. METHODS: A hundred mandibular first molar teeth were randomly divided into 5 groups. In group 1 (the control group), samples were kept intact. In group 2, TECs were prepared, and the samples were restored with EverX Posterior and composite resin. In group 3, CECs were prepared, and the samples were restored with EverX Posterior and composite resin. In group 4, TECs were prepared, and the samples were restored with SDR and composite resin. In group 5, CECs were prepared, and the samples were restored with SDR and composite resin. This load was applied on the samples at 1-mm/min speed using a 6-mm round-head tip until fracture. The forces resulting in fracture were recorded in newton units. The data were analyzed using Kruskal-Wallis and Pearson correlation tests at a 5% significance level. RESULTS: The fracture strengths of the samples in the control group were significantly higher than the experimental groups (P < .05). There was no statistically significant difference in the endodontic access cavities prepared used the TEC and CEC methods and restored using the same composite base material (P > .05). CONCLUSIONS: CEC preparation did not increase the fracture strength of teeth with class II cavities compared with TEC preparation. The fracture strength of teeth restored with the SDR bulk-fill composite was higher than that of teeth restored with EverX Posterior.

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INTRODUCTION: The purpose of this study was to compare in vitro the fracture strength of root-filled and restored teeth with traditional endodontic cavity (TEC), conservative endodontic cavity (CEC), or ultraconservative "ninja" endodontic cavity (NEC) access. METHODS: Extracted human intact maxillary and mandibular premolars and molars were selected and assigned to control (intact teeth), TEC, CEC, or NEC groups (n = 10/group/type). Teeth in the TEC group were prepared following the principles of traditional endodontic cavities. Minimal CECs and NECs were plotted on cone-beam computed tomographic images. Then, teeth were endodontically treated and restored. The 160 specimens were then loaded to fracture in a mechanical material testing machine (LR30 K; Lloyd Instruments Ltd, Fareham, UK). The maximum load at fracture and fracture pattern (restorable or unrestorable) were recorded. Fracture loads were compared statistically, and the data were examined with analysis of variance and the Student-Newman-Keuls test for multiple comparisons. RESULTS: The mean load at fracture for TEC was significantly lower than the one for the CEC, NEC, and control groups for all types of teeth (P < .05), whereas no difference was observed among CEC, NEC, and intact teeth (P > .05). Unrestorable fractures were significantly more frequent in the TEC, CEC, and NEC groups than in the control group in each tooth type (P < .05). CONCLUSIONS: Teeth with TEC access showed lower fracture strength than the ones prepared with CEC or NEC. Ultraconservative "ninja" endodontic cavity access did not increase the fracture strength of teeth compared with the ones prepared with CEC. Intact teeth showed more restorable fractures than all the prepared ones.

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