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Background: The aim of this study was to compare the fracture strength and fracture modes of post-cores produced with CAD-CAM from modified polyetheretherketone (PEEK) materials with other custom-produced post-cores. Methods: Sixty human mandibular first premolars with equal root sizes were used. The teeth were divided into six groups (n = 10), and root canal treatment was performed. The teeth were separated from the roots over 2 mm from the cemento-enamel junction. As a result of the decoronation process, a 1 mm wide shoulder line was obtained for all teeth. For the fracture strength test, 10 mm deep post spaces were created on the teeth with a 1.6 mm diameter driller. Post-core groups consisted: everStick® glass fiber post-core (Group GF), zirconia post-core (Group Z), metal (Cr-Co) post-core (Group M), PEEK post-core without filler (Group UP), PEEK post-core with 20% TiO2 Filler (Group TP), and post-core with 20% ceramic filler (Group CP). Following the application of posts to post spaces, copings were created and cemented on the samples. With the universal tester, a force was applied to the long axis of the tooth with a slope of 135°. The mean fracture strength (N) between the groups was statistically evaluated using one-way ANOVA, and pairwise mean differences were detected using post hoc Tukey's HSD test among the groups. Results: According to the results of the statistical analysis, a significant difference was found between the groups in terms of mean fracture resistance (p < 0.05). Group Z (409.34 ± 45.72) was significantly higher than Group UP (286.64 ± 37.79), CP (298.00 ± 72.30), and TP (280.08 ± 67.83). Group M (376.17 ± 73.28) was significantly higher than Group UP (286.64 ± 37.79) and Group TP (280.08 ± 67.83). There were no statistically significant differences between the means of the other groups (p > 0.05). Among all the groups, Group Z exhibited a higher prevalence of repairable failure modes, while the rest of the groups predominantly experienced irreparable failure modes. Conclusion: In our study, zirconia and metal post-core samples showed higher average fracture strength values than PEEK post-cores groups. Repairable failure modes were more common in the zirconia post-cores, whereas the opposite was observed in the other groups. Further experimental and clinical trial studies are needed before PEEK materials can be used as post materials in the clinic.

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BACKGROUND: Use of flowable resin composites for ocluso-proximal restorations in primary molars could improve cervical adaptation, and reduce the failure risk. AIM: To investigate the fracture strength of occluso-proximal restorations in primary teeth using different flowable resin composites (as an intermediate layer or entire cavity) and a conventional resin composite (incremental technique). DESIGN: Two standardized occluso-proximal cavities were prepared on mesial and distal surfaces of 50 sound primary molars. The teeth were randomly assigned into five groups (n = 10): 2 mm Filtek Bulk Fill Flow + Z350 XT; 4 mm Filtek Bulk Fill Flow; 2 mm Z350 XT Flow + Z350 XT; 4 mm Z350 XT Flow; and Z350 XT inserted by incremental technique. All restored teeth were subjected to cariogenic challenge and then submitted to fracture strength test. The failure pattern of each specimen was categorized as reparable or irreparable/need for replacement based on the World Dental Federation (FDI) criteria. Fracture strength means were submitted to one-way ANOVA and Tukey's post hoc tests. Failure pattern was analyzed descriptively. RESULTS: There was no statistically significant difference on fracture strength among groups (p = .48). A similar distribution of reparable (35%-40%) and irreparable (60%-65%) failures was observed among groups. CONCLUSION: Based on a laboratorial setting, the use of different flowable resin composites (as an intermediate layer or entire cavity) may be an option to restore occluso-proximal cavities in primary molars.

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OBJECTIVE: The demand for esthetics has increased in today's world and most parents prefer to preserve their children's primary anterior teeth until their natural exfoliation. However, an intracanal post is required to provide retention for reconstruction of severely damaged anterior teeth due to caries or trauma. Various materials and methods may be used for the fabrication of intracanal posts. This study assessed the fracture strength and fracture mode of primary canine teeth reconstructed with prefabricated and customized polyethylene and glass fiber posts. MATERIALS AND METHODS: This in vitro study evaluated 60 extracted primary canine teeth in four groups (n = 15). After pulpectomy and post space preparation with 4 mm depth, composite resin post, prefabricated glass fiber post (Whitepost), customized glass fiber post (Interlig), or customized polyethylene fiber post (Ribbond) were placed in the root canals to provide retention, and the tooth crown was restored with bulk-fill composite resin. The fracture strength was then measured in a universal testing machine. The fracture mode was also evaluated visually. RESULTS: The mean fracture strength was 22.45 ± 5.06, 33.10 ± 8.5, 30.20 ± 7.33, and 32.61 ± 5.73 N/mm2 in the composite resin post, Whitepost, Interlig, and Ribbond groups, respectively. The fracture strength was significantly lower in the composite group than in the remaining three groups (p = 0.000). No other significant differences were found (p > 0.05). Also, no significant difference was observed among the study groups in the fracture mode (p = 0.241). CONCLUSION: The composite resin post yielded a significantly lower fracture strength than the prefabricated and customized glass and polyethylene fiber posts, but the fracture mode was not significantly different among the four groups.

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In solid-state welding, the basis of joining is the combination of materials in the weld area using the tool. The tool pin is a key parameter that can facilitate tool penetration into the parts and result in better material mixing. On the other hand, the presence of the end cavity of the process can be a factor in reducing the mechanical properties of the weld. To address these two conflicting issues, this study examined the effect of pin thickness on the mechanical and metallurgical properties of aluminum 6061 and 5052 plates. The variable parameters included pin diameters (4 mm, 8 mm, and no pin) and three tool penetration depths (0.5 mm, 1.5 mm, and 2.5 mm). The impact of changing the arrangement of the plates on each other was also investigated regarding the properties and quality. Experimental results showed that decreasing the pin diameter and increasing the tool penetration depth improved the weld breakage force. The failure modes of all welds were button pull-out and ductile failure. Using a pinless tool increased microhardness in the weld nugget area and led to more uniform microhardness variations. Placing the aluminum 6061 alloy on top of the arrangement improved shear tensile strength and microhardness of the joints. The microstructure in the heat-affected zone showed an increase in grain size, which was accompanied by a decrease in microhardness. The microstructure in the stirred zone was dense and compacted, and with increasing tool penetration depth and decreasing pin diameter, the grain size became finer.

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OBJECTIVES: The objective of this in vitro study was to evaluate the effects of different preparation designs on the mean colour change (ΔE*), marginal adaptation, fracture resistance, and fracture types of maxillary and mandibular premolar endocrowns (ECs). METHODOLOGY: A total of 40 extracted maxillary and mandibular premolars were treated endodontically, and each type was subdivided according to the remaining axial height (remaining walls on all surfaces; 2-4 mm) and 2 mm inside the pulp chamber. Specimens were immersed in coffee for 14 days, ΔE* was determined, marginal adaptation was observed, fracture forces test was conducted, and the samples were examined visually at 10× magnification to evaluate failure type and identify fracture origin. The data were entered and analyzed using Statistical Package for Social Sciences, and significance between and within groups was evaluated through ANOVA. The p-value ≤ 0.05 was considered statistically significant. RESULTS: The ΔE* values of the maxillary premolar with 2 mm axial height were the highest (6.8 ± 0.89 units), whereas the lowest value was observed in the mandibular premolar with 4 mm axial height (2.9 ± 0.53 units). Significant differences (p < 0.05) in teeth and design were observed. The marginal adaptation of the mandibular premolar with 4 mm axial height was the highest (30.20 ± 1.53 µm), whereas the lowest marginal adaptation was observed in the maxillary premolar with 2 mm axial height (14.38 ± 0.99 µm), and the difference was statistically significant (p < 0.05). The maximum fracture force was observed in maxillary premolars with 2 mm axial height (2248.15 ± 134.74 N), and no statistically significant difference (p = 0.07) was observed between maxillary and mandibular premolars at 4 mm axial height. CONCLUSION: The recorded ΔE* values of the ECs were within clinically acceptable values or slightly higher, and the marginal adaption values were within acceptable and recommended clinical values in µm. EC preparation with 2 mm axial height in both arches recorded the highest fracture forces. Type III (split fracture) failure was recorded as the highest in the maxillary and mandibular premolar ECs with different axial wall heights.

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Crack generation and propagation are critical aspects of grinding processes for hard and brittle materials. Despite extensive research, the impact of residual cracks from coarse grinding on the cracks generated during fine grinding remains unexplored. This study aims to bridge this gap by examining the propagation law of existing cracks under indentation using the extended finite element method. The results reveal that prefabricated cracks with depths less than the crack depth produced on an undamaged surface tend to extend further without surpassing the latter. Conversely, deeper prefabricated cracks do not exhibit significant expansion. A novel method combining indentation and prefabricated cracks with fracture strength tests is proposed to determine crack propagation. Silicon wafers with varying damaged surfaces are analyzed, and changes in fracture strength, measured by the ball-on-ring method, are utilized to determine crack propagation. The experimental results confirm the proposed crack evolution law, validated by damage assessments across different grinding processes, which is suitable for crack damage. The findings demonstrate that residual cracks from coarse grinding are negligible in predicting the maximum crack depth during fine grinding. This research provides a crucial foundation for optimizing the wafer thinning process in 3D stacked chip manufacturing, establishing that changes in fracture strength are a reliable indicator of crack propagation feasibility.

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PURPOSE: This study aimed to evaluate how different tooth substrates affect the survival rate, shear bond strength, fracture strength, and mode of failure of laminate veneers (LVs). METHODS: This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. In vitro studies comparing the bonding of laminate veneers to different substrates were included. Electronic databases and manual searches were performed to identify relevant studies. Data on survival rate, shear bond strength, fracture strength, and failure modes were extracted and analyzed using Review Manager software. RESULTS: A total of 10 studies were included in the review, comprising 621 laminate veneers. The findings revealed that laminate veneers bonded to enamel substrate had lower failure rates than those bonded to tooth substrate with severely exposed dentin or existing composite restorations (ECRs). The failure modes observed were debonding, chipping, cracks, or fractures. CONCLUSIONS: Bonding laminate veneers to enamel substrate showed higher survival rates compared to bonding to tooth substrates with severely exposed dentin or ECRs, underscoring the significance of enamel preservation. When dealing with exposed dentine surfaces or ECRs, it is crucial to perform appropriate surface treatment before luting to improve adhesion. This involves immediate dentine sealing, as well as the use of suitable primers and bonding agents.

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PURPOSE: The purpose of this study was to compare the wear, fracture strength, and mode of failure of various brands of 3D-printed resin denture teeth with prefabricated acrylic resin. Additionally, the study aimed to analyze the different modes of failure exhibited by these teeth. MATERIALS AND METHODS: The study utilized 90 3D-printed and 30 prefabricated, 3D-printed resin teeth from three brands: L = Optiprint Lumina, A = ASIGA DentaTooth, P = Power resins, along with prefabricated acrylic teeth from M = Major Super Lux. Each of the 30 samples per main group was divided into two subgroups: The first subgroup samples (M1, A1, L1, P1) were subjected to thermal cycling and mechanical loading; M2, A2, L2, and P2 were not aged and tested directly. A scan of a prefabricated acrylic tooth was taken using an intraoral scanner, and then the STL file was printed using an Asiga 3Dprinter. The specimens underwent aging to simulate 5 years of clinical use with 10,000 thermal cycles and 1,200,000 dynamic load cycles on a chewing simulator. Surface roughness parameters (Rz, Ra, Rq) were measured using a 3D Optical Profilometer, fracture resistance was assessed using a universal testing machine, and SEM analysis was performed to observe failure modes. Statistical analysis using T-test, one-way analysis, and two-way analysis processed by the Statistical Package for Social Sciences (SPSS) software version 23.0 (SPSS: Inc., Chicago, IL, USA) was done with a level of significance set at <0.05. RESULTS: The results showed that the difference in surface roughness parameters (Rz, Ra, Rq) before and after aging for Group M, Group A, Group L, and Group P was statistically significant (p < 0.05). Two-way ANOVA for wear resistance between aging and groups on dependent variable Rz (p = 0.002), Ra (p = 0.001), Rq (p = 0.001) were significant. Multiple comparisons for surface roughness parameters showed Group A and Group L were lower than Group P and Group M (p < 0.05). For fracture strength, One-way ANOVA showed a significant difference between groups for fracture strength either without or after the aging procedure (p < 0.05). Multiple comparisons for fracture strength without aging showed no significant difference between Group M, Group A, and Group L (p > 0.05). After the aging procedure fracture strength for Group M was higher than Group A, Group L, and Group P (p < 0.05). CONCLUSION: 3D-printed resin teeth showed a greater and comparable wear resistance to prefabricated acrylic teeth. Fracture strength was comparable between prefabricated acrylic teeth and 3D-printed resin (Asiga and Lumina) before aging, but after aging 3D-printed resin teeth showed less fracture strength.

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Background/purpose: Recently, an effective core build-up system for teeth with flared root canals is needed. This research aimed to evaluate the effect of foundation restorations using a composite resin core with a fiber post reinforced with a zirconia tube for the surface strain at the cervical area and the fracture load of teeth with flared root canals. Materials and methods: Bovine teeth were shaped to mimic human premolars with flared root canals and restored using three types of composite resin foundation restorations with each materials described below: a fiber post (FC), a zirconia tube (ZC), a fiber post and zirconia tube (ZFC). Each specimen was restored with a zirconia crown. The surface strains of the specimens at the cervical area and fracture loads were analyzed using a one-way analysis of variance (ANOVA), followed by Tukey's honest significant difference test. Results: The surface strains of Groups ZFC and ZC were significantly lower than that of Group FC in the buccal root. The fracture strengths of Groups ZFC and ZC were significantly higher than that of Group FC. The strength of Group ZFC was significantly higher than that of Group ZC. Conclusion: The use of a composite resin core with a zirconia tube for the simulated premolar with flared root canals reduced surface strain at the cervical area and provided higher fracture strength compared to using a composite resin core with a fiber post. And the zirconia tubes provided even higher fracture strength when used with a fiber post.

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OBJECTIVE: To investigate the fracture resistance and failure modalities of anterior endocrown restorations fabricated employing diverse ceramic materials, and bonded using various cementation methodologies. MATERIALS AND METHODS: Forty maxillary central incisors were divided into two main groups based on the ceramic materials used; GroupI (Zir): zirconia endocrwons (Zolid HT+, Ceramill, Amanngirrbach) and GroupII (E-Max): e-max endocrowns (IPS e.max CAD, Ivoclar Vivadent). Both groups were further split into two subgroups depending on the cementation protocols; subgroup IA "ZirMDP": endocowns cemented with MDP primer + MDP resin cement, subgroup IB (ZirNon-MDP): cemented with MDP primer + non-MDP resin cement, subgroup IIA (E-maxMDP): cemented with MDP primer + MDP resin cement, subgroup IIB (E-maxNon-MDP): cemented with MDP primer + non-MDP resin cement. (n = 10/subgroup). Endocrowns were manufactured using CAD/ CAM. Teeth were subjected to 10,000 thermal cycles. The fracture test was performed at 45o with a palatal force direction until the fracture occurred. Test results were recorded in Newton. The failure mode was examined using a stereomicroscope. A One-way ANOVA test was utilized to compare different groups regarding fracture strength values. Tukey`s Post Hoc was utilized for multiple comparisons. RESULTS: The comparative analysis of fracture strength across the diverse groups yielded non-significant differences, as indicated by a p-value exceeding 0.05. Nonetheless, an observable trend emerged regarding the mode of failure. Specifically, a statistically significant prevalence was noted in fractures localized within the endocrown/tooth complex below the cementoenamel junction (CEJ) across all groups, except for Group IIB, "E-max Non-MDP," where fractures within the endocrown/tooth complex occurred above the CEJ. CONCLUSIONS: Combining an MDP-based primer with an MDP-based resin cement did not result in a significant effect on the anterior endocrown fracture strength. CLINICAL RELEVANCE: Regardless of the presence of the MDP monomer in its composition, adhesive resin cement achieved highly successful fracture strength when used with MDP-based ceramic primers. Additionally, ceramic materials exhibiting elastic moduli surpassing those of dentin are discouraged due to their propensity to induce catastrophic fractures within the tooth structure.

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Currently, it is still challenging to develop a hydrogel electrolyte matrix that can successfully achieve a harmonious combination of mechanical strength, ionic conductivity, and interfacial adaptability. Herein, a multi-networked hydrogel electrolyte with a high entanglement effect based on gelatin/oxidized dextran/methacrylic anhydride, denoted as ODGelMA is constructed. Attribute to the Schiff base network formulation of ─RC═N─, oxidized dextran integrated gelatin chains induce a dense hydrophilic conformation group. Furthermore, addition of methacrylic anhydride through a grafting process, the entangled hydrogel achieves impressive mechanical features (6.8 MPa tensile strength) and high ionic conductivity (3.68 mS cm-1 at 20 °C). The ODGelMA electrolyte regulates the zinc electrode by circumventing dendrite growth, and showcases an adaptable framework reservoir to accelerate the Zn2+ desolvation process. Benefiting from the entanglement effect, the Zn anode achieves an outstanding average Coulombic efficiency (CE) of 99.8% over 500 cycles and cycling stability of 900 h at 5 mA cm-2 and 2.5 mAh cm-2. The Zn||I2 full cell yields an ultra-long cycling stability of 10 000 cycles with a capacity retention of 92.4% at 5 C. Furthermore, a 60 mAh single-layer pouch cell maintains a stable work of 350 cycles.

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PURPOSE: Compare Neodent Zi® zirconia implants' insertion torque (IT) and removal torque (RT) with Neodent Alvim® titanium. Measure the maximum torque supported by the zirconia implant until its fracture (MT) and the maximum torque sustained by the assembler of this implant (MTA) until its fracture. MATERIAL AND METHODS: In this in-vitro study twenty four implants were used. Two groups of implants with the same macrogeometry and from the same manufacturer were compared, Zirconia (n=12) and Titanium (n=12). Implant bed preparations were completed in bovine ribs following a standardized drilling protocol. Then, the insertion torque (IT), removal torque (RT), maximum torque to fracture (MT) and maximum torque to fracture of the assembler (MTA) were completed using a calibrated torque meter. Data was presented using descriptive statistics including means, standard deviations (SD), medians, and quartiles. The Shapiro-Wilk test was used to verify data normality and the Wilcoxon test was used to evaluate differences between groups. Statistical significance was established as p < 0.05. RESULTS: Zirconia implants showed: IT 89.33 ± 31.18 Ncm and RT 84.89 ± 32.92 Ncm. Titanium implants showed: IT 77.58 ± 28.96 Ncm and RT 76.75 ± 31.29 Ncm without significant differences (p>0.05). In relation to fracture under rotational force, the zirconia implants fractured at 106.17 ± 22.54 Ncm, and the implant assembly fractured at 84.00 ±13.14 Ncm. CONCLUSION: Neodent Zi® implants showed stability but lower fracture torque than Alvim® titanium. As the fracture values of the assembler were significantly lower than the fracture values of the zirconia implants, it can be stated that, as recommended by the manufacturer, they act as a safety measure during installation.

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OBJECTIVES: Multilayer monolithic zirconia (M-Zr) crowns can be engineered to achieve gradational translucency and color intensity. However, this modification may compromise the mechanical strength, raising concerns regarding the ability of M-Zr crowns to withstand occlusal stresses. The effects of M-Zr crown thickness on translucency and ability to endure occlusal forces were investigated at different tooth positions (incisors, premolars, and molars). The objective was to determine the minimal thickness of M-Zr crowns used in tooth preparation to meet aesthetic and functional demands. METHODS: M-Zr samples (Vita A1) with four thicknesses (0.5, 1.0, 1.5, and 2.0 mm) were prepared and subjected to translucency testing using a digital colorimeter by 3-third and 9-square division methods. Crown-shaped M-Zr samples with three thicknesses (1.0, 1.5, and 2.0 mm) and three tooth positions (incisor, premolar, and molar) were digitally designed, and 2.0 mm metal abutments were fabricated. The samples were bonded to the abutments; their fracture characteristics were evaluated using a universal testing machine, and their fracture surfaces examined using an optical microscope. Statistical analyses included the Shapiro-Wilk test, Pearson correlation, and one-way and two-way ANOVA with a post hoc Tukey HSD test (α = 0.05). RESULTS: Color analysis results revealed a significant negative correlation between thickness and translucency (r < -0.96, P < 0.01), with the highest values in the incisal region. Cross-sectional profiles confirmed the uniform thickness and morphology of the digitally designed M-Zr crowns. The results of fracture strength analysis showed position-dependent variability, a strong positive correlation with thickness (r > 0.96, P < 0.01), and fracture strengths consistently exceeding 1200 N across all tooth positions. Fracture patterns indicated that thinner crowns at the incisors and molars were more prone to cracking, whereas those at the premolars demonstrated significantly higher strength (4872.51 N, P < 0.05), only with crack or even no fracture occurring at 2.0 mm. CONCLUSIONS: Thickness significantly influenced both the translucency and fracture strength of M-Zr, with the tooth position playing an additional role, albeit to a lesser extent. Although thinner crowns exhibited lower strength at each tooth position, even at a thickness of 1.0 mm, fracture strength exceeding 1200 N was maintained, surpassing the typical occlusal forces. Thus, it can be asserted that M-Zr crowns with a minimum thickness of 1.0 mm can meet both aesthetic and functional requirements.

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OBJECTIVE: To investigate the effectiveness of the original oblique conformal anastomosis presented in this research in reducing the incidence of cervical anastomotic leak after performing totally minimally invasive esophagectomy (TMIE). METHODS: The esophagus and stomach of 27 fresh pigs, termed the esophagogastric model, were used to simulate human esophagogastric organs for this study's in vitro experimental objectives. Nine esophagogastric models of similar weight were divided into three groups. Esophagogastrostomy with circular-stapled end-to-side anastomosis was performed. A tension gauge was used to pull the anastomosis, and the tension at which anastomotic leakage occurred was recorded. Furthermore, a retrospective assessment of 539 patients who underwent TMIE was conducted to analyze the influencing factors of cervical anastomotic leakage. RESULTS: Experiments on the esophagogastric models showed a higher fracture strength of oblique conformal anastomosis than that of conventional anastomosis (F2,18 = 40.86, P < 0.05), which was associated with a lower incidence of cervical anastomotic leakage (X2 = 9.0260, P = 0.0027). Retrospective analysis of 539 esophageal cancer patients who underwent TMIE showed that in contrast to conventional anastomosis, oblique conformal anastomosis was an independent protective factor against cervical anastomotic leakage (P = 0.0462, OR = 0.5872, 95% CI = 0.3497-0.9993). CONCLUSION: Oblique conformation anastomosis was stronger and involved a more prominent reduced risk of cervical anastomotic leakage than conventional anastomosis after TMIE.

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Background: Scientific literature lacks strong support for using narrow diameter implants (NDI) in high masticatory force areas, especially in molars. Implant splinting in cases of multiple missing teeth reduces lateral forces, improves force distribution, and minimizes stress on implants. However, no studies have evaluated the fatigue load resistance of unitary or splinted implants. Methods: This in vitro study compares five groups of new metal alloy implants, including unitary and splinted implants with varying diameters. Mechanical characterization was assessed using a BIONIX 370 testing machine (MTS, Minneapolis, MN, USA) according to ISO 14801. For each of the five study sample groups, (n = 5) specimens underwent monotonic uniaxial compression at break testing and (n = 15) cyclic loading to determine the maximum force (Fmax) and the fatigue life (LF) values. Scanning electron microscopy (SEM) was employed for the fractographic analysis of the fractured samples. Results: The Fmax values for unitary samples ranged from 196 N to 246 N, whereas the two-splinted samples displayed significantly higher values, ranging from 2439 N to 3796 N. Similarly, the LF values for unitary samples ranged from 118 N to 230 N, while the two-splinted samples exhibited notably higher values, ranging from 488 N to 759 N. Conclusions: The observed resistance difference between sample groups in terms of Fmax and LF may be due to variations in effective cross-sectional area, determined by implant diameter and number. Additionally, this disparity may indicate a potential stiffening effect resulting from the splinting process. These findings have significant implications for dental clinical practice, suggesting the potential use of splinted sets of small-sized NDI as replacements for posterior dentition (premolars and molars) in cases of alveolar bone ridge deficiencies.

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OBJECTIVES: This in vitro study aims to compare the fracture resistance of three CAD/CAM materials used in endocrown restoration of interproximal defects in maxillary premolars. MATERIALS AND METHODS: 45 maxillary premolars extracted as part of orthodontic treatment were included. Following standardized root canal treatment, all teeth were prepared into Mesial-Occlusal (MO) cavity types. The samples were then randomly divided into three groups: LD [repaired with lithium disilicate glass ceramics (IPS e.max CAD)], VE [treated with polymer-infiltrated ceramics (Vita Enamic)], and LU [repaired with resin-based nanoceramics (Lava Ultimate)]. Axial static loading was applied using a universal testing machine at 1 mm/min until fracture, and fracture resistance and failure modes were recorded. RESULTS: Regarding Fracture Resistance Values (FRVs), the LD group exhibited significantly higher values than the other two groups, VE (P = 0.028) and LU (P = 0.005), which showed no significant difference (P = 0.778). On the other hand, regarding failure modes, the LD group had a higher prevalence of irreparable fractures compared to the other two groups, VE (P < 0.001) and LU (P < 0.001), which showed no significant difference. CONCLUSIONS: Although lithium disilicate glass ceramics exhibited higher FRVs, they had a lower repair probability. In contrast, polymer-infiltrated ceramics and resin-based nanoceramics contributed to tooth structure preservation. CLINICAL RELEVANCE: For maxillary premolars with interproximal defects following root canal treatment, resin ceramic composites are recommended for restoration to enhance abutment teeth protection.

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BACKGROUND: Endocrowns (ECs) are alternatives for rebuilding severely damaged teeth and show superior efficacy in molars over premolars. OBJECTIVE: The objective of this in vitro study is to evaluate the effects of different preparation designs with short pulp chambers on the mean color change (Δ⁢E), fracture resistance, and failure types of mandibular molar ECs. METHOD: A total of 40 extracted mandibular molars were treated endodontically and divided into four groups. Samples in groups 1, 2, 3, and 4 had occlusal preparation depths of 5 mm, 3 mm, 3 mm with ferrule, and 3 mm with boxes, respectively. The samples were immersed in coffee and their Δ⁢E values were measured by using the Commission Internationale de l'Eclairage color system. They were also subjected to a fracture test. Next, all specimens were examined visually under a stereomicroscope to evaluate their failure modes and identify their fracture origins. Data were entered and analyzed by using Statistical Package for Social Sciences. RESULTS: Among all groups, group 4 (3 mm + boxes) presented the highest Δ⁢E (4.15) after immersion in coffee. Moreover, ANOVA revealed that the Δ⁢E of group 4 (occlusal preparation depth of 3 mm with boxes) was significantly different (p< 0.05) from that of group 2 (3 mm + ferrule, 3.07). The EC with a 3 mm chamfer and ferrule showed the highest maximum load of 2847.68 ± 693.27 N, whereas that with a 5 mm chamfer finish line had a marginally reduced load at fracture of 2831.52 ± 881.83 N. The EC with a 3 mm chamber and boxes had a slightly increased maximum load of 2700.75 ± 436.40 N, whereas that with the 3 mm chamber had the lowest maximum load at fracture of 2385.97 ± 465.61 N. One-way ANOVA showed that different EC preparation designs had no effect on maximum fracture load (F [3,16] = 0.550, p= 0.6). CONCLUSION: The recorded Δ⁢E values of ECs in all groups were equal or marginally higher than the acceptable values. The EC with a 3 mm chamfer and ferrule displayed the highest mean maximum load. The EC with a 5 mm chamfer finish line had a marginally lower maximum load at fracture than other ECs. Failures, such as ceramic fracture, split fracture, and ceramic and tooth splitting above the cemento-enamel junction (CEJ) or vertically were predominant in samples with occlusal preparation depths of 3 mm with ferrule and 5 mm.

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BACKGROUND: While the concept of angled screw channels has gained popularity, there remains a scarcity of research concerning the torque loss and fracture strength of monolithic zirconia restorations with various screw channel angulations when exposed to thermomechanical cycling. This in-vitro study aimed to evaluate the reverse torque value and fracture resistance of one-piece screw-retained hybrid monolithic zirconia restorations with angulated screw channels after thermomechanical cycling. METHODS: One-piece monolithic zirconia restorations, with angulated screw channels set at 0°, 15°, and 25° (n = 6 per angulation) were fabricated and bonded to titanium inserts using a dual-cure adhesive resin cement. These assemblies were then screwed to implant fixtures embedded in acrylic resin using an omnigrip screwdriver, and reverse torque values were recorded before and after thermomechanical cycles. Additionally, fracture modes were assessed subsequent to the application of compressive load. One-way ANOVA and Bonferroni post hoc test were used to compare the groups (α = 0.05). RESULTS: The study groups were significantly different regarding the fracture resistance (P = 0.0015), but only insignificantly different in the mean percentage torque loss (P = 0.4400). Specifically, the fracture resistance of the 15° group was insignificantly higher compared to the 0° group (P = 0.9037), but significantly higher compared to the 25° group (P = 0.0051). Furthermore, the fracture resistance of the 0° group was significantly higher than that of the 25° group (P = 0.0114). CONCLUSIONS: One-piece hybrid monolithic zirconia restorations with angulated screw channels can be considered an acceptable choice for angulated implants in esthetic areas, providing satisfactory fracture strength and torque loss.

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Limited research is available evaluating whether the reported in vitro benefit of immediate dentin sealing (IDS)-namely, increased bond strength to tooth structure-can be acquired in the era of same-day (SD) dentistry. The purpose of this study was to compare the fracture strengths of ceramic overlays fabricated with a delayed dentin sealing (DDS) technique or an IDS technique under 1-hour SD or 2-week multiple-day (MD) delivery conditions. Forty extracted, healthy maxillary third molars were prepared for a lithium disilicate overlay restoration and divided into 4 groups of 10 teeth each. In the SD-DDS group, the teeth were prepared and then stored for 1 hour in artificial saliva, and the adhesion protocol (bonding agent and resin cement) was applied at the time of delivery of the ceramic overlay. In the SD-IDS group, the teeth were prepared, the adhesive protocol was applied immediately, and the teeth were stored for 1 hour before delivery of the overlay. The protocols for the MD-DDS and MD-IDS groups were identical to SD-DDS and SD-IDS, respectively, except that the teeth were provisionalized and stored for 2 weeks prior to delivery of the overlay. Specimens were thermocycled and subjected to cyclic functional loading before they were loaded to failure in a universal testing machine using a rod resting on the buccal incline of the palatal cusp. Two-way analysis of variance tests revealed no statistically significant differences in fracture strength between the groups based on dentin sealing (P = 0.331) or delivery time (P = 0.314). The specimens demonstrated 2 fracture types; either a portion of the ceramic cohesively fractured, leaving the tooth intact, or the ceramic and part of the tooth fractured. There were no instances in which the restoration itself delaminated during fracture testing. A Kruskal-Wallis test indicated there were no statistically significant differences in fracture modes between the groups. In this in vitro study, IDS did not provide a significant increase in the fracture strength of overlay restorations compared with DDS, regardless of whether the restorations were delivered the same day or after 2 weeks of storage.

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BACKGROUND: Paediatric-preformed zirconia crowns have been associated with several issues, primarily their inability to be crimped and the need for extensive tooth preparation. Additionally, the capacity to adjust the size, shape, and fit of these crowns is very limited. AIM: To evaluate and compare the fracture strength of four different types of dental crowns intended for paediatric patients. DESIGN: The fracture resistance of four types of paediatric crowns was evaluated using the universal testing machine; freshly extracted primary molars received one of the following: preformed zirconia crowns, custom-made computer-aided design and computer-aided manufacturing (CAD-CAM) zirconia crowns, custom-made CAD-CAM ceramic crowns, and custom-made CAD-CAM hybrid composite crowns. Data were statistically compared using the Kruskal-Wallis test followed by the Bonferroni test, and the level of significance was set at 5%. RESULTS: Results showed that there was a statistically significant difference among the four groups (p < .001). The highest value of fracture force was observed for the milled zirconia crown and the lowest for the prefabricated zirconia. CONCLUSION: The implementation of the CAD-CAM digital crown fabrication technique has the potential to address issues associated with preformed crowns in paediatric patients, particularly in terms of fracture resistance.