Lower Fracture Resistance Research Articles

Resistance of Resin-Bonded Ceramic Endocrowns of Different Intracoronal Depths.

This in-vitro study was conducted to assess the fracture resistance of resin-bonded ceramic endocrowns with different designs at varying intracoronal depths. Forty-eight (n = 48) extracted mandibular first molar teeth were randomly divided into four groups (n = 12). In the control group, the specimens remained untreated. Whereas the specimens in the test groups A, B, and C were decapitated 2 mm above the cementoenamel junction (CEJ) and endodontically treated. The test groups were prepared with a butt-joint design in a standardised manner with varying intracoronal depths. Groups A, B, and C were prepared to receive lithium disilicate endocrown with intracoronal cores at 0 mm, 2 mm, and 4 mm, respectively. Crowns were fabricated as a non-anatomical design with a thickness of 3 mm. After ceramic bonding procedures, specimens underwent thermocyclic ageing prior to the fracture resistance test. Specimens were loaded at a 15-degree angle using the Universal Testing Machine and the failure modes were observed. One-way analysis of variance (ANOVA) and Chi-square were utilised for data statistical analyses. Significant statistical results in fracture resistance tests were found in all experimental groups. The highest load was found in group B, followed by group C, and lastly group A (P 0.05). Although endocrowns with no extension had the lowest fracture resistance, they showed a favourable cohesive failure with statistically no significant difference from the control group. In bonded ceramic endocrowns, the fracture resistance is not newcessarily proportional to the intracanal depth. The intrcoronal cores of 4 mm did not show the highest fracture resistance, and their mode of failure was catastrophic compared to endocrowns with no intracoronal extensions.

Understanding the lower fracture resistance of cold sintered ceramics

The cold sintering process (CSP) enables densification of ceramics at unprecedented low temperatures, unlocking unique opportunities in microstructural design. However, the mechanical behaviour of cold sintered ceramics remains unexplored. This study aims to compare the mechanical strength and fracture resistance of cold sintered (140°C) with conventionally sintered (1000°C) ZnO. The effect of grain size is investigated in samples sintered using conventional, cold and rapid sintering. It was found that cold sintered ZnO exhibits ∼50 % lower strength compared to conventionally sintered parts (∼120 vs. ∼240 MPa). This is explained by the lower fracture toughness of the former (0.57 vs. 1.15 MPa·m1/2), resulting from a grain size effect that favours intergranular fracture along nanometric grains. This grain size effect is supported by the higher hardness measured on cold vs. conventionally sintered ZnO (4.5 vs. 1.8 GPa). The lower toughness of cold sintered ceramics is demonstrated to be related to their nanocrystalline nature.

The World's first 3D-printed PEEK cranial implant: a new horizon in precision and personalized neurosurgery.

Cranioplasty is a reconstructive neurosurgical procedure that fixes the cranial bone defects after the craniotomy for brain surgeries like tumours, aneurysms, arterio-venous malformations, subdural empyemas and hematomas. Personalized 3D-printed implants offer various advantages, including anatomical accuracy, functional restoration, time-sparing surgery, excellent cosmetic outcomes through their impeccable adjustment to cranial vault defects, and better clinical outcomes. PEEK has a meritorious profile in terms of high success rate, low complication rate, fracture resistance and low toxicity profile, high strength, high toughness, and excellent biocompatibility in cranioplasty. On the other hand, the need for more cost-effective yet ideal biomaterials must be met for nations and patients with financial constraints. Nevertheless, this additively manufactured 3D-printed cranial implant marks the dawn of a new era in precision and personalized neurosurgery.

Comparison of Peri-Implant Soft Tissue Around Zirconia and Titanium Abutments in the Aesthetic Zone: A Narrative Review.

This narrative review compares the peri-implant soft tissue responses around zirconia and titanium abutments in the aesthetic zone, emphasizing their mechanical, biological, and aesthetic properties. Titanium abutments, known for their excellent mechanical strength and fatigue resistance, have traditionally been the standard in dental restorations but face challenges in aesthetic integration due to their metallic appearance and potential for higher inflammatory responses. Zirconia abutments, emerging as a promising alternative, offer superior aesthetic outcomes, reduced plaque accumulation, and lower inflammatory responses, making them ideal for use in visible areas with thin soft tissue biotypes. However, zirconia's mechanical properties, such as lower fracture resistance, necessitate careful clinical application. The review also highlights rare instances of titanium allergies, underscoring the importance of individualized treatment planning and regular monitoring to ensure the longevity and success of implant restorations.

Conventionally and digitally fabricated removable complete dentures: manufacturing accuracy, fracture resistance and repairability

ObjectivesConventionally and digitally manufactured removable complete dentures with different dentition forms were examined for manufacturing accuracy (trueness, precision), fracture forces under torsional loading and subsequent repairability. MethodsA total of 90 mandibular prostheses were manufactured. Ten were made using the injection molding technique and finished with prefabricated teeth. 40 bases each, were manufactured subtractively and additively. Digitally the prosthesis’ dental arch was divided either into two quadrants or three sextants, or kept as full arch. Afterwards, ten additive and subtractive bases were finished with prefabricated teeth and ten of each with milled quadrants, sextants and full arches. After manufacturing, all specimens were rescanned for accuracy comparisons using the Root Mean Square (RMS). Lastly, all specimens were tested to failure under torsional loading. ResultsConventionally manufactured dentures showed the greatest deviation in accuracy. The type of base manufacturing did not determine the fracture resistance of the prostheses. The dentition form had a significant influence. While prefabricated teeth (86.01 ± 19.76 N) and quadrants (77.89 ± 9.58 N) showed a low fracture resistance, sextants (139.12 ± 21.41 N) and full arches (141.05 ± 17.14 N) achieved the highest fracture forces. Subtractive bases with prefabricated teeth or quadrants were assessed to be repairable, digital dentures with full arch were assessed as not repairable. SignificanceThe presented testing set-up is suitable to determine the fracture behavior of dentures rather than of standards. With the possibility of digital design and individual manufacturing, dentures’ mechanical stability can be significantly increased, especially with suitable dentition forms.

Low cycle fracture resistance of the superalloy at single- and two-frequency modes of loading

Fatigue and long static damages to the majority of high-loaded units develop under repeated stresses and strains of large amplitudes in elastic and elastoplastic regions at a low number of the main cycles and superimposition of dynamic stresses of significantly smaller value with higher frequencies which results in the so-called two-frequency modes of loading. It is shown that in the region of elevated and high temperatures, which determine the manifestation of temperature and time effects in the material, parameters of the rate and duration of deformation which enter the basic equation for determination of the fatigue life through the frequency and time of loading become the most significant parameters determining the fracture process. The results of theoretical and experimental study carried out on nickel superalloy specimens under a hard mode of loading and high temperatures have shown that estimation of the strength and fatigue life in this case for the single-frequency and two-frequency modes of loading can be performed on the basis of the analysis of strain parameters and diagrams of cyclic elastoplastic deformation using the deformation-kinetic criterion of summation of damages accumulated in the material. A decrease in the fatigue life under two-frequency mode of loading and the possibility of estimating it using the specified criterion and corresponding dependences with the introduction of the parameters of frequency/amplitude ratios of the strains (both full and that imposed on the main process) is experimentally proved. The calculated dependences include the parameters of temperature conditions, frequency and duration of loading which allows (when assessing damage from low-frequency and high-frequency components of cyclic strains) taking into account the effects of cyclicity and time of loading, as well as the existence of a variable coefficient of the asymmetry of high-frequency cycles of the two-frequency mode during high-temperature cyclic elastoplastic deformation.

Pre-Sealing of Endodontic Access Cavities for the Preservation of Anterior Teeth Fracture Resistance.

Sodium hypochlorite solution (NaOCl) is an effective canal irrigant but interferes with the mechanical features of dentin and the bonding capability of adhesives when restoring endodontically treated teeth. This study evaluated whether access cavity resin sealing before using canal irrigant would augment the resistance of endodontically treated anterior teeth against fracture. Sixty maxillary incisors underwent endodontic treatment in five groups (n = 12). Irrigation with 5.25% NaOCl and 17% ethylenediaminetetraacetic acid (EDTA) was performed in all groups except for Group 5. After root canal obturation, in Group 1, the access cavity was kept unrestored. In Group 2, immediate restoration after obturation was achieved. For Group 3, delayed restoration after 1 week was provided. In Group 4 (pre-sealed), before canal irrigation, the dentin surface of access cavities was sealed using self-adhesive composite resin (Vertise Flow) and then restored after obturation. In Group 5, which was saline irrigated, immediate restoration was performed. After storage and thermal cycling for 5000 cycles at 5°C-55°C with a dwell time of 15 s and a transfer time of 5 s, teeth were statically loaded by a universal testing machine until a fracture occurred. Data were collected as the fracture resistance (FR) and analyzed using the one-way analysis of variance and Tukey's tests. FR significantly differed between all groups (p < 0.001). The lowest FR was recorded in the unrestored group (284 ± 86 N), which was not statistically different from the immediately restored group (p = 0.065). The pre-sealed group exhibited the highest FR value (810 ± 127 N, p ≤ 0.02 vs. other groups). The FR of the saline-irrigated and delayed restored groups was almost similar (p = 0.13). NaOCl/EDTA irrigation resulted in an adverse effect on FR. Delayed restoration could reduce this adverse effect. Access cavity pre-sealing with flowable composites led to a higher FR than conventional methods and may be considered an effective step during treatment procedures.

Investigation on fracture resistance behaviour of dissimilar metal weld joint of modified 9Cr–1Mo steel and AISI 316LN SS

Fracture behavior of dissimilar metal weld joint consisting of mod. 9Cr–1Mo steel, AISI 316LN stainless steel, Inconel 82 butter layer and Inconel 182 weld has been investigated through experiments and FE simulations. The metallographic studies on weld joint and its interfaces have been carried out to determine the influence of microstructure on tensile and fracture properties. Tensile properties of different weld regions viz., weld metal, butter layer and HAZ have been evaluated using sub-size specimens. Fracture resistance behavior of weld joint has been studied through testing of compact type specimens with initial cracks machined at different locations. The plastic η factors for estimation of J-R curve have been obtained using FE analysis for crack in different regions viz., weld metal, butter layer and HAZ. Crack in weld metal exhibits lower fracture resistance as compared to butter layer and HAZ. Further, the constraint acting on crack and its susceptibility for deviation have been discussed in terms of stress triaxiality ahead of crack tip.

Exploring the impact of thickness, scale and printing sequence on the tensile and fracture properties of PLA specimens fabricated via fused deposition modeling

Geometrical factors play a key role in determining the dimensional accuracy and mechanical properties of additively manufactured components. This research investigates the influence of thickness, scale, and printing sequence on Polylactic Acid (PLA) specimens produced via Fused Deposition Modeling (FDM) with special focus on tensile and fracture properties of the printed parts. The trends of experimental results were then linked to the microstructures and observations on failure mechanisms and the fabrication process conditions. Tensile test results indicate that increasing the build thickness significantly boosts elongation at failure and slightly raises ultimate tensile strength, while downscaling the printed specimens initially causes minor decreases, but further reductions lead to significant drops in mechanical properties due to higher ratio of intrinsic defect to specimen size. Similar to the tensile properties, fracture analyses revealed that larger build thickness and smaller scale of printed parts lead to lower fracture resistance, with an increasing impact by scale reduction, which is attributed to the formation of defects during fabrication and the thermal history of the printed parts. Printing sequence was found to have limited impact on the mechanical performance of the printed parts with effects below 10%. Additionally, a boundary effect model was employed to evaluate fracture behavior of tested specimens, demonstrating its applicability as an engineering tool for fracture prediction of FDM parts with different scales and thicknesses. The findings of this work underscore the importance of considering geometric factors and printing strategies for effective design and failure analysis of additive manufacturing components.

Novel zirconia ceramics for dental implant materials

Ceria-stabilized tetragonal zirconia (Ce-TZP) has become an interesting alternative for the widely used yttria-stabilized zirconia (Y-TZP), whereas efforts are needed to control its microstructure in order to improve the strength of Ce-TZP ceramics. In this work, CaO was used to co-dope Ce-TZP ceramics. More specifically, 0.2–2.0 mol% Ca(NO3)3·4H2O precursor-based CaO was used to dope 10 mol% ceria-stabilized zirconia. Sintering was performed at 1300, 1350, or 1400 °C, which is lower than the temperatures commonly applied for zirconia ceramics. The microstructure and mechanical properties were investigated and correlated, revealing that 0.2 mol% CaO-doped CeO2-stabilised zirconia sintered at 1350 °C exhibited a fully dense fine-grained tetragonal ZrO2 microstructure with high toughness (10.4 MPa m1/2) and biaxial bending strength (1210 ± 43 MPa), and a narrow strength distribution (weibull modulus of 32.5). 1.5 and 2.0 mol% CaO-doping resulted in excellent biaxial bending strength but wider strength distribution and lower fracture resistance. The homogeneously distributed Ca(NO3)3·4H2O precursor prevented cubic zirconia-phase formation for CaO-doping up to 2.0 mol%. CaO-doped (≥ 0.2 mol%) 10Ce-TZP sintered at 1350 °C also highly resisted hydrothermal degradation. Furthermore, CaO-doping enabled to make Ce-TZP ceramics as translucent as different commercially available 3Y-TZP ceramics, opening possibilities to use Ce-TZP for dental restorations.

The Effects of Different Beverages on Fracture Resistance of CAD/CAM Monolithic PEEK and Monolithic Zirconia Crowns

Aim: To assess the impact of various beverages on the fracture resistance of CAD/CAM polyetheretherketone (PEEK) and monolithic zirconia materials. Materials and Method: We fabricated eighty CAD/CAM materials from PEEK polymer (CopraPeek; Whitepeaks Dental Solutions GmbH, Germany) and monolithic zirconia (inCoris TZI; Dentsply Sirona Systems GmbH, Bensheim, Germany), with ten samples per group. These samples were submerged in either distilled water, cola, coffee, or red wine and stored at 37°C for 12 days. We utilized a universal testing machine (Lloyd LRX; Lloyd Instruments Ltd., West Sussex, UK) to measure each sample’s fracture resistance. The t-test provided a comparison of normally distributed variables between the two groups. For multiple group comparisons, we executed an analysis of variance (ANOVA). Results: A statistically significant difference was observed between the PEEK and zirconia groups in terms of maximum load and elastic load-bearing capacity values (p˂0.05), with zirconia materials yielding higher values. However, there was no critical difference in these measures obtained from different solutions for neither PEEK nor zirconia samples (p&gt;0.05). Conclusion: CAD/CAM monolithic PEEK material stored in various solutions demonstrated lower fracture resistance and elastic strength than monolithic zirconia materials. Despite this, PEEK exhibited the highest fracture resistance to intraoral occlusal forces. Accordingly, due to its chemically inert nature and superior force absorption, we recommend PEEK as a viable alternative material for posterior crowns in fixed restorations.

Crack-insensitive fracture of elastomer-based soft network materials under monotonic and cyclic loads

In various applications of stretchable electronics and soft robots, soft materials are subjected to long-term load-bearing conditions, requiring them to possess good extreme mechanical properties such as highly stretchable, strong, fracture-resistant and anti-fatigue. Conventional soft materials with a single polymer network typically exhibit relatively low fracture resistance, while commonly employed toughening method involves introducing mechanical dissipation into original polymer networks often require complicated chemical synthesis and result in significant hysteresis under cyclic loads. Designing soft solid materials into soft network materials with periodic lattice structure paving another effective route to improve the fracture-resistant performance of soft materials, which has not been reported in the literature. This work provides a combined experimental and computational study on the mechanical properties and fracture behaviors of elastomer-based soft network materials with/without a precut crack under monotonic and cyclic loads, aiming to present a structural design strategy for fracture-resistant soft materials. The elastomer-based soft network materials are proven to be crack-insensitive, low-hysteresis and anti-fatigue. The nonlinear finite element analysis (FEA) is employed to reveal the underlying mechanism of crack-insensitivity in elastomer-based soft network materials. Both the mechanical properties and deformed configurations of soft network materials with/without a precut crack are accurately predicted by the FEA method. The effect of microstructure geometry and network topology on the mechanical properties of soft network materials is systematically studied. Under various amplitudes of cyclic applied strain, the elastomer-based soft network materials can survive even after individual microstructures ruptured, and the fatigue fracture process slows down as the applied strain amplitude decreases. In contrast to the behavior observed in monotonic loads where fracture initiates at the microstructure located ahead of the crack tip, fatigue fracture initiation in soft network materials with a precut crack exhibits a random distribution.

Analyzing the Impact of Different Bonding Protocol Strategies to Improve the Fracture Resistance of Uncomplicated Crown Fractures on Tooth Fracture Reattachment in Permanent Anterior Teeth: An In-vitro Study.

Objective This study aims to analyze three different bonding protocol strategies in determining the fracture resistance on the reattachment of fragments in permanent anterior teeth. Methodology This study evaluated the ability of three bonding methods (Group A, total-etch technique; Group B, selective-etch technique; and Group C, self-etch technique) to enhance the fracture resistance of reattached tooth fragments. Sixty permanent maxillary central incisors were chosen, segmented at 3 mm from the incisal edge, and randomly distributed among the three groups. Tooth fragments were stored for 24 hours in GC Tooth Mousse (GC Corporation, Tokyo, Japan), and then reattachment was done using respective bonding techniques. Fracture resistance was gauged using a universal testing machine. Results The mean fracture resistance values were as follows: total-etch (419.5995 N), selective-etch (359.1448 N), and self-etch (192.0887 N). One-way analysis of variance (ANOVA) and post hoc Tukey tests revealed a statistically significant difference between the groups. It was inferred that the total-etch technique exhibited the highest fracture resistance, while the self-etch technique resulted in the lowest fracture resistance (P < 0.05). Conclusions The choice of bonding technique for reattaching tooth fragments should be made based on clinical context and patient needs. Total-etch provided the highest fracture resistance, but selective etch can be preferred for anterior teeth with lower occlusal loads to prevent sensitivity.The self-etch technique may not provide sufficient strength and should be used cautiously. More clinical studies are required to validate these findings and guide clinical decision-making in traumatic dental injury management.

Fracture-Resistant Stretchable Materials: An Overview from Methodology to Applications.

Stretchable materials, such as gels and elastomers, are attractive materials in diverse applications. Their versatile fabrication platforms enable the creation of materials with various physiochemical properties and geometries. However, the mechanical performance of traditional stretchable materials is often hindered by the deficiencies in their energy dissipation system, leading to lower fracture resistance and impeding their broader range of applications. Therefore, the synthesis of fracture-resistant stretchable materials has attracted great interest. This review comprehensively summarizes key design considerations for constructing fracture-resistant stretchable materials, examines their synthesis strategies to achieve elevated fracture energy, and highlights recent advancements in their potential applications.

Effect of long-term aging on the microstructure evolution and fracture mechanism of 9% Cr steels

The fracture toughness of pressure pipe steels is vital for their design and safe operation. Understanding the deterioration of the fracture toughness and the corresponding fracture mechanisms is instructive and meaningful for material selection and development. The elastic–plastic fracture toughness of 9% Cr steels aged at 873 K and 923 K from the initial state to 20000 h was investigated at ambient temperature and 873 K. The deterioration of the fracture toughness and the corresponding fracture mechanisms are discussed in detail. For 9% Cr steels, voids mainly initiated from primary inclusions such as silicides, sulfides, alumina and manganides in as-received state, while voids initiated from both primary inclusions and secondary particles such as the Laves phase after long-term aging. These voids grew and coalesced with neighboring voids and crack tips subsequently until ultimately fracture. After aging at 873 K, the fracture toughness values tested at 873 K decreased from the initial state to 3000 h and then increased to 10000 h. The peculiar deterioration of the fracture properties after 3000 h of aging at 873 K can be attributed to the high number density of Laves phase particles in the steels. It was found that the densely distributed hard Laves phase particles induced strain concentration at the interface between the Laves phase and the matrix under plane-strain tension condition and promoted nucleation of voids. It was suggested that the spatial distribution of the Laves phase played a significant role on the void formation. 9% Cr steels with a denser distribution of Laves phases brings about voids with shorter interspaces, which are more susceptible to coalesce into crack tip, resulting in lower fracture resistance. After aging at 923 K from 10000 h to 20000 h, the number density, size and volume fraction of precipitates, block size, misorientation angle and dislocation density remained almost constant. The slight increase in the fracture toughness from 10000 h to 20000 h can be mainly ascribed to the coarsening of the martensite lath in this stage.

Fracture resistance after root canal filling removal using ProTaper Next, ProTaper Universal Retreatment or hybrid instrumentation: an ex vivo study.

This study evaluated the effect of ProTaper Next (PTN), ProTaper Universal Retreatment (PTR) and hybrid instrumentation (HI) for canal filling removal on the fracture resistance (FR), mode of failure (MoF), and filling removal time. Ninety-six, mandibular premolars were decoronated and randomly divided into 6 groups (n = 16), as follows: sound (S), untreated canals; prepared teeth (P), canals only prepared to ProTaper Universal finishing instrument (F4); endodontically-treated (ET), prepared and obturated canals using the single-cone technique; and groups PTN, PTR, and HI where filling was removed using PTN, PTR, or HI respectively. FR under vertical loading; MoF and time were assessed. Data were analyzed (Significance level [α] = 0.05). There was a significant difference in FR among all groups (p < 0.001) (HI < P < PTN < S < ET < PTR). HI showed lower FR than S, ET and PTR, and P showed lower FR than PTR (p < 0.05). For experimental groups, there was a significant difference between every group pair (p < 0.05) No significant difference was found regarding MoF distribution (p > 0.05). HI required the highest filling removal time, while PTR required the least (p < 0.05 between every group pair). The effect of filling removal on FR may depend on the filling removal technique/system used. PTR could be faster and protect against fracture followed by PTN; HI could adversely affect FR. FR may be associated with filling removal time.

Fracture Resistance of Chairside CAD/CAM Molar Crowns Fabricated with Different Lithium Disilicate Ceramic Materials

To compare the fracture resistance of five different groups of chairside CAD/CAM molar crowns fabricated from various lithium disilicate ceramic materials (LDC): one conventional precrystallized CAD/CAM LDC, two novel precrystallized LDCs, and one fully crystallized LDC tested both with and without optional sintering. A total of 60 chairside CAD/CAM lithium disilicate molar crowns (n = 12 per group) with 1.5-mm occlusal thickness and a 1.0-mm chamfer finish were designed and fabricated with a chairside CAD/CAM system (CEREC, Dentsply Sirona). The restorations were divided into five groups: (1) IPS e.max CAD; (2) Amber Mill; (3) Straumann n!ce; (4) Straumann n!ce with optional sintering; and (5) Supreme CAD. Restorations were cemented using conventional resin luting cement and primer system to 3D-printed resin dies. Bonded restorations were loaded for 100,000 cycles with 275-N force, and the load at break (LB) and peak load (PL) until fracture were measured. SEM images of fracture surfaces on the printed dies were obtained. Fracture resistance was significantly different depending on the material. Supreme CAD showed the highest fracture resistance (LB: 1,557.2 N; PL: 1,785.8 N), followed by Amber Mill (LB: 1,393.0 N; PL: 1,604.2 N) and IPS e.max CAD (LB: 1,315.7 N; PL: 1,461.9 N). Straumann n!ce without (LB: 862.4 N; PL: 942.9 N) and with the optional sintering (LB: 490.4 N; PL: 541.0 N) showed significantly lower fracture resistance than the others. The fracture resistance of chairside CAD/CAM lithium disilicate molar crowns varied depending on the material, and the novel materials did not perform as well as the conventional equivalents. Fully crystallized lithium disilicate ceramic block materials showed lower fracture resistance than precrystallized counterparts and should be used with caution in the clinic, especially with optional sintering.

Fracture resistance and failure mode of endodontically treated premolars reconstructed by different preparation approaches: Cervical margin relocation and crown lengthening with complete and partial ferrule with three different post and core systems.

To assess the fracture resistance and failure mode of endodontically treated premolars reconstructed by different preparation approaches: cervical margin relocation (CMR) and crown lengthening (CL) with complete ferrule (CLF) and partial ferrule (CLPF) with three different post and core systems. In this in vitro study, 100 maxillary premolars were assigned to the following 10 groups according to their preparation approach and type of post and core system (n = 10): (I) control (intact teeth), (II) prefabricated fiber post (PFP) and composite core with CMR (PFP-CMR), (III) polyethylene fiber-reinforced composite (PEFRC) with CMR (PEFRC-CMR), (IV) casting post (CP) and core with CMR (CP-CMR), (V) PFP-CLPF, (VI) PEFRC-CLPF, (VII) CP-CLPF, (VIII) PFP-CLF, (IX) PEFRC-CLF, and (X) CP-CLF. After thermomechanical loading, the fracture resistance and failure mode were assessed. Data were analyzed statistically (α = 0.05). In all post and core systems, the CLPF approach had lower fracture resistance than CMR (p<0.05); CLF showed higher fracture resistance than CLPF only in the PFP system (p = 0.038). In PEFRC and CP systems, the difference between CLF and CLPF was not significant (p > 0.05). No significant difference was found in fracture resistance of different post and core systems with the same preparation approach (p > 0.05). CLPF showed the highest frequency of favorable, and CLF showed the highest frequency of unfavorable fractures. CLPF yielded lower fracture resistance than CMR. The difference in fracture resistance was not significant between CLF and CMR but the frequency of unfavorable fractures was higher in CLF than in other groups.

Effect on the Fracture Resistance of Monolithic Zirconia Custom Abutment in Different Angulation: An In Vitro Study

The study was designed to find out the effect of different angulations of monolithic Zirconia custom-made abutments on fracture resistance. In this experimental type in vitro study, a total of thirty implant analogs with a diameter of 4.3 mm and a length of 11.5 mm were obtained for the maxillary central incisor. A total of thirty abutments specimens in three groups- 0-degree, 15-degree, and 25-degree, ten in each group were fabricated with monolithic zirconium by CAD/CAM system. Each abutment was subjected to load until fracture in a Universal testing machine and data was collected to a data collection sheet. One-way ANOVA was done to compare the fracture load among the three groups and pairwise comparison was done by Tukey post hoc test. The statistical significance p-value was considered as less than 0.05. The range of fracture load of 0-degree, 15-degree, and 25-degree angulated abutments were 590.55-1305.43N, 755.89-1720.55N, and 496.68-820.88N respectively. The highest fracture resistance was shown in 15-degree angulated custom-made zirconium abutments with a mean ± SD of 1223.442 ± 317.771N and the lowest fracture resistance was shown in case 25-degree with a mean ± SD deviation of 653.139 ± 102.045N. The mean ± SD of the 0-degree abutment was 948.944±245.588N. 95% Confidence interval of the mean were 773.260-1124.627N, 996.122-1450.761N, and 580.140-726.137N were assessed in cases of 0-degree, 15-degree, and 25-degree respectively. The fracture load or fracture resistance among the three groups of custom-made monolithic zirconium abutments were significantly different. 15-degree angulated abutment had higher fracture resistance properties. straight abutment had more fracture resistance properties than that of 25-degree abutments, but less than 25-degree abutments.

Effect of Root Canal Taper on the Ability of Endodontically Treated Teeth using the TruNatomy and Protaper Next File Systems to Resist Fracture.

This research was done to evaluate how the root canal taper affects the Endodontically Treated Teeth (ETT) prepared with the TruNatomy and Protaper Next file systems in terms of fracture resistance. Forty recently extracted mandibular premolar teeth were used in this research, which was classified into four groups at random. Groups 1a and 1b used TruNatomy 4% and 6%, respectively, while groups 2a and 2b used the Protaper Next 4% and 6% file systems, respectively. The root canals were cleaned, shaped, and sealed using cold lateral compaction. The root canals were then fixed in standardized autopolymerizing acrylic resin blocks and tested for vertical root fracture using a universal testing machine. Newtons were used to measure the forces needed to cause fractures. Data were statistically analyzed. In comparison with other groups, group 1a (TruNatomy 4%) displayed greater fracture resistance (423.322.43 Newtons), and group 2b (Protaper Next 6%) displayed the least fracture resistance (264.512.76 Newtons). Protaper Next file system had lower fracture resistance than TruNatomy file system. With the use of greater taper instruments, a notable decrease in the fracture resistance of ETT was observed.