Testing Machine Research Articles

Comparative evaluation of fracture resistance of wide and flared endodontically treated teeth with new techniques of postplacement – An in vitro study

Aim: This study aims to compare and evaluate the fracture resistance of endodontically treated maxillary anterior teeth restored using new postplacement techniques. Methodology: Forty-five single-rooted maxillary anterior teeth (n = 15) were selected and decoronated at the cementoenamel junction. The working length was determined using a 15K file. Biomechanical preparation was done up to size 70 and the teeth were obturated. After 1 week, the root-filling material, gutta-percha, was removed, and postspace was prepared using a size 3 and 4 peeso reamer. The samples were divided into three groups (n = 15). Group I: Coltene Tenax fiber Post-reinforced with composite (anatomical post). Group II: Coltene Tenax fiber postreinforced with a leno-woven polyethylene; Ribbond fibers. Group III: Coltene Tenax fiber Post-luted with a dual cure cement. After postcementation, core buildup was done. Fracture resistance was measured using a universal testing machine. Results: Statistical analysis was done using one-way analysis of variance and Tukey’s post hoc tests. A statistically significant difference was seen in the mean maximum load (N) between the groups. Group I showed the highest mean maximum load (N), followed by Group II and Group III. A significant P value (P = 0.025) was noted. Conclusion: Coltene Tenax fiber postreinforced with composite (anatomical post) showed the highest fracture resistance in endodontically treated maxillary anteriors.

A comparative evaluation of the effect of matrix metalloproteinase inhibitor on the fracture resistance of endodontically treated teeth restored with Everstick-reinforced composite resin: An in vitro study

Aim: To evaluate the effect of applying a matrix metalloproteinase (MMP) inhibitor on the fracture resistance of root-filled teeth restored with Everstick fiber-reinforced composite resin. Subjects and Methods: After the selection of 60 freshly extracted human mandibular first molar, root canal access and standard uniformly sized mesio-occluso-distal (MOD) cavities were made and the teeth were randomly assigned into three groups (n = 20 each): Group I, the MOD cavity was first lined with flowable composite resin and then restored with composite resin. In Group II, Everstick fiber was placed into the bed of flowable composite in buccal–pulpal–lingual direction before the composite restoration was placed. In Group III, after etching of the cavity, a 2% chlorhexidine MMP inhibitor was applied. Then, the MOD cavity was restored same as group II. A universal testing machine was employed to compressively load the teeth at a cross-head speed of 0.5 mm/min till fracture. The maximum fracture loads were recorded in Newtons (N) and data were analyzed with one-way ANOVA and post-hoc Tukey tests. Results: Group III exhibited significantly higher fracture resistance compared to all other groups (P < 0.001), whereas Group I demonstrated the lowest fracture resistance. Conclusion: The utilization of Everstick glass fiber, combined with MMP inhibitor treatment, yielded the greatest fracture resistance. Hence, this method may be prioritized over conventional restoration techniques for strengthening root canal-treated teeth with structurally compromised crowns.

Investigation of fracture resistance with different diameters of polyetherketoneketone posts and cores material: A pilot study

Objectives: The primary objective of this study is to investigate the resistance to fracture of Polyetherketoneketones PEKK, used as post and core by fabrication in different diameters in the canal, and comparing the test results for each group. Methods: Thirty extracted mandibular premolars were selected, endodontically treated and prepared to receive the post and cores milled from polyetherketoneketone disk. The specimens were randomly divided into five groups (n = 6) respectively: group 1 received pekk post with diameter = 0.70 mm, group 2 received pekk post with diameter = 0.90 mm, group 3 received pekk post with diameter = 1.10 mm, group 4 received pekk post with diameter = 1.50 mm, and group 5 received pekk post with diameter = 1.70 mm. All the posts were cemented using a self-adhesive resin cement. Fracture resistance was tested using a universal testing machine, failure patterns were then observed visually and radiographically. For the fracture resistance test, the Universal Testing machine employed the load cell of 10KN and the speed of the cross head of 1mm/min. Data was analyzed using Oneway analysis of variance (ANOVA) followed by Tukey post-hoc test in order to determine significant differences among groups and the materiality threshold was set at α = 0.05. Results: Statistical analysis revealed that the observed differences among the five groups were not significant. None of the PEKK posts caused any fracture in the root, and this observation was visually and radiographically confirmed across all groups. Conclusions: The dentist will be able to turn the diameter of the PEKK post and core as thin as 0.70mm till 1.70mm depending on the clinical requirement with no risk of root fracture, as specified by the guidelines of this research.

Effect of heat treatment process on microstructure and properties of copper modified 1Cr11MoNiW1VNbN

Abstract The purpose of this study was to investigate the effects of Cu element content and heat treatment process on the microstructure and mechanical properties of 1Cr11MoNiW1VNbN martensitic heat-resistant steel. Microstructure was characterized by optical microscope (OM) and scanning electron microscope (SEM), tensile testing machine and impact testing machine were used to test the mechanical property. The results show that with the increase of Cu content, the precipitation of Cu-rich phase in the steel increases, while the formation of δ-ferrite and coarse carbides decreases, which significantly improves the strength of the material. When the Cu content is 2.14%, the tensile strength at 600 °C reached 542 MPa and the yield strength reached 484 MPa after normalizing at 1000 °C and tempering at 700 °C. With the increase of the normalizing temperature, the strength of the test steel decreases slightly, and the impact energy improved significantly.

Experimental Investigation The Effect of Bamboo Micro Filler on Performance of Bamboo-Sisal-E-Glass Fiber-Reinforced Epoxy Matrix Hybrid Composites

The numerous advantages of natural fiber reinforced hybrid composites, such as their light weight, biodegradability, recyclability, availability, and low cost, have brought them to the forefront for various structural applications in the automotive and aerospace industries. Aim of this study was to evaluate the impact of varying the weight fractions of bamboo micro filler on the tensile, flexural, impact, and water absorption properties of the Sisal-Bamboo-E-glass fiber reinforced epoxy matrix hybrid composite prepared by manual hand layup method. To enhance the bond between natural and synthetic fibers and reduce the hydrophilic nature of natural fibers, bamboo and sisal fibers were treated with 5% NaOH for 6 and 8 hours, respectively. The E-glass fiber content was kept constant at 10%, while the weight fractions of sisal, bamboo fiber, epoxy matrix, and bamboo micro filler were varied. The bamboo micro filler size ranged from 75 to 100 μm. Tensile and flexural tests were conducted using a computer-controlled universal electromechanical testing machine, while impact testing was performed with a Charpy impact test machine. The results showed that the hybrid composite containing 15% sisal, 10% glass, 15% bamboo fiber, 57% epoxy, and 3% bamboo micro filler exhibited the highest tensile strength (87 MPa),flexural strength (77 MPa), high impact energy (8.9 J) and high toughness (24.64 J/cm2). Conversely, the highest water absorption capacity was observed in composites with 6% bamboo micro filler. Overall, the tensile, flexural, impact, and water absorption properties of the hybrid composites were significantly influenced by the weight fractions of the fibers and bamboo micro filler.

Reuse of polyvinyl chloride residues—in powder and fiber forms—as potential components for green mortar pavers

Plastic wastes are considered a significant environmental pollution load because of their mostly non-biodegradable nature. Consequently, the need to lessen the environmental impact calls for employing eco-friendly strategies such as reusing materials in construction. The objective of this study is to analyze the mechanical behavior and environmental impacts of mortar elements, with a specific focus on pavers, by incorporating waste polyvinyl chloride (WPVC) as aggregate and partially replacing cement. Two distinct forms of this waste were considered in the investigation: (i) as it is generated in industrial processes, mainly in fiber form, WPVCf, and in the form of powder obtained by sieving the former, WPVCp. The ratio of conventional mortar materials replaced by WPVC and the final water-to-binder ratio changed based on waste type and mix workability. The experimental work involved preparing 84 pavers, each measuring 100 mm × 150 mm × 60 mm. For each type of paver, 12 samples were prepared, ensuring a minimum of 4 sets of test data for each curing period (7, 14, and 28 days). Flexural strength tests, conducted in accordance with the Colombian standard NTC 2017, utilized a standard flexural test machine with a 150 kN capacity. A specially designed steel tool applied a point load at the center of each paving block, maintaining a minimum distance of 10 millimeters from the edges. The findings demonstrated that pavers containing fiber plastic waste exhibited the requisite strength for paved walkways, even in the short term, when the weight ratio of WPVCf to sand (WPVCf/S) was 24 %. These results derive an eco-friendly solution for reusing PVC wastes currently deposited directly in landfills. Moreover, to analyze the environmental impacts of this solution, a Life Cycle Assessment (LCA) analysis was carried out in this research. The LCA results pointed out that dosing with a WPVCf/S ratio of 24 % emerges as the most ecologically responsible, manifesting substantial reductions across impact categories, such as a significant 23 % decrease in climate change, a 23 % reduction in Photochemical ozone formation, and a 22 % reduction in renewable energy consumption. This underscores the potential of WPVCf incorporation as a consequential step toward eco-friendly construction materials. Furthermore, this solution not only translates to diminished paving block costs by requiring less fine aggregate and cement but also contributes to reduced transportation expenses owing to the decreased weight of the pavers.

Tempering behavior and mechanical properties of tempered AISI H13 steel

Abstract Microstructural evolutions of AISI H13 steel during tempering were quantitatively investigated by scanning electron microscopy (SEM), x-ray diffractometer (XRD), impact test machine, rockwell hardness tester, ball-on-disk tester in order to describe the main mechanism of softening. Under the condition that the tempering time is 2 h, the hardness increases slightly as the tempering temperature increases, but decreases rapidly when the tempering temperature exceeds 500 °C, while the impact energy increases in proportion to the tempering temperature. Friction tests were conducted in dry condition with a load of 30 N, and the friction coefficient and wear rate according to tempering conditions were measured to prove the correlation with hardness and microstructure. In addition, primary tempering from 300 °C to 700 °C was performed at various times to establish a kinetic model to predict hardness under specific tempering conditions.

Experimental and Statistical Investigations for Tensile Properties of Hemp Fibers

This study investigated the tensile behaviors of hemp fiber bundles and examined how properties including tensile strength and Young’s modulus vary with the bundle diameter. Hemp fibers were extracted, degummed, and separated into bundles of different diameters ranging from less than 50 μm to over 150 μm. Tensile tests were conducted on these fiber bundles using a rheometer-based tensile testing machine. The results showed that hemp fibers exhibited a tensile strength of 97.33 MPa and a Young’s modulus of 3.77 GPa at a 50% survival probability. However, the scale parameters for breaking stress and Young’s modulus were determined to be 620.57 MPa and 29.88 GPa, respectively. As the fiber bundle diameter increased, the tensile strength decreased significantly. This was attributed to the higher probability of defects and irregularities acting as weakness points in larger fiber bundles. In contrast, Young’s modulus (stiffness) increased with increasing bundle diameter, likely due to improved fiber–fiber interactions. To further understand the variability and reliability of the tensile properties, statistical models were developed. The Weibull distribution analysis was applied, revealing critical insights into the variability of diameter, stress at break, Young’s modulus, and strain at break. The Weibull parameters provided a comprehensive understanding of the fibers’ mechanical reliability. Additionally, the Griffith model was employed to predict the strength and Young’s modulus based on fiber diameters, supporting the observation that thinner fibers generally exhibited higher tensile strength due to fewer defects. Overall, this work highlights the importance of understanding structure–property relationships in natural fibers like hemp for optimizing their performance in composites.

Enhancing dry sliding wear resistance of high-Mn austenitic steel by adding N

In this study, the wear resistance of two high-Mn austenitic steels, i.e., Fe−18.5Mn−7Cr−0.6C and Fe−18.5Mn−7Cr−0.6C−0.21N was tested in dry sliding friction on a disc friction and wear testing machine (MMU-5G). The wear behavior and microstructure evolution of the two tested steels were investigated. The results revealed that adding N enhanced the wear resistance of high-Mn austenitic steel due to the synergistic effects of hardness, wear hardening, and oxide layer. Interstitial N atoms increased the matrix hardness and decreased the stacking fault energy (SFE). The lower SFE facilitated wear hardening, and the active mechanical twins along with the higher dislocation density induced the formation of a thicker nanocrystalline layer with finer grains. The nanocrystalline layer with higher surface activity promoted the adsorption of a protective oxide layer. These factors decreased the surface roughness, coefficient of friction (COF), and wear rate of N-alloyed high-Mn austenitic steel. This study provided valuable insights into the application of N-alloyed high-Mn austenitic steels under dry sliding friction conditions.

Evaluation of microtensile bond strength and marginal adaptation of fiber-reinforced composites

Background: Long-term durability of a restoration relies on the marginal integrity and its ability to withstand the occlusal forces. Fiber-reinforced composites (FRCs) exhibited superior properties in terms of fracture toughness, flexural strength, and wear resistance. Aim: The aim of this study was to assess and compare marginal adaptation and microtensile bond strength (µTBS) of posterior FRCs comparing with a condensable composite. Materials and Methods: Standardized mesio- and disto-occlusal cavities were prepared on 60 maxillary molars with 3.5 mm pulpal floor depth, 3 mm buccolingual width, and 1.5 mm axial depth. The mesial cavities were restored with everX Posterior and Build-It FRCs, while distal cavities of all teeth were restored with Alert composite and were thermomechanically aged. Half of the specimens from each group (n = 15) were evaluated for marginal adaptation under scanning electron microscope (SEM), and the other half were sectioned for μTBS testing with Instron testing machine. Bond failure mode was examined under SEM. Results: Marginal microgaps were significantly high for the Alert group than FRC groups. Gingival surface showed more gaps. Mean µTBS values were significantly high for FRCs. Cohesive failures are more among FRCs, and adhesive failures are more in condensable composite. Conclusion: The short FRCs showed superior marginal adaptation and better bond strength than condensable composite.

Experimental study of polyurethane rubber with half-sine waveform generator

Abstract Impact mechanics environmental testing technology is booming. Polyurethane rubber, as a typical semi-sinusoidal waveform generator, is particularly important to understand its stiffness performance. This paper presents an experimental investigation utilizing a pneumatic impact testing machine to evaluate the performance of polyurethane rubber waveform generators, varying in both hardness and height. By recording their compression under varying impact pressures, as well as the rebound height of the table and the corresponding velocity changes, we observed that the data generated by the 60mm thick waveform generator exhibited greater regularity. Notably, these data adhered to the principle that increased hardness correlates with decreased compression and reduced rebound height of the table. Additionally, we successfully designed an initial prototype of a rebound collision acceleration amplifier, which, under an impact pressure of merely 0.038MPa, achieved an impressive impact acceleration of nearly 2700g, accompanied by a smoother half-sine waveform curve.

Characterization of UF-18 cacao pods using Arduino-based load compressor testing machine

Characterization of UF-18 cacao pods using Arduino-based load compressor testing machine

Experimental Study on the Crushing Strength of Diamond Grains

This study investigates the crushing strength of single diamond grains of varying grades and particle sizes using the WDW-100 electronic universal testing machine. The research aims to understand the mechanical properties of diamond particles, which are critical for optimizing the performance of diamond tools in industrial grinding processes. High-grade diamond particles, characterized by their regular polyhedral shapes and minimal impurities, exhibit higher and more stable maximum load forces compared to medium- and low-grade particles. Medium-grade particles show a balance between strength and brittleness, while low-grade particles display significant variability in their structural integrity due to higher impurity levels and defects. The study also reveals that larger diamond particles tend to have lower average maximum load forces, attributed to increased crystal defects and pronounced grain boundary effects. These findings underscore the importance of considering both the grade and particle size of diamond grains in applications requiring high mechanical strength. The insights gained from this research are essential for improving the design and durability of diamond tools, ensuring their efficiency and longevity in industrial applications.

INFLUENCE OF FILLER SIZE ON THE STRUCTURE AND PROPERTIES OF THE POLYMER MATRIX

Purpose. The aim of the study is to investigate the influence of aluminum oxide (Al2O3) particle size on the mechanical properties of a polymer composite with added chopped glass fiber, as well as to explore the interaction between aluminum oxide particles and chopped glass fiber. Research methods. Specimens were tested for tensile strength according to DSTU EN ISO 527-5:2018. Testing was conducted using an MTS Criterion Model 43 universal testing machine with a maximum load of 50 kN. Metallographic analysis was performed using a KEYENCE VHX microscope at magnifications of 50× and 500×. The microstructure of the polymer matrix was determined on unetched samples. Scanning electron microscopy was carried out using a JEOL JSM-5510LV microscope. Results. The influence of introducing different sizes of aluminum oxide fraction on the polymer matrix was studied. It was found that with an increase in the fraction size, the strength of the polymer composition decreases. Additionally, the interaction between chopped glass fiber and various fractions of aluminum oxide on the mechanical characteristics and morphology of the connection with the polymer composition was investigated. Scientific novelty. The interaction of chopped fiber with aluminum oxide fractions may affect the mechanical properties of the composite, such as strength, stiffness, and elasticity. Investigation of the morphology of the connection between chopped fiber and aluminum oxide fractions can help understand how they interact within the composite structure. This includes analyzing the adhesion between components, the structure of junctions, and possible defects that may arise during the manufacturing process. Studying this interaction opens up opportunities for the development of new composite materials with improved properties and diverse applications in industry, construction, aviation, automotive, and other fields. Practical value. The practical significance lies in refining manufacturing technologies and implementing new materials in industry. The ability to control the mechanical properties of composites by changing the size of aluminum oxide fractions can contribute to the creation of more efficient materials for the production of automobiles, aircraft, building constructions, and more. Additionally, understanding the interaction between chopped glass fiber and aluminum oxide fractions may open up new possibilities for developing composites with unique mechanical characteristics that meet the requirements of modern technologies and industrial production.

Evaluating mechanical performance of coconut fibre reinforced polymer composites with variable fibre content

The rapid growth of composite materials, leveraging natural ingredients such as dried fruit, rice husk, wheat husk, straw, and hemp fibres, has expanded their applications and market presence. Among these, coconut fibre stands out due to its high tensile strength, making it a promising reinforcement for polymer composites. However, increasing the coconut fibre content can reduce the cohesion and some properties of the composites. This study investigates the impact of the weight percentage of coconut fibres on the mechanical properties of coconut fibre-reinforced composites. Various composites were prepared with different weight percentages of coconut fibre, and their mechanical properties were evaluated using tensile tests with a Universal Testing Machine Instron 8872 and hardness tests with a Digital Shore Scale “D” Durometer. The results indicate significant changes in tensile strength, tensile strain, and hardness corresponding to the weight percentage of coconut fibre. This research highlights the importance of optimizing fibre content to achieve balanced mechanical properties in coconut fibre-reinforced composites.

OPTIMIZATION OF HEAT TREATMENT REGIME FOR A NEW BIODEGRADABLE Mg-Zr-Nd ALLOY WITH ENHANCED MECHANICAL PROPERTIES

Purpose. To develop a rational heat treatment regime for a new biodegradable magnesium alloy of the Mg-Zr-Nd system, to ensure enhanced mechanical properties throughout the entire treatment period. Research methods. Differential thermal analysis (DTA) was used to determine phase transformation temperatures. Microstructure analysis was conducted using optical microscopy (“Neophot 32” and “OLYMPUS IX 70”) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SELMI RЕМ-106I). Mechanical properties were determined using an INSTRON 2801 testing machine. The influence of cooling rate on microstructure and properties was studied using ProCAST simulation software. Heat treatment was carried out in a Bellevue type shaft furnace and a PAP-4M furnace. X-ray analysis was used to detect internal defects in samples. Results. A new heat treatment regime was developed for the biodegradable Mg-3.15Nd-1.25Zr-0.6Zn (wt%) alloy. Using differential thermal analysis and microstructure studies at various quenching temperatures, the optimal quenching temperature was established at 560 °C. Empirical relationships describing the influence of heat treatment parameters on the alloy's microstructure were calculated. The new heat treatment regime (quenching from 560 °C for 8 hours, air cooling + aging at 200 °C for 16 hours) resulted in improved mechanical properties (UTS = 276–282 MPa, δ = 5.2–5.8%) compared to the standard T6 regime. Scientific novelty. For the first time, a comprehensive study of the influence of heat treatment parameters on the structure and properties of a new Mg-3.15Nd-1.25Zr-0.6Zn (wt%) alloy with increased content of alloying elements was conducted. New dependencies describing the influence of quenching temperature on the alloy's grain size were established. Practical value. A new heat treatment regime for the biodegradable magnesium alloy was developed, which ensures complete dissolution of the pseudoeutectic phase and formation of strengthening phases, resulting in improved mechanical properties compared to the standard alloy Mg-2.5Nd-0.4Zn-0.5Zr (wt%) and the standard T6 regime.

Effect of Sandstone Pore Morphology on Mechanics, Acoustic Emission, and Energy Evolution

Roadway section form is an important part of the underground engineering structure, and it directly affects the overall stability of the roadway and the occurrence of underground disasters in coal mines. Based on this, this paper adopts a TYJ-500 electro-hydraulic servo rock shear rheology testing machine to conduct a uniaxial compression test on sandstone containing different prefabricated hole section morphology and analyzes the damage characteristics seen during the damage evolution process, with the help of a high-speed camera and acoustic emission monitoring equipment. The test results show that the pore morphology is the main factor affecting the mechanical parameters of sandstone, and the peak stress and elastic modulus of sandstone with pore sections have the characteristics of increasing and decreasing at the same time, except for the intact rock samples. The pore morphology exhibits central symmetry (circular holes and rectangular holes) damage, more pressure-shear cracks and shear cracks, and the acoustic emission characteristics of high-energy–low-amplitude–low-count of the “two low-trend and one high-trend characteristic curves” attributes; moreover, due to the special existence of its pore morphology, it leads to the rock samples having less energy accumulation and release. The axisymmetric hole types (trapezoidal holes and straight-wall domed holes) are damaged by tensile cracks and shear cracks, and their acoustic emission characteristics show the characteristic properties of “three high-trend characteristic curves” of high-energy–high-amplitude–high-count, and there is a strong elastic energy accumulation and output. The conclusions of this article can provide a certain theoretical basis for the design of coal mine roadway sections in underground structures, failure analysis, and stability evaluation of roadway structures.

Harnessing Limestone powder to enhance the thermal crack resistance of manufactured sand.

Manufactured sand concrete (MSC) has increasingly applied in engineering. However, how to enhance the thermal crack resistance of MSC has not clearly studied yet, which limits the wide applications of manufactured sand in engineering. We have adopted the method of mixing limestone powder (LP) to make MSC with four mass fractions (wt.%) of 5%, 10%, 15%, and 20% of LP content, designed the mix proportion of concrete, tested their mechanical properties, observed their microstructure by scanning electron microscopy (SEM) and investigated the effect of LP on anti-cracking performance using temperature stress testing machine (TSTM). These findings reveal that the mechanical properties and thermal crack resistance of 15% LP MSC are the best. Our results also provide a research basis for the MSC to be widely used in engineering.

Effect of thermocycling on flexural strength of dental CAD/CAM ceramics of variable thicknesses and structures: an in vitro study

Background This study examined the effect of thermocycling on the flexural strength properties of four CAD/CAM ceramic materials at different thicknesses. Methods Four CAD/CAM ceramics of different types: advanced lithium disilicate (ALD), zirconia-reinforced lithium silicate (ZLS) lithium disilicate (LD), and leucite reinforced (LE), and at three varying thicknesses 0.5, 1.0 and 1.5 mm were examined. After subjecting all specimens to 5000 thermomechanical cycles, flexural strength was determined using a universal testing apparatus. Scanning electron microscopy (SEM) was employed for analysis. Two factorial ANOVA models assessed the association of different factors (ceramic type and thickness) with flexural strength and elastic modulus. The 95% confidence intervals (CIs) and adjusted means were computed. A p-value < 0.05 was designated significant. Results ZLS exhibited the highest flexural strength at 1.5 mm thickness, while LD showed the highest Young’s modulus of elasticity. The lowest flexural strength was observed in the 0.5 mm thickness group. There were notable variations in flexural strength across all ceramic materials, with the highest adjusted mean strength in the ZLS group, ALD, LD, and LE, respectively. Additionally, significant differences were noted in ceramic thickness, with 1.5 mm thickness showing the highest strength and 0.5 mm thickness the lowest. Conclusions Ceramic material thickness significantly impacts flexural strength, with 1.5 mm thickness deemed suitable for posterior restorations. Ceramic materials with zirconia fillers or matrix demonstrated higher flexural strength than other ceramics.

The Influence of Different Pontic Designs on Fracture Resistance of Implant-supported Fixed Partial Dentures Anchored in Polyurethane Simulating Bone-blocks of Two Different Densities: An In Vitro Study.

This study aimed to evaluate the fracture resistance of implant-supported fixed partial prostheses fabricated from monolithic zirconia with different pontic framework designs and anchored in different bone-like simulation models of two different densities. A total of 60 implants were anchored in two different in vitro bone simulation models of two different densities, namely, solid polyurethane foam blocks, 20 and 10 pounds per cubic foot (PCF) to construct implant-supported fixed partial dentures (FPDs), the pontic constructed to replace missing second premolar and first molar. Thirty models were constructed and then divided into two groups according to anchoring material D2 (n = 15) and D3 (n = 15). Each group of models was subdivided into three groups according to pontic design (n = 5). Each model was tested against fracture in a universal testing machine. The data were analyzed with a two-way univariate ANOVA and Tukey HSD test (α = 0.05). The results were statistically analyzed, and the values were considered significant at p≤0.05. The findings showed that neither change in pontic design nor change in bone type has a significant influence on the fracture resistance of the prostheses (p > 0.05). All the tested materials fell within the acceptable range for functioning under mastication, with a slight change in resistance when the pontic design was changed. Zirconia is considered the material of choice when planning implant-supported FPDs because of its high fracture strength values. Within the limitations of this study, the pontic design and synthetic polyurethane bone-simulating model had no effect on the fracture resistance of four-unit implant-supported FPDs. This study postulated that any pontic design could be used in four units of implant-supported FPDs according to functional and aesthetic needs, as long as the histological nature of the alveolar bone falls within the D2 or D3 bone type. How to cite this article: Othman MS, Abu-Eittah MRH. The Influence of Different Pontic Designs on Fracture Resistance of Implant-supported Fixed Partial Dentures Anchored in Polyurethane Simulating Bone-blocks of Two Different Densities: An In Vitro Study. J Contemp Dent Pract 2024;25(7):684-690.