Significant Difference In Flexural Strength Research Articles

Strong and densified 3D metal-ceramic composite with strengthened layer structure by material extrusion additive manufacturing

Material extrusion (MEX) of high-filled polymers with metal or ceramic powders has showed great potential in fabricating 3D structure combined via the powder metallurgy route. However, defects between deposited layers adversely affect the final performance of 3D components. Here, we introduced a high-flow filling approach based on effective viscosity control and optimized printing strategies for preparing high-density NiFe2O4-based cermet. We investigated the influence of powder loading and filling paths on both green and sintered samples regarding density, microstructure and mechanical properties. Polyformaldehyde (POM)-based feedstocks were developed with powder loading of 62 vol% and 56 vol%. 3D cermet with high powder loading demonstrated good shape retention but contained periodic pores due to low-flow filling between adjacent filament. Cermets with high relative density were achieved using 56 vol% POM-based feedstock because of satisfactory fluidity and high-filling effect during deposition. Filling paths determined the distribution and size of the pores, with cermet based on the (45°, 135°) trace exhibiting the most uniform and dense structure. Cermets using 62 vol% feedstock showed significant differences in flexural strength depending on the filling path, much lower than those achieved with the high-flow filling approach. Finally, 3D NiFe2O4-based cermets utilizing 56 vol% feedstock demonstrated an optimal average flexural strength of 173.5 MPa, close to 178.4 MPa of conventional injection molded samples. Hence, high-qualified metal-ceramic composites can be fabricated using MEX via the high-flow filling approach, with potential applications in complex-shaped anode, cutting tools and wear-resistant parts.

The Effect of Sintering on Zirconia Manufactured via Suspension-Enclosing Projection Stereolithography for Dental Applications: An In Vitro Study.

Zirconia is a widely used material in the dental industry due to its excellent mechanical and aesthetic properties. Recently, a new 3D printing process called suspension-enclosing projection stereolithography (SEPS) was introduced to fabricate zirconia dental restorations. However, the effect of the sintering time and temperature on the properties of zirconia produced via SEPS has not been fully investigated. Zirconia slurries were prepared with varying percentages of zirconia powders and 3D printing resins, and 5Y-TZP (5 mol% yttria-stabilized zirconia) (n = 40) and 3Y-TZP (3 mol% yttria-stabilized zirconia) (n = 40) bar specimens were fabricated via SEPS manufacturing. The specimens were sintered at different temperatures and dwell times, and their flexural strength, density, and phase composition were measured. The viscosity of the slurries was also measured. Statistical analysis was performed using Welch's ANOVA and Kruskal-Wallis tests to evaluate the impact of the sintering conditions. Significant differences in flexural strength (p < 0.01) were observed between the 5Y-TZP samples, with those sintered at 1530 °C for 120 min showing an average strength of 268.34 ± 44.66 MPa, compared to 174.16 ± 42.29 MPa for those sintered at 1450 °C for 120 min. In terms of density, significant differences (p < 0.01) were noted for the 3Y-TZP specimens, with an average density of 6.66 ± 0.49 g/cm3 for samples sintered at 1530 °C for 120 min, versus 5.75 ± 0.55 g/cm3 for those sintered at 1530 °C for 10 min. X-ray diffraction confirmed the presence of a predominantly tetragonal phase in both materials. Zirconia printed via SEPS manufacturing can be sintered at a higher temperature with shorter dwell times, thereby producing high density samples. Different sintering conditions can be used to fully sinter 3D-printed zirconia for potential dental applications.

Evaluation of physicomechanical properties of milled versus 3D-printed denture base resins: A comparative in vitro study

Statement of problemStudies comparing the physicomechanical characteristics of denture base resins manufactured by computer-aided design and computer-aided manufacturing (CAD-CAM) milling and 3-dimensional (3D) printing are sparse, resulting in challenges when choosing a fabrication method for complete dentures. PurposeThe purpose of this in vitro study was to evaluate and compare the impact strength, flexural strength, and the surface roughness of denture base resins manufactured by CAD-CAM milling and 3D printing before and after thermocycling and polishing. Material and methodsEvaluation of the physicomechanical properties (n=35) was completed before and after 500 thermocycles. Impact strength (n=14) was measured with a Charpy impact tester and flexural strength (n=14) with the 3-point bend test. Surface roughness (Ra) was evaluated (n=7) with a profilometer before and after thermocycling and polishing and by viewing the surface topography before and after polishing using a scanning electron microscope at ×2000. The Mann-Whitney U test and Wilcoxon sign rank test were used for statistical analysis (α=.05). ResultsMilled specimens showed statistically significantly higher impact strength before thermocycling and statistically significantly higher flexural strength before and after thermocycling (P=.004) compared with 3D-printed specimens. The Ra values for the milled group were significantly lower than for the 3D-printed group both before and after thermocycling (P=.006) and after polishing (P=.027). Thermocycling resulted in a statistically significant difference in flexural strength (P=.018) in both groups and in surface roughness in the milled group (P=.048); but no significant effect was found on impact strength (P>.05). Ra values for the 3D-printed group decreased after polishing (P=.048). ConclusionsMilled specimens had higher flexural and impact strength and lower surface roughness values than 3D-printed specimens. Polishing significantly reduced the surface roughness in 3D-printed specimens but had no significant effect on milled specimens.

The effect of sandblasting versus acid etching on the surface roughness and biaxial flexural strength of CAD/CAM resin-matrix ceramics (In vitro study)

BackgroundCAD/CAM resin matrix ceramics are one of the materials used in dental offices. The long-term success of the restoration depends on the bond strength of the restoration to the tooth and other materials; thus, surface treatment of the restoration is necessary to achieve this. But such treatment may affect the restoration strength. The purpose of this study is to assess the impact of various surface treatments on the surface roughness (Ra) and the biaxial flexural strength of two CAD-CAM resin-matrix ceramics.MethodsThirty-six-disc-shaped specimens, each measuring 1.2 mm in thickness and 12 mm in diameter, were machined from two resin-matrix ceramic blocks (Lava Ultimate and Cerasmart) (n = 18). Based on the surface treatments, each material was divided into 3 groups: control (no treatment), 50-μm Al2O3 sandblasting, or 9% hydrofluoric acid etching (n = 6). The surface roughness (Ra) was evaluated by the 3D laser scanning microscope. Then, specimens were aged by thermal cycling (5000 cycles) and tested for biaxial flexural strength using a universal testing machine at a crosshead speed of 1.0 mm/min.ResultsNo significant differences in flexural strength or Ra were found for Lava Ultimate among the surface treatment groups. For Cerasmart, only the sandblasting group showed significantly higher Ra values than the control group. Also, the Ra values for the sandblasting group were significantly higher than those for the acid etching group. The flexural strengths of the sandblasting and acid etching groups for Cerasmart were statistically similar, and both were significantly lower than the control group.ConclusionsAlthough all of the applied surface conditioning techniques improved Ra, they had a negative impact on the flexural strength of resin-matrix ceramics. Thus, clinicians should utilize the appropriate surface treatment techniques, taking into account their effects on the surface roughness and mechanical properties of resin-matrix ceramics.

Effect of shape of titanium dioxide nanofillers on the properties of dental composites

The main objective of the present study was to evaluate the effect of the morphology of titanium dioxide nanofillers on the flexural strength and shear bond strength of the dental composite. Spherical and rhombic-shaped nano titanium dioxide fillers were synthesized via solvothermal method and were characterized. Subsequently, these fillers were incorporated into a flowable composite (Filtek™ Z350 XT Flowable Restorative) at 0.5 wt.% and 1.5 wt.% and the prepared specimens were stored in water for 24 h. The specimens were then evaluated for flexural strength using a universal testing machine. Similarly, the shear bond strength of modified composites to the tooth was evaluated and bond failures were analyzed using stereomicroscope magnification. Incorporation of nanofillers significantly enhanced the flexural strength of flowable composite (p = 0.009) with a significant increase at 0.5wt.% of spherical (p = 0.015) and rhomboidal-shaped fillers (p = 0.010). However, no statistically significant difference in flexural strength was observed among the different shapes of nanofillers. The results of our study did not show a significant effect on the shear bond strength of the composites. Thus the reinforcing ability of titanium dioxide nanofillers on dental composite was confirmed in this study, although the effect of using nanofillers with different morphology was not significant.Graphical abstract

The Effect of Repeated Pressing on the Flexural Strength, Color Stability, Vickers Hardness, and Surface Topography of Heat-Pressed Lithium Disilicate.

The aim of this study was to investigate the effect of repressing leftover heat-pressed lithium disilicate material on its mechanical and optical properties. A lithium disilicate ingot (IPS e.max® Press, IvoclarVivadent, Schaan, Liechtenstein) shade (A1) low translucency was first heat-pressed to yield ceramic bars and disks. Then, the second and third presses were fabricated from the leftovers of the previous pressing cycles. A total of 36 bars and 15 disk specimens were fabricated and divided into three groups according to the number of pressing cycles (n = 12 bars and n = 5 disks): P1: first press (control), P2: second press, and P3: third press. The specimens were tested for flexural strength, color change, Vickers hardness, and surface topography under scanning electron microscopy. One-way ANOVA testing was used to evaluate flexural strength and hardness, while an independent t-test was performed to evaluate color change. There was no significant difference in flexural strength as the number of heat-pressed cycles increased (p = 0.283). Similarly, there was no significant difference in the microhardness values between all groups (p = 0.220). The overall color change ∆E between P1–P2 and P1–P3 were 2.01 and 2.14, respectively. The SEM images showed evenly distributed and densely packed lithium disilicate crystals in the P1 group. However, larger and less densely packed crystals were noticeable in P2 and P3. The IPS e.max Press could be repressed up to two times without an adverse effect on mechanical properties or color stability. These results may support the reuse of pressed lithium disilicate for economical purposes, but further clinical evaluation should be conducted to confirm these findings.

Influence of CAD/CAM Milling and 3D-Printing Fabrication Methods on the Mechanical Properties of 3-Unit Interim Fixed Dental Prosthesis after Thermo-Mechanical Aging Process.

This study assessed the influence of CAD/CAM milling and 3D-printing fabrication methods on mechanical properties of 3-unit interim fixed dental prosthesis (IFDPs) after thermo-mechanical aging. Forty 3-unit IFDPs were fabricated on a mandibular right second premolar and second molar of a typodont cast. Samples were fabricated from the following materials; auto-polymerized polymethyl methacrylate (conventional resin), CAD/CAM PMMA (milled resin) and two different CAD/CAM 3D-printed composite resins; digital light processing Asiga (DLP AS) and stereolithography NextDent (SLA ND). Mechanical properties were compared between the studied materials using Kruskal–Wallis test, followed by multiple pairwise comparisons using Bonferroni adjusted significance. There was a significant difference in flexural strength and microhardness between the studied materials (p < 0.001), with the highest mean ± SD reported in the milled IFDPs (174.42 ± 3.39, 27.13 ± 0.52), and the lowest in the conventional IFDPs (98.02 ± 6.1, 15.77 ± 0.32). Flexural strengths differed significantly between the conventional IFDPs and all materials except DLP AS. The highest elastic modulus was recorded in the milled group, and the lowest in the SLA ND group (p = 0.02). In conclusion, superior flexural strength, elastic modulus, and hardness were reported for milled IFDPs. SLA ND printed IFDPs showed comparable mechanical properties to milled ones except for the elastic modulus.

Microstructure, Flexural Strength, and Fracture Toughness Comparison between CAD/CAM Milled and 3D-Printed Zirconia Ceramics

The present study comprehensively compared the microstructure, flexural strength, and fracture toughness of zirconia ceramics prepared via two different methods, subtractive milling (SM) and stereolithography (SLA). Disc- or rectangular-shaped zirconia specimens (Prettau (SM) and 3DMix Zirconia (SLA)) were prepared following each manufacturer’s instructions and polished. The microstructures of the two different zirconia specimens were studied by scanning electron microscopy, X-ray diffractometry, energy-dispersive X-ray spectroscopy, and electron backscattered diffractometry. The flexural strength and fracture toughness based on the indentation fracture method were measured for the two different zirconia ceramics. A greater number of small pores and smaller grains were found in the SLA specimen than in the SM specimen. The crystal structure and microstructure analysis revealed that both ceramics had a similar phase composition to each other. No significant differences in flexural strength (p = 0.242) or fracture toughness (p = 0.101) were detected between the two ceramics. The mean flexural strength of the SLA-fabricated zirconia as well as the SM zirconia satisfied the class 5 criteria (&gt;800 MPa) in the ISO 6872 standard.

Comparison of Testing Designs for Flexural Strength of 3Y-TZP and 5Y-PSZ Considering Different Surface Treatment.

The aim of this study was to analyze the influence of different surface treatments and the corresponding surface roughness on the ball-on-three-balls test and piston-on-three-balls test for measuring flexural strength 3Y-TZP and 5Y-PSZ. Additionally, the influence of cutting the material into the specimens when pre-sintered or fully sintered was analyzed. A total of 120 specimens for each material group, 3Y-TZP zirconia (Katana HT, Kuraray) and the 4 different layers of multilayered 5Y-PSZ zirconia (Katana UTML, Kuraray), were produced. The used material was cut into half of the specimens in a fully sintered stage, the other half was cut when pre-sintered. Each subgroup was divided into 3 different surface treatment groups being air abraded with 50 µm alumina particles at 1 bar pressure, ground with 600 SiC paper or polished up to 1 µm with a polycristalline diamond suspension. These were then analyzed by X-ray diffraction (XRD) (N = 3) and tested for flexural strength using the ball-on-three-balls test (N = 10) or piston-on-three-balls test (N = 10). For 3Y-TZP groups different surface roughness did not result in statistically significant differences in flexural strength but cutting the specimens in fully sintered state significantly reduced flexural strength of 1133 ± 109 to 741 ± 81 MPa. For 5Y-PSZ groups air abrasion of the specimens with alumina particles significantly reduced the flexural strength of 562 ± 68 MPa to 358 ± 58 MPa. Cutting and surface treatment in pre-sintered or fully sintered state had no significant influence. Flexural strength testing with the ball-on-three-balls test resulted in about 20% higher strengths compared to the piston-on-three-balls test. Results of both tests showed the same tendencies when compared.

The Effect of Curing Modes and Times of Third-Generation Led LCU on the Mechanical Properties of Nanocomposites

This study evaluates the effect of curing modes and times on the mechanical properties of nanocomposites. Two nanocomposite resins were investigated: supra-nanohybrid (Estelite Posterior Quick; EP) and nanohybrid (Solare X; SX). They were polymerized with a light-emitting diode light-curing units (LED LCU, Valo) as follows: standard mode for 20s (ST20), high power mode for 12s (HP12), high power mode for 20s (HP20), extra power mode for 6s (XP6), and extra power mode for 20s (XP20). For Vickers microhardness (HV), disc-shaped specimens were fabricated (n=10). For the three-point bending test, bar-shaped specimens were fabricated (n=10). Flexural strength and resilience modulus were calculated. The fractured surfaces and specimen surfaces of composites were observed using scanning electron microscopy. The data were analyzed with repeated measures ANOVA, two-way variance, and Bonferroni tests (p&lt;0.05). On the top and bottom surfaces of the EP nanocomposite resin, ST20 and HP12 revealed statistically higher HV than with XP6. Moreover, HP20 and XP20 had statistically higher HV than HP12 and XP6. For the SX nanocomposite resin, HP20 had statistically higher HV than HP12. For EP and SX, there were no significant differences in flexural strength and resilience modulus regarding the curing modes and times. Furthermore, SX demonstrated lower mechanical properties than EP. Scanning electron microscopy indicated that both nanocomposites had similar surface appearances. However, with all curing modes and times, SX exhibited layered fractures and more crack formations than EP. Different curing modes and times could influence the microhardness of nanocomposites.

Preparation and evaluation of novel bio-based Bis-GMA-free dental composites with low estrogenic activity

ObjectiveAlthough bisphenol Aglycidyl methacrylate (Bis-GMA) are widely used in the dental composite, its raw materials include the petroleum-based product bisphenol A (BPA) with high estrogenic activity (EA). In this study, two new BPA-free dimethacrylate monomers from bio-based material creosol were synthesized and evaluated. MethodsThe renewable bisphenol monomer 5, 5'-methylenedicreosol (BCF) was prepared from bio-based material creosol. By the human breast cancer cells (MCF-7 cells) proliferation assay, a risk assessment of BCF was performed to determine if BCF possessed reduced EA in comparison to BPA. Then, the novel monomers 5, 5'-methylenedicreosol diglycidyl ether diacrylate (BCF-EA) and 5, 5'-methylenedicreosol diglycidyl ether dimethacrylate (BCF-GMA) were synthesized from BCF with epichlorohydrin and (meth)acrylate. All products were investigated by 1H NMR and FT-IR spectra. The control resin was a mixture based on Bis-GMA and tri(ethyleneglycol) dimethacrylate (TEGDMA) with a weight ratio of 5:5 (5B5T). Similarly, experimental resin matrix was a mixture based on BCF-EA/TEGDMA (5E5T) and BCF-GMA/TEGDMA (5G5T). And their corresponding composites were then prepared with corresponding resin matrices and hybrid SiO2 (5E5TC, 5G5TC and 5B5TC). The properties of these composites were investigated according to the standard or referenced methods. Each sample was evaluated for double bond conversion (DC), shrinkage stress (SS) and volumetric polymerization shrinkage (VS). Water sorption (WS), water solubility (SL), mechanical properties and cytotoxicity were also measured. Results1H NMR and FT-IR spectra confirmed the chemical structure of each monomer. EA test revealed that bio-based bisphenol monomer BCF as the precursor of BCF-EA and BCF-GMA showed lower EA than BPA. Cured resin matrix: Both 5E5T and 5G5T had nearly the same DC (p < 0.05), which was higher than 5B5T (p < 0.05); 5E5T and 5G5T had lower VS, SL and cytotoxicity than 5B5T (p < 0.05); mechanical properties of 5E5T and 5G5T were all better than those of 5B5T (p < 0.05). Cured composite: There was no significant difference in conversion (p < 0.05); 5E5TC and 5G5TC had significantly lower VS (p < 0.05); WS of 5E5TC and 5G5TC were similar (p < 0.05), but higher compared to 5B5TC (p < 0.05); 5E5TC and 5G5TC had the deeper depth of cure (p > 0.05); before water immersion, there was no significant difference in flexural strength between 5E5TC and 5G5TC (p > 0.05), and higher than 5B5TC (p < 0.05); 5E5TC and 5G5TC showed less cytotoxicity than 5B5TC (p < 0.05). SignificanceThe new BPA-free di(meth)acrylates are promising photocurable dental monomers owning to bio-based raw material, high degree of conversion coupled with low curing shrinkage and good mechanical properties. Therefore, BCF-EA and BCF-GMA has a potential to be used as the substitution for Bis-GMA to prepare Bis-GMA-free dental composite.

Surface Properties of Polymer Resins Fabricated with Subtractive and Additive Manufacturing Techniques.

This study aimed to compare the surface roughness, hardness, and flexure strength of interim indirect resin restorations fabricated with CAD-CAM (CC), 3D printing (3D), and conventional techniques (CV). Twenty disk (3 mm × Ø10 mm) and ten bar specimens (25 × 2 × 2 mm) were fabricated for the CC, 3D, and CV groups, to be used for surface roughness, micro-hardness, and flexural strength testing using standardized protocol. Three indentations for Vickers micro-hardness (VHN) were performed on each disk and an average was identified for each specimen. Surface micro-roughness (Ra) was calculated in micrometers (μm) using a 3D optical non-contact surface microscope. A three-point bending test with a universal testing machine was utilized for assessing flexural strength. The load was applied at a crosshead speed of 3 mm/min over a distance of 25 mm until fracture. Means and standard deviations were compared using ANOVA and post hoc Tukey–Kramer tests, and a p-value of ≤0.05 was considered statistically significant. Ra was significantly different among the study groups (p < 0.05). Surface roughness among the CC and CV groups was statistically comparable (p > 0.05). However, 3D showed significantly higher Ra compared to CC and CV samples (p < 0.05). Micro-hardness was significantly higher in 3D samples (p < 0.05) compared to CC and CV specimens. In addition, CC and CV showed comparable micro-hardness (p > 0.05). A significant difference in flexural strength was observed among the study groups (p < 0.05). CC and 3D showed comparable strength outcomes (p > 0.05), although CV specimens showed significantly lower (p < 0.05) strength compared to CC and 3D samples. The 3D-printed provisional restorative resins showed flexural strength and micro-hardness comparable to CAD-CAM fabricated specimens, and surface micro-roughness for printed specimens was considerably higher compared to CAD-CAM and conventional fabrication techniques.

Biaxial Flexural Strength of High-Translucence Monolithic Ceramics upon Various Thicknesses.

Introduction High-translucence ceramics have been used increasingly. This study evaluated the biaxial flexural strength of different ceramics as a result of varying thicknesses. Materials and Methods Circular discs with varied thickness of 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, and 2.0 mm were prepared from high-translucence yttria-partially stabilized zirconia (HTY-PSZ); Bruxzir® Anterior (Bc), and zirconia-reinforced lithium silicate (ZLS) including Celtra® DUO (Cc) and VITA Suprinity® (Vc) (n = 15 discs/group). Biaxial flexural strength (σ) was evaluated utilizing piston-on-three-balls in a testing machine at a speed of 0.5 mm/min. A scanning electron microscope (SEM) was used to determine the microscopic structure. ANOVA and multiple comparisons were analyzed for significant differences (a = 0.05). Results The mean ± sd value of σ (MPa) for thickness 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, and 2.0 mm was 672.66 ± 107.54, 655.93 ± 93.98, 589.01 ± 63.63, 624.89 ± 87.08, 618.82 ± 83.36, 672.64 ± 84.61, 659.81 ± 122.89, 632.79 ± 92.54, and 657.86 ± 73.17, for Bc; 477.64 ± 88.23, 496.39 ± 86.36, 461.56 ± 57.00, 450.26 ± 86.60, 468.28 ± 83.65, 472.45 ± 53.63, 453.05 ± 72.50, 462.67 ± 47.57, and 535.28 ± 84.33, for Cc; and 500.97 ± 76.36, 506.70 ± 87.76, 557.82 ± 62.78, 543.76 ± 87.29, 507.53 ± 86.09, 502.46 ± 64.75, 557.70 ± 80.91, 527.04 ± 80.78, and 499.88 ± 57.35, for Vc. A significant difference in flexural strength was indicated among groups (p < 0.05). Bc was significantly stronger than Cc and Vc (p < 0.05). Varying thickness did not have a significant influence on strength (p > 0.05). SEM revealed a tight arrangement of crystals for Bc and needle-like crystals diffusing in glass for Vc and Cc. Conclusion Flexural strength of ceramics varied among types, but each retained strength equitably with varying thickness. HTY-PSZ was stronger than ZLS, but each was equally strong for thickness in the range of 0.4–2.0 mm.

Effect of Denture Cleansers on Color Stability and Flexural Strength of Heat Polymerized Acrylic Resin an In-Vitro Study

Heat polymerized poly methyl methacrylate is the most commonly used denture base material. Selecting a denture cleanser, compatibility between various type of denture base material and cleanser must be considered to avoid harmful effects. Study objective was to evaluate the changes in flexural strength and colour change of heat cured denture base resins when treated using denture cleansers. Method: The disk shaped specimens15mm in diameter and 4mm in thickness and rectangular shaped specimens 65mm x 10mm x 3.3mm were fabricated using split mould technique. A total of 60 standardized specimens were fabricated and stored in distilled water for 24hrs. After 1 day, the specimens were appropriately labelled and immersed in groups of 20 to prepared denture cleanser solutions for treatment. Solutions were prepared and immersed according to manufactures instructions (Corega tab: one tablet to 200ml of water and immersion time is 15min; Fitty dent: one tablet to 200ml of water and immersion time is 30min). After immersion, the resin specimens will be removed, thoroughly cleanedunder running water, dried with absorbent paper, and then the procedure of immersion will be repeated. This procedure will be performed for a total of 30 times over a period of 6 days simulating patients180 days of cleansing. 10 specimens of each group where tested for flexural strength using universal testing machine. Specimens were loaded until fracture occurred. The peak load was recorded in Newton and the flexural strength was calculated from peak load and another 10 specimens were tested for colour change using spectrophotometer .The specimens were tested on the measuring head of the spectrophotometer. The colour characteristics, tristimulus values X, Y, Z, and CIE (Lab) of specimens, were evaluated. The findings were statistically analysed using ONE -WAY ANOVA and students T test. Results: Heat cure denture base resin used for this study showed significant difference in flexural strength and..... , , , , , Sch J Dent Sci | - DOI :

Effect of Incorporation of Different Concentrations of Silver Nanoparticles as an Antimicrobial Agent on the Flexural and Impact Strength of Heat-Cured Denture Base Resin

Abstract Aim This article evaluates the effect of incorporating different concentrations of silver nanoparticles as an antimicrobial agent on the flexural and impact strength of heat-cured denture base resin. Material and Methods A total of 80 specimens of polymethyl methacrylate resin were fabricated (40 for flexural strength and 40 for impact strength). Specimens were fabricated using stainless steel die of dimension 65 mm × 10 mm × 2.5 mm as per the American Dental Association specification no. 12, and 50 mm × 6 mm × 4 mm as per ISO 1567:1999 for flexural strength and impact strength, respectively, and were divided into four groups (A, B, C, and D) based on the concentrations of silver nanoparticles (0%, 2.5%, 5%, and 10%). The specimens were subjected to three-point bending test and Izod impact tester for testing flexural and impact strength, respectively. Data obtained was compiled and analyzed using one-way analysis of variance and post hoc tests. Results Results showed that for both the properties, maximum strength was observed in group A (control) followed by groups B and C, and minimum was observed in group D. A statistically significant difference in flexural strength was found among all the groups, whereas no statistically significant difference in impact strength was found among any of the groups. Conclusion Within the limitations of this in vitro study, it was concluded that though incorporation of silver nanoparticles exhibited no effect on the impact strength of heat cure denture base resin, it decreased the flexural strength, so it should be used cautiously.

Bulk-Fill Direct Restorative Materials: An In Vitro Assessment of Their Physio-Mechanical Properties

Bulk-fill restorative material has gained popularity in clinical practice, due to their perceived timesaving aspect. Objective was to compare the properties of bulk-fill direct restorative materials. Filtek Z350 (CR), Filtek One Bulk Fill Restorative (BF), Fuji IX and EQUIA Forte (EF) were compared. Thirty specimens from each material were prepared according to ISO 4049 for three-point flexural strength. Elastic moduli and hardness (n = 20) were evaluated using nanoindentation. Depth of cure (DC) (n = 20) was measured for BF at three different depths (2, 3, 4 mm) and at two irradiation times (20 and 40 s). Wear testing was carried out for three different periods (3, 6, 12 month(s)). All specimens were stored in 37 °C water for 24 h prior to testing. Results were evaluated using one-way ANOVA followed by a post hoc Bonferroni test (p &lt; 0.05). BF and CR showed a significantly higher flexural strength than other groups (p &lt; 0.05), and the highest Weibull modulus was found in CR. BF showed sufficient DC with at least 85%, at all thicknesses. CR and BF also had a high level of translucency than EF and Fuji IX. Significant differences in flexural strength were found among all materials except between Fuji IX and EF. While all material tested are suitable for use clinically, BF and CR have superior properties than GIC based bulk-fill.

Ceramic Printing - Comparative Study of the Flexural Strength of 3D Printed and Milled Zirconia.

To determine and compare the mechanical properties of 3D-printed yttriastabilized zirconia to milled isostatic pressed yttria-stabilized zirconia, with the following hypotheses: (1) The flexural strength of 3D-printed yttria-stabilized zirconia is comparable to milled yttria-stabilized isostatic pressed zirconia; and (2) thermocycling and chewing simulation do not affect the flexural strength of 3D-printed yttria-stabilized zirconia. A total of 30 bars of an experimental 3D-printed 3 mol% yttriastabilized zirconia (LithaCon 3Y 230, Lithoz) and 10 bars of milled isostatic pressed zirconia (Prettau Zirconia, Zirkonzahn) were utilized. The printed zirconia bars were divided into three groups (n = 10 bars per group): (1) untreated (control); (2) thermocycled; and (3) tested after chewing simulation. A flexural strength test was performed on all samples using a three-point bend test in an Instron Universal testing machine. One-way analysis of variance on ranks was used to compare milled to printed zirconia. The effects of thermocycling and load cycling on 3D-printed zirconia were also determined. The flexural strength values for milled and printed zirconia were 936.3 ± 255.0 MPa and 855.4 ± 112.6 MPa, respectively. There was no statistically significant difference in flexural strength between the milled and printed zirconia (P = .178). No statistically significant differences were observed between the control 3D-printed zirconia group and the thermocycled (888.4 ± 59.3 MPa) or load-cycled printed zirconia (789.6 ± 133.8 MPa; P = .119). Printed 3 mol% yttria-stabilized zirconia has comparable flexural strength to milled yttria-stabilized isostatic pressed zirconia. The thermocycling and chewing simulation used in this study did not significantly alter the flexural strength of the printed 3 mol% yttria-stabilized zirconia. These results indicate a promising role for 3D printing in the fabrication of zirconia restorations. Additional studies are needed to explore the full potential of this technology.

Comparative evaluation of flexural strength and depth of penetration following dentin pretreatment with proanthocyanidin and phytosphingosine

This study aimed to comparatively evaluate the cell viability, flexural strength (FS) and depth of penetration following surface pretreatment of demineralized dentin with phytosphingosine (PHS) and proanthocyanidin (PAC). Cytotoxicity of PAC and PHS was assessed by MTT assay on mouse fibroblasts. 52 dentin slabs from human mandibular molars were randomly divided into 4 groups for FS analysis (n = 13); groups I (negative control)- no intervention, II (positive control)- etching, bonding and composite buildup, III and IV- pretreatment with 6.5% PAC and 6.5% PHS respectively for 10 min followed by bonding protocol. For depth of penetration, groups I (no pre-treatment), II (PAC) and III (PHS) with bonding protocols similar to FS analysis were evaluated. Results were statistically analysed by Kolmogorov-Smirnov test, one-way ANOVA and post hoc tukey test (p < 0.05). MTT assay revealed 96.7% and 91.06% at 10 µg/mL of PAC and PHS respectively. There was a significant difference in FS between control groups [I (0.91 ± 0.54), II (0.60 ± 0.27)], while there was no difference between experimental groups [III (1.13 ± 0.10), IV (1.10 ± 0.08)]. Statistical significant differences were observed in depth of penetration among three groups [I (14.50 ± 2.95), II (33.67 ± 2.42) and III (47.67 ± 2.80)]. Therefore, PHS may serve as a promising alternative to PAC when applied over demineralized dentin.

Effect of Hydrofluoric Acid Surface Treatments on Surface Roughness and Three-Point Flexural Strength of Suprinity Ceramic.

Objectives:This study aimed to evaluate the effects of hydrofluoric acid (HF) concentration and etching time on the surface roughness (SR) and three-point flexural strength of Suprinity and to analyze the surface elements before and after etching.Materials and Methods:To measure the SR, 70 specimens of Suprinity (2×4×5mm3) were assigned to seven groups (n=10). Six groups were etched for 20, 60, and 120 seconds with 5% and 10% HF and 7th group was the control group. Specimens were evaluated using atomic force microscopy (AFM). One specimen from each group was used to analyze the surface elements using scanning electron microscopy (SEM). For measuring the three-point flexural strength, 60 specimens were divided into six groups (n=10) and etched as previously described. The flexural strength was measured using a universal testing machine. T-test, one-way analysis of variance (ANOVA), and two-way ANOVA were used for statistical analyses (P<0.05).Results:The 10% concentration of HF caused higher SR compared to the 5% HF. The effect of HF concentration on the flexural strength was significantly different in the 20- and 60-second etching groups. Different etching times had no significantly different effect on the SR. With 5% HF, the flexural strength was significantly higher for 20-second etching time than for the etching times of 60 and 120 seconds. With 10% HF, there was a significant difference in flexural strength between etching times of 20 and 120 seconds. The atomic percentage (at%) of silica was enhanced by increasing the etching time.Conclusion:The best surface etching protocol comprises 10% HF used for 20 seconds.

Effect of Short-Term Aging on the Flexural Strength of a Novel Experimental CAD/CAM Fiber-Reinforced Composite Material: A Pilot Study.

To investigate the three-point flexural strength of a novel CAD/CAM fiber-reinforced composite (FRC) material following different aging conditions. The specimens were randomly assigned to one of five groups based on aging condition: (1) control (no treatment); (2) short-term water storage; (3) thermal degradation with autoclaving; (4) chemical degradation with hydrochloric acid; and (5) chemical degradation with citric acid (n = 10 per group). The specimens in the control group received no treatment. Following each treatment protocol, the three-point bending test was used to calculate the flexural strength. Data were statistically analyzed (α = .05), and scanning electron microscopy (SEM) analysis of the specimens was conducted. No significant differences in flexural strength were observed among the groups (P = .199). In addition, no distinct morphologic differences were detected in the SEM images of the specimens. The flexural strength of this novel CAD/CAM FRC material was unaffected by different aging methods.