Strength Of Resin Research Articles

Improved bleached eucalyptus kraft pulp-based tissue papers incorporating wet-strength resins

Abstract Common tissue paper manufacturing trends aim at partial or total replacement of softwood pulp with hardwood pulp for its production, such as bleached eucalyptus kraft pulp (BEKP), in order to optimize the process and the final product properties such as softness. However, the use of a single type of hardwood fiber results in lower strengths of both wet and dry webs. To maintain necessary strength and desired properties, the incorporation of several additives is often required. In this context, low molecular weight polyethylene glycol (PEG) and different wet strength resins, such as polyamideamine-epichlorohydrin (PAE) and glyoxalated polyacrylamide (GPAM) resins, were combined to achieve an innovated product with improved properties. In particular, wet and dry tensile strength was significantly improved when combining PEG and wet strength resins, especially observed in tissue papers prepared with PAE resin, high-charge cationic agent and bulk applied aqueous PEG solution. Noteworthy that water absorption capacity and softness of tissue paper were not critically affected by PEG incorporation, regardless of application method used (in bulk or by spray).

Bond Strength of Laser-Treated Titanium Alloy with Glass Based Ceramic/Porcelain: A Systematic Review and Meta-Analysis

Objective: The study systematically reviewed the bonding strength of laser-treated titanium (Ti) alloy with porcelain compared to other conditioning methods. Methods: A search was performed using Scopus, Web of Science, and PubMed for PICO focused question, “Does the laser treatment (I) of titanium surface enhances the bonding strength (O) between a titanium substrate and porce- lain/composite (P) as compared to other surface treatments (C)?” The standard mean difference (SMD) was calculated with a 95% confidence interval (95% CI) through the use of meta-analyses. Results: Of the 8 included studies, five studies used the shear bond strength (SBS) test, one study used tensile bond strength (TBS) analysis, and two utilized the flexural bond strength (FBS) test. Sandblasting showed SBS values ranging between 6.02 ±0.91 MPa and 7.00±2.45 MPa; while lased samples demonstrated scores of 6.16 ±0.37 MPa and 21.22±3.41 MPa. A TBS score of 52.62 MPa for the samples treated with air abrasion (control group) and 24.02 MPa for the laser- welded samples was observed. The meta-analysis revealed improvement in SBS (p = 0.04) scores for laser treatment, compared to the controls. Conclusion: The application of laser treatment of Ti alloy with ceramic is a promising alternative to improve the bonding strength of acrylic resin to titanium.

Synthesis and optimization of a Novel epoxy-based nanofluid for sand consolidation in oil wells

In loose reservoirs, where the pressure and stresses around the wellbore are greater than the formation strength, the sand production problem is exacerbated. Sand production leads to a number of potential and costly problems. Chemical sand consolidation as a less costly method is performs to strengthen the oil well formation based on various polymer resins.In the present paper, a new epoxy-based nanofluid for controlling sand production with chemical strength was presented. Epoxy/g–C3N4–NS nanofluid has two special properties. First, a carbon nitride nanosheet as an active functional agent was used to increase the compressive strength of the epoxy resin after the curing process. Second, a bubbling agent was used to create micro and macro pores for production fluid movement and ultimately increase permeability. The FTIR, XRD, TEM, FESEM, and TGA analyses were performed to investigate and characterization of synthesized materials. The effect of different concentrations of resin, solvent, bubbling agent and g–C3N4–NS on the consolidation was studied. The compatibility of epoxy/g–C3N4–NS nanofluid with brine and crude oil from the Ahvaz oilfield was also investigated.The optimum amount of nanofluid composition containing resin, diluent, bubbling agent, and strength agent has a compressive strength of nearly 3000 psi and an absolute permeability of 4000 mD. The results of core flooding experiments showed that for synthetic plug samples whose initial permeability is more than 500 mD, after chemical consolidation with the epoxy/g–C3N4–NS nanofluid, the retained permeability was almost 86%. Based on the experiments conducted, the epoxy/g–C3N4–NS nanofluid was compatible with the brine and crude oil and it can be commercialized as a new formulation to control sand production in oil wells.

Effect of Ghatti gum content on mechanical properties of epoxy composite using multicriteria optimization techniques

In the recent years particles-based composites are more attractive due to many of the applications. The reinforcing of particles, micro or nano powders enhanced the properties by crosslinking with polymers. The partial based polymer composites are playing a major role in enhancing the strength of pure resins. In many of common particle reinforcements materials are fly ash, Nano clay, silica powders etc… these are more predominately used to enhance the properties of the pure resin and even with fiber reinforced composites. This paper focuses on the effect of microns size natural powder reinforcement in synthetic resin to evaluate the tensile, flexural, impact and hardness properties behavior of composites. The Gum Ghatti which is obtained from the plant and processed to obtain the powder. The 5, 10, 15 and 20 % of gum Ghatti natural powders are reinforced in Araldite LY 556 (Bisphinol-A-Diglycidyl-ether) epoxy resin to observe the mechanical strength and interfacial adhesion strength between matrixes with reinforcement materials. These composites are post-cured at 80℃ for three hours to improve the residual stresses. The 10% natural particular reinforcement exhibits better tensile and flexural properties as compared to other compositions. However, Barcol hardness number of 15 percentage of reinforcements shows better. These mechanical properties are further analyzed using MCDM techniques to identify best weight fraction. The Preference Selection Index (PSI), Multiobjective Optimization on The Basis of Ratio Analysis (MOORA), Combinative Distance-based Assessment (COMDAS), VIekriterijumsko KOmpromisno Rangiranje (VIKOR), Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) methods are used and observed that 10% gum Ghatti exhibited better mechanical properties.

Study on Blending Modification of Bisphenol A Epoxy.

Epoxy-resin-based composites in the field of current electrical materials often work in high temperature, high humidity or salt spray conditions. In order to improve the operation reliability of the composite insulator cross arm in a high temperature, high humidity and high salt spray environment, and analyze the aging mechanism and performance characteristics of resin, in this paper, wet heat aging and salt spray aging experiments were carried out on the blended resin system composed of bisphenol A type epoxy resin (E-51), aliphatic epoxy modified bisphenol A epoxy resin (2021P/E-51) and dimeric acid modified bisphenol A epoxy resin (EPD-172/E-51). Among them, 10 wt% and 20 wt% of 2021P blend resin and 10 wt% of EPD blend resin have superior thermo-mechanical properties. Under humid and hot conditions, the dielectric loss of 10 wt% EPD blend system before and after aging is 39.9% and 49.5% lower than that of pure E51 resin system, respectively. Under the condition of salt spray, the dielectric loss of 20 wt% and 10 wt% EPD blends decreased by 73.1% and 74.6% after aging. The leakage current of 10 wt% 2021P blend resin and 10 wt% EPD blend resin decreased by 7% and 3.8% before aging, respectively. After aging, they decreased by 3.7% and 2.2%, respectively. The bending strength of 2021P blend resin before and after aging reached 29.3 MPa and 26.6 MPa, respectively. The above three blending resin systems exhibit good electrical properties and good mechanical properties, their ageing resistance performance is strong and they are suitable as the matrix resin of compound cross arm mandrel material.

Adhesion and Cohesion Strength of Phenol-Formaldehyde Resin Mixed with Different Types and Levels of Catalyst for Wood Composites

Phenol-formaldehyde (PF) resin is one of the most well-known adhesives for exterior use. PF adhesive is one of the commercial thermoset polymers that is used extensively due to its many benefits. This study investigated the influence of different types and levels of catalysts, i.e., NaOH and CaCO3 at 1% and 5% based on the solids content of PF resin on the adhesive properties, adhesion, and cohesion strength of PF resin. The results show that the catalyst type significantly influenced the PF adhesive viscosity and pH. Furthermore, the catalyst level significantly affected the PF adhesive’s solids content, viscosity, and gelation time. The cohesion strength of PF-CaCO3-1% was more significant than the PF control at 75 °C. According to the DMA analysis, the mixed PF-NaOH-5% provided the highest storage modulus, followed by the PF-CaCO3-1%, with values that were not statistically different from one another. The adhesion strength of PF-CaCO3-1% was the highest, whereas the adhesion strength of the PF control was the lowest, as confirmed by the cohesion strength. According to the findings, adding CaCO3-1% as a catalyst of PF resin would result in better adhesive adhesion and cohesion properties for wood composites in the future.

Investigation on the mechanical, thermal and electrical properties of polyoxymethylene composites modified by thermoplastic polyurethane elastomer and carbon fiber

As we all know, adding thermoplastic polyurethane elastomer(TPU) into Polyoxymethylene(POM) by melt blending can not only improve its toughness, but also improve the brittleness and cracking of POM products at low temperatures. However, there are some problems in the use of above POM/TPU modified material. For example, after adding TPU, the strength and rigidity of POM resin will be significantly reduced, and its antistatic performance is not very good. In this paper, we use melt-extrusion blending method to improve the strength, rigidity and antistatic properties of toughened POM material by adding CF. In addition, the aggregation and properties of the blends are studied by DSC, FTIR, PLM, DMA and mechanical tests, surface resistivity. Mechanical analysis show us that the tensile strength, flexural modulus increase significantly with the increase of CF content, and the notched impact strength of the POM/TPU/CF materials are all better than that of the pure POM resin. It can also be found that after adding 2% to 8% CF, the surface resistivity of the composites gradually decreases with the increase of CF content, and CF forms a conductive network in the POM matrix. The anti-static test shows that when the CF content is 6% the surface resistivity of POM/TPU/CF blend is 109Ω, and when the CF content is 8% which can reach to 104Ω.

Characterization of Eumelanin as an Additive in High‐Temperature Phthalonitrile‐Based Resin Blends

AbstractBio‐manufactured eumelanin is investigated as a sustainable high‐char carbon additive for use with moldable high temperature resins. Blends of Bisphenol A poly‐ether‐ether‐ketone (PEEK)‐based phthalonitrile (PN) with 0–30 wt% melanin are prepared and characterized for their compositional, thermal, and mechanical properties. Although the char yield increases from 10 to 30 wt% melanin loading, the presence of melanin decreases the thermal stability compared to PN resin alone. Despite this, the melanin‐PN resins still maintain a very high char yield (>64%) up to 1000 °C under nitrogen. Rheology, thermal analysis, and mechanical measurements suggest off‐gassing of the melanin and increased crosslinking between the melanin and PN, leading to a lower flexural strength resin with higher additive loadings. Spectroscopic studies suggest possible interaction between melanin and PN during co‐curing, which ultimately can affect the processing and final properties of melanin‐additive composite materials.

Evaluation of Different Priming Agents with Conventional and Bioactive Self-Adhesive Resin Cements on Shear Bond Strength to Zirconia

The aim of this study was to evaluate the effect of different priming agents on the shear bond strength (SBS) of conventional and bioactive self-adhesive resin cements to zirconia. One hundred and twenty zirconia discs were randomly divided into four main groups according to the priming agents used (n = 30): no priming agent (control), zirconia primer (Z-PRIME Plus), universal adhesive (All-Bond Universal), and universal ceramic primer (Monobond N). Then, each group was subdivided into three subgroups according to the type of self-adhesive resin cement used: TheraCem, Activa BioActive, and RelyX U200 Automix (n = 10). All specimens were subjected to thermocycling. The mean SBS data were analyzed using One-Way ANOVA, followed by multiple comparison Bonferroni test. Without the application of priming agents (control), most of the specimens failed during thermocycling. The priming agent, cement type, and their interaction had a significant effect on the SBS to zirconia (p < 0.001). Only the type of priming agent showed a significant effect on the mode of failure (p < 0.001), resulting in mainly mixed failure with Monobond N and adhesive failure with other primers. Regardless of the type of primer, Bioactive resin cements did not improve the SBS to zirconia compared to conventional cements.

The comparison of the repair bond strength of the composite resin to direct and indirect composite restorations with different surface preparations.

Indirect restorations have been employed in restorative dentistry to solve some of the drawbacks of direct restorations. The aim of this study was to evaluate the effect of different modes of a universal adhesive resin on the repair capacity of two indirect resin composites and a direct resin composite. Indirect composite resins (Ceramage and Gradia Plus) and a direct composite resin (Filtek Z250) were prepared in a plastic mold with a height and diameter of 2-mm and 6-mm, respectively. Composite blocks were thermocycled (5000 cycles, 5°C-55°C). Then, according to their surface treatments, composite blocks were categorized into six-groups: Group 1: ER (etch&rinse), Group 2: SE (self-etch), Group 3: Bur+ER (bur+etch&rinse), Group 4: Bur+SE (bur+self-etch), Group 5: Bur+Silane+ER (bur+silane+etch&rinse), Group 6: Bur+Silane+SE (bur+silane+self-etch), respectively. After surface treatments and adhesive application for bonding with a direct resin composite, all groups were then thermocycled before performing shear-bond-strength-test. Failure modes were evaluated using a stereomicroscope. Data were analyzed by two-way-ANOVA and Bonferroni-test (P<0.05). The highest bond-strength values were obtained for Bur+Silane+SE groups, while the lowest values were obtained for the Bur+Silane+ER groups for all materials. Statistically significant differences were observed between the Bur+Silane+ER group and ER, Bur+ER and Bur+Silane+SE groups in Gradia Plus (P<0.05). The self-etch-mode of the universal-adhesive and silane applications led to the increase in the repair-strength of the adhesive in the Filtek Z250 and Ceramage. The self-etch-mode of the universal-adhesive might be used to reduce adhesive-application-steps in the clinical repair procedures.

Microtensile bond strength of resin cements to 3-D printed and milled temporary restorative resins

To evaluate the microtensile bond strength (µTBS) of two resin cements to 3D printed and milled CAD/CAM resins used for provisional fixed partial dentures. Blocks (5 x 5 x 5 mm) of three 3D-printed resins (Cosmos3DTemp / Yller; Resilab3D Temp / Wilcos and SmartPrint BioTemp, / MMTech) were printed (Photon, Anycubic Technology Co.). A milled material (VitaCAD-Temp, VITA) was used as control. Half the specimens were sandblasted and the rest were untreated. Two blocks were bonded with the corresponding resin cement: PanaviaV5 (Kuraray Noritake) and RelyX Ultimate (3M Oral Care). After 24 hours, the bonded blocks were sectioned into 1 x 1 mm side sticks. Half the beams were tested for µTBS and the other half was thermocycled (5000 cycles, 30s dwell-time, 5s transfer time) before µTBS testing. A four way Generalized Linear Model (material*sandblasting*cement*aging) analysis was applied. VITA exhibited the lowest µTBS, regardless of the cement, sandblasting and thermocycling. Sandblasting significantly improved the µTBS of VIT, especially after aging, but did not improve the µTBS of 3D printed resins. Sandblasting was not beneficial for 3D printed resins, although is crucial for adhesive cementation of milled temporary resins. Airborne particle abrasion affects the integrity of 3D-printed resins, without producing a benefit on the microtensile bond strength of these materials. However, sandblasting is crucial to achieve a high bond strength on milled temporary resins.

Novel Denture Cleanser Formulated From Virgin Coconut Oil and The Anionic Emulsifier Against Candida albicans Biofilms Formed on 96-Wells Plate and Acrylic Resin Surfaces

Abstract The objectives of this study were to investigate the inhibitory effect of coconut oil denture-cleansing (CDC) formula against Candida albicans biofilm formed on 96-wells plate and acrylic surfaces at various immersion times and to determine the effects on physical properties of heat-cured acrylic surfaces. A total of twenty-seven CDC formulas were prepared. All CDC formulas were evaluated the stability and anticandidal activity by freeze-defrost cycles and broth microdilution assays, respectively. The formula 22th (F22) containing 0.3 g of anionic emulsifier at a ratio 40:60 of virgin coconut oil to distilled water showed the highest stability and anticandidal activity. The percent inhibition against C. albicans biofilm formed on 96-well plate and acrylic resin surfaces of the F22 after 8 hours of immersion were 86.87 ± 0.65%, and 91.19 ± 1.81%, respectively. However, the F22 had significantly lower inhibitory activity than 0.12% chlorhexidine gluconate (P &lt;0.05). Furthermore, flexural strength of acrylic resin specimens was determined using a 3-point bending test and surface roughness was measured with a profilometer. The flexural strength and the change in surface roughness of F22 were not significant different compared with chlorhexidine and distilled water after 8 hours immersion for 30 days (P &gt;0.05). In conclusions, F22 which containing 0.3 g of anionic emulsifier at the ratio of coconut oil to distilled water at 40:60 exhibited the potent inhibitory activity to Candida albicans biofilms and had no significant effect on the flexural strength and surface roughness of acrylic resins after immersion for 30 days. Keywords: Denture cleanser, Coconut oil, Anionic emulsifier, Biofilm, Candida albicans, Acrylic resins

Interplay between resin cements and surface-treated Poly-Ether-Ether-Ketone (PEEK)

Aim: This study assessed the effect of thermal aging on the interfacial strength of resin cements to surface-treated PEEK. Methods: Ninety-six PEEK blocks were allocated into 4 groups (n=24), according to following surface treatments: SB - sandblasting with aluminum oxide; SA - acid etched with 98% sulfuric acid; CA – coupling agent (Visio.link, Bredent) and CO - control group (untreated). Surface roughness (Ra) was measured and one cylinder (1-mm diameter and height) of Rely-X Ultimate - ULT (3M/ESPE) and another one of Panavia V5 - PAN (Kuraray) were constructed on the treated or untreated PEEK surfaces. Half of the samples of each group were thermal aged (1,000 cycles). Samples were tested at a crosshead speed of 1 mm/min in shear mode (μSBS). Ra and μSBS data were compared using one- and three-way ANOVA, respectively, and Tukey’s tests. Results: SA and SB samples had the roughest surfaces, while CA the smoother (p&lt;0.001). Thermal aging reduced μSBS regardless the surface treatment and resin cement used. There was interaction between surface treatment and resin cement (p &lt;0.001), with ULT showing higher μSBS values than PAN. SA provided higher μSBS than SB for both resin cements, while for CA μSBS was higher (PAN) or lower than SB (ULT). Conclusion: Aging inadvertently reduces interfacial strength between PEEK and the resin cements. If ULT is the resin cement of choice, reliable interfacial strength is reached after any PEEK surface treatment. However, if PAN is going to be used only SA and CA are recommended as PEEK treatment.

Evaluation and Comparison of Impact Strength and Transverse Strength of Heat Polymerized Polymethylmethacrylate (PMMA) Denture Base Resin Repaired Using Heat Polymerizied PMMA Denture Base Resin, Auto-Polymerized PMMA Resin and A New Light Polymerizied Denture Resin: An In Vitro Study.

Repaired denture prosthesisdemands adequate transverse and impact strength. A new repairdenture base resin- "Lukafix" require to fulfil these criteria. This study evaluates and compares the transverse and impact strength of heat polymerizing, auto polymerizing and LUKAfix denture resin. 20 specimens were control(without repair), and other were test specimens which were fractured and repaired with heat polymerized PMMA resin, chemically polymerized PMMA resin and LUKAfix light polymerizing denture resin. Each group wasdivided in two subgroups. Subgroup A was subjected to transverse strength test and subgroup B to impact strength test. One way ANOVA was used to identify the mean difference among the four groups. Post-Hoc-Bonferroni was done to observe the difference between the groups. Maximum transverse strength was observed in specimens repaired with heat polymerized (48.33 ± 9.19) and least in LUKAfix denture resin (6.56 ± 1.15). Also, impact strength was maximum for heat polymerized (3.64 ± 0.41) followed by LUKAfix denture resin (2.34 ± 0.44). Repair with LUKAfix denture resin resulted inferior transverse and impact strength as compared to heat polymerized PMMA resin.

The combined impact of voids and thermal aging on the mechanical reliability of epoxy resin evaluated by statistical analysis

Epoxy resin is widely used in electrical engineering, and its long-term mechanical performance is directly related to the durability of the equipment. The issue might be aggravated when voids are introduced during manufacturing process and when the material is used under high temperature environment. This study aims to precisely reveal the effects of voids and thermal aging on mechanical strength of epoxy resin. Specimens with low and high void content were prepared and thermally aged at 105 ℃ for various lengths of time. Tensile test, scanning electron microscope (SEM) and the finite element simulation were employed to investigate the failure mechanism. The chemical change due to thermal aging was studied by Fourier Transform Infrared Spectroscopy (FTIR). The results illustrate the crack is initiated at the edge of the void due to stress concentration. With the increased void content, there was a slight decrease in the mean tensile strength but a large (108%) increase in the standard deviation. During thermal aging, the chain scission and oxidation were observed via FTIR, along with the inhomogeneity of chemical compounds. A defect density parameter ρ was proposed and integrated into the Weibull distribution to study the synergistic effect of voids and thermal aging on the mechanical properties. This statistical analysis quantitatively describes the decrease in average tensile strength and the increase in data scattering with ascending defect density ρ, due to higher void content and thermal aging. When 0.0005% failure probability is required, the predicted failure stress is significantly reduced from 49.6 MPa to 1.18 MPa for the specimen with high level of void after the long-term aging. In this work, we demonstrate that Weibull statistical analysis can quantitatively evaluate the impact of void defects and thermal aging and provide strength design for the high-reliability epoxy material.

Tamir Materyali Tipi ve Yaşlandırmanın Çeşitli Suni Dişlere Olan Bağlanma Dayanımı Üzerine Etkisi

Objectives: To compare repair bond strength of acrylic and composite resin to different type of artificial teeth with and without thermocycling aging (TMC).&#x0D; Materials and Methods: A total of 192 specimens were prepared using four different types of artificial teeth (n=48) (Group CA-Conventional polymethylmethacrylate, Group IS-Isosite, Group DCL-Double cross-linked acrylic, Group NC-Nanohybrid composite). All specimens were aged with thermocycling (TMC; 5000 cycles, 5◦C/55◦C) and repaired with auto-polymerized acrylic resin or composite resin. Half of the repaired samples were subjected to shear bond strength (SBS) test while the other half were subjected to TMC to simulate the aging of the repair material. Then, artificially aged specimens were also subjected to SBS test. Data were statistically analyzed by three-way analysis of variance (ANOVA). Paired comparisons were made using one-way ANOVA, and multiple comparisons were made using Tukey HSD test (α=0.05).&#x0D; Results: The bond strength of both non-aged and artificially aged composite resin and non-aged acrylic resin did not differ according to artificial teeth type (p&gt;0.05). However, artificially aged acrylic resin showed higher bond strength for group CA (9.25±2.96) than for group NC (5.01±3.09) (p

Epoxy polymer using tannic acid as the green crosslinker, exhibiting globally enhanced mechanical, insulating and thermally conductive properties

Epoxy resin polymers are characteristic of outstanding mechanical and insulating performances, establishing them as critical insulating components in modern electronic devices and power systems. Bio-based polyphenol organics, a substitute for petroleum-based anhydride to cure epoxy resins, can restrict the waste of non-recyclable petroleum resources, meeting the current demand for sustainable development. However, due to rapidly developing industrial demands, such epoxy polymers using bio-based organics as curing agents need further exploration to realize excellent comprehensive properties. Herein, epoxy resin with significantly high crosslink density and few intermolecular defects has been successfully prepared using 1,4-butanediol diglycidyl ether-modified tannic acid as the green crosslinker. The most outstanding comprehensive properties have been realized by adjusting the mass ratio of 1,4-butanediol diglycidyl ether to bisphenol-A epoxy resin to 3: 10. Specifically, the tensile strength, elongation at break, breakdown strength and intrinsic thermal conductivity of tannic acid cross-linked epoxy resin reached 67.6 MPa, 5.4%, 29.8 kV/mm and 0.59 W/(m·K), respectively, globally higher compared with epoxy/anhydride system, which is attributed to the tighter molecular structure, fewer molecular entanglements and less internal defects. Therefore, this work provides a simple and feasible method for preparing tannic acid cross-linked epoxy resin polymers with excellent comprehensive properties, offering potential application value.

Predicting the Effect of Hardener Composition on the Mechanical and Fracture Properties of Epoxy Resins Using Molecular Modeling

Improving the toughness of brittle epoxy while keeping its high strength-to-weight ratio is challenging, as these two properties work against each other. Fracture processes are difficult to ascertain with experiments, as they occur at nanoscopic lengths and time scales and require higher efficiency than what can be attained with atomistic simulations. To overcome this challenge, we utilize a recently developed chemistry specific coarse-grained model to examine two different hardeners, diamine 4,4′-methylenebis(cyclohexylamine) (PACM) and propylene oxide diamine (Jeffamine), to cure bisphenol A diglycidyl ether (DGEBA) at varying stoichiometries and understand how hardener composition influences the elasticity, yield strength, and fracture toughness of epoxy resins. The results indicate that PACM mainly contributes to the modulus and that long Jeffamine chains increase fracture toughness by making the epoxy ductile, whereas short Jeffamine chains significantly improve the yield strength. Longer Jeffamines also lead to larger voids and the formation of fibrils that carry a significant amount of stress and contribute to toughness. Interestingly, the Ashby plots reveal that epoxies with intermediate-length Jeffamine chains (D800 and D2000) outperform other systems, as the toughness enhancement from flexible Jeffamine chains and the stiffness due to PACM help to overcome the strength–toughness trade-off. Our modeling framework and findings establish a path toward resin design from predictive multiscale models with no empirical input and reveal new insights into the molecular failure mechanisms of epoxy resins.

Effect of green tea extract antioxidant on dentin shear bond strength and resin-tag penetration depth after non-vital bleaching

Background: 35% Hydrogen peroxide (H2O2) as an active material for internal bleaching can produce free radicals that can affect resin tag penetration into the dentinal tubules. Application of 10% and 35% green tea (GT) extract as an antioxidant after 2 minutes are expected to remove free radical residues and increase dentin shear bond strength and resin tags penetration depth after non-vital bleaching. Methods: 30 extracted healthy human premolars were cut horizontally 2 mm from the Cemento Enamel Junction margin to the crown part, then cut in a mesio-distal direction into two parts. The specimens were divided into five groups: normal dentin, post bleaching dentin, delayed 2 weeks, 10% GT, and 35% GT group. Non-vital walking bleach with 35% H2O2 gel was done to all groups except control group. Soon after, 10% and 35% GT extract gel were applied on dentin for 2 minutes, then the specimens were rinsed-off with aquabidest for 2 minutes and dried. All specimens were etched and bonded with an etch-and-rinse adhesive system and filled with resin composite. The shear bond strength assessment was carried out using a Universal Testing Machine (UTM) with a cross-head speed of 0.5 mm/minute. Confocal laser scanning microscopy (CLSM) with a wavelength of 560 nm and a lens magnification of 40x was used to analyze the resin tag penetration. Data were analyzed by one way ANOVA and t-test. Results: There was a significant difference in resin tag penetration depth and shear bond strength between applying 10% and 35% GT extract (p &lt; 0.05). The 35% GT extract group resulted in a significantly longer resin tag penetration than the 10% GT extract group. Conclusions: The application of 35% GT extract is more effective than 10% GT extract as an antioxidant for increasing the shear bond strength of composite resin after internal bleaching.

Evaluation of the Influence of Build Orientation on the Surface Roughness and Flexural Strength of 3D-Printed Denture Base Resin and Its Comparison with CAD-CAM Milled Denture Base Resin.

The purpose of this study was to determine the surface roughness and flexural strength of a three-dimensional (3D)-printed denture base resin printed with two different build plate orientations and to compare them with a computer-aided design-computer-aided manufacture (CAD-CAM) milled denture base resin. Sixty-six specimens (n = 22/group) were prepared by 3D printing and CAD-CAM technology. The group A and B specimens were 3D-printed bar-shaped denture base specimens printed at 120-degree and 135-degree build orientation, respectively, whereas group C specimens were milled using a CAD-CAM technology. The surface roughness was assessed using a noncontact profilometer with a 0.01 mm resolution and the flexural strength was determined using a three-point bend test. The maximum load in Newtons (N) at fracture, the flexural stress (MPa), and strain (mm/mm) was also measured. Data were analyzed by a statistical software package. One-way analysis of variance test was applied to determine whether significant differences existed among the study groups, followed by Bonferroni post-hoc test to determine which resin group significantly differed from the others in terms of flexural strength and surface roughness (p ≤ 0.05). The flexural stress (MPa) of group C was 200% of group A and 166% of group B. The flexural modulus was 192% of group A and 161% of group B. In contrast, group A had the lowest mean value among the three groups for all the parameters. No significant difference was seen between group A and group B. The mean roughness values of the CAD-CAM denture base resin specimens (group C) were the least (127356 nm) among all the three groups. The mean surface roughness of the 3D-printed denture base specimens (group A) was 1,34,234 nm and that of group B was (1,45,931 nm); however, it was statistically nonsignificant (p > 0.05) CONCLUSIONS: The CAD-CAM resin displayed superior surface and mechanical properties compared to the 3D-printed resin. The two different build plate angles did not have any significant effect on the surface roughness of the 3D-printed denture base resin.