Influence of polymerization mode on flexural properties of esthetic resin luting agents

The aim of the present study was to evaluate mechanical properties, including surface hardness, flexural strength, and flexural modulus, of two dual-cured resin luting agents [Clearfil Esthetic Cement (CEC) and Variolink II (VLII)] irradiated through four thicknesses of leucite ceramics (0, 1, 2, and 3 mm) and to evaluate their shear bond strength to zirconia ceramic (Cercon) using each ceramic primer. Knoop hardness was measured on a thin layer of resin luting agent on the ceramic surface. Three-point bending tests were performed after 24 hours of storage at 37 degrees C. Two differently shaped zirconia ceramic specimens with or without sandblasting with alumina were treated with each primer. The specimens were then cemented together with each resin luting agent. Half of the specimens were stored in water at 37 degrees C for 24 hours and the other half were thermocycled 5000 times. VLII revealed statistically higher Knoop hardness and flexural modulus than CEC for each thickness of ceramic. No significant differences in flexural strength were observed between VLII and CEC for each ceramic spacer. Reduction of the mechanical properties with increase of ceramic thickness varied for each property; however, these properties were similar in the two materials. Blasting with alumina was significantly effective for increasing shear bond strength of both resin luting agents before and after thermal cycling. The use of Clearfil Ceramic Primer showed the highest shear bond strength and maintained bond durability after 5000 thermocycles. Mechanical properties of CEC dual-cured resin luting agent appear adequate for ceramic restorations.

The effect of filler loading and morphology on the mechanical properties of contemporary composites

The aim of this study was to assess the effect of printing orientation and water ageing on the flexural strength and flexural modulus of 3D printed resins for occlusal splints. Bar-shaped specimens were designed with dimensions of 64 × 10 × 3.3 mm according to ISO 20795-2:2013. Specimens were 3D printed with the Form 3B printer (Formlabs), using Dental LT Clear Resin (CL) or Comfort Resin (CO) (Formlabs), and 3 different printing orientations: as per manufacturer's recommendation (40° N = 20), parallel (0° N = 20), or perpendicular to the build platform (90° N = 20). To simulate intraoral ageing, half of the specimens per material and printing orientation (N = 10) were stored in distilled water at 37 °C for 30 days prior to testing. Specimens were tested in a three-point bending apparatus using a universal testing machine equipped with a 50 N load cell moving at a crosshead speed of 5 mm/min. Flexural strength (MPa) and flexural modulus (GPa) data were collected and statistically processed with separate analyses for unaged and aged specimens (Two-Way or One-Way ANOVA; Tukey test; p < 0.05). As for unaged specimens, both resin materials exhibited the highest flexural strength and modulus in the 90° orientation and the lowest values in the 40° orientation group. After water aging, all groups showed reduced flexural strength and modulus, with CO displaying up to 52% loss in flexural strength and values falling below ISO thresholds. CO consistently exhibited significantly lower flexural strength and modulus than CL, irrespective of aging.

Mechanical properties, cytotoxicity, and protein adsorption of three-dimensionally printable hybrid resin containing zwitterionic polymer and silicate-based composites for dental restorations

Digital dentures can be fabricated by subtractive milling or, more recently, by 3D-printing technology. Several different 3D-printing technologies and materials are commercially available, and the differences in printing accuracy and mechanical behavior among them are unknown. Aim: This study evaluated the printing accuracy of 3D-printed denture base resins and assessed their flexural properties when compared with conventional heat-polymerized ones. Methods: A total of 40 acrylic specimens were prepared with four different materials: three 3D-printed resins, and a conventional heat polymerized resin was used as a control. The printing accuracy was evaluated by calculating the error rate of 3D-printed specimens compared with dimensions of the virtual design. Flexural strength and elastic modulus were assessed with a universal testing machine. One-way ANOVA and Kruskal–Wallis tests were used for analysis. Results: Printing accuracy across the tested materials was statistically different. Specimen length showed error rates between 1.3% and 2.4%, specimen width had error rates between 0.2% and 0.7%, and specimen thickness had error rates between 0.2% and 0.6%. Three-dimensional-printed specimens had lower flexural strength and elastic modulus values when compared with heat-polymerized specimens. Conclusions: The choice of material seems to influence printing accuracy, and to a lesser extent, flexural strength. However, it has no effect on the elastic modulus.

Objective: This study evaluated the effect of the activation mode on flexural strength and elasticity modulus of four dual cure resin-based cements. Methods: Two self-adhesive resin cements (Clearfil SA Cement (CSA) and RelyX U100 (U)) and two conventional resin cements (Clearfil Esthetic Cement (CE)and RelyX ARC (ARC)) were used to produce a total of 45 bar specimens (7x2x2 mm) using three different activation modes (n=15): Direct light-cure (D), Indirect light-cure using a 2mm composite resin barrier (I) and Self-cure (S). Three-point flexural tests were performed after 24 hours water storage at 37° C, using a universal testing machine (Instron) at a cross-speed of 0.5 mm/min until fracture. Flexural strength (MPa) and elasticity modulus values were subjected to ANOVA and Tukey’s Test (=0.05). Results: Data revealed that light polymerized groups presented statistically higher flexural strength (CSA/D=113.63 ± 19.65; CSA/I=80.66 ± 23.74; U/D=101.33 ± 9.8; U/I=94.96 ± 36.9; CE/D=219.08 ± 39.94; CE/I=226.42 ± 34.59; ARC/D=150.03 ± 26.15; ARC/I=111.78 ± 14.28) and also elasticity modulus values (CSA/D = 2.9 ± 0.6; CSA/I = 1.5 ± 0.4; U/D = 2.9 ± 0.5; U/I = 2.6 ± 1.4; CE/D = 6.5 ± 1.3; CE/I = 5.8 ± 1.0; ARC/D = 4.2 ± 0.93; ARC/I = 2.5 ± 0.5) compared to self-cured groups (flexural strength: CSA/S=65.81 ± 21.84; U/S=53.62 ± 28.73; CE/S=129.02 ± 51.67; ARC/S=77.98 ±19.61 and elasticity modulus: CSA/S = 1.4 ± 0.5; U/S = 1.2 ± 0.7; CE/S = 2.2 ± 1.5; ARC/S = 1.0 ± 0.5). The usage of a composite resin barrier only affected the mechanical properties of ARC and CSA. Conventional resin cements presented higher flexural strength values than the self-adhesive cements. CE presented the highest values compared to all other cements. No statistical difference was observed between self-adhesive cements. Conclusion: Light-curing of resin luting cements produced higher flexural strength for all tested materials. Similar mechanical behavior was observed for the tested self-adhesive cements.

To determine and compare the microstructure, flexural strength, flexural modulus, fracture strength, and microhardness of four types of computer-aided design/computer-aided manufacturing (CAD/CAM) materials for monolithic dental restorations. A lithium disilicate (LD; IPS e.max CAD), a zirconia-reinforced lithium silicate (ZLS; VITA Suprinity), a hybrid high-performance polymer (HPP) composite resin (GC Cerasmart), and a hybrid polymer-infiltrated ceramic network (PICN) material (VITA Enamic) were used to manufacture monolithic ceramic posterior crowns (n = 10) that were adhesively cemented on resin-based composite dies and loaded until fracture. In addition, 40 rectangular bars (n = 10) were milled and polished for three-point flexural strength testing. Microhardness (Vickers indentation), as well as quantitative (energy dispersive spectroscopy) and qualitative (scanning electron microscopy) structural analysis were conducted on fracture surfaces. Data were analyzed by one-way ANOVA and Tukey HSD post-hoc test (p = 0.05). Mechanical testing results showed that the material type has a significant effect on the fracture strength (p < 0.0001) of the monolithic crowns with ZLS and LD presenting significantly higher fracture strength than the PICN and HPP hybrid materials. LD showed the highest flexural strength (p < 0.0001) followed by ZLS, HPP, and PICN, respectively. The lowest flexural modulus and hardness were presented by HPP whereas ZLS had the highest flexural modulus and hardness. The LD presented the highest modulus of resilience and the PICN the lowest. All CAD/CAM crown materials exhibited high values of fracture and flexural resistance, making them suitable materials for posterior full-crown restorations. Glass-ceramics suffered more from catastrophic and nonreparable fracture patterns, whereas minimal chipping and type II fracture patterns were more common in hybrid materials. The combination of more flexibility, less stiffness, and increased softness with satisfactory flexural and fracture strength values observed in PICN and HPP makes these two hybrid materials suitable choices for chairside monolithic crown fabrication.

This study investigates the effect of the curing mode (dual-cure vs. self-cure) of resin cements (four self-adhesive and seven conventional cements) on their flexural strength and flexural modulus of elasticity, alongside their shear bond strength to lithium disilicate ceramics (LDS). The study aims to determine the relationship between the bond strength and LDS, and the flexural strength and flexural modulus of elasticity of resin cements. Twelve conventional or adhesive and self-adhesive resin cements were tested. The manufacturer's recommended pretreating agents were used where indicated. The shear bond strengths to LDS and the flexural strength and flexural modulus of elasticity of the cement were measured immediately after setting, after one day of storage in distilled water at 37 °C, and after 20,000 thermocycles (TC 20k). The relationship between the bond strength to LDS, flexural strength, and flexural modulus of elasticity of resin cements was investigated using a multiple linear regression analysis. For all resin cements, the shear bond strength, flexural strength, and flexural modulus of elasticity were lowest immediately after setting. A clear and significant difference between dual-curing and self-curing modes was observed in all resin cements immediately after setting, except for ResiCem EX. Regardless of the difference of the core-mode condition of all resin cements, flexural strengths were correlated with the LDS surface upon shear bond strengths (R2 = 0.24, n = 69, p < 0.001) and the flexural modulus of elasticity was correlated with them (R2 = 0.14, n = 69, p < 0.001). Multiple linear regression analyses revealed that the shear bond strength was 17.877 + 0.166, the flexural strength was 0.643, and the flexural modulus was (R2 = 0.51, n = 69, p < 0.001). The flexural strength or flexural modulus of elasticity may be used to predict the bond strength of resin cements to LDS.

The aim of this study was to evaluate mechanical properties of six new-generation all-ceramic materials for CAD/CAM (Lava Ultimate [LU], VITA Mark II [VM], InCoris TZI [IC], IPS e.max CAD [EM], VITA Suprinity [VS], IPS Empress CAD [EC]) and two different provisional restoration CAD/CAM materials (Telio CAD [TC], Vita CAD-Temp [VC]) after different storage conditions. 36 bar-shaped samples of 4 mm in width and 14 mm in length with 1.2 mm thicknesses were prepared from each material group (N=288). The specimens from each material were kept under three different storage conditions (n=12): under dry conditions at room temperature; 37°C distilled water for 7 days; and 37°C distilled water for 7 days followed by 10,000 thermal cycles. All specimens were subjected to a 3-point flexural test with a crosshead speed of 1.0 mm/min. The specimens were loaded until failure. Twelve fractured specimens after the flexural test from each group were used for the Vickers hardness test (under 300 gf of loading in 15 seconds). The flexural modulus, flexural strength and Vickers hardness values were separately analyzed with two-way analysis of variance, Tukey’s multiple comparison tests at a significance level of p&lt;0.05. There were statistically significant differences between materials and storage conditions according to flexural modulus, flexural strength and Vickers hardness values (p&lt;0.05). The flexural strength, flexural modulus and Vickers hardness values of LU, VC, TC, VS and IC decreased after water storage followed by thermal cycling (p&lt;0.05). The mechanical properties of provisional restoration CAD/CAM materials had showed a significantly decrease after water storage followed by thermal cycles but their mechanical properties were acceptable for fabrication of provisional restorations. The mechanical properties of VM, EC and EM were not affected by different storage conditions whereas IC and VS were affected.

The current investigation is focused on improving the flexural properties of perlite/sodium silicate composites using fly ash as reinforcement. Perlite/sodium silicate composites are reinforced with varying amount of fly ash (15 %, 30 %, and 45 %). Formica sheet was used as skins of the sandwich structures with fly ash reinforced perlite/sodium silicate composite as core. To attach the formica sheet skins with core pure epoxy and fly ash reinforced epoxy was used. The flexural strength and modulus of perlite/sodium silicate composite, fly ash reinforced perlite/sodium silicate composite, and two types of sandwiches are determined by three point bending test according to the standard. Results showed that the flexural strength of fly ash reinforced perlite/sodium silicate composite for 30 % fly ash content was maximum and 147.62 % greater than perlite/sodium silicate composite without reinforcement. The flexural modulus increased with increasing fly ash content up to 40 % fly ash content. The maximum enhancement in flexural strength and modulus of fly ash reinforced core-based sandwiches were also found at a fly ash content of 30 %. Utilization of fly ash reinforced epoxy as adhesive layer in the interface between the core and the skin improved the flexural modulus of the sandwiches significantly but the flexural strength slightly decreased. The study suggests that fly ash is an excellent reinforcing agent for the improvement of the flexural properties of perlite/sodium silicate composites and their sandwich structures.

The purpose of this study was to evaluate the influence of study protocols on the effects of bleaching on the surface roughness, substance loss, flexural strength (FS), flexural modulus (FM), Weibull parameters, and color of 7 restorative materials. The test materials included 4 composite resins, 1 glass-ionomer cement, 1 dental ceramic, and 1 polyacid-modified composite. The specimens were randomly divided into 4 groups (n = 20) according to different study protocols: a bleaching group at 25°C (group 25B), a bleaching group at 37°C (group 37B), a control group at 25°C (group 25C), and a control group at 37°C (group 37C). The specimens in the bleaching group were treated with 40% hydrogen peroxide for 80 min at the respective environmental temperatures. The surface roughness, substance loss, FS, FM, and color of the specimens were measured before and after treatment. FS data were also subjected to Weibull analysis, which was used to estimate of the Weibull modulus (m) and the characteristic strength (σ0 ). Surface roughness increased and significant color changes were observed for all tested specimens after bleaching treatment, except for the ceramic. After bleaching at 37°C, the polyacid-modified composite showed significantly reduced FS, FM, m, and σ0 values in comparison to the control specimens stored at 37°C in whole saliva. Significant differences were also found between the 37B and 25B polyacid-modified composite groups in terms of surface roughness, FS, m, σ0 , and color changes. Varying effects of bleaching on the physical properties of dental restorative materials were observed, and the influences of the study protocols on bleaching effects were found to be material-dependent. The influence of study protocols on the effects of bleaching on the surface roughness, flexural properties, and color of dental restorative materials are material-dependent and should be considered when evaluating the effects of bleaching on dental restorative materials.

Ferrite and nano‐barium titanate reinforced poly(ether ether ketone) (PEEK) composites were made by compression moulding technology. The effects of reinforcement of the ferrite and nano‐barium titanate on the PEEK matrix were studied with the aim assessing its potential as a radar‐absorbing structural material (RASM). With an increase in the percentage filling of ferrite in the PEEK matrix, the specific gravity, hardness, tensile and flexural moduli, brittleness, dielectric constant, loss tangent and reflection losses were increased, while the tensile and flexural strengths, and elongation at break, were decreased. With increasing nano‐barium titanate reinforcement in the ferrite‐filled PEEK composites, the specific gravity, hardness, tensile and flexural strengths, tensile modulus and dielectric constant were comparatively increased, while the elongation at break, flexural modulus and loss tangent (marginally) were decreased. Reinforcement of the nano‐barium titanate caused a comparatively marginal reduction in the loss tangent, although no effect on reflection losses was observed. The solubility resistance of the ferrite‐filled PEEK composites was improved with reinforcement by the nano‐barium titanate. Copyright © 2004 Society of Chemical Industry

Nanocomposites were formed by curing the dispersion of carbon nanofillers—nanographene platelets and vapor grown carbon nanofibers—in resole type phenolic resin. X-ray diffraction, fourier transform infrared spectroscopy, scanning electron microscopy, thermal expansion, and thermogravimetric and flexure testing were carried out to study the morphology and thermal and mechanical properties of the manufactured nanocomposites. The coefficient of thermal expansion decreased by 15.36% (73.83 µm/m℃) and 14.23% (74.81 µm/m℃) with 1.5 wt% nanographene platelets and 1.5 wt% vapor grown carbon nanofibers, respectively, compared with neat phenolic (87.23 µm/m℃) in the temperature range 60–80°. The flexure strength of neat phenolic resin increased by 31.62% (48.57 MPa) and flexure modulus by 42.23% (2.9 GPa) at 0.5 wt% nanographene platelets. Comparatively, vapor grown carbon nanofibers at 1.5 wt% increased the flexure strength by 14.3% and flexure modulus by 23.5%. Nanographene platelets and vapor grown carbon nanofibers increased the char content of neat phenolic resin. The char content increased by 200% at 800℃ in 5 wt% nanographene platelet nanocomposites, compared with 75% increase in 3 wt% vapor grown carbon nanofibers nanocomposite. Nanographene platelets were more effective than vapor grown carbon nanofibers in lowering the coefficient of thermal expansion of neat phenolic, in improving its flexure strength and modulus and in increasing the char yield. The results indicate that nanographene platelets can be effectively used as carbon nanofiller in the manufacture of carbon/carbon composites.

Effect of uniaxial bending methods on the flexural strength and Weibull analysis of heat-polymerized, CAD/CAM milled, and 3D-printed denture base resins.

BackgroundThe use of composites in dental restoration has been commonly criticized, due to their underwhelming mechanical properties. This problem may be solved partially by preheating. The present research aims to determine the effect of preheating on the mechanical properties of two different classes of composites. Material and Methods A Silorane-based (Silorane) and a Methacrylate-based (Z250) composite were preheated to different temperatures (25, 37, and 68 °C) and afterwards were tested with the appropriate devices for each testing protocol. The material’s flexural strength, elastic modulus, and Vickers microhardness were evaluated. Two-way ANOVA, and Tukey’s post hoc were used to analyze the data. Results Microhardness and elastic modulus increased with preheating, while flexural strength values did not increase significantly with preheating. Furthermore the methacrylate-based composite (Z250) showed higher values compared to the Silorane-based composite (Silorane) in all the tested properties. Conclusions Preheating Silorane enhances the composite’s microhardness and elastic modulus but does not affect its flexural strength. On the other hand, preheating Z250 increases its microhardness but does not change its flexural strength or elastic modulus. In addition, the Z250 composite shows higher microhardness and flexural strength than Silorane, but the elastic modulus values with preheating are similar. Therefore Z250 seems to have better mechanical properties making it the better choice in a clinical situation. Key words:Composite, elastic modulus, flexural strength, microhardness, preheating.