Unfilled Resin Research Articles

Effect of Hydrofluoric Acid Concentration and Etching Time on Bond Strength to Lithium Disilicate Glass Ceramic.

The aim of this study was to evaluate the influence of different concentrations of hydrofluoric acid (HF) associated with varied etching times on the microshear bond strength (μSBS) of a resin cement to a lithium disilicate glass ceramic. Two hundred seventy-five ceramic blocks (IPS e.max Press [EMX], Ivoclar Vivadent), measuring 8 mm × 3 mm thickness, were randomly distributed into five groups according to the HF concentrations (n=50): 1%, 2.5%, 5%, 7.5%, and 10%. Further random distribution into subgroups was performed according to the following etching times (n=10): 20, 40, 60, 120, and 20 + 20 seconds. After etching, all blocks were treated with a silane coupling agent followed by a thin layer of an unfilled resin. Three resin cement cylinders (∅=1 mm) were made on each EMX surface, which was then stored in deionized water at 37°C for 24 hours before testing. The μSBS was in a universal testing machine at a crosshead speed of 1 mm/min until failure. Data were submitted to two-way analysis of variance, and multiple comparisons were performed using the Tukey post hoc test (α=0.05). One representative EMX sample was etched according to the description of each subgroup and evaluated using scanning electron microscopy for surface characterization. The HF concentrations of 5%, 7.5%, and 10% provided significantly higher μSBS values than 1% and 2.5% (p<0.05), regardless of the etching times. For 1% and 2.5% HF, the etching times from 40 to 120 seconds increased the μSBS values compared with 20 seconds (p<0.05), but etching periods did not differ within the 5%, 7.5%, and 10% HF groups (p>0.05). The effect of re-etching was more evident for 1% and 2.5% HF (p<0.05). Different HF concentrations/etching times directly influenced the bond strength and surface morphology of EMX.

Antimicrobial and biological activity of leachate from light curable pulp capping materials

ObjectivesCharacterization of a number of pulp capping materials and assessment of the leachate for elemental composition, antimicrobial activity and cell proliferation and expression. MethodologyThree experimental light curable pulp-capping materials, Theracal and Biodentine were characterized by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. The elemental composition of the leachate formed after 24h was assessed by inductively coupled plasma (ICP). The antimicrobial activity of the leachate was determined by the minimum inhibitory concentration (MIC) against multispecies suspensions of Streptococcus mutans ATCC 25175, Streptococcus gordonii ATCC 33478 and Streptococcus sobrinus ATCC 33399. Cell proliferation and cell metabolic function over the material leachate was assessed by an indirect contact test using 3-(4,5 dimethylthiazolyl-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. ResultsThe hydration behavior of the test materials varied with Biodentine being the most reactive and releasing the highest amount of calcium ions in solution. All materials tested except the unfilled resin exhibited depletion of phosphate ions from the solution indicating interaction of the materials with the media. Regardless the different material characteristics, there was a similar antimicrobial activity and cellular activity. All the materials exhibited no antimicrobial activity and were initially cytotoxic with cell metabolic function improving after 3days. ConclusionsThe development of light curable tricalcium silicate-based pulp capping materials is important to improve the bonding to the final resin restoration. Testing of both antimicrobial activity and biological behavior is critical for material development. The experimental light curable materials exhibited promising biological properties but require further development to enhance the antimicrobial characteristics.

Laboratory evaluation of the effect of unfilled resin after the use of self-etch and total-etch dentin adhesives on the Shear Bond Strength of composite to dentin.

BackgroundBased on the frequent application of composite resins as tooth-colored fillings, this method is considered a viable alternative to dental amalgam. However, this method has the low bond strength of the composite to dentin. To solve this issue, various dental adhesive systems with different characteristics have been developed by dentistry experts.AimTo assess the effect of an additional layer of unfilled resin in self-etch and total-etch dentin adhesives on the shear bond strength (SBS) of composite to dentin. Moreover, we assessed the effects of sample storage in artificial saliva on the SBS of composite to dentin.MethodsMethods: This experimental study was conducted on 160 freshly extracted human first or second premolar teeth, which were randomly divided into 16 groups. The teeth were prepared from Mashhad University of Medical Sciences, Mashhad, Iran (2008–2009). Scotchbond Multi-purpose (SBMP), single bond (SB), Clearfil SE Bond, and Clearfil S3 Bond were applied to dentin surface with or without the placement of hydrophobic resin (Margin Bond) in accordance with the instructions of the manufacturers. To expose the coronal dentin, the teeth were abraded with 600 grit SiC paper. Immediately after restoration, half of the samples were tested in terms of SBS, while the other samples were evaluated in terms of SBS after three months of storage in artificial saliva. SBS rates of dental composites evaluated by universal testing machine and samples were studied by optical stereomicroscopy to verify the failure type. Data analysis was performed in SPSS V.16 using Kolmogorov-Smirnov test, independent-samples t-test, ANOVA, and Duncan’s logistic regression test.ResultsIn this study, a significant reduction was observed in the SBS rates of SB and S3 bond adhesive systems after storage with and without hydrophobic resin (p>0.000). Without storage in normal saline, a significant increase was observed in the SBS rate of the SE bond (p=0.013). In addition, SBS rate of SBMP significantly increased after storage with hydrophobic resin (p=0.001). Finally, the highest and lowest rates of SBS were observed in the SE and S3 bonds in all the experimental groups, respectively.ConclusionThe effects of using a hydrophobic resin layer on shear bond strength values seem to be effective. The mild self-etch adhesive exhibited the best resin-dentine bond strength after aging

IN VITRO EVALUATION OF WEAR RESISTANCE OF DIFFERENT FISSURE SEALANTS AFTER AGING PROCEDURES

Objective: The purpose of this study is to evaluate the ability of unfilled resin based sealant (Clinpro), glass ionomer fissure sealants (Fuji Triage) and nanofilled resin based fissure sealant (Tetric N-Flow) to resist surface degradation using chewing simulator combined with thermocycling. Methodology: A total of 30 disk shaped specimens were prepared, 10 disks for each material. Surface roughness (Ra) and weight loss were quantitatively measured after 2-body wear testing by using a chewing simulator ‎integrated with thermocycling. Data were statistically analyzed using one-way ANOVA and Bonferroni’s post-hoc test (P ≤ 0.05)Result: Both unfilled resin based sealant (RS) and glass ionomer fissure sealant (GI) showed statistically significant higher (Ra) than nanofilled resin based fissure sealant (NS) before aging procedure. After chewing simulator and thermocycling; there was no statistically significant difference between the (Ra) of three fissure sealant materials. As regard to weight loss (GI) showed the highest mean weight loss followed by (RS) while (NS) showed the lowest mean weight loss. Conclusion: nanofilled resin based fissure sealant showed good resistance to surface degradation compared to other sealants.

Kinetics and mechanics of photo-polymerized triazole-containing thermosetting composites via the copper(I)-catalyzed azide-alkyne cycloaddition

ObjectiveSeveral features necessary for polymer composite materials in practical applications such as dental restorative materials were investigated in photo-curable CuAAC (copper(I)-catalyzed azide-alkyne cycloaddition) thermosetting resin-based composites with varying filler loadings and compared to a conventional BisGMA/TEGDMA based composite. MethodsTri-functional alkyne and di-functional azide monomers were synthesized for CuAAC resins and incorporated with alkyne-functionalized glass microfillers for CuAAC composites. Polymerization kinetics, in situ temperature change, and shrinkage stress were monitored simultaneously with a tensometer coupled with FTIR spectroscopy and a data-logging thermocouple. The glass transition temperature was analyzed by dynamic mechanical analysis. Flexural modulus/strength and flexural toughness were characterized in three-point bending on a universal testing machine. ResultsThe photo-CuAAC polymerization of composites containing between 0 and 60wt% microfiller achieved ∼99% conversion with a dramatic reduction in the maximum heat of reaction (∼20°C decrease) for the 60wt% filled CuAAC composites as compared with the unfilled CuAAC resin. CuAAC composites with 60wt% microfiller generated more than twice lower shrinkage stress of 0.43±0.01MPa, equivalent flexural modulus of 6.1±0.7GPa, equivalent flexural strength of 107±9MPa, and more than 10 times higher energy absorption of 10±1MJm−3 when strained to 11% relative to BisGMA-based composites at equivalent filler loadings. SignificanceMechanically robust and highly tough, photo-polymerized CuAAC composites with reduced shrinkage stress and a modest reaction exotherm were generated and resulted in essentially complete conversion.

Elaboration and characterization of composite material based on epoxy resin and clay fillers

The present work aims at investigating the effect of locally produced clay (Algeria), along with the effect of their size and rate on physical and mechanical properties of the composite material. This study is divided into two parts: The first one is devoted to the study of the composite material based on epoxy resin with kaolin, using different size fractions at rates ranging from 2% to 20%. The second part examines epoxy resin-based composite with calcined kaolin (metakaolin) with regard to the influence of the structure, the particle size and the charge rate on the properties of the material. It is shown that the clay fillers give the epoxy resin different properties compared to the epoxy resin alone and, additionally, reduce the cost of materials. It was also observed that the fillers enhance the mechanical properties by increasing the rigidity of the material. There is a maximum value of 2.4 GPa to 18% kaolin, or more than 325% increase in the modulus of elasticity with respect to unfilled resin for the finer particle size. It was also found that the modulus of elasticity increases with increasing the loading rate. Indeed, the rigidity increases with increasing the filler rate. Moreover, for both fillers, lower fraction yields better results. Moreover, for both types of added fillers, lower fraction yields better results.

Reinforcement of Stereolithography Resin with Silica-Based Fillers

This study investigated the improvement of hardness and flexural properties of a commercial stereolithography (SLA) resin by reinforcement with silica-based fillers. Three types of fillers were studied: synthetic amorphous silica, milled fiberglass, and geothermal scale powder. Particle size and aspect ratio of fillers were estimated from scanning electron microscopy (SEM) images, while chemical structure was characterized by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Fillers were added to SLA resin at 0, 10, and 20 vol%. Hardness and flexural properties of SLA composites are higher than unfilled resin. Moreover, both hardness and flexural properties of SLA composites are improved according to type (milled fiberglass &gt; synthetic amorphous silica &gt; geothermal scale powder) and loading (20 vol% &gt; 10 vol%). The observed effect of filler type and loading on hardness and flexural properties of SLA composites is due to aspect ratio, intrinsic properties and dispersion of filler.

Detection of nanoparticles released at finishing of dental composite materials

Newly developed dental composite materials contain increased concentrations of filler particles of the nanometer size to produce materials with high mechanical and wear resistance, improved polishability, and long-lasting gloss. With nanocomposites, however, a question arises on possible health risk caused by filler nanoparticles released during finishing and polishing nanocomposite restorations in dental cabinets. As data in the current literature are conflicting, our study was focused on detailed characterization of aerosol particles released during grinding nanocomposites Filtek Ultimate and Estelite Sigma Quick by diamond and tungsten carbide bladed burs. The results were compared with the aerosol particle size obtained from a composite Charisma reinforced with micrometer-size filler particles and an unfilled resin. Using a scanning mobility particle sizer and aerodynamic particle sizer, the release of nano- and micro-sized particles generated during high-speed grinding was detected. The mode of nanoparticle size distribution ranged not only from less than 16.0 to 51.6 nm for both nanocomposites, but also for the microhybrid composite and the unfilled resin. However, the amount of nanoparticles in the aerosol (5.0–68) × 103 cm−3 was not high exceeding 1–8.5 times their background concentration. The release of nanoparticles independently on the filler particle size and their content might suggest that the aerosol nanoparticles may originate from thermal decomposition of composite polymeric matrix due to friction heat rather than from filler nanoparticles. Due to the potential adverse health effects of nanoparticles, more detailed research is needed to investigate the effect of finishing conditions on the nanoparticle generation and their chemical composition to avoid any potential risk to dental staff. A study of the aerosol formed during grinding with water cooling to avoid heating will also be carried out.

Comparative analysis of the mechanical properties of fiber and stainless steel multistranded wires used for lingual fixed retention

ObjectiveTo evaluate the effect of different resins used for the co-polymerization of EverStick fiber-reinforced fixed orthodontic retainer on its mechanical properties and to compare the mechanical properties of these configurations to commonly used multistrand wires. Materials and methodsTen 0.0175-in. WildCat (WC175), ten 0.0215-in. WildCat (WC215) three-strand twisted wires and thirty EverStick fibers were tested in this study. The EverStcik fibers were equally shared in three groups (n=10). The samples of first group (ESRE) were polymerized employing Stickresin (Light cure enamel adhesives), the second one (ESFT) employing Flow Tain (Light cured composite), whilst the specimens for the third group (ES) were not combined with resin. All samples were loaded in tensile up to fracture in a universal tensile testing machine and the modulus of elasticity, tensile strength and strain after fracture were recorded. The same groups were also tested employing Instrumented Indentation Testing (IIT) and Martens Hardness (HM), Indentation Modulus (EIT) and elastic index (ηIT) were determined. The results of tensile testing and IIT were statistically analyzed employing one way Anova and the Student Newman Keuls test (SNK) at a=0.05 level of significance. ResultsWC175 and WC215 showed higher modulus of elasticity and tensile strength but lower strain after fracture compared to Everstic groups. IIT illustrated significantly higher values for HM, EIT, and ηIT for WC groups compared to ESRE, ESFT and ES. ESFT showed higher HM and elastic index compared to ESRE and ES, a finding which is attributed to the fact the FlowTain is a filler-reinforce composite with higher hardness compared to unfilled resins. SignificanceMultistrand wires demonstrated higher values in mechanical properties compared to EverStick ones. The co-polymerization with difference resins does not affect the tensile properties of Everstic, however the use of a light cured composite has a beneficial effect on hardness.

Zastosowanie systemu optycznego ATOS II w technikach szybkiego prototypowania modeli kół zębatych otrzymywanych na bazie żywicy epoksydowej

The mechanical and processing properties of composites with epoxy resin (EP) matrix and hybrid fillers, especially with regard to their use in rapid prototyping methods for the preparation of gear models, were evaluated. The accuracy assessment of geometric model shape mapping was performed using a non-contact optical system based on the coordinate optical scanner ATOS Triple Scan II Blue Light from GOM company. The produced hybrid composites show much better mechanical properties than those of unfilled epoxy resin. By introducing the hybrid fillers into EP matrix, a reduction in radial and axial shrinkage was achieved, which led to a radical improvement in the accuracy of geometric shape mapping of gear castings.

Sealing effectiveness of fissure sealant bonded with universal adhesive systems on saliva-contaminated and noncontaminated enamel.

BackgroundThe effectiveness of sealants is dependent upon their adhesion to enamel surface. The aim of the study was to evaluate the sealing ability of a pit and fissure sealant used with a universal adhesive (etch-and-rinse vs. self-etch modes) when the site is contaminated with saliva. Adhesive properties were evaluated as microleakage and scanning electron microscopic (SEM) characteristics.Material and MethodsA total of 72 mandibular third molars were randomly divided into 6 groups (n=12). Occlusal pits and fissures were sealed with an unfilled resin fissure sealant (FS) material with or without saliva contamination. The groups included: 1) phosphoric acid etching + FS (control), 2) phosphoric acid etching + Scotchbond Universal (etch-and-rinse) + FS, 3) phosphoric acid etching + saliva + Scotchbond Universal (etch-and-rinse) + FS, 4) Scotchbond Universal (self-etching) + FS,5) Scotchbond Universal (self-etching) + saliva + FS, and 6) Scotchbond Universal (self-etching) + saliva + Scotchbond Universal + FS. After thermocycling, the teeth were placed in 0.5% fuchsin, sectioned, and evaluated by digital microscopy. Two samples from each group were also observed by SEM. The data were analyzed with Kruskal-Wallis and Mann-Whitney tests for a significance of p<0.05.ResultsThere were significant differences among groups. Groups 1,2 and 4 showed the least microleakage, with no significant differences among groups. Saliva contamination led to increased microleakage and gap formation in SEM images in groups 3, 5 and 6.ConclusionsThe fissure sealing ability of the universal adhesive in etch-and-rinse or self-etch modes was similar to that of conventional acid etching. Saliva contamination had a negative effect on sealant adhesion to pretreated enamel. Key words:Pit and fissure sealant, Universal adhesive, Saliva.

Effect of protective coating on microhardness of a new glass ionomer cement: Nanofilled coating versus unfilled resin.

Background and Objectives:EQUIATM is a new gastrointestinal (GI) system with high compressive strength, surface microhardness (MH), and fluoride release potential. This in vitro study aimed to assess the effect of aging and type of protective coating on the MH of EQUIATM GI cement.Materials and Methods:A total of 30 disc-shaped specimens measuring 9 mm in diameter and 2 mm in thickness were fabricated of EQUIATM GI and divided into three groups of G-Coat nanofilled coating (a), no coating (b) and margin bond (c). The Vickers MH value of specimens was measured before (baseline) and at 3 and 6 months after water storage. Data were analyzed using repeated measures ANOVA.Results:Group B had significantly higher MH than the other two groups at baseline. Both G-Coat and margin bond increased the surface MH of GI at 3 and 6 months. The MH values of G-Coat and margin bond groups did not significantly increase or decrease between 3 and 6 months.Conclusion:The increase in MH was greater in the G-Coat compared to the margin bond group in the long-term. Clinically, margin bond may be a suitable alternative when G-Coat is not available.

The Effect of Hydrofluoric Acid Concentration and Heat on the Bonding to Lithium Disilicate Glass Ceramic.

The aim of this study was to evaluate the effects of hydrofluoric acid (HF) concentration and previous heat treatment (PHT) on the surface morphology and micro-shear bond strength (mSBS) of a lithium disilicate glass ceramic (EMX) to resin cement. One hundred four EMX specimens were randomly assigned to two groups (n=52) according to the HF concentration: 5% and 10%. A new random distribution was made according to the PHTs (n=13): control (no PHT); previously heated HF (70 °C); previously heated EMX surface (85 °C); the combination of heated HF + heated EMX surface. The etching time was set at 20 s. All EMX blocks were silanated and received a thin layer of an unfilled resin. Five resin cement cylinders were made on each EMX surface using Tygon tubes as matrices, and then stored for 24 h at 37 °C. One random etched EMX sample from each group was analyzed using field-emission scanning electron microscopy (FE-SEM). The data were subjected to two-way ANOVA and multiple comparisons were performed using the Tukey post hoc test (a=0.05). For the control groups, 5% HF showed statistically lower mSBS values when compared to 10% HF (p<0.05). PHT increased the mSBS values for 5% HF, yielding statistically similar results to non-PHT 10% HF (p<0.05). FE-SEM images showed increased glassy matrix removal when PHT was applied to HF 5%, but not to the same degree as for 10% HF. PHT has the potential to improve the bond strength of 5% HF concentration on lithium disilicate glass ceramic.

Polymer-based material containing calcium phosphate particles functionalized with a dimethacrylate monomer for use in restorative dentistry.

Dicalcium phosphate dihydrate particles functionalized with triethyleneglycol dimethacrylate were synthesized and added to a photocurable mixture of bisphenol-A glycidyl dimethacrylate and triethyleneglycol dimethacrylate with the purpose of developing a resin composite capable of releasing calcium and phosphate ions to foster dental remineralization. Particle functionalization would minimize the deleterious effect of adding low cohesive strength nano-structured particles with no chemical interaction with the organic matrix on the material's mechanical properties. The results showed that calcium release over 28 days was not impaired by particle functionalization. A statistically significant 32% increase in strength was recorded with the use of functionalized dicalcium phosphate dihydrate in comparison to the material containing non-functionalized particles. However, the strength of the unfilled resin was not matched by the composite with functionalized particles. Elastic modulus increased with particle incorporation, regardless of functionalization. Degree of conversion and optical properties (total transmittance and color change/ΔE) of the resin-based materials were not affected by the addition of dicalcium phosphate dihydrate particles (functionalized or not).

Novel urethane-based polymer for dental applications with decreased monomer leaching

The aim of this study was to synthesize and characterize new multifunctional-urethane-methacrylate monomers to be used as the organic matrix in restorative dental composites, and evaluate the main physical-chemical properties of the resulting material. Bis-GMA (bisphenol-A-diglycidylmethacrylate) and GDMA (glycerol dimethacrylate) were modified by reacting the hydroxyl groups with isocyanate groups of urethane-methacrylate precursors to result in the new monomeric systems U-(bis-GMA)-Mod and U-(GDMA)-Mod, U=Urethane and Mod=Modified. The modifications were characterized by FTIR and 1H NMR. The final monomeric synthesized system was used to prepare dental resins and composites. The physical-chemical properties were evaluated and compared with those of bis-GMA composites with varying filler contents or unfilled resins. U-(bis-GMA)-Mod and U-(GDMA)-Mod can be used to prepare dental restorative composites, with some foreseeable advantages compared with bis-GMA composites. One significant advantage is that these composites have the potential to be less toxic, once they presented a reduction of 50% in leaching of unreacted monomers extracted by solvent.

Cure kinetics and physical characterization of epoxy/modified boehmite nanocomposites

Nanocomposites based on a cross-linked epoxy matrix with the addition of a reinforcing organically modified boehmite nano-phase were realized and characterized with the aim to produce systems possessing enhanced properties over commercial epoxy systems. Different amounts of a commercially available organically modified boehmite were added to a diglycidyl ether of bisphenol A (DGEBA) epoxy matrix. The rheological characteristic and kinetic behavior of the liquid nano-filled mixtures were analyzed and compared to those displayed by the un-filled resin. A mathematical model was applied to the experimental rheological data in order to assess the aspect ratio of the nano-filler. A proper equation was employed to model the cure kinetics of the nano-filled epoxy systems. The nanocomposites were heat-cured in the presence of an aromatic amine hardener. They were, then, characterized by scanning electron microscopy with EDS analysis, dynamic mechanical thermal analysis, differential scanning calorimetry, and Flexural and Hardness tests. Significant increase in the glass transition temperature, Shore D hardness and maximum flexural strength was found. The experimental results demonstrated the effectiveness of the o-boehmite nano-filler to improve the physical and mechanical properties of the epoxy resin. Further studies are in progress to verify the protective efficiency of the epoxy-boehmite nanocomposite when applied on different substrates as adhesive or coating for construction materials, such as porous stones, concrete, wood, and metal.

Antibacterial activity of a modified unfilled resin containing a novel polymerizable quaternary ammonium salt MAE-HB.

Resins with strong and long-lasting antibacterial properties are critical for the prevention of secondary dental caries. In this study, we evaluated the antibacterial effect and the underlying mechanism of action of an unfilled resin incorporating 2-methacryloxylethyl hexadecyl methyl ammonium bromide (MAE-HB) against Streptococcus mutans UA159 (S. mutans UA159). MAE-HB was added into unfilled resin at 10 mass%, and unfilled resin without MAE-HB served as the control. Bacterial growth was inhibited on 10%-MAE-HB unfilled resin compared with the control at 1 d, 7 d, 30 d, or 180 d (P < 0.05). The growth inhibitory effect was independent of the incubation time (P > 0.05). No significant differences in the antibacterial activities of eluents from control versus 10%-MAE-HB unfilled resins were observed at any time point (P > 0.05). The number of bacteria attached to 10%-MAE-HB unfilled resin was considerably lower than that to control. Fe-SEM and CLSM showed that 10%-MAE-HB unfilled resin disturbed the integrity of bacterial cells. Expression of the bacterial glucosyltransferases, gtfB and gtfC, was lower on 10%-MAE-HB unfilled resin compared to that on control (P < 0.05). These data indicate that incorporation of MAE-HB confers unfilled resin with strong and long-lasting antibacterial effects against S. mutans.

Physical characterization of unfilled and nanofilled dental resins: Static versus dynamic mechanical properties

ObjectiveThe aim of this study was to evaluate the mechanical properties of dental resins and dental nanocomposites by means of 3-point bending, 4-point bending and piston-on-three ball biaxial static tests and also to investigate their dynamic mechanical properties. The obtained results from the static 3-point bending test also were compared with the corresponding mode in DMTA. MethodsThe hydrophilic surface of the inorganic OX-50 particles was treated with γ-MPS and the resulting silanized OX-50 was characterized using FTIR and TGA. The test specimens with a specified shape and dimensions for each type of flexural static and dynamic tests were prepared for Bis-GMA/TEGDMA (70/30wt%/wt%) and the corresponding nanocomposite containing 50wt% of silanized OX-50. The specimens were stored in distilled water at 37°C for 24h prior to the mechanical tests and then they were subjected to different types of static mode and also to dynamic mode of flexural test. The effect of test speed, type of the test and the presence of silanized nano-particles were investigated for specimens under static flexural tests. The results were then statistically analyzed and compared using one-way ANOVA and the Tukey's post hoc test (significance level=0.05). Fractured surfaces were observed by means of scanning electron microscopy. Finite element analyses were also performed to compare the static tests. On the other hand, the effect of frequency, temperature and the presence of silanized nano particles on the viscoelastic properties were investigated for dynamic mechanical tests. ResultsThe grafting of γ-MPS onto the OX-50 nano particles was confirmed. The results of 3-point bending and 4-point bending uniaxial and biaxial flexural tests of resin and composite showed the highest strength values for biaxial test specimens and the lowest strength value for 4-point bending specimens in accordance with finite element analysis results. Also, an increasing trend was observed for flexural strength of all resin samples with increasing the test speed up a critical speed which decreased beyond it. The nanocomposite specimens showed higher modulus and lower tanδ than the unfilled resin. The storage modulus measured in the dynamic tests approached the static elastic modulus values with decreasing the frequency. SignificanceDifferent static and dynamic test methods are used to evaluate the mechanical properties of dental resins and composites. This study provides an insight into the tests and presents more details on the effect of test conditions.

Acid Etching and Surface Coating of Glass-Fiber Posts: Bond Strength and Interface Analysis.

The aim of this study was to evaluate the bond strength of a composite resin to glass-fiber post (GFP) treated or not with phosphoric acid, silane coupling agent, and unfilled resin. GFPs were etched or not with 37% phosphoric acid and different surface coating applied: silane coupling agent, unfilled resin, or both. Composite resin blocks were built around a 4-mm height on the GFP. Unfilled resin (20 s) and composite resin (40 s) were light activated by a light-emitting diode unit. The specimens were stored in distilled water at 37 °C for 24 h. Microtensile bond test was performed using a mechanical testing machine until failure (n=10). The data were analyzed using two-way ANOVA followed by Student-Newman-Keuls' test (p<0.05). Failure modes were classified as adhesive, mixed, or cohesive failures. Additional specimens (n=3) were made to analyze the bonded interfaces by scanning electron microscopy. The statistical analysis showed the factor 'surface coating' was significant (p<0.05), whereas the factor 'HP etching' (p=0.131) and interaction between the factors (p=0.171) were not significant. The highest bond strength was found for the silane and unfilled resin group (p<0.05). A predominance of adhesive and cohesive failures was found. Differences regarding the homogeneity and thickness of the unfilled resin layer formed by different GFP surface treatments were observed. The application of silane and unfilled resin can improve the bond strength between GFP and resin composite.

Assessment of the resistance to tracking of polymers in clean and salt fogs due to flashover arcs and partial discharges degrading conditions on one insulator model

This paper describes the assessment of the resistance to tracking of various polymers after (i) flashover voltage (FOV) and flashover gradient (FOG); and (ii) partial discharges (PDs) measurements in dry, clean and salt fogs on one insulator model using standardised electrodes; the aim being the development of optimised methods based on flashover and PDs to the conception of new generation of piercing connectors. The investigated materials belong to two distinct classes widely used in the electrical industry: thermoplastics (namely polyphenylene sulfide and high density polyethylene) and thermosetting cycloaliphatic epoxy resins namely one unfilled material (UnCEP) and another unfilled and hydrophobic resin (UnHCEP). FOV measurements are based on the electro-geometrical parameters of each specimen and the resistance to tracking, both may be assessed through the slope of FOV curves against the leakage distance as an indicator of surface damages. Regarding PDs, the suggested technique is devoted to clean and salt fogs and provides quicker and more accurate information about PDs effects on materials deteriorations rather than IEC60109 where the exposition time to discharges is much longer at lower voltage levels by using only liquid contaminants such as sulfuric or nitric acids or ammonium chloride as described in IEC60587 or ASTM D2303.