The Effect of Aging on the Decrease in Tensile Strength of Composites with Palm Oil Kernel Shell Powder

Polymeric composite materials with natural renewable fillers are materials that are environmentally sensitive and can be an important alternative to conventional materials. One of the possibilities of using natural fillers is to use natural secondary sources. This paper describes the use of natural waste produced in the processing of palm oil fruits. The experiment describes a change in tensile strength due to an aging of the epoxy resin-based material and particles prepared from palm fruit (PKS). Specifically, the concentration was 30 wt. % and particle size up to 100 μm, 100-200 μm and 200-300 μm. To simulate the aging of the material, a climatic chamber was used which, at regular intervals for 840 hours, changed the ambient temperature from +70 ° C to-40 ° C and humidity. This process caused a decrease in tensile strength of 18.73 MPa for the unfilled epoxy resin and up to 19.27 MPa for the composite system. Comparison with unfilled resin was used to describe the effect of PKS particles on the aging rate. Interphase interaction was described by electron microscopy.

Clinical Trial Concerning the Effectiveness of Two Types Dental Sealants in Children with Bruxism

Dental sealants are important components of preventive dentistry. The aim of this clinical trial was to compare the effectiveness of an unfilled resin-based sealant and a carbomer-based dental sealant. 42 child patients with completely erupted inferior first molars and with diagnosed bruxism were included in the study. At 2 weeks, respectively 6, 12 and 18 months were evaluated the effectiveness of sealants after marginal deterioration, retention and the presence of caries. The results of the trial showed that unfilled resin-based sealant presented fewer modifications.

Composite Laminates with Recycled Carbon Fibres and Carbon Nanotubes

Carbon fibre reinforced composites were manufactured by using recycled carbon fibres (CF) and carbon nanotubes (CNT). Dry fabrics were impregnated by hot melting with 1 wt% CNT filled epoxy resin to produce prepregs. Subsequently, composite laminates were manufactured by vacuum bagging and autoclave moulding. Only materials and industrial equipment were used for the laminate production. Laminates with unfilled resin and virgin CFs were also manufactured for comparison. Samples were extracted for physical and mechanical measurements. Dynamic mechanical analyses and bending tests were carried out to evaluate the interaction between CNTs, resin matrix and recycled CFs.

In Vitro Microleakage Comparison of Flowable Nanocomposites and Conventional Materials Used in Pit and Fissure Sealant Therapy

Objectives: Pit and fissure sealants are recognized as an effective preventive approach in pediatric dentistry. Composite resin is the most commonly used sealant material. Adding nanoparticles to composite resin could result in production of flowable composite with higher mechanical properties and better flowability than previous sealants. This study aimed to compare the microleakage of a flowable nanocomposite and materials conventionally used as pit and fissure sealants. Materials and Methods: A total of 185 extracted mandibular third molar teeth were selected and randomly divided into 5 groups (n=36): flowable nanocomposite, flowable composite, filled sealants, nano-filled sealants, and unfilled sealants. Five teeth were reserved for examination under a scanning electron microscope (SEM). The samples were thermocycled (5-55°C, 1-minute dwell time) for 1000 cycles and immersed in 0.2% fuchsine solution for 24 hours. Teeth were sectioned buccolingually. Microleakage was assessed qualitatively and quantitatively by means of dye penetration and SEM. Data were analyzed using chi-square, Kruskal-Wallis, and Bonferroni-corrected Mann-Whitney U tests. Results: Qualitative microleakage assessment showed that flowable composite and nanofilled flowable composite had almost no microleakage (P<0.001). Regarding quantitative scores, the nanofilled flowable composite and unfilled fissure sealant showed the lowest and the highest rate of microleakage, respectively. No statistically significant difference was found between the two flowable composites (P=0.317). Filled resin-based sealant had significantly lower microleakage than unfilled resin-based sealant (P<0.001). Conclusion: Use of flowable and nanofilled flowable composites (but not unfilled resin-based fissure sealant) is recommended for sealing of pits and fissures of molars.

Effect of Surface Coating on Bond Strength between Etched Feldspar Ceramic and Resin-Based Luting Agents

This study evaluated adhesive protocols (silane, silane and unfilled resin, and universal adhesive) of bond strength between feldspar ceramic and resin-based luting agents (RBLAs). Thirty ceramic disks were embedded into acrylic resin, polished, etched, and randomly divided into 6 groups: S-RC: silane (S) and light-cured resin cement (RC) (RelyX Veneer; 3M ESPE); SB-RC: S followed by bond (B) (Clearfil SE Bond, Kuraray) and RC; UA-RC: universal adhesive (UA) (Single Bond Universal; 3M ESPE) and RC; flowable composite resin (F) was used on groups S-F, SB-F, and UA-F, and luting agent cylinders were built. The response variables (n=20) were microshear bond strength (MPa), characteristic strength (σ0, MPa), and Weibull modulus (m). The RC groups presented similar bond strengths regardless of whether or not bond was used. The S-F group with only silane application showed the highest bond strength, while the universal adhesive showed the lowest bond strength. The reliability was only affected in the UA-RC group, which was lower than the S-F group. Silane application is fundamental since the universal adhesive only decreased the bond strength between the feldspar ceramic and the RBLAs. Overall, the use of unfilled resin did not positively influence bond strength.

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 > synthetic amorphous silica > geothermal scale powder) and loading (20 vol% > 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.

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.