Evangelia C. Vouvoudi

Physical properties of current dental nanohybrid and nanofill light-cured resin composites

OBJECTIVES The purpose of this work was the detailed study of sorption characteristics of water or artificial saliva, the determination of flexural strength and the flexural modulus, and the study of the thermal stability of some current commercial dental light-cured nanocomposites containing nano-sized filler particles. METHODS Three nanohydrid dental composites (Tetric EvoCeram (TEC), Grandio (GR) and Protofill-nano (PR)) and two nanofill composites (Filtek Supreme Body (FSB) and the Filtek Supreme Translucent (FST)) were used in this work. The volumetric shrinkage due to polymerization was first determined. Also the sorption, solubility and volumetric increase were measured after storage of composites in water or artificial saliva for 30 days. The flexural strength and flexural modulus were measured using a three-point bending set-up according to the ISO-4049 specification, after immersion of samples in water or artificial saliva for 1 day or 30 days. Thermal analysis technique TGA method was used to investigate the thermal stability of composites. RESULTS GR and TEC composites showed statistically no difference in volumetric shrinkage (%) which is lower than the other composites, which follow the order PR<FSB<FST. The amount of sorbed water and solubility is not statistically different than those in artificial saliva. In all the composites studied the amount of water, which is sorbed (% on composite) is not statistically different than the amount of water, which is desorbed and follows the order: GR<TEC<PR<FSB<FST. After immersion in water for 1 day the highest flexural strength showed the FSB and the lowest TEC. GR, PR and FST showed no statistically different flexural strength. The flexural modulus of composites after immersion for one day follows the order TEC<PR≤FST<FSB<GR. SIGNIFICANCE Among the composites studied, Grandio had the lowest polymer matrix content, consisting mainly of Bis-GMA. It showed the lowest polymerization shrinkage and water sorption and the highest flexural strength and flexural modulus after immersion in water or artificial saliva for 30 days. The water and artificial saliva generally showed the same effect on physical properties of the studied composites. Thermogravimetric analysis gave good information about the structure and the amount of organic polymer matrix of composites.

Thermal degradation characteristics and products obtained after pyrolysis of specific polymers found in Waste Electrical and Electronic Equipment

Modern societies strongly support the recycling practices over simple waste accumulation due to environmental harm caused. In the framework of sustainable recycling of plastics from WEEE, pyrolysis is proposed here as a means of obtaining secondary value-added products. The aim of this study was to investigate the thermal degradation and the products obtained after pyrolysis of specific polymers found in the plastic part of WEEE, using thermogravimetric analysis and a pyrolizer equipped with a GC/MS. Polymers studied include ABS, HIPS, PC and a blend having a composition similar to that appearing in WEEE. It was found that, PC shows greater heat endurance compared to the other polymers, whereas ABS depolymerizes in three-steps. The existence of several polymers in the blend results in synergistic effects which decrease the onset and final temperature of degradation. Moreover, the fragmentation occurred in the pyrolyzer, at certain temperatures, resulted in a great variety of compounds, depending on the polymer type, such as monomers, aromatic products, phenolic compounds and hydrocarbons. The main conclusion from this investigation is that pyrolysis could be an effective method for the sustainable recycling of the plastic part of WEEE resulting in a mixture of chemicals with varying composition but being excellent to be used as fuel retrieved from secondary recycling sources.

Dental Polymer Nanocomposites Light-Cured under Polyester Strip: Effect of Water or Ethanol/Water Solution on Surface Characteristics Studied by SEM and AFM

The purpose of this work is the study of surface characteristics of four dental light-cured dimethacrylate-based resin nanocomposites after immersion in water or an ethanol/water solution, using scanning electron microscopy and atomic force microscopy. Water and ethanol treatment affected the morphology and component distribution on the surface of samples. Scanning electron microscopy revealed changes on a large scale in the surface morphology of treated samples caused by immersion in water while the ethanol/water solution treatment influenced sample integrity too. It was proven that the use of atomic force microscopy in the phase-imaging mode is crucial in revealing subtle changes in component distribution on the polymer composite surface which are not accompanied by significant morphological changes. GRAPHICAL ABSTRACT

Contemporary Dental Polymer Nanocomposites Light-Cured Under Polyester Strip: Evaluation of Surface Characteristics Using SEM and AFM

The aim of this investigation was the evaluation of both the morphology/surface roughness and the texture/phase distribution of four contemporary dental light-cured nanocomposites using scanning electron microscopy and atomic force microscopy. The materials evaluated were a nanofill composite and three nanohybrids. Scanning electron microscopy coupled with EDS analysis was able to see and identify the large filler particles of the materials. Atomic force microscopy in the tapping mode provided topography of the nanocomposites while the tapping mode coupled with phase imaging information on the surface texture. The differences observed are attributed to differences in the shape, size distribution, amount, and surface coverage of filler particles. GRAPHICAL ABSTRACT

Sorption characteristics of oral/food simulating liquids by the dental light-cured nanohybrid composite Kalore GC

OBJECTIVE This work presents the results obtained from the study of sorption/desorption process of some food/oral simulating liquids (FSLs) by the new marketed dental light-cured nanohybrid composite Kalore GC. METHODS The sorption/desorption process followed is recommended by ISO 4049:2009. The samples were immersed in various liquids proposed by ADA as FSLs, such as H2O, artificial saliva, EtOH, EtOH/H2O solution (75vol%) or C7H16, while the mass change for totally 30 days was recorded on defined time intervals. Afterwards the samples were put in dry desiccators at 37°C for the study of desorption process. RESULTS The weight percentage of sorption of the above mentioned FSLs by Kalore GC was determined; also the wt% of the desorbed liquid, the diffusion coefficient of sorption and desorption, the wt% solubility and the % volume increase due to the liquid sorption. SIGNIFICANCE The sorption characteristics of a dental composite depend both on composite structure and liquid. Ethanol/water and ethanol showed the highest effect on the determined characteristics. Then, the water and SAGF(®) saliva follows and finally the heptane solvent.