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    A study on the discoloration of different dental porcelain systems
    (Istanbul Univ Press, Istanbul Univ Rectorate, 2023) Ulucan, Mehmet Cagatay; Avsar, Melek Kilic; Bolayir, Giray
    PurposeThis study aimed to investigate the discoloration of four types of dental porcelain systems (feldspathic, monolithic zirconia, lithium disilicate, and leucite glass -ceramic) with various surface treatments (glazed and mechanically polished) after undergoing chewing simulation against a natural tooth antagonist.Materials and Methods Disc-shaped porcelain groups (9x3mm) were produced for the following categories: feldspathic glazed (FG), feldspathic mechanically polished (FM), zirconia glazed (ZG), zirconia mechanically polished (ZM), lithium disilicate glazed (ExG), lithium disilicate mechanically polished (ExM), leucite glass-ceramic glazed (EG), and leucite glass-ceramic (EM). In vitro chewing simulation was conducted on all porcelain groups, and a spectrophotometer was used to compare the color changes between their initial states. Results The Delta E values (discoloration) of all porcelain samples were statistically different (p<0.05), and the Delta E values of the glazed samples were higher than those of the mechanically polished samples. ConclusionAll the glazed samples are more likely to show more color change than the mechanically polished sample groups.
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    Effect of Hemp Fiber Addition on Mechanical Properties of Acrylic Resin: Coupled Experimental and Theoretical Study
    (Korean Fiber Soc, 2022) Bolayir, Giray; Soygun, Koray; Avsar, Melek Kilic; Boztug, Ali; Kaya, Savas; Katin, Konstantin P.
    We present experimental and theoretical study of the fiber-matrix composites based on polymethyl methacrylate (PMMA) prosthetic material. Hemp fibers of different lengths and concentrations were added to PMMA. In total, ten groups of composite samples were prepared. Flexural strength test was performed for each sample. We found that the addition of hemp fibber significantly change the mechanical properties of pristine PMMA. The nature of the interaction between PMMA and hemp fiber were further investigated with scanning electronic microscopy, infrared spectrometry and density functional theory. This interaction were described atomistic level in terms of quantum descriptors of reactivity, such as chemical potential, electronegativity, chemical hardness and softness, electrophilicity, electrodonating and electroaccepting powers and electrons transfer. We observed the formations of strong hydrogen bonds between the matrix and fibers, which explain the observed improvement of mechanical properties.
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    Investigation of colour and surface changes of ceramic CAD/CAM blocks with different surface treatments after immersion to different beverages
    (Springer, 2022) Avsar, Melek Kilic; Bolayir, Giray; Saygin, Aysegul; Ulucan, Mehmet Cagatay
    This study aims to investigate the colour and surface changes of CAD-CAM porcelain blocks with different surface finishing treatments after being deposited into beverages. A total of 128 disc-shaped samples obtained from different CAD/CAM materials [Monolithic Zirconia (Z), Vita Suprinity (VS) and Vita Enamic (VE)] and feldspathic porcelain (FP) as the control group were divided into two subgroups [manual polish (M), glaze (G)] according to their surface finishing treatments. Measurements of the samples kept in different liquids (coffee and wine) after initial surface roughness and colour measurements (Delta E) were repeated on the 14th day. It was measured using a spectrophotometer for colour value measurement and an optical profilometer for surface roughness values, and SEM images were taken. When the initial and 14th-day surface roughness measurements were compared, significant differences were found in all groups (p < 0.05). The lowest roughness value (0.10 +/- 0.001) was obtained in the VS-M group aged into wine, while the highest roughness value (0.33 +/- 0.001) was obtained in the VE-M group aged into wine. Comparing the averages of colour changes (Delta E), the highest Delta E average was found in the FP-M group deposited into coffee (3.70 +/- 0.50), while the lowest Delta E value was found in the VE-M group deposited into wine (0.50 +/- 0.13). Depending on the structural characteristics of porcelain groups in terms of surface roughness and colour, we can say that the surface finishing treatment and beverage types have different effects.