Abstract: Dentists are exposed to the highest risk of occupational respiratory and droplet infections by working face-to-face with patients. The aim of this study was to investigate the knowledge of symptoms and modes of transmission of COVID-19, stress levels and clinical practice modifications of Turkish dentists during the COVID-19 pandemic. An online survey (15 questions) was sent to Turkish dentists from May 5 to 12 May, 2020. The survey comprised questions about dentists’ demographic characteristics, their knowledge about COVID-19, stress levels and the measures taken in dental clinics against COVID-19. This study included a total of 1,095 Turkish dentists. The data were expressed as frequency with percentage values for overall variables. Dentists were most familiar with high fever among the symptoms of COVID-19 (99.4%) and 99.2% of them reported that COVID-19 was transmitted with eye, mouth and nasal mucosa contact on surfaces contaminated with the droplets of infected persons. While the stress levels of females were higher than males, the stress levels of dentists with more than 20 years of professional experience were found to be lower. Regarding the precautions to be taken as a preventive measure when working again, 86.6% of the dentists took precautions by increasing daily patient care intervals and only 38.4% of the dentists wore an N95 mask. During this pandemic, knowing the conditions about when the treatments can be applied and the precautions to be taken will shed light on dentistry staff. Current recommendations of national authorities about the coronavirus should be followed.

Resumen Objetivo: Los estudios se han concentrado en el uso de resinas compuestas no vencidos. Desafortunadamente, algunos clínicos aún usan resinas caducadas sin considerar sus efectos. El objetivo de este estudio preliminar in vitro fue investigar la citotoxicidad de resinas compuestas caducadas (6 meses) y no caducadas. Materiales y métodos: muestras caducadas (E) y no caducadas (NE) de una resina bulk-fill (Tetric N-Ceram Bulk-fill (TNB), Ivoclar Vivadent) y dos resinas nanohíbridas (Tetric N-Ceram (TN) Ivoclar Vivadent) (Clearfil Majesty ES-2 (CM), Kuraray), se probaron en células de fibroblastos L929. Se retiraron las células que cubrían el medio, luego se llenaron anillos de plástico (2 mm de altura) con resinas no polimerizadas, se colocaron en contacto directo con las células y se polimerizaron con una unidad de fotocurado LED (LCU). Se prepararon tres muestras para cada grupo. Después de la polimerización, se añadió el medio eliminado a las células. Las células que quedaron sin medio (WOM) y las células que se expusieron a LCU se usaron como grupos de control positivo. Las células sin ningún tratamiento se utilizaron como grupo de control negativo (C). Las células se incubaron con las resinas durante 7 días para evaluar la citotoxicidad. La viabilidad celular se calculó mediante la prueba de sulforodamina B como un porcentaje (%). ANOVA unidireccional y pruebas post-hoc de Tukey se utilizaron para los análisis estadísticos (p <0.05). Resultados: La comparación entre los grupos E y NE de las mismas resinas compuestas no mostraron diferencias estadísticamente significativas (p> 0.05), excepto entre TN NE y TN E (p <0.05). El grupo TN E fue significativamente más citotóxico que el grupo TN NE. Cuando los grupos de resinas compuestas de NE se compararon entre sí, solo se obtuvo una diferencia estadísticamente significativa entre TNB NE y TN NE (p <0.05). Entre todos los grupos probados, el grupo TN NE mostró el perfil menos citotóxico. No se encontraron diferencias estadísticamente significativas cuando los grupos de resina compuesta E se compararon entre sí (p> 0.05). Todos los grupos experimentales en comparación con el grupo C mostraron citotoxicidad estadísticamente significativa (p <0,05). Existió una diferencia estadísticamente significativa entre LCU y grupos C (p <0.05). Conclusiones: En la práctica clínica, las resinas compuestas caducadas nunca deben usarse. Aunque se encontró una correlación entre las fechas de vencimiento de las resinas compuestas nano-híbridas y la viabilidad celular, se obtuvieron datos opuestos para la resina bulk-fill. Se requieren nuevas investigaciones para evaluar la biocompatibilidad de las resinas bulk-fill en distintos espesores con las LCU actuales.

Astracts Objective: Studies have focused on use of non-expired composites. Unfortunately some clinicians still use expired composite resins without considering their effects. The objective of this in vitro preliminary research was to investigate cytotoxicity of expired(6-months) and non-expired composite resins. Materials and methods: Expired (E) and non-expired (NE) samples of one bulk-fill (Tetric N-Ceram Bulk-fill (TNB), Ivoclar Vivadent), two nano-hybrid (Tetric N-Ceram (TN), Ivoclar Vivadent; Clearfil Majesty ES-2 (CM), Kuraray) composite resins were tested on L929 fibroblast cells. Medium covering cells was removed then plastic rings (2-mm height) were filled with non-polymerized composite resins, placed in direct contact with cells and polymerized with LED light curing unit (LCU). Three samples were prepared for each group. After polymerization, removed medium was added to the cells. Cells that were left without medium (WOM) and cells that were exposed to LCU were used as positive control groups. Cells without any treatment were used as negative control group (C). Cells were incubated with tested materials for 7-days to evaluate cytotoxicity. Cell viability was calculated by sulforhodamine B test as a percentage (%). One-way ANOVA and post-hoc Tukey tests were used for statistical analyses (p<0.05). Results: Comparison between E and NE groups of same composite resins did not result in statistically significant differences (p>0.05), except between TN NE and TN E (p<0.05). TN E group was significantly more cytotoxic than TN NE group. When NE composite resin groups were compared to each other, statistically significant difference was only obtained between TNB NE and TN NE (p<0.05). Among all tested groups, TN NE group showed the least cytotoxic profile. No statistically significant differences were determined when E composite resin groups were compared to each other (p>0.05). All experimental groups compared with C group showed statistically significant cytotoxicity (p<0.05). A statistically significant difference existed between LCU and C groups (p<0.05). Conclusions: In clinical practice, expired composite resins should never be used. Although a correlation was found between expiration dates of nano-hybrid composite resins and cell viability, opposite data were obtained for bulk- fill composite resin. Researches are still required to evaluate biocompatibility of bulk- fill composite resins at various thicknesses with current LCUs.

Abstract Gap formation of composite resin restorations is a serious shortcoming in clinical practice. Polymerization shrinkage stress exceeds the tooth-restoration bond strength, and it causes bacterial infiltration within gaps between cavity walls and the restorative material. Thus, an intermediate liner application with a low elastic modulus has been advised to minimize polymerization shrinkage as well as gap formation. Objective: The purpose of this in vitro study was to assess gap formation volume in premolars restored with different bulk-fill composites, with and without a resin-modified glass-ionomer cement (RMGIC) liner, using x-ray micro-computed tomography (micro-CT). Methodology: Sixty extracted human maxillary premolars were divided into six groups according to bucco-palatal dimensions (n=10). Standardized Class II mesio-occluso-distal cavities were prepared. G-Premio Bond (GC Corp., Japan) was applied in the selective-etch mode. Teeth were restored with high-viscosity (Filtek Bulk Fill, 3M ESPE, USA)-FB, sonic-activated (SonicFill 2, Kerr, USA)-SF and low viscosity (Estelite Bulk Fill Flow, Tokuyama, Japan)-EB bulk-fill composites, with and without a liner (Ionoseal, Voco GmbH, Germany)-L. The specimens were subjected to 10,000 thermocycles (5-55°C) and 50,000 simulated chewing cycles (100 N). Gap formation based on the volume of black spaces at the tooth-restoration interface was quantified in mm3 using micro-computed tomography (SkyScan, Belgium), and analyses were performed. Data were analyzed using repeated-measures ANOVA and the Bonferroni correction test (p < 0.05). Results: The gap volume of all tested bulk-fill composites demonstrated that Group SF (1.581±0.773) had significantly higher values than Group EB (0.717±0.679). Regarding the use of a liner, a significant reduction in gap formation volume was observed only in Group SFL (0.927±0.630) compared with Group SF (1.581±0.773). Conclusion: It can be concluded that different types of bulk-fill composite resins affected gap formation volume. Low-viscosity bulk-fill composites exhibited better adaptation to cavity walls and less gap formation than did sonic-activated bulk-fill composites. The use of an RMGIC liner produced a significant reduction in gap formation volume for sonic-activated bulk-fill composites.