Light sources were held at a distance of 2 mm
The aim of this study was to investigate the variations in shade change in various beverages of dental nano-filled resin composite cured with QTH and LED light curing systems (Paul et al., 2002; Zafar, 2013; Zafar and Ahmed, 2015; Ullah and Zafar, 2015).Materials and MethodsTwo different light curing systems were evaluated on various resin composites for colour stability. A QTH light cure unit (Optilight Plus, Curing Light, Gnatus, Ribeirão Preto, SP, Brazil) and a LED cure unit (Elipar™ LED Curing Light, 3M ESPE, Deutschland, GmBH, 41453, Germany). The cured samples were conditioned in various staining beverages and analysed for time dependency of their colour changes (Table 1).Sample PreparationFor each material, 100 disc shaped specimens (6 mm diameter and 3 mm thickness) were prepared using specially tailor made Teflon moulds. A glass slide was used to compress and flatten the materials and to remove the excess resin. Before curing, all samples were divided randomly in to two study groups: QTH and LED (n = 50 for each group). QTH group samples were cured for twenty seconds using a halogen light source (Optilight Plus, Curing Light, Gnatus, Ribeirão Preto, SP, Brazil). LED groups samples were light cured for twenty seconds using a diode electronic light source.Light sources were held at a distance of 2 mm from the surface of sample (Petrescu and Calautit, 2016 a-b; Petrescu et al., 2015; Petrescu et al., 2016 a-e). All samples were inspected carefully for uniformity. Samples with any defect, visible crack or voids were excluded. Each sample was polished using a finishing discs kit (Sof-LEX disks; 3M ESPE, ST Paul.MN) and slow speed air turbine handpiece (uniform pressure and circular motions were used) according to manufacturer's guidelines. The final thickness of samples after polishing was 2.0±0.01 mm. Prepared samples from each materials under investigation (n = 100) were randomly divided into various study groups for longevity analysis (Fig. 1).Preparation of Beverage Solutions and Aging TreatmentThe effects of four hot beverages (karkada, tea, yansoon and coffee) on the colour stability after light curing were investigated (Table 1). All beverage solutions were prepared by boiling tea leave/coffee granules in deionized distilled water for 5 min. Final concentration of each solution was maintained at 3.5% and pH in the range of 3.5-4.5.The pH of the solution was maintained throughout the experimental period using a digital pH meter (Clean PH500, First Clean Co. 14656 Valley Blvd, City of Industry, 91746). Additives such as sugar, milk or flavourings were not added to any experimental solutions.Specimens were immersed in 50 mL of ageing media in air tight containers and were stored in an incubator at 37°C. Ageing beverage medium was changed cyclically after every 6 h to mimic the daily consumption of the beverage daily. Specimens were rinsed using deionized water before colour shade measuring and change of the ageing beverage media.Five groups of samples for each curing light source type were prepared: Karkada [Group I; n = 10]; black tea [Group II; n = 10]; yansoon [Group III; n = 10]; coffee [Group IV; n = 10]; deionized distilled water used as control group for aging (n = 10).
