The spectrophotometer returned linear led light Factory a precise quantitative measurement of surface colours by recording the spectral reflectance/transmittance curve of the specimen.

A prism disperses tungsten-filament bulb light into a spectrum of wavelength (5 and 20 nm) bands (Bowen and Marjenhoff, 1992; Kim-Pusateri et al., 2007; Dozi et al., 2007; Al-Dharrab, 2013; Eldiwany et al., 1995; Ruchi et al., 2010). The colour changes (E) of each specimen were calculated by analysing the coordinate values before and after beverage ageing. Colour changes were quantified using the following equation (Imirzalioglu et al., 2010):

The results were statistically analysed by using SPSS version 20 and 95% Confidence Intervals (CI). Chi-square tests were used to evaluate the experimental data significance. A P-value < 0.05 was considered significant.

The regression parameter (R2), which measures the relationship between the two variables colour change and time, was evaluated for all staining tests at significance p<0.05. All samples exhibited increasing discoloration with time upon ageing in the staining liquids. Discolouring kinetics was investigated by plotting the digital spectrophotometry colour change values as a function of the exposure time. The colour changes linearly related to the square root of time (Fig. 2) with a near unity regression parameter (last column of Table 2). All colour changes data were grouped for type of composite resin, cure light and staining beverage and plotted as a function of the square root of time. Significant differences in staining properties among the four beverages (karkada, tea, coffee and yansoon were observed (Fig 3a through d). Figure 3a-c show the colour changes observed for GC Fuji II LC, Filtek Z250 XT and Filtek Z350 XT, respectively. The colour differences between LED and QTH cured samples become higher and statistically significant at week 2 and week 4 for all beverages. The colour differences following aging in any of the staining media (Fig. 3a and raw data in Table 2) were significantly higher for QTH light cured samples (red regression lines in the figure) than for LED cured specimens (blue regression lines in the figure). QTH and LED cured samples reached at four weeks mean grade colour changes for GC Fuji II LC of 15.60±0.19 and 7.90±0.47, respectively. Filtek Z250 XT reached 6.33±0.23 and 4.24±0.71 respectively for QTH and LED. Tea and coffee produced slightly higher discolouring compared to yansoon and karkada both for QTH and LED cured composites.