Effect of Illuminance and Colour of Light Source on Assessing Tooth Whiteness

The aim of this work is to investigate whether light source illuminance and colour affects the rank order of tooth-coloured samples assessed for whiteness. Four different light sources varying in colour temperature (CCT) and illuminance (Lux) have been used: 3000K/700Lux, 6500K/700Lux, 6500K/350Lux and 8500K/700Lux. A total of 30 observers ranked the Vita Toothguide 3D-Master with Bleached shade guide (29 artificial tooth tabs) in terms of whiteness under each of the four illumination conditions. The rank data were used to generate interval-scale perceptual whiteness values. Instrument whiteness results were obtained from CIE XYZ tristimulus values that were calculated under each of the illumination conditions. The WIO whiteness index that was especially developed for use in dentistry was explored and the importance of using the correct white point in this equation was investigated. Performance of the instrumental results was assessed by correlation (using coefficient of determination) and an empirical test using a wrong decisions criterion. Results indicate that the rank order of visual whiteness for tooth-coloured samples is invariant to changes in the colour and intensity of the viewing illumination. Variation in the white point of the WIO equation does not affect agreement with interval-scale visual whiteness values because changing the white point is simply an affine transform.