Investigation of Hue Effects in Tooth Whiteness Perception

Objectives: To identify the optimal hue angles that provide the greatest perception of tooth whitening.
Methods: Following independent ethical review and informed consent, a psychophysical study with male/female adult observers (n=33) with normal colour vision was conducted to investigate the hue effects in tooth whitening. Teeth images were simulated with colour changes in eight hue directions in the CIE a*b* chart, all had equal colour difference to a baseline tooth colour. Two baseline tooth colours were tested, an average tooth colour (Baseline 1) and a random tooth colour (Baseline 2) obtained from a whitening clinical study. Using a paired comparison study design, images were shown in a random order on a colour calibrated display. Observers were asked to indicate which image had whiter teeth. The data was converted into an interval scale using Thurstone’s Law of Comparative Judgment. Each image stimulus corresponds to a value in the scale for perceived tooth whiteness. The relationship between the hue angles and the scores was modelled by curve fitting.
Results: The optimal hue angles for tooth whitening perception are shown in the table. It was found that hue did have an effect in tooth whiteness perception. The optimal hues were found in a region between green and blue in the CIE a*b chart. When the tooth colour travels in an optimal hue direction (between the 80% borders), the same amount of colour change will result in greater change in whiteness perception than travelling in other hue directions.
Conclusions: The optimal hues for tooth whitening were identified from the visual perception study. The most effective tooth whitening direction is to change tooth colour towards the greenish-blue hue direction.