Method: A psychophysical experiment with a group of observers (n=32) has been conducted to determine the perceptual thresholds in tooth whiteness. A yes-no psychophysical paradigm was used to determine thresholds based on visual assessments of digital images of teeth on a calibrated display. Digital simulations of a tooth that is identical in shape to the left incisor in the image of teeth were superimposed on to images. The colour of the simulated tooth was varied and observers were asked to respond whether there was a difference in whiteness between the left incisor and the simulated tooth. Thresholds for detection of differences in whiteness were independently determined for ΔL*, Δa* and Δb*. Raw data were fitted using a non-parametric approach and thresholds of CIE (1976) L*a*b* were reported for p = 0.5 (corresponding to detection of differences in 50% of cases) and WIO thresholds were also calculated.
Result: The threshold values from the three trials are listed in the table.
Conditions |
Parameters |
Threshold (Std) |
Corresponding threshold of WIO |
1 |
L* |
1.14 (0.04) |
2.77 |
2 |
a* |
3.24 (0.33) |
6.52 |
3 |
b* |
1.11 (0.04) |
3.09 |
Conclusion: The thresholds for tooth whiteness perception in CIELAB space were determined. The uncertainty in Δa* was much greater than for the L* and b* conditions. The findings suggest that for whitening treatments that predominantly affect ΔL* and Δb* a colour change of about 2-3 WIO units would be noticeable.