The measurement of tooth whiteness by image analysis and spectrophotometry: a comparison

Digital image capturing and analysis techniques have been used to measure the colour of teeth and to compare with spectrophotometric results and visual observations. A non-linear image analysis approach was developed and, for the colour range of human teeth, allows device-dependant digital camera colour data to be quantitatively transformed to Commission Internationale de l'Eclairage (CIE) colorimetric values. With reference to a CIE standard illuminant, two different lighting arrays have been used. For flat and non-translucent white and yellow surfaces, spectrophotometric results showed that this transformation achieves required accuracy. It was found, in all of the present studies, which included measurements on the VITA Lumin(R) Vacuum shade guide and extracted teeth, that spectrophotometry invariably underestimated values of the CIE whiteness index. However, the results from these two types of measurement correlated well. There was also a reasonably good correlation between earlier data obtained by visual assessment and the present data by the two instrumental methods. For extracted teeth, both instrumental methods used in this work did not confirm a whitening effect for 2-min brushing with toothpaste, but did show significant whitening results for bleaching with 15% hydrogen peroxide.