Objectives: This study aims to assess the suitability and reliability of a modified image analysis system, including a device independent whiteness algorithm, for measuring tooth whiteness in vivo and to compare this method with the traditional approach of visual shade guide matching.

Method: Before use each day a calibration was carried out. An image was taken of a white calibration standard tile (level 17b, Lot 98-0910 #33; Avian Technologies, Ohio, USA) with a Commision Internationale de l'Eclairage (CIE) whiteness index (WI) value of 140.9. This data was used to provide an automatic ratio adjustment for test whiteness readings that day. Images of 6 maxillary anterior teeth of 20 subjects were obtained using an image analysis system adapted for tooth whiteness measurement. The teeth were seperated into upper left and upper right quadrants. Red, green and blue values from each image and CIE WI values were calculated. A visual shade match was then carried out using a Vitapan 3D Master shade guide.

Results: There was a moderate Pearson's correlation for whiteness using the two measurement techniques giving 0.502 for the upper right quadrant (UR1,2, and 3) and 0.464 for the upper left quadrant (UL1, 2, and 3), significant at the 0.01 level. A two-tailed Student T-test with a 95% confidence level showed significant differences (p=0.021) between the paired CIE WI values of each tooth in both quadrants for the two techniques. As the accuracy of the image analysis system has been previously shown the differences between the methods are probably related to the inherent subjectivity of visual shade matching.

Conclusion: The adapted digital image analysis system was more sensitive and accurate than the Vitapan 3D Master shade guide.

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