Objective: To investigate the effect of deviation of chromameter measurements of human incisors on tooth color assessment. Methods: Ten extracted human maxillary central incisors with no cavity, stain and restoration were selected. The root of each tooth was embedded in denture resin. Seven positioning devices were fabricated so that the aperture (3 mm in diameter) of a Minolta Chroma Meter (CR-321, Osaka, Japan) would be placed at seven defined labial surface areas of the tooth, including the center, 1 mm deviations to the apical, incisal, left and right, and 2 mm to the apical and incisal. In addition, measurements were performed at the center of each tooth with hand-held positioning (no positioning device). Three measurements were made for each position on each tooth by repositioning the aperture for each measurement. Care was taken to avoid dehydration of the teeth during the investigation. The delta L*a*b* and the delta E were calculated, and the data were analyzed using the One-Way ANOVA and Student-Newman-Keuls multiple comparison methods. Results: The delta L*a* b* values were higher for vertical deviations compared to the horizontal ones. The variations for the hand-held group were similar to those for the 1 mm apical deviation except for delta b*. The delta E values were 1.20 for either right or left horizontal deviation, 1.72 and 2.01 for 1 mm apical and incisal vertical changes, respectively, 2.99 and 3.04 for 2 mm apical and incisal vertical changes, respectively, and 1.41 for the hand-held group. The differences in the L*, a* and b* values were less evident for horizontal deviations. Significant differences (p<0.05) were detected in L* values in all deviations compared to the center except that for the 1mm right deviation. Conclusion: Deviations of chromameter measurement area on tooth, particularly for vertical deviations, significantly affect the tooth color assessment.

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