Digital Imaging System for Tooth Color Measurements

Objective: Develop a robust digital imaging (DI) system and protocol that can measure teeth color and shade as accurately as colorimetric or spectrophotometric devices, and further demonstrate its efficiency in a teeth whitening clinical study.

Methods: A DI system was constructed using a diffused light flash (Novoflex) and a digital SLR camera (D1X, Nikon) separated by approximately 20 degrees and positioned at a distance of 50 cm from the subject's oral cavity. VITAPANŽ classical and VITAPANŽ 3D shade guides were used as standards, and measurements (L*a*b* values) from a colorimetric device (Shadescan), a spectrophotometric device (MHT SpectroShade) and the DI system were recorded. The DI system configuration and design was optimized in an iterative fashion to achieve minimal difference in color reads from the spectrophotometric and colorimetric techniques. Images from the shade guides were cropped, converted from RGB to CIELAB color space and the median values were computed for comparison to the colorimetric and spectrophotometric measurements. The optimized DI system was used in a teeth whitening clinical study and the data was compared to spectrophotometric and dental examiner reads.

Results: The cross tabulation statistical analysis showed no statistically significant difference (p<0.05) between these methods for the L* value. The absolute values for a* and b* obtained with the DI method exhibited slight differences (shifts) to the results from the other instrumental and clinical shade guide measures but the relative data (Delta a* and Delta b*) showed excellent correlation.

Conclusion: The DI system being reported here has shown promising results for the ability to quantify the change in color and shades. Implementation of the DI system in the clinical study substantiated the robustness of system in measuring color as well as demonstrated its ability to acquire and document data of the entire oral cavity in a time efficient manner.