The in vitro and in vivo reproducibility of a video-based digital imaging system for tooth colour measurement

Objectives: To assess the robustness of a new custom built video-based digital imaging system (VDIS) for measuring tooth colour and whiteness under in vitro and in vivo conditions. Methods: The VDIS imaging system was developed for tooth colour measurement and evaluated in vitro and in vivo. The in vitro validation used extracted human teeth (HT, n = 14) stored in water and VITA Classical shade guide tabs (SG, n = 16). These were measured by the VDIS at baseline, 5 min, 2 h, 1 week and 2 weeks to evaluate the system repeatability. For in vivo validation, adult volunteers (male/female, n = 34) with two natural, unrestored central incisors had their teeth imaged using the VDIS at baseline, 5 min and 2 h (3 images each) by two different operators to evaluate time and operator effects. Between taking individual images, subjects moved from the imaging-frame to assess the effect of re-positioning on reproducibility. From the in vitro and in vivo images, the average tooth RGB values were obtained, and the CIELAB values and a tooth whiteness index WIO value were calculated. Repeatability and reproducibility of VDIS imaging system was assessed using appropriate repeated measurement analysis techniques and ANOVA. Results: The measurement variations in vitro were between 1 and 2 units of ΔWIO and the average colour differences were less than 1 ΔE*ab unit. For the in vivo study, analysis of the CIELAB parameters and WIO showed that subject variability accounted for between 82 and 99% of the observed variability in the measurement process. The operator variability was less than 0.5% and the overall measurement error was found to be only 0.3% for WIO. Across assessment times the variability was less than 0.5%. Conclusions: The dental imaging system V-DIS was shown to be a highly reproducible means for tooth colour and whiteness measurement. Clinical significance: Digital imaging based techniques gives a highly reproducible approach to measuring tooth colour