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, 5min, 2h, 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, 5min and 2h (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.