Digital Tooth Colour Acquisition: Agreement Between Spectrophotometric and Intraoral Scanner Measurements in Dental Students

Objectives. To describe the shade distribution and regional colour variation in a cohort of dental students and to quantify the agreement and shade-designation-derived colour difference between the VITA Easyshade V (VITA Zahnfabrik H. Rauter GmbH & Co. KG, Bad Saeckingen, Germany) spectrophotometer and the 3Shape TRIOS 5 (3Shape A/S, Copenhagen, Denmark) intraoral scanner at the cervical, middle and incisal thirds of the maxillary right central incisor, in both the VITA Classical and VITA 3D-Master systems. Methods. Tooth 11 was measured in 146 dental students with both devices at the three regions, the middle third serving as the representative body shade. The primary agreement outcome was the quadratic-weighted kappa of the Classical body shade, complemented by the paradox-robust Gwet AC1 and Brennan–Prediger coefficients; colour differences were obtained from published tab coordinates and not from coordinates measured on the teeth. Results. For the body shade (n = 144 teeth with an interpretable Classical designation from both instruments), exact agreement was 25.0% and Cohen’s kappa was near zero, the shades having clustered in a few light tabs. The primary outcome, the quadratic-weighted kappa, was 0.20 (95% confidence interval 0.09 to 0.34), with Gwet’s AC1 0.21 (0.12 to 0.27), Brennan–Prediger 0.19 (0.10 to 0.26) and an intraclass correlation coefficient, ICC(3,1), of 0.22 (0.03 to 0.39), none of them better than fair, and agreement on the 3D-Master lightness group was lower still. The scanner read lighter than the spectrophotometer by a mean of 1.80 value-ordered Classical units (Wilcoxon signed-rank p < 0.001) and by close to one lightness group on 3D-Master, and the two instruments distributed the shades differently at every region in both systems (Stuart–Maxwell p < 0.001). The scanner assigned a bleached 3D-Master shade in at least one region in 16.4% of participants against 1.4% for the spectrophotometer. On the Classical scale, agreement was weakest at the incisal third (Cohen’s kappa −0.03, quadratic-weighted kappa 0.03, Spearman 0.07, p = 0.42), where the mean signed difference was the smallest of any region, −0.39 units, and the dispersion the widest, with a mean absolute difference of 2.96 units and a standard deviation of 3.98 units. Colour varied across the three regions with both devices (Friedman p < 0.001), and the colour difference implied by the assigned tabs was above the 1.8-unit CIEDE2000 acceptability threshold for most tab pairs, carried by the lightness axis. Conclusions. The two instruments are not interchangeable. The scanner reads teeth as systematically lighter, most clearly at the cervical third and, on the Classical scale, least reliably at the incisal third, so a single device should be used throughout a case. With no independent reference standard, these data describe agreement and relative bias rather than accuracy. The scanner remains convenient for digital shade communication provided its lighter bias is taken into account.