Effect of Lighting on Color Determination Using Different Objective Methods

Objectives: To assess the influence of light on tooth color determination accuracy using different objective methods, including a spectrophotometer and two different intra-oral scanners.
Methods: Color was evaluated under three light conditions: no light (NL), room light (RL) and room light with dental unit light (UL), using a spectrophotometer (VitaEasyshade) and two scanners (Trios4; PrimeScan). Standardized color specimens from the VitaClassic shade guide (A1-D4, 16 shades) were employed. A qualified dentist conducted ten measurements per specimen for each device in all light conditions. The tooth color determination accuracy was calculated as the percentage of matches with the specimen's known color. Additionally, differences in CIELAB L*, a*, and b* values between NL-RL and NL-UL were analyzed.
Results: A total of 1,440 measurements were taken. Under NL, the VitaEasyshade, Trios4, and PrimeScan had accuracies of 43.75%, 74.38%, and 59.38% respectively. In RL, the VitaEasyshade's accuracy remained at 43.75%, but the Trios4 and PrimeScan dropped to 50.00% and 40.63%, respectively. Under UL, the VitaEasyshade’s accuracy dropped to 36.63%, while the Trios4 and the PrimeScan fell further to 20.63% and 28.75%, respectively. Light exposure significantly decreased the accuracy of these devices in both RL (p<0.0001, OddsRatio=0.5123) and UL (p<0.0001, OddsRatio=0.2491). The a* value increased under both RL (p=0.0052, MeanDifference=0.0500) and UL (p=0.0089, MeanDifference=0.0638) compared to NL, while L* and b* values remained stable.
Conclusions: Light affects tooth color measurement when using objective methods. In our study, light specifically increased the a* value, causing teeth to appear redder than their color under no light conditions. Objective methods are valuable tools for assisting in tooth color determination, particularly for less experienced dentists. For more reliable outcomes, it's advised to conduct these measurements in low-light settings. Nonetheless, the final shade selection should be visually confirmed and mutually agreed upon by both dentist and patient.