title: Comparison of two color-difference formulas using the Bland-Altman approach based on natural tooth color space.
abstract: BACKGROUND
  Several formulas to measure color differences have been proposed to improve the correlation between color measurements and visual perception. Despite the progress obtained, equating between formulas is complex, rendering the exchange of information in scientific papers difficult.
  
  
  OBJECTIVE
  The purpose of this study was to determine the relationship between the results provided by classic CIELab (ΔEab∗) and the CIEDE2000 (ΔE00) formulas in the natural tooth color space using the Bland and Altman limits of agreement, to use this relationship to establish the equivalences between the tooth color thresholds of acceptability and perceptibility of both formulas, and to evaluate whether the relationship between ΔEab∗ and ΔE00 is modified depending on the axis on which the changes occur.
  
  
  METHODS
  The L∗, a∗, and b∗ means coordinates in the 26 shade tabs of the Toothguide 3D Master were used, and color differences were calculated in 325 pairs of shade tabs using the CIELab (ΔE∗ab) and CIEDE2000 (ΔE00) color difference formulas. The results obtained with these formulas were compared, and the limits of agreement after a logarithmic transformation of the data were obtained.
  
  
  RESULTS
  The linear relationship between both formulas was ΔE00 =0.66ΔE∗ab. The results obtained with the CIELab formula were between 1.15 (95% confidence interval 1.11 to 1.18) and 2.09 (95% confidence interval 2.03 to 2.15) times higher than those obtained with the CIEDE2000 formula.
  
  
  CONCLUSIONS
  In the natural tooth color space, the scale factor between CIEDE2000 and CIELab values changes from 0.46 to 0.90, such that providing an accurate scale factor between both values is difficult. Furthermore, the ΔE00/ΔE∗ab ratio increases with the increase in ΔL∗ and the decrease in Δb∗. The pairs for which the ratio is highest are those in which the difference in color is mainly due to changes in lightness, whereas the pairs for which the ratio is the smallest are those in which the difference in color is mainly due to changes on the blue-yellow axis.
authors.affiliation: Associate Professor, Department of Dentistry, School of Medicine, University of Salamanca, Salamanca, Spain. Electronic address: crisgodent@usal.es.
authors.forename: Cristina
authors.initials: C
authors.lastname: Gómez-Polo
authors.affiliation: Associate Professor, Department of Dentistry, School of Medicine, University of Salamanca, Salamanca, Spain.
authors.forename: María
authors.initials: M
authors.lastname: Portillo Muñoz
authors.affiliation: Associate Professor, Department of Dentistry, School of Medicine, University of Salamanca, Salamanca, Spain.
authors.forename: Mari Cruz
authors.initials: MC
authors.lastname: Lorenzo Luengo
authors.affiliation: Associate Professor, Department of Statistics, Faculty of Medicine, University of Salamanca, Salamanca, Spain.
authors.forename: Purificación
authors.initials: P
authors.lastname: Vicente
authors.affiliation: Lecturer of Prosthodontics, Department of Statistics, Faculty of Medicine, University of Salamanca, Salamanca, Spain.
authors.forename: Purificación
authors.initials: P
authors.lastname: Galindo
authors.affiliation: Associate Professor, Department of Statistics, Faculty of Medicine, University of Salamanca, Salamanca, Spain.
authors.forename: Ana María
authors.initials: AM
authors.lastname: Martín Casado
mesh_terms: D003116:Color; D003118:Color Perception; D003124:Colorimetry; D003764:Dental Materials / Q000737:chemistry*; D006801:Humans; D066298:In Vitro Techniques; D017797:Prosthesis Coloring / Q000379:methods*
chemical_list: D003764:Dental Materials