BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI

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54 Irina Grădinaru et al. The CIE tristimulus values system uses 3 parameters (X,Y,Z), based on the spectral response functions defined by the CIE observer. Sometimes is used a CIE chromaticity diagram to define color. Fig.2 – Schematic representation of the interaction between the light source, the dental material and the observer after O’Brien. Fig. 3 – Schematic representation of the Munsell three-dimensional color system after O’Brien. The CIE color system (CIE L*a*b*) uses L* (lightness), a* (hue and chroma on a red-green scale), b* (hue and chroma on a yellow-blue scale) parameters for defining the color. The values for the three mentioned parameters can be calculated from the tristimulus X,Y and Z values (Fig. 4). In the color system CIE L*a*b*, the color difference ΔE* = [(ΔL*) 2 +(Δa*) 2 +(Δb*) 2 ] 1/2
Bul. Inst. Polit. Iaşi, t. LVIII (LXII), f. 3, 2012 55 ΔL*, Δa*, Δb* represents the differences between the CIE L*a*b* color parameter of 2 samples. Fig. 4 – Schematic representation of the CIE and Munsell color system after O’Brien. In Table 1 is presented the clinical color matching between dental structure and dental restorations, according to ΔE* values. Table 1 Color-matching tolerances by the clinical point of view after O’Brien The color difference ΔE* The clinical color matching between dental structure and dental restorations Color match by the clinical point of view 0 Clinically perfect 0.5…1 Clinically excellent 1…2 Clinically good 2…3.5 Clinically acceptable > 3.5 Clinically mismatch The color perception is sometimes a source of disagreement among the dentists, technicians and patients. There are different methods for color measurements: visual comparison using color standards such as Munsell color chips,color measurements made by using spectrophotometric or colorimetric methods [2]. Spectrophotometric measurements, done with spectrophotometers that measure the amount of light reflected at each wavelength, are used to evaluate the color parameters for porcelains, restorative resins, denture teeth, shade guides, and color modifications in dental materials. A double-beam spectrophotometer compares the responses from the object with a reference standard. From the spectral response can be calculated the color parameters for the object. Colorimetric measurements are done with colorimeters that measure the amount of light reflected at selected colors (eg. red, green, blue).
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