# Color Differences of Polimerized Resin-Based Composites and Corresponding Shade Guides  
[PERSON]  
1 Researcher Digital Density and New Technologies Unit, Faculty of Medicine and Dentistry, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain1  
2 School of Dentistry, Faculty of Medicine and Dentistry, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain; [EMAIL_ADDRESS] (J.M.P.R. ); [EMAIL_ADDRESS] (G.L.C. ); victorap@mundo-room (V.A.d.I.P. ); [EMAIL_ADDRESS] (M.G.T.) [PERSON]  
2 School of Dentistry, Faculty of Medicine and Dentistry, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain; [EMAIL_ADDRESS] (J.M.P.R. ); [EMAIL_ADDRESS] (G.L.C. ); victorap@mundo-room (V.A.d.I.P. ); [EMAIL_ADDRESS] (M.G.T.) [PERSON]  
2 School of Dentistry, Faculty of Medicine and Dentistry, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain; [EMAIL_ADDRESS] (J.M.P.R. ); [EMAIL_ADDRESS] (G.L.C. ); victorap@mundo-room (V.A.d.I.P. ); [EMAIL_ADDRESS] (M.G.T.) [PERSON]  
2 Correspondence: [EMAIL_ADDRESS]; Tel. : +34-6265826002024  
Shade determination in dentistry can be classified as either instrumental or visual [3]. Visual determination can be carried out by comparing patients' teeth with a shade guide, the most frequently used method [4; 5]. A shade guide is made up of a set of colors designed to represent the range of colors in human dentition [6]. Most composite manufacturers cross-reference their colors to the VITAPAN Classical(r) shade guide in particular (Vita Zahnfabrik H. Rauter GmbH & Co KG, Bad Sackingen, Germany), which is a universally accepted shade guide [7]. The range of colors for VITAPAN's guide is split into four groups assigned with the letters A, B, C and D, depending on the hue, and also classified according to increasing chroma and decreasing value, which are designated in numerical order (e.g., A1, A2, A3) [8]. According to the manufacturer, these shades are reddish-brown, reddish-yellow, grayish and reddish-gray, respectively [9]. Instrumental shade determination can be performed with spectrophotometers, colorimeters and digital camera systems with their corresponding software [5; 10]. Instrumental color measurement could be preferred over visual color determination because instrumental readings are objective and more rapid [5]. Spectrophotometers calculate tooth color by measuring the quantity and spectral composition of the light reflected from the tooth's surface [11]. They express the results in the CIE L*a*b*, as well as in another or several conventional shade guides [11]. The CIE L*a*b* space was developed by the International Commission on Illumination (CIE for short in French, standing for Commission internationale de l'eclairage) in 1978 [12]. In the CIE L*a*b* colorimeter system, all of the colors that are visible can be described [13] and represented by way of a point in the space. L* characterizes the lightness of a color and can range between 0 (dark) and 100 (light); a* defines a color on a red-green axis; and b* defines a color on a blue-yellow axis. These coordinates, which are obtained with an electronic color measurement device, can be compared, making it possible to estimate color differences between two points (\(\Delta\)E*\({}_{\text{ab}}\)) (1). Despite this, in 2001, the CIEDE2000 formula was published by the CIE [14], which also allows color differences to be calculated and is considered to be more sophisticated than its predecessor [15]. Resin-based composites (RBCs) have been widely used in direct restorative procedures [16]. Nowadays, there are two main nano-sized composite categories on the market: nanofilled and nanohybrid composites [17]. The latter deals with combining nanometer and micrometer-sized fillers [17]. The VITAPAN Classical(r) shade guide is in wide use and many composite brands base their shade selection on this guide and adopt the standard A, B, C and D assignations of the VITAPAN Classical tabs.