# Color Differences of Polimerized Resin-Based Composites and Corresponding Shade Guides
Various manufacturers offer their own color guides, while others suggest comparing them to commercial color guides [18]. It should be noted that there is no standardization regarding the manufacturing of color guides. The selection of the ideal color in RBC restorations with the correct opacity and translucency is essential to achieve a natural look to the final restoration. Other aspects, such as the thickness and/or the surface texture of the outer layer, influence the final appearance of the RBCs' restorations [19; 20]. Most RBC color guides are made of plastic but very few of them are made of composite materials. Some commercial companies provide a ceramic color guide, while others offer a painted plastic color guide [19]. They can also differ in other features such as the shape of the samples, their thickness, or the type and material of the handling grip [19]. Moreover, there is no standardization regarding the nomenclature of colors in these color guides. Each manufacturer uses its own color designation for its composites and often uses the names from the VITAPAN Classical(r) shade guide. However, there is no precise match between the manufacturers' color classification and the VITAPAN(r) shade guide [21]. Meanwhile, selecting a composite resin color can be a complicated and inaccurate process if a satisfactory result is sought [1]. Cosmetic criteria can vary from one individual to the next and are dependent on their level of education, their age and their social environment [22; 23; 24]. Environmental factors, such as light conditions, can also play an important role in the selection [25]. Firstly, it has been proven that there are variations for the same color depending on the manufacturer [26] and secondly that the hue (how color families are distinguished from one another), chroma (intensity/saturation of the hue) and value (the amount of white in an object, distinguishing light and dark colors) from different cosmetic restorative materials did not match what was included in the VITAPAN Classical(r) shade guide [27]. Furthermore, despite a perfect color match, composites show color instability due to different agents like liquids, stains or smoke [16; 28]. There is evidence that reveals that the VITAPAN Classical(r) shade guide shows differences among its own guides [29; 30]. In addition, shade guides must be disinfected after each use, in accordance with the requirements set by the Occupational Safety and Health Administration (OSHA). It has been suggested that this procedure may cause variations in color samples [2]. Therefore, the purpose of this study is to analyze and compare the colors (A2, A3 and A3.5) of current RBCs with respect to the shade numbers within each product line and the VITAPAN Classical(r) shade guide, showing its CIEDE200 values. We also aim to evaluate and represent graphs of the CIE L*a*b* space, showing the CIELAB value with the color difference. The null hypothesis is that there are no significant color differences between the RBCs and the VITAPAN Classical(r) shade guide or the RBCs and their own commercial color guides.