# An Overview of Shade Selection in Clinical Dentistry
## 2 Literature Review
### Measurement of Colour
#### 2.3.1 Visual Technique  
The Munsell system, which may be depicted in three dimensions of color, is a commonly used method for visually measuring tooth shade (Figure 2). The use of visual shade guides is the conservative technique of shade selection, which is the most common and suitable approach in shade selection of a tooth. It is very economical and easily available in the market; the color of a tooth can also accurately match with a regular reference shade guide. When employing the shade tab approach, choosing a tooth's shade entirely depends on the observer's sight. [21]. The visual approach is used most frequently in clinical dentistry to identify the shade of a patient's teeth. However, it has been shown that the visual approach for determining shade matching is inaccurate. The visual shade matching approach has some limitations, including inadequate ambient lighting conditions, age, eye impairment and a strong reliance on individual abilities in shade matching and metamerism [22; 23; 24; 25]. In dentistry, shade guides are used to match with the natural tooth structure that comprise of a set of standard or independently fabricated shades [26]. Shade guides can be classified on the basis of material from which they are made, such as composite resin based, acrylic based and ceramic based [27; 28; 29]. Generally, shade guides should have a full range of natural color for dental structures. As a general standard, each shade tab is composed of an incisal, middle and cervical part that varies in shade on the basis of translucency and color density [30]. In prosthetic dentistry, selection of shade is a significant phase in all directions, which, later on, is delivered to the laboratory technician to fabricate indirect restoration [31]. Vita Classical Shade Guide  
In Vita Classical, the color space is classified into four groups: A, B, C and D; these comprise the leading HUE (name of color). These are red and brown in group A, red and yellow in group B, gray in group C, and red and gray in group D. Every letter group has sub-divisions indexed with Arabic numbers, ranging from 1 to 4, which makes the overall number of tabs 16 (Figure 3). As the number increases, the value decreases, whereas the chroma increases simultaneously [33]. Vita 3D Master Shade Guide  
This shade guide entails 26 tabs that are organized into five groups with respect to their value. Figure 4 shows the shade tabs are further arranged along with two axes inside the groups, i.e., vertical in relation to chroma and horizontal axes according to hue. The first group consists of two tabs, the second, third and fourth comprise seven each, whereas the fifth one has three tabs. Moreover, every shade tab has three markers ranging from 1 to 5, presenting the group and the level of value that decreases as the number increases [34]. Figure 3: Vita Classical Shade Guide. It has been observed that a number of improvements have been developed for the Vita 3D Master shade guide, as compared to Vita Classical:  
* There is an extensive range of value. * The red spectra are wide-ranging. * The shade tabs are more correspondingly divided into the color space. * The development in distribution of groups has improved and become more concise [32]. Chromascop Shade Guide  
To identify hues, the Chromascop numbering system is employed. Depending on the color, it is divided into categories (100 = white, 200 = yellow, 300 = orange, 400 = gray, 500 = brown) and within the groups, as chroma increases from 10 to 40 [35] Figure 5.  
Figure 4: Vita 3D Master Shade Guide. Figure 5: Chromascop Shade Guide. Merits of Shade Guides  
1. The most common method of shade selection is using a visual shade guide [6]. 2. It is economical and durable, i.e., does not require frequent replacement of the shade guide. 3. It provides an efficient comparison with natural tooth color. 4. Most frequently used by dentists, dental assistants and dental laboratory technicians to communicate the proper tooth color, brightness and translucency [9]. 5. Easily available. Demerits of Shade Guides  
1.