# Level of Agreement in Subjective Selection of Gingival Colour
## 1 Introduction  
All forms of therapeutic rehabilitation performed in dentistry should aim to achieve a good level of dental functionality and aesthetics. To meet the second of these objectives, it is vital for the \"white aesthetics\" to be in harmony with the so-called \"pink aesthetics\" [1]. Several studies have noted that colour is the aesthetic factor in dentistry which patients deem most important [2, 3, 4], although it is also the factor that is most difficult to determine, convey, and reproduce accurately. Colour is a psychophysical sensation that results when the human visual system captures light reflected from an object [5]. Three factors influence this perception of colour [6]: the observer, the light source used, and the object, defined by its own chromatic information. Selecting dental colour by making a direct comparisonwith the colour of the tooth in question--or the adjacent teeth, if missing teeth are being replaced--is the classic, most widely used methodology [7; 8; 9]. The subjectivity involved in the visual selection of colour in dentistry is well-documented [10; 11; 12; 13; 14], as is the lack of consistency, given the range of variables that have been seen to condition it, such as the following: the observer's experience, theoretical and practical training, gender, age, and emotional state, as well as ocular fatigue, ambient light and colour, etc. With the aim of reducing the errors involved in the traditional colour selection method and increasing the accuracy and reliability [14] of dental shade matches, objective electronic devices have come into use [15; 16; 17; 18] which record dental colour using CIELAB colour coordinates and also provide the resulting colour as given in dental shade guides (Vita Classical or Vita 3D Master) [14; 19]. Comparisons between visual selection and instrumental methods have suggested that the latter provides better results [20; 21; 22; 23], although recent publications have recommended a combination of various methods [8; 18; 24; 25]. There is no consensus in prior studies about whether there is any difference in the subjective perception of the dental colour space by men and women. Some have concluded that men and women perceive dental colour in a similar manner [11; 26; 27; 28; 29; 30; 31; 32], while other articles [11; 33; 34; 35; 36] have identified statistically significant differences in favour of women's identification of colour. To enable the quantitative study of colour, the Commission Internationale de l'Eclairage (CIE, International Commission on Illumination) has defined a colour space as a uniform, three-dimensional space of colour coordinates formed by three axes: (1) the L* coordinate, which corresponds to the vertical axis and refers to the lightness of the colour, from black when L* = 0 to white when L* = 100; (2) the horizontal a* coordinate--a positive value for a* indicates the amount of red, while the more negative the a* coordinate is, the more green is present; and (3) the horizontal b* coordinate--an increasingly positive value for b* indicates a larger amount of yellow, while an increasingly negative b* coordinate indicates a larger amount of blue [37]. In dentistry, the most frequently used formulae for quantitatively calculating the difference between two objects are the Euclidean formula (\(\Delta\)Eab*) [37] and the CIEDE2000 formula, whose purpose is to solve the problem of discrepancies between colour measurements performed with colorimeters and the human eye [15; 38; 39]. The aforementioned results apply solely to the dental colour space and have yet to be explored in the gingival colour space, due primarily to the lack of a gold standard for the gingival shade guides used in dentistry [40; 41; 42]. There is, therefore, a lack of knowledge about how subjective visual perception works within the \"pink\" colour space.