Introduction: The colour of our teeth changes throughout our whole lives. It depends on the absorption properties of the enamel, light scattering, and the ability to absorb different substances into the enamel. The colour of our natural teeth is commonly represented with the CIE L*a*b* colour space or the L*C*h* colour space. We can determine tooth colour manually, with the help of shade guides, or with different devices, such as a spectrophotometer. Tooth discolouration can be internal or external. Internal discolouration is commonly the result of trauma or developmental disorders, while external discolouration occurs due to the accumulation of organic and inorganic material found in plaque or due to the accumulation of chromogens on the surface of the tooth. We can treat internal and external discolouration with different methods, such as tooth whitening, aesthetic dental restoration, or orthodontic whitening trays. Purpose: The aim of this thesis is to determine which liquid causes the greatest discolouration of dental restorations, depending on the material used for their production. Methods: For the purpose of writing this thesis, we reviewed the literature found in databases such as Google Scholar and ScienceDirect. During the search, we mainly used English keywords related to tooth discolouration. Based on the literature we found, we conducted an experiment to evaluate the colour stability of the materials. The experiment was carried out at the Faculty of Health Sciences, University of Ljubljana. The samples of dental restorations were made from three different materials (polymethyl methacrylate, composite, zirconia) and were exposed to four different liquids (coffee, wine, black tea, juice). The experiment lasted 34 days. After 27 days of exposing the samples to the liquids, we additionally exposed them to hydrogen peroxide for bleaching. For our measurements, we used a chromameter. Results: Based on the results of the experiment, wine causes the greatest discolouration. Zirconia has been proven to be the most colour-stable material, while polymethyl methacrylate was the material with the greatest discolouration. Discussion and Conclusion: The results of our experiment do not entirely correspond with some of the reviewed studies. According to the literature, black tea causes the most discolouration, but based on our experiment, wine causes even greater discolouration. During the staining process, all values remained within the threshold limits defined in the literature. For conducting the measurements, instrumental devices were more suitable, as they were faster, more objective, and more accurate. Teeth discolouration can be managed with whitening or ceramic veneers.
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