# Influence of Food Pigments and Thermal Aging on the Color Stability of Denture Base Resins
## 4 Discussion  
The present laboratory study aimed to evaluate the color change effects of immersion in food pigments such as coffee, red wine, and a carbonated soft drink on three different heat-polymerized Villacryl acrylic resins (Villacryl H Plus V2, V4, and H Rapid FN V4) and one self-polymerized Villacryl acrylic resin (Villacryl S V4), as well as to assess the influence of thermal aging on these resins. It was concluded that thermal aging and red wine significantly affected all resins, and that that effect did not depend on the type of resin studied. Acrylic resins are frequently used in dentistry, particularly as a base for dentures, due to their numerous advantages [26]. However, after their insertion into the oral cavity, a process of biodegradation begins in their structure, leading to color changes that are aesthetically unsatisfactory and a reflection of unrealistic aging. These changes are caused by extrinsic factors, particularly the pigments present in food and beverages that discolor the resin through adsorption or absorption phenomena [11, 12]. After penetrating, these pigments often cannot be removed through cleaning or polishing, potentially necessitating a denture replacement, which increases cost and patient dissatisfaction [24]. To minimize the color instability of acrylic resins, it is important to understand which pigments are present in the daily diets of patients that may alter the color of these materials. Coffee, red wine, and carbonated soft drinks were selected for the present study, since they showed a high consumption frequency among the general population, as well as due to their high pigmentation capacity. To mimic the oral cavity, the specimens were stored at a temperature of 37 \({}^{\circ}\)C and wrapped in aluminum foil to minimize the influence of natural light. The beverages were replaced daily at the same time to avoid pigment concentration resulting from water evaporation. The type of beverage, its specific pigments and concentration, and the frequency of ingestion determine the amount of pigment and the level of resin pigmentation [17, 23]. It is estimated that each person consumes an average of 3.2 cups of coffee per day, with each cup taking approximately 15 min to drink. Thus, the 7 days of immersion in the present study was aimed to simulate 7 months of prosthesis use [12]. We currently have devices available that help us quantify color changes in dental materials. The Vita Easyshade equipment was selected for being a cordless, small, portable and contact-type spectrophotometer that is able to provide enough shade information for the color analysis process and is usually used for research on clinical ambience [30, 31]. These devices are based on the CIE Lab* system or the CIEDE2000 system and allow for the calculation of the color difference (\(\Delta\)E) between the measured object and a baseline value using the coordinates L, a, and b or L, C, and h, respectively. For this study, the \(\Delta\)E value was obtained using the CIEDE2000 system, as it quantifies coordinates that are critical for the visual perception of an object, such as chroma and hue. The Vita Easyshade mode for restoration color verification operates in L*C*h, while tooth color measurement operates in L*a*b*. The L*C*h color space correlates well with how the human eye perceives color and has the same diagram as the L*a*b* color space, but uses cylindrical coordinates instead of rectangular coordinates. Nevertheless, L*C*h values can easily be converted to L*a*b* values using mathematical formulas [30, 31, 32]. A high \(\Delta\)E value indicates a significant change in the chromatic properties of the resin, which could lead to patient dissatisfaction. Several studies indicate that \(\Delta\)E values greater than 3.3 are not clinically acceptable [3, 7, 8, 22, 33]. All specimens in this study demonstrated statistically significant changes after 7 days of immersion in the beverages, which allows us to reject the first null hypothesis.