# Influence of Food Pigments and Thermal Aging on the Color Stability of Denture Base Resins
## 1 Introduction  
The loss of dental structures is a common reality today, prompting many patients to seek functional and aesthetic solutions from dental professionals. Among the various treatment options available, removable prostheses often emerge as the most practical solution for rehabilitating multiple missing teeth and surrounding tissues due to their affordability and straightforward fabrication process [1]. Acrylic resins have long been considered the gold standard for fabricating removable dentures [2, 3]. These resins are primarily composed of poly(methyl methacrylate) (PMMA),a polymer that minimizes polymerization shrinkage while enhancing the mechanical strength of the final product. Depending on the type of the activator, acrylic resins can be heat-cured (heat activated), self-cured (chemically activated), or light-cured (light-activated), exposing different internal properties [4]. Most commercially available acrylic denture base resins used in conventional fabrication of total or partial dentures come in a powder-liquid system. The powder contains PMMA and a benzoyl peroxide initiator that triggers the polymerization process when mixed with the liquid. The liquid component includes methyl methacrylate (MMA) and stabilizers such as hydroquinone, which prolong the material's working time [5]. Acrylic resins are favored due to their ease of manipulation, affordable cost, biocompatibility, and aesthetically pleasing results [3,4]. However, these benefits may be compromised over time as the material undergoes changes when exposed to the oral environment. Factors such as reduced elasticity, increased porosity, and water absorption can affect its structural stability, leading to fractures and deformation [2,6]. Additionally, prolonged contact with moisture, pigments from foods and beverages, and varying temperatures can cause significant color changes [7]. Color stability, defined as the ability of a material to maintain its original shade despite environmental exposure, is one of the most critical clinical properties of acrylic resins [2,8,9]. Color changes can be influenced by intrinsic factors, such as the resin's natural aging due to physical and chemical reactions, and extrinsic factors, such as staining from food pigments, mouth rinses, and poor oral hygiene [10-13]. The accumulation of stains, artificial food dyes, and high surface roughness caused by inadequate polishing during manufacturing can further exacerbate discoloration [13-15]. It is essential to distinguish between discoloration caused by aging and pigments intentionally added for aesthetic customization. Acrylic resin powders often contain pigments like mercury sulfide, cadmium sulfide, cadmium selenide, and iron oxide, which provide a range of natural-looking shades. These pigments can be embedded in the material during production or added later by dental technicians using specialized paints to replicate the natural appearance of the gums. Zinc and titanium oxides are also used to enhance opacity [4]. Given that dental prostheses remain in continuous contact with oral fluids, food, and beverages, extended exposure increases the risk of color changes over time [12]. Numerous studies have investigated how different beverages [2,3,16-26], mouth rinses [1,2,27,28], and thermocycling procedures [2,13,17,23,27] affect the color stability of acrylic resins. To simulate real-life conditions in the laboratory, aging methods such as thermocycling, ultraviolet light exposure, and water storage have been employed. These techniques provide valuable insights into the long-term behavior of acrylic materials used in dental prosthetics [13]. In this context, the present study aims to evaluate the influence of food pigments present in beverages and thermal changes on the color stability of acrylic denture resins with different characteristics of the curing process and of the intrinsic pigments.