## 1 Introduction  
Tooth discoloration is a change in hue, color, or dental translucency due to extrinsic and intrinsic factors [1, 2, 3, 4]. Intrinsic discoloration can be caused by pulp necrosis, intra-pulal hemorrhage, dentin hyper-calcification, age, defects during tooth formation, drug influence during root canal treatment, and restorative materials (amalgam, pin, wedge, and composite) [5, 6, 7, 8, 9]. Crowns, labial veneers, and intra-coronal bleaching are all options for treating intrinsically discolored teeth [9, 10]. These treatments can change the color of discolored teeth such that they become bright. Due to globalization and the growing modernization of all sectors, both men and women have developed heightened aesthetic sensibilities and place a premium on any aspect of their look that would improve their appearance, including smiling brightly and whitely [11, 12, 13, 14]. Because tooth whitening is an affordable, quick, and minimally invasive process, it is now the treatment of choice for tooth staining among all available alternatives for treating tooth discoloration [11, 12].  
Intra-coronal bleaching is a method of whitening nonvital teeth after root canal treatment and involves placing strong oxidizing agents in the pulp chamber [10; 15]. Bleaching agents include hydrogen peroxide, sodium perborate, sodium hypochlorite, and carbamide peroxide. However, in the case of intra-coronal bleaching, 10-15% sodium perborate and 35% hydrogen peroxide are often used [1; 4; 6; 7; 15].  
Hydrogen peroxide has a clear liquid form and is highly unstable, odorless, and acidic [6; 7; 8; 16]. This bleaching material is a strong oxidizer and is easily mixed with water, alcohol, or ether [4; 7]. The oxidation reactions of peroxides produce gaseous bubbles under the enamel surface. The oxygen-containing surface layer that inhibits the polymerization of bonding agents affects the strength of enamel-resin bonds [6; 10; 17; 18]. Various studies suggest suspending the restoration procedure for 2-4 weeks to prevent bond failure between enamel and composite restorations [18]. However, this poses a clinical problem when the tooth should be immediately restored with a composite restoration. Therefore, a material that can accelerate the loss of peroxide residue is required [6; 10; 17; 19].  
Antioxidants, such as vitamin C (ascorbic acid), glutathione, beta caroten, vitamin E, CoQ10, flavonoids, and lipoic acid, are able to neutralize hydrogen peroxide residue and the oxygen-rich molecule [20; 21; 22; 23; 24].  
Propolis is a natural antioxidant source and is relatively easier to obtain than synthetic antioxidants such as sodium ascorbate [24; 25]. Propolis, or bee glue, is a resin material collected by honeybees from various plant species [25; 26; 27]. A species of bee that can produce propolis in large quantities is _Trigona_ spp. This type of bee is commonly found in South Sulawesi, both in the highlands and lowlands. Propolis has vigorous antioxidant activity against oxidants and free radicals (H\({}_{2}\)O\({}_{2}\), O\({}_{2}\)-, and OH) compared with other bee products [28; 29]. The matrix of flavonoids in propolis can reduce the harmful effects of free radicals. Therefore, the present study aimed to assess the potential of propolis _Trigona_ spp. as an antioxidant agent to reduce residual peroxide after an intra-coronal bleaching treatment. Accordingly, patients could obtain esthetic restoration immediately after the intra-coronal bleaching treatment.