## 1 Introduction  
Achieving an aesthetically pleasing smile often holds greater significance for patients than prioritizing their oral health [1, 2]. Consequently, a considerable number of individuals opt for over-the-counter whitening toothpastes, often without a comprehensive understanding of associated risks or its appropriate usage protocols [3]. Tooth discoloration represents a prevalent concern among the population; its origins derive often from dental pigmentation, characterized by the deposition of pigments within the tooth structure. The pigmentation can be of intrinsic and/or extrinsic origin, the latter being the most predominant type that can be removed prophylactically through daily oral hygiene practices and with the use of toothpastes. This discoloration occurs when chromogenic substances adhere to the enamel surface and change its original color [4, 5]. Whitening toothpastes have been observed to effectively remove and manage the deposition of chromophores responsible for extrinsic pigmentation [6, 7, 8, 9] and the color of teeth is altered by increasing the brightness of the tooth structure, through a combination of mechanical and chemical reactions [10]. These toothpastes commonly contain abrasive particles, optical agents, and/or chemical agents [11]. Whitening toothpastes incorporating abrasive microspheres rely on a mechanical mechanism for pigment removal targeting biofilm and extrinsic pigmentation. Amongthe abrasives commonly employed in these formulations are calcium carbonate, hydrated silica, dicalcium phosphate, aluminum oxide, and sodium bicarbonate [8; 9; 12; 13; 14; 15]. Activated charcoal toothpastes typically incorporate various abrasives, with silica as the most prevalent. The more abrasive the formulation, the more effective it is at removing extrinsic pigmentation; however, prolonged use may lead to the removal of tooth surface, which can lead to changes in surface roughness [12; 13]. Activated charcoal operates by binding to the deposits, bacteria, and pigments (hydrophobic) present on the tooth surface, facilitated by its high surface area, porous nature, and high hydrophobicity. This high adsorption capacity can counteract the effects of fluoride ions, which are typically present in lower concentrations (950 ppm) compared to those found in conventional toothpaste formulations [9; 12]. Recently introduced to the market, blue covarine-based whitening toothpastes incorporate a whitening agent that has an optical effect on the color of the tooth surface, altering its perceived shade [7; 8]. This optical operates by altering the apparent color of the tooth surface through a uniform deposition of a thin, semi-transparent layer of bluish pigment uniformly on it, with the intensity of the effect correlating with pigment concentration. Examining the additional constituents of whitening toothpastes that include blue covarine reveals the presence of modified silica particles that have an abrasive action on enamel. This coating immediately modifies the interaction and perception of incident light, which is an advantage of this agent and results in yellowed teeth that convey the effect of being whiter and brighter due to the change in the b* axis of the CIE L*a*b* [7; 8; 14]. In 2019, [PERSON] et al. conducted a study to evaluate a range of whitening toothpastes with different mechanisms of action, including activated charcoal, blue covarine, hydrogen peroxide, and microbeads [8]. However, this study was limited to the evaluation of color and used a visual assessment method, which is highly subjective. Visual assessments of color variation have a high risk of bias and cannot accurately correlate to the in vivo performance. In an attempt to achieve a more realistic assessment, in our study a colorimeter (Optishade Style Italiano, Smile Line, St-Imier, Switzerland) was used. However, there is a lack of scientific support for this type of instrument [16].