## 1 Introduction  
Resin composites, which allow the application of minimally invasive approaches, are now widely used in the restoration of both anterior and posterior teeth due to their acceptable aesthetic and mechanical properties [1]. Nanotechnology, which allows the addition of nano-sized filler particles to the resin composite, has made a significant contribution to this [2]. However, it is very difficult to achieve a colour match between these resin composites, which have different opacities and translucencies, and the dental tissues (enamel and dentin) in a way that provides harmony with the natural tooth tissues. The colour matching between the resin composite and the tooth structure is achieved using a layering technique [3]. Numerous clinical and in vitro studies have demonstrated the ability of the layering technique to achieve shade matching [4]. However, this technique demands precision [5]. Attempts to reduce technical precision have led to the development of universal resin composites that exhibit a chameleon effect, which facilitates colour selection and colour matching with surrounding dental tissues [4; 6]. The chameleon effect refers to the ability of restorative materials to match the colour of the surrounding tooth tissue owing to their optical properties, such as light transmission, diffusion, and reflection [7; 8]. Numerous studies have reported that universal resin composites with this effect blend well with tooth tissue colour. However, these studies have also found that the effect is more successful in restorations involving less tooth tissue loss [9]. In recent years, resin composites that match the colour of dental tissues with a single shade have been produced. These composites have been reported to better match the colour of dental tissues than multi-coloured ones. This smart chromatic effect is largely attributed to the minimization of the difference between the refractive indices of the resin matrix and filler particles. When these indices are closely matched, light scattering at the filler-matrix interface is reduced, increasing translucency and allowing the composite to effectively reflect and transmit surrounding tooth colours, thus achieving a chameleon-like adaptation [10; 11; 12]. Despite these developments, aesthetic problems such as colour changes at the edges of restorations, secondary caries and fractures, and general deterioration of the colour match of the restoration are still encountered clinically in resin composite restorations. Colour change is the main reason for replacing restorations, particularly in the anterior region [2]. The extent of colour change is crucial for the longevity of the restoration. Internal colour change occurs as a result of changes in the material's structure. This is influenced by factors such as the type of monomer used, the filler ratio, and the degree of conversion in the resin composite. External colour change, on the other hand, is mainly caused by consuming products containing dye, such as food and drink and cigarettes [2]. It is also known that roughness of the restoration surface contributes to external colour change. Surface roughness can be measured in vitro using mechanical or optical profilometers, scanning electron microscopy (SEM), or atomic force microscopy (AFM). However, the most preferred method is measurement using a profilometer because no additional application to the samples is required for measurement and the measurements can be repeated [13]. It has been reported that a surface roughness value (Ra) of less than 0.15 \(\upmu\)m obtained with a profilometer reduces the adhesion of Streptococcus mutans to the surface, while a value greater than 0.2 \(\upmu\)m creates an accessible adhesion area for bacterial plaque [14]. Translucency is defined as the light transmission of a material that causes the background to be visible and the state between partial opacity or full opacity and full transparency [15].