## 4 Discussion  
Tooth discoloration is an undesirable condition in contemporary dentistry, particularly because of its aesthetic implications. It is also envisaged as unpleasant and, in some cases, psychologically traumatizing [23,24]. Tooth discoloration can occur after traumatic injuries and different dental treatments, and discoloration associated with the biomaterials used in endodontics has been documented in a previous study [25]. Preventive strategies, including the application of DBA and Nd-YAG laser treatment, have been proposed to minimize the diffusion of discoloring agents by sealing dental tubules [17,19]. The effect of two dentin surface conditioning methods (Nd-YAG laser and DBA) on the discoloration potential of three PPSCs was evaluated in this in vitro study: ECPR, Bio-C Repair, and NeoPUTTY. None of the PPSCs or surface treatments tested produced a statistically or clinically detectable discoloration (\(\Delta E_{00}<3.5\)) within the limits of our 180-day in vitro model. Accordingly, the null hypothesis is accepted. Our study was performed in vitro using freshly extracted human teeth. The distance between the labial surface of the crowns and the cavity floor was standardized in all samples, in line with a previous study [19]. This ensured that color changes could be perceived using teeth of the same thickness. Color measurements were performed using a spectrophotometer, a reliable instrument that has been widely utilized in previous studies [26, 27, 28]. The spectrophotometer determines color based on the internationally accepted ISO standards using the CIE color model. To assess color change, the \(\Delta\)E value was calculated, with a threshold of 3.5 being considered a clinically perceptible difference [16,28]. At each time point (T0, T7, T30, T90, and T180), the groups showed no significant difference, and all mean \(\Delta\)E\({}_{00}\) values remained below this threshold value. Therefore, in this 180-day in vitro study, none of the CSCs tested caused clinically significant discoloration. However, longer-term clinical studies with increased sample size are needed. We used a DSLR camera with a dual flash system and a mini-softbox to take digital photographs of dental specimens. Although the lighting conditions were kept constant during all photo taking, the recent literature has highlighted the importance of the type of light source used regarding accurate shadow assessment. A previous study emphasized that intraoral scanners offer superior accuracy in terms of color registration and that dual-flash systems provide results closer to spectrophotometric values than ring flash systems [29]. Similarly, a recent study reported that the use of polarizing filters, in combination with standardized illumination conditions, improved color-matching accuracy, especially for light tones [30]. These findings suggest that the spectral characteristics of the light source and the use of filters may impact tooth color assessment and should be considered in future research. Although previous studies have shown that DBAs and laser irradiation can reduce tooth discoloration [17,19], our results suggest that such surface treatments may offer limited additional benefits when using next-generation CSCs. While Nd-YAG lasers are widely used for dental tubule occlusion and hypersensitivity management, their presence in our study did not significantly affect the color results. The effects of adhesive systems on the pulp have long been investigated, and there are many studies showing that these materials can be used as temporary or permanent closure materials [31,32]. In the context of minimally invasive dentistry, the protection of dental tissues and the maintenance of pulpal viability are of great importance. Therefore, adhesive systems should be used carefully and strictly in accordance with the manufacturers' instructions, especially in procedures performed near the pulp [32]. Universal adhesives can etch enamel and dentin surfaces and penetrate dental tubules.