## 4 Discussion
Additionally, ProRoot MTA showed lower \(\Delta\)E during measurements over a longer span of time [52]. Although MTA Angelus showed lower discoloration than Biodentine in our study, it is not visible to the naked eye. In our study, the \(\Delta\)E value of the Angelus MTA group was measured at the lowest at 3 months and was different during other time points (1 week and 1 and 6 months). The irrigation protocol included washing with 2.5% NaOCl and 17% EDTA followed by saline solution for the removal of the smear layer. For maximum material penetration into the dental tubules, this irrigation protocol was chosen. According to [PERSON] et al. [41], if the smear layer is left, discoloration is less common or lasts longer. Irrigation with NaOCl has been shown to cause dark brown discoloration when it reacts with materials containing bismuth oxide [18]. Although Angelus MTA was the only material containing bismuth oxide, the color change in the Angelus MTA group did not differ significantly compared to Biodentine or BIOfactor MTA. The interaction of Angelus MTA with NaOCl was likely minimal because the teeth had extensively been dried off. NaOCl is frequently used to irrigate root canals in endodontics. NaOCl residues have been demonstrated to penetrate into dentin and cannot be easily removed from root canals. A black precipitate is produced when NaOCl is exposed to bismuth and other heavy metal oxides. Although the effect is potent, hypochlorite is not necessary for discoloration to occur [53]. [PERSON] et al. [29] did not use any irrigation solution to chemically remove pulp tissue or the smear layer from dental walls, and discoloration caused by WMTA was seen but lower than that reported in other studies. This demonstrates that irrigation solutions cannot be the only factor responsible for the discoloration. Unlike [PERSON] et al. [29], we used an irrigation solution and observed discoloration in our study, but we are unable to distinguish whether this is a result of the irrigation solution or the material itself. In the 1 st week and 1 st month, the experimental materials showed similar tooth discoloration. However, tooth discoloration after six months was similar in BIOfactor MTA and Angelus MTA, but less so in Biodentine. To the best of our knowledge, this is the first research that investigates the tooth discoloration effect of BIOfactor MTA. The findings of this study over 6 months reveal that BIOfactor MTA showed more favorable results than Biodentine. Here, we would note that Biodentine and BIOfactor MTA are categorized differently from Angelus MTA according to the classification depending on the material chemistry [54]. Less discoloration of BIOfactor MTA could be attributed to the ytterbium oxide content. Regarding the limitations of the second step of the study, clinical trials are required in the patient's mouth for any vital pulp therapy. This in vitro study did not entirely mimic clinical conditions. Other factors were not considered in this study, such as the contact with irrigation fluids, presence of blood, and homeostatic temperature changes, which may all play a role in tooth discoloration. To gain a comprehensive understanding of the tooth discoloration potential of calcium silicate-based dental materials, extensive clinical research is essential to elucidate the underlying mechanisms. Additionally, conducting assessments in a more clinically relevant context, such as in vivo studies or simulations that better replicate real clinic conditions, would offer valuable insights into the practical implications of the tooth discoloration potential of dental materials.