## 4 Discussion
However, there are several benefits; when a blood clot interacts with the coronal tooth structures, red blood cells that enter the dental tubules undergo hemolysis. The accumulation of released hemoglobin and hematin molecules in the dental tubules leads to tooth discoloration [33]. Another cause of color change associated with regenerative endodontic treatment (RET) is the contact between blood and calcium silicate cement and dentin. The tendency for color change upon contact with blood is reported in all calcium silicate cements, even in those known to have a lower potential for color change. Given the fact that a blood clot is the most commonly used matrix in RET [34], the significance of procedures to prevent discoloration becomes apparent. In order to prevent tooth discoloration induced by RET procedures or triple antibiotic paste TAP applications, Teethmate desensitizer, a bonding agent, Nd:YAG laser, and Er:YAG laser have been used in the literature [18; 20; 27]. [PERSON] et al. [20] evaluated for the first time, using an ex vivo model, the role of sealing the dentin walls of the pulp chamber with a dentin bonding agent (DBA) in preventing crown discoloration prior to a regenerative endodontic procedure (REP). While the application of the DBA did not completely prevent clinically perceptible coronal color changes, it was observed that there was significantly less crown discoloration in each stage of the regenerative treatment. This outcome directed the researchers to find another method. The Nd:YAG laser is frequently preferred in the treatment of dentine sensitivity due to its highly effective dental tubule occlusion and high penetration depth effects [35; 36; 37]. Additionally, the Nd:YAG laser, when applied with appropriate parameters, reduces unwanted side effects such as cracks and pulp damage in teeth [23; 36]. Within this aspect, [PERSON] et al. [18] used an Nd:YAG laser to prevent tooth discoloration induced by triple antibiotic paste and compared its effectiveness with those of a bonding agent and Teethmate desensitizer. They reported no significant difference between these three experimental groups. [PERSON] and [PERSON] performed a similar study with an additional experimental group, Er:YAG laser, and they applied Biodentin directly over the blood clot [27]. Their results were also in accordance with those of [PERSON] et al. In the present study, no significant differences were observed among Optibond FL, Optibond Universal, and Nd:YAG laser treatments across all time intervals. Surprisingly, the effect of Clearfill SE Bond on the prevention of the tooth discoloration was lesser than those of the other bond systems. The possible reason could be the yellowish color of this bond, which may induce coloration. Another reason for this result could be the application of the primer on the unetched surface, which may cause discoloration as reported by the manufacturer (Figure 5) [38]. In using extracted teeth that were kept in saliva, an attempt was made to standardize the clinical conditions. The groups were also divided by taking into account the initial color of the teeth. On the other hand, the color analysis was conducted from the same region each time. The alteration of certain key parameters in the study could have led to variations in the results, which is the limitation of the present study. The teeth allocations of each group were conducted based on the previous studies [24; 39]. According to this, an equal number of color tones were distributed to each group based on colors A2, B1, B2, and A3. The initial luminosity values were recorded but not considered for the allocation of the groups. For this reason, in the result part, luminosity change was evaluated within each group, rather than between the groups. Accordingly, the luminosity value of each group decreased compared to that on T0. In this research, various methods were employed to prevent tooth discoloration caused by MTA-blood contact. Different outcomes might have been obtained using another calcium silicate-based material.