## 4 Discussion  
Based on the spectrophotometric results, the null hypothesis must be rejected. CA caused changes in the colors of the CSCs and also changed some of their structures, specifically those of Biodentine, Retro MTA, and MTA Repair HP. However, CA did not cause dark discoloration observable with the naked eye of any of the materials. The spectrophotometric colors of all the CSCs changed under the influence of all the irrigation solutions. Visual spectrophotometry was used in this study because it is considered to be the gold standard for the evaluation of color, and it has been successfully used in dentistry studies [26; 27; 28]. Visual spectrometry is the most widely used method of determining color: it meets international standards, and it is compliant with ISO standards (International Commission on Illumination) [29]. To the best of our knowledge, this is the first study evaluating the effects of CA on CSCs. We have demonstrated that CA has a significant influence on spectrophotometric color change in CSCs at all time intervals. There was a greater spectrophotometric color change after immersion in CA than after immersion in EDTA. After 24 h immersion in CA, MTA Repair HP, Biodentine, and Retro MTA disintegrated, dissolved, and took the form of wet sands on the surface. These changes were visible to the naked eye. This material disintegration phenomenon may be related to the effect of the acid on the cement structure. Furthermore, these results are similar for both concentrations of CA. CA is used in architecture as a retarder of setting and hardening of Portland cement. Citric acid does not have any beneficial effect on enhancing the calcium silicate phase, as was initially assumed, and instead it reduces the strength of Portland cement at all levels of concentration [30]. It is remarkable that CA had no influence on the material structure of the bismuth-oxide-containing CSCs ProRoot MTA, Ortho MTA, and MTA Plus. In one study, the microstructure of Biodentine changed, showing a relatively smooth surface with morespheroidal crystals [31]. No information has been found as to whether the radiopacifer may have an effect on material structure dissolution. In the study by [PERSON] et al. [32], MTA material containing bismuth oxide had a reduction in radiopacity after 30 days, and it was hypothesized that this may be caused by the dissociation of bismuth oxide. Therefore, it can change the color of the material, but also the structural stability of the CA [32]. The effect of an acidic environment on the loss of CSC volume was also assessed. In the case of Biodentine, it was much lower in an acidic environment than in a saline environment. There was no significant difference in the volume of ProRoot MTA between these two environments [33]. In another case, it was proved that the exposure to acidic pH decreased Ca(OH)\({}_{2}\) crystalline formation in ProRoot MTA, Retro MTA and Biodentine [34]. Accordingly, more detailed research is needed regarding the material strengths of CSCs after using CA. MTA Repair HP was the least sensitive to NaOCl solution of all the tested CSC materials. It also exhibited the slightest spectrophotometric color changes upon immersion in CHX and EDTA. Only in contact with CA solution did its surface structure disintegrate. Irrigation solutions do not cause darkening of MTA Repair HP, which could be visible to the naked eye. A recent study has shown that MTA Repair HP shows better push-out bond strength than its predecessor white MTA Angelus [35] and does not cause discoloration of teeth [36]. It is believed that the presence of calcium tungstate as a radiopacifier in MTA Repair HP contributes to higher calcium release in the initial periods [37], promoting greater biomineralization and aiding the resistance of this material [38; 39]. Furthermore, its high plasticity may improve marginal adaptation. This study revealed a significant change in the colors of ProRoot MTA, MTA Plus, and Ortho MTA upon immersion in NaOCl.