Numerous studies have been conducted on the discoloration effect of SDF [4, 5, 9]. However, the number of studies investigating the discoloration effect of SDF/KI and NSF on dental tissues is quite limited in the literature. This study is the first to investigate and compare the discoloration effect of SDF, SDF/KI, and NSF solutions on commonly used compomer filling material in pediatric dentistry.

In accordance with the findings of the systematic review published by Roberts et al., it is established that application of KI after SDF offers advantages in diminishing staining [11]. Fröhlic et al. [12] examined the impact of KI on staining by partitioning 30 dentin specimens derived from bovine teeth into three groups following demineralization. Group 1 underwent no treatment, Group 2 received SDF, and Group 3 was treated with SDF/KI. The findings demonstrated that KI application reduced staining. Nguyen et al. [13] conducted an in vitro study to investigate the staining efficacy of a 10% KI solution on various restoration materials. Teeth that were treated with SDF and then subjected to light-curing exhibited immediate grayish staining. All groups treated with SDF/KI showed similar color change to the control groups, indicating that it was effective in lessening the staining. According to our study, after one week of measurements, it was observed that there was a similar decrease in brightness and color change between SDF/KI and SDF groups. However, it was found that it caused a greater decrease in brightness and color change compared to the control and NSF groups. After four weeks, although the use of SDF/KI was found to be advantageous compared to SDF, it was observed that it did not completely prevent color change compared to the control group.

Zhao et al. [14] assessed the staining effect of SDF and SDF/KI on glass ionomer restoration margins in their in vitro study. Pairwise comparisons reveal that SDF/KI induces less staining compared to SDF, although KI does not completely eliminate the staining effect of SDF at the restoration margins. Miller et al. [15] conducted an in vitro study using a subjective scale ranging 0–5, focusing on the preventive impact of KI on staining of glass ionomer. In contrast, no significant difference in staining were found between SDF and SDF/KI treated groups. In our study, it was found that KI did not completely prevent the black staining effect of SDF, but it could be advantageous compared to SDF in the long term. However, the use of only compomer is one of the limitations of the study. In future research, it is believed that comparing the effect of SDF, SDF/KI, and NSF solutions on staining using a non-light-curing filling material alongside light-curing ones could be beneficial in understanding the effect of light-curing.

Kamble et al. [9] collected 30 carious primary molars and carried out various restoration applications. They treated with SDF in Group 1, SDF/KI in Group 2, and SDF + Glutathione (GSH) in Group 3 followed by restoration with glass ionomer. Color evaluations were conducted using spectrophotometer. Measurements taken at the end of day 1, 1 week, and 4 weeks revealed the highest ΔE values and staining in SDF. The study underlined the need for further research in this area while highlighting the potential advantages of KI and GSH in decreasing staining. In our study, GSH was excluded due to the increase in sample size and costs. However, it is believed that future research would benefit from understanding whether the combination of SDF with KI or GSH is more advantageous and comparing the staining effect with NSF solution.

Hamdy et al. [16] conducted an in vitro study, in which they carried out color assessments using spectrophotometer. Initial measurements were recorded before the experimental materials were applied. SDF, SDF + composite, SDF/KI, and SDF + glass ionomer was performed in groups respectively. Second color measurements were taken immediately after the application of these materials, and third color measurements were taken after 24-hour suntest aging protocol. In the SDF group, noticeable decrease in L*, a*, and b* values over time was observed. It was reported that SDF caused significant black staining in the carious dentin, and the restorative material and KI could reduce the staining effect of SDF. The masking effect of the composite was noted to be the most successful material that was not fully reversed by the aging procedure. Another limitation of our study is that we only conducted color measurements after applying the filling material. Considering the potentially masking effect of the filling material’s black staining, the obtained values may not reflect the true black staining effects of the solutions. In future research, it would be beneficial to follow staining both with and without applying the filling material after the application of the solutions to compare the results.

There is a limited amount of research in the literature that examines the staining-inducing effect of NSF on teeth and restorative materials. Therefore, our study aimed to explore whether NSF causes staining on filling materials. The formation of oxides is not observed when nanosilver particles come into contact with teeth. Therefore, it is noted that NSF does not cause staining on teeth, but slight level of staining may occur in those with nanoparticle sizes of approximately 100 nm [17].

Espíndola-Castro et al. [18] examined the color changes that occurred following the application of NSF formulations with 600 and 1500 ppm concentrations on dentin samples compared to SDF and SDF/KI. The assessments were conducted using spectrophotometer immediately after application, 2 weeks, and 4 weeks. The samples were stored in artificial saliva until the end of the experimental period. At the end of 4 weeks, before the color measurement process, the samples were brushed without the use of any abrasive materials. The results revealed that the NSF formulations resulted in less staining compared to other groups. The yellowish stains caused by NSF led to decrease in brightness at the measurement after 2 weeks, but it was observed that the brushing process could remove the stains. In their in vitro study conducted on dentin samples obtained from bovine teeth, Sayed et al. [17] examined SDF, AgNPs (Silver Nanoparticles), KF (Potassium Fluoride), and AgNPs/KF applications and conducted color measurements before treatment, immediately after, and at the 1st, 2nd, and 7th days, and analyzed ΔE. They found that SDF exhibited significantly higher staining compared to other groups, while the materials present in the other groups did not cause significant staining. Zhao et al. [19] produced PEG (Polyethylene Glycol)-AgNPs solution containing 11.600 ppm fluoride and 400 ppm silver, with silver nanoparticle size of 2.56 ± 0.43, and conducted color assessments. They found no significant difference in terms of staining between water and PEG-AgNPs solution. The L*, C*, and h* values in the SDF group were notably lower than in the other two groups, and indicating a substantial color change compared to the others. Therefore, it was concluded that PEG-AgNPs solution could serve as a promising alternative to counter the drawback of black staining caused by SDF. Similarly in our study, NSF caused significantly less color change compared to SDF and SDF/KI. However, the limitation of our study lies in the nanoparticles not being coated with PEG. Comparing the staining effect of NSF solutions with both features would be beneficial for future research.

There is a need for further research on materials that can reduce the staining effect of SDF while not compromising its caries-inhibiting, remineralizing, and antibacterial properties or providing alternatives. Ongoing studies focus on the use of KI, GSH, their combination with restorative materials, and determining which content of NSF yields better results. In recent biomedical research, attention has turned to selenium nanoparticles (SeNPs), which are reported to possess antimicrobial, antioxidant, and antiviral capabilities, and investigations are underway in this area [20].

The environment in which teeth are stored during the period of color assessment are crucial. Various methods such as thermal cycling, UV light exposure, incubation in distilled water, storage in phosphate buffered saline, or artificial saliva can be utilized in studies. Distilled water containing NaHCO3 and KCl, due to its chemical composition resembling human saliva, can serve as an alternative to artificial saliva in research [21]. Some researchers suggest storing the samples in a dry environment to prevent undesirable reactions that could arise from the interaction between SDF and the storage conditions, and to accurately assess the absolute effect of SDF [17]. Patel et al. [22] have noted that SDF reacts with sodium chloride present in artificial saliva, resulting in the formation of insoluble white silver chloride, which could potentially have a negative impact on color measurements. The use of artificial saliva, which is closer in composition to the oral environment due to its enzymatic content, could provide results that are more realistic. However, researchers have indicated that it might reduce the material’s staining effect and that the clear color change effect could be better observed in a dry environment because there is no risk of the staining effect being removed by liquid’s removal effect. Hence, it is considered beneficial for future studies to compare color changes in different storage environments.