## 4 Discussion
This difference could potentially explain the outcomes observed in the present study, especially concerning the comparison in the apical region between White ProRoot MTA(r) and TotalFill(r) BC RRM Fast Set Putty(tm). In addition to solubility, the chemical composition of hydraulic calcium silicate cements also plays a crucial role in tubular penetration. Hydrophilic materials tend to penetrate dentinal tubules more deeply than hydrophobic materials [17]. Studies have shown that hydraulic calcium silicate cements exhibit superior marginal adaptation when compared to epoxy resin-based materials, attributed to the small particle size of hydraulic calcium silicate cement materials, facilitating enhanced penetration through dentinal tubules [18]. This favorable characteristic of hydraulic calcium silicate cements materials may contribute to the positive outcomes obtained in this study for both tested materials. Various methodologies are employed to compare the marginal adaptation of materials used in apical plugs. Techniques for assessing the sealing ability of materials include bacterial infiltration [59], dye penetration [60], fluid filtration [61] and the use of radioisotopes [8]. In this study, scanning electron microscopy (SEM) was chosen to evaluate the marginal adaptation by analyzing the perimeter of the gaps between the materials used in the plugs and the canal walls. The selection of scanning electron microscopy was justified by its advantages over optical microscopy, including higher precision, greater resolution and superior magnification capabilities for analyzing the interface between materials and root canal walls [36; 62]. Unfortunately, this method is less explored in studies on the same topic. Despite several studies using dye penetration to assess marginal adaptation and microleakage, limitations of this method have been documented such as dye dissolution during the process and difficulties in observing the maximum penetration [63]. Furthermore, the size of molecules, pH and chemical reactivity of the dye can disrupt the extent of penetration and influence the outcomes [64]. As a result, scanning electron microscopy is recognized as a reliable approach for assessing marginal adaptation [65]. Concerning electron microscopes and their impact on samples, a higher power has the potential to increase artifacts or cracks in the hard tissues of the samples [36; 66; 67; 68]. This phenomenon may arise due to the contraction and expansion of both the material and the tooth [11]. Since the use of SEM in this study could have introduced artifacts that might potentially influence the interpretation of the images collected, the samples underwent careful observation under an optical microscope before and after SEM analysis. Samples with cracks affecting the material-dentin interface were excluded, in line with a similar approach adopted by [PERSON] et al. [62]. Other images showing cracks which did not occur in the targeted area of the study (i.e., the canal dentin and material interface) were deemed suitable for the study as they did not compromise the results. Certainly, while this study suggests that White ProRoot MTA(r) exhibits superior marginal adaptation compared to TotalFill(r) BC RRM Fast Set Putty(tm), further research with a larger sample size is warranted. Additionally, future studies should incorporate volumetric measurements of compressive forces and direct assessment of the solubility of both materials.