**3. Results**

None of the techniques used was able to provide a pore-free root canal filling in the apical 5 mm pores; size and shape diversity were observed in all apical plugs, with open pores being the dominant type of porosity. The results of quantitative volumetric analysis of open and closed pores are summarized in Table 1. The micro-CT assessment revealed that volumes of prepared root canals had no considerable volumetric variances before the root obturation procedure (*p* = 0.34), indicating the initial equality among all experimental groups. However, the porosity distribution in root canal fillings was significantly different between all experimental groups evaluated (*p* < 0.05).

**Table 1.** Mean values (%) and standard deviations (SD) of open and closed pores in the respective groups.


Different superscript letters in the same column indicate significant differences between groups (pairwise Mann-Whitney test; *p* < 0.05).

A considerably higher quantity of open and closed pores was observed in both MF groups (with/without ultrasonic agitation), when compared to the fillings of BR/SC and BR/SC-UA (*p* < 0.05). The interaction between the MF and MF-UA groups was detected to be statistically significant (*p* < 0.05), with the highest porosity being in the MF-UA group (Figure 1).

**Figure 1.** Representative cross-sections of random samples at the level of 5 mm, 3 mm and 1 mm from the apex (**A**) and longitudinal sections (**B**), demonstrating the porosity distribution within the fillings of MF (MTA Flow) and MF-UA (MTA Flow with ultrasonic agitation) groups.

However, no significant differences were observed between the specimens of the BR/SC and BR/SC-UA groups, where the quantity of open and closed pores within the fillings remained similar (*p* = 0.82 and *p* = 0.57, respectively) regardless of a lower mean porosity determined in the BR/SC group (Figure 2).

**Figure 2.** Cross-sectional images at the level of 5 mm, 3 mm and 1 mm from the apex (**A**) and longitudinal images (**B**), representing the quality and homogeneity of BR/SC (BioRoot RCS/single cone) and BR/SC-UA (BioRoot RCS/single cone with ultrasonic agitation) apical plugs.
