## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multicolumn{10}{c}{**Single Cone (\(n\) = 11)**} & \multicolumn{3}{c}{**Guttafusion (\(n\) = 10)**} & \multicolumn{3}{c}{**Difference**} \\ \cline{2-10}  & **Mean** & **SD** & **95\% CI** & **Mean** & **SD** & **95\% CI** & **Mean** & **_p-Value_ & **95\% CI** \\ \hline RB40 & & & & & & & & & & \\  Coronal & 0.00 & 0.00 & 0.00, 0.00 & 0.01 & 0.02 & 0.00, 0.03 & \(-\)0.01 & 0.048 \({}^{\ddagger}\) & \(-\)0.02, 0.00 \\  Middle & 0.23 & 0.44 & \(-\)0.06, 0.52 & 0.33 & 0.55 & \(-\)0.06, 0.73 & \(-\)0.10 & 0.637 & \(-\)0.56, 0.35 \\  Apical & 0.25 & 0.47 & \(-\)0.07, 0.56 & 0.25 & 0.28 & 0.05, 0.45 & 0.00 & 0.991 & \(-\)0.36, 0.35 \\  R50 & & & & & & & & & \\  Coronal & 0.00 & 0.00 & 0.00, 0.00 & 0.01 & 0.00, 0.01 & 0.00 & 0.153 & \(-\)0.01, 0.00 \\  Middle & 0.17 & 0.37 & \(-\)0.08, 0.42 & 0.20 * & 0.36 & \(-\)0.07, 0.48 & \(-\)0.03 & 0.835 & \(-\)0.38, 0.31 \\  Apical & 0.22 & 0.44 & \(-\)0.07, 0.52 & 0.11 * & 0.12 & 0.00, 0.22 & 0.11 & 0.525 & \(-\)0.25, 0.48 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Remnants area (mm\({}^{2}\)) calculated on periapical radiographs after retreatment with Reciproc Blue (RB) 40 and 50, by third (coronal, middle, and apical) and obturation technique. areas, facilitating their proliferation in unfilled spaces or voids [21]. This scenario highlights the complexity of achieving a systematic cleaning during retreatment, especially in oval-shaped canals where anatomical challenges represent additional challenges [22; 23]. Despite the development of advanced instrumentation techniques, irrigant techniques, and devices [24; 25], evidence from in vitro studies (radiographic analysis, CBCT, and Micro-CT imaging) suggests the clinical impossibility of completely removing all filling material [17; 26; 27]. Interestingly, our study reported that some samples from both groups showed very low amounts of remnants that were difficult to observe through X-ray/CBCT imaging. In particular, the percentages of remnants after the complete instrumentation (RB50) were approx. 5% in the area and approx. 2% in the volume of the total obturation (Table 6a, 6b). The high standard deviation values were due to the high number of teeth with no remaining filling material (9 out of 21 teeth) and the low number of teeth with a considerably (>15%) high percentage of filling material (4 out of 21). Another study using a similar methodology but a different sealer (epoxy resin-based sealer) showed different results [28], with higher amount of radiographically detectable remnants. This is an interesting finding because if the only variable is the sealer, it implies that premixed bioceramic sealers may adhere less to the canal walls, making them easier to remove during retreatment. Additionally, this difference can be attributed to the lower radiopacity of bioceramic sealers compared to epoxy resin-based sealer. The lower radiopacity may result in less residual material able to be detected on radiographic images, potentially leading to an underestimation of remnants. These findings confirm the importance of the sealer physical and chemical properties, such as the adhesion to the root canal denitinal walls and radiopacity, when evaluating their performance in endodontic treatments and retreatments. The findings presented in Tables 3 and 4 reveal that the remnants detected through both X-ray and CBCT analyses are quantitatively minimal. These data could be explained by analyzing the methodologies used, particularly the decision to decoronate the teeth and the decision to perform an enlargement of the root canal anatomy with a Reciproc file up to 50.05. Decoronation simplifies access to the endodontic system, potentially enhancing the efficiency of removing previous filling materials in the coronal thirds. As observed in Table 5, the presence of remnants in the coronal third is almost absent. This can be attributed to the ease of access to the coronal third and the use of Gates Glidden burs in the initial retreatment phase.