## 4 Discussion  
The first theoretical reports on the effect of gas entrapment in closed systems were by [PERSON], subsequently demonstrated by [PERSON] [25, 32]. Since then, several studies have characterized the phenomenon of vapor lock [1, 2, 17, 19, 29]. The root canal system is a closed tubular system at one end, and this anatomical condition is the main cause of vapor lock formation, resulting in the formation of air bubbles that can hinder the irrigation of the canal walls [1, 17, 29]. The diffusion of the irrigant into the endodontium is influenced by various factors, such as the contact angle established with the surface it flows on, the length and diameter of the root canal system, the flow rate of the irrigant, the delivery technique, and the volume of the solution [19, 29, 30, 32, 33]. The position of the tooth can also contribute to the formation of vapor lock; according to [PERSON] et al., it is easier for gas bubbles to become trapped in the endodomtion of upper teeth, while in lower teeth, they are more likely to float and escape [28, 29]. In vitro experimentation of the vapor lock effect presents numerous difficulties that could result in procedural biases and compromise the research results. For instance, the size and position of a trapped bubble can change due to sample vibration or temperature variations, which can cause air expansion or contraction [29]. Furthermore, altering the physicochemical properties of the irrigant due to mixing with a contrast medium may affect bubble formation. Lastly, the different characteristics of teeth, such as canal width, length, presence of curves, and position in the arch, can lead to varying results. Our experimental design, compared to previous ones, not only involved qualitative evaluation but also quantitative assessment, allowing for a more accurate analysis of the vapor lock phenomenon. The authors who used the same protocol to observe the vapor lock phenomenon evaluated only the presence of bubbles and whether the phenomenon occurred or not [17, 30]. Our protocol instead envisaged the measurement of the number \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Volume Percentage** & **t Student** & \(p\)**-Value** &
\begin{tabular}{c} **Statistical** \\ **Significance** \\ \end{tabular} \\ \hline Coronal vs. Middle & 0.719 & 0.484 & No \\ \hline Coronal vs. Apical & 5.74 & \textless{}0.001 & Yes. \\ \hline Middle vs. Apical & 6.452 & \textless{}0.001 & Yes \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Statistical analysis of the volume of bubbles (%) in the canal thirds. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Bubbles (n\({}^{\circ}\))** & **t-Student** & \(p\)**-Value** &
\begin{tabular}{c} **Statistical** \\ **Significance** \\ \end{tabular} \\ \hline Coronal vs. middle & 0.333 & 0.743 & No \\ \hline Coronal vs. Apical & 3.433 & \textless{}0.05 & Yes \\ \hline Middle vs. Apical & 3.683 & \textless{}0.05 & Yes \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Statistical analysis of the presence of bubbles (n\({}^{\circ}\)) in the canal thirds. of bubbles and the measurement of the volume; therefore, the extent of the vapor lock. The methodology used and the results obtained, following the advice of the authors, can serve as a basis for further evaluations of various techniques aimed at improving root canal irrigation. The results of our research demonstrate the presence of vapor lock in all the teeth that underwent endodontic treatment, as has been confirmed in the literature [30,34]. The bubbles mainly occupy the apical third. In this root portion, gas bubbles occupy most of the canal volume, thus hindering the cleaning and debridement procedures. As previously demonstrated by other authors, cleaning procedures are less effective in the apical third compared to the coronal and middle thirds [35, 36, 37, 38, 39]. Samples three, four, and five exhibit a column of gas. In line with the physicochemical mechanisms of vapor lock formation, multiple gas bubbles can merge to form a larger column [17,19].