Regenerative endodontic therapy (RET) for immature permanent teeth with necrotic pulps involves disinfecting the root canal system, followed by mesenchymal stem cell recruitment and coronal barrier placement. Disinfection often uses irrigants and intracanal medicaments, avoiding mechanical instrumentation to protect fragile root canal walls. Antibiotic combinations, like double antibiotic paste (DAP), are recommended for effective disinfection. However, the open apices of immature teeth make them susceptible to apical extrusion of medicaments during placement and debris extrusion during removal, potentially causing inflammation and pain. This extrusion may also harm periapical stem cells crucial for RET success. Therefore, complete removal of antibiotic paste remnants before inducing bleeding is essential. Various techniques exist for removing intracanal medicaments, including passive ultrasonic irrigation (PUI) and the XP-Endo Finisher (XPF). PUI uses ultrasonic waves to enhance cleaning, while XPF is a shape-memory alloy file that expands to clean complex canal morphologies. However, previous in vitro studies comparing these techniques have conflicting results due to variations in methodologies. This study aimed to compare the efficacy of XPF, PUI, and SVN in removing DAP from immature root canals, measuring both canal cleanliness and the amount of apically extruded debris. The null hypotheses were that there would be no differences among the irrigation activation techniques in canal cleanliness and apical extruded debris after the removal procedure.

Several studies have investigated the removal of intracanal medicaments, with PUI being a common method. PUI utilizes ultrasonic waves to generate cavitation and acoustic streaming, improving canal cleanliness. The XP-Endo Finisher (XPF) is another instrument used for agitation; its shape-memory alloy allows it to adapt to complex canal shapes. Studies have shown XPF's ability to improve debris and medicament removal, reduce bacterial load, and enhance irrigant agitation. However, inconsistencies exist in the literature due to the heterogeneity of methodologies across studies, including variations in root canal systems, intracanal medicaments, irrigation times, solutions, concentrations, and outcome measurements. While some studies have evaluated DAP removal, none, to the authors' knowledge, have measured the amount of apically extruded debris and correlated it with canal cleanliness in immature teeth.

Forty-eight extracted mandibular premolars were used. Teeth were prepared to simulate immature apices using peeso drills to create a 1.3 mm apical opening. Canals were filled with DAP (a 1:1 mixture of metronidazole and ciprofloxacin) and randomly assigned to three groups (n=16): XPF, PUI, and SVN. A custom model using Eppendorf tubes was used to collect extruded debris. After 2 weeks, the DAP was removed using the assigned technique for each group. Debris extrusion was measured using an analytical balance. Teeth were sectioned longitudinally, and stereomicroscopic images were analyzed using ImageJ software to quantify residual DAP. A scoring system (0-3) was used to assess canal cleanliness based on the percentage of remaining DAP. Kruskal-Wallis and Dunn's tests were used for statistical analysis, and Spearman's correlation coefficient was used to assess the correlation between extruded debris and residual DAP scores.

There was no statistically significant difference (P=0.237) in the amount of apically extruded debris among the three irrigation techniques (XPF, PUI, and SVN). However, there was a statistically significant difference (P<0.001) in canal cleanliness. Both XPF and PUI groups showed significantly lower amounts of remaining DAP compared to the SVN group (Table 1). No statistically significant difference was observed between XPF and PUI. Spearman's correlation analysis revealed a non-significant positive correlation (P=0.087) between the amount of apically extruded debris and the debris score of remaining DAP (Figure 4). The median debris score for XPF and PUI was 1, while for SVN it was 3 (Table 1). Figure 2 shows box plots illustrating the distribution of apically extruded debris across the groups. Figure 3 displays stereomicroscopic images of root canal walls illustrating the remaining DAP in each group. The intraobserver agreement for the canal cleanliness assessment was excellent (Supplemental File 1).

The study demonstrates that while all three techniques resulted in some apical debris extrusion, XPF and PUI were significantly more effective in removing DAP from simulated immature root canals than SVN. This supports the use of XPF and PUI for improved canal cleanliness during RET. The lack of significant difference in debris extrusion between the groups suggests that the enhanced cleaning effect of XPF and PUI did not lead to a proportional increase in apical extrusion. The non-significant positive correlation between extruded debris and residual DAP suggests that more effective removal of the medicament is not necessarily associated with increased apical extrusion. The findings are in agreement with previous studies that have shown the superiority of XPF and PUI over conventional irrigation in removing intracanal medicaments. The discrepancy with some studies may be attributed to differences in methodology (e.g., medication application time, irrigation parameters). One limitation of the study is the inability to perfectly simulate clinical conditions, such as the effect of periodontal tissues on debris extrusion. The study's use of a preheated irrigant solution at 37°C attempted to account for the optimal working temperature of XPF, though this was not an exact replication of body temperature.

This in vitro study demonstrated that XPF and PUI are superior to SVN for removing DAP from simulated immature root canals, improving canal cleanliness. However, all three methods resulted in similar levels of apical debris extrusion. Further research should investigate the effect of longer activation times for XPF and the combined use of XPF and PUI in removing intracanal medicaments.

The study used an in vitro model with extracted teeth, which does not perfectly mimic the in vivo situation. The model lacked periodontal tissue, which could influence debris extrusion. The limited sample size might also affect the generalizability of the results. The effect of intracanal temperature variations on XPF efficacy, despite attempts to account for it, remains a limitation.