The efficacy of various irrigation techniques on the removal of double antibiotic paste from simulated immature roots and the amount of apically extruded debris

Regenerative endodontic therapy (RET) aims to treat immature permanent teeth with necrotic pulps by disinfecting the canal, inducing bleeding to recruit stem cells, and sealing the coronal portion. Mechanical instrumentation is minimized to avoid weakening thin canal walls, so disinfection relies on irrigants and intracanal medicaments, including antibiotic combinations such as double antibiotic paste (DAP). Immature teeth with open apices are prone to apical extrusion of medicament during placement and to debris extrusion during removal, which may trigger inflammation, flare-ups, postoperative pain, and toxicity to periapical stem cells essential for RET success. Hence, thorough removal of antibiotic paste before inducing bleeding is critical. Passive ultrasonic irrigation (PUI) and the XP-Endo Finisher (XPF) have been proposed to enhance irrigation efficacy. However, heterogeneity across in vitro studies and limited data on DAP removal in immature models exist, and no prior study has correlated apical debris extrusion with canal cleanliness in this context. This study compared XPF, PUI, and side-vented needle (SVN) irrigation for canal cleanliness and apical debris extrusion after DAP removal in simulated immature roots, testing the null hypothesis of no differences among techniques.

Prior reports describe PUI enhancing cleanliness via cavitation and acoustic streaming, and XPF (a Max-wire NiTi instrument that changes shape at body temperature) improving removal of debris, calcium hydroxide, and filling materials, as well as bacterial reduction and irrigant agitation. Studies on medicament removal vary widely in tooth models, medicaments, irrigants, activation times, and outcome measures, leading to conflicting findings. Few studies assessed DAP removal, and none evaluated apically extruded debris in immature teeth while correlating it to canal cleanliness. Previous work generally indicates no irrigation method renders canals completely free of residual medicament. Some studies found PUI and XPF superior to conventional needle irrigation for medicament removal, though results can depend on variables like intracanal time of medicament and irrigant temperature, which affects XPF phase transformation and efficacy.

Design: In vitro study with 48 extracted straight, single-rooted mandibular premolars. Ethical approval obtained (Minia University, Egypt; Reg. no 59/311). Sample size calculation based on prior data (alpha=0.05, power=85%) indicated n=16/group. Sample Preparation: Teeth cleaned, radiographed, decoronated to 15 mm length, WL set 1 mm short of apex. Immature apex simulated using peeso drills sizes 1–4 to obtain ~1.3 mm apical diameter. Irrigation during preparation included 1.5% NaOCl. Final irrigation: 5 mL 17% EDTA (1 min), 5 mL 1.5% NaOCl (1 min), then 5 mL distilled water; canals dried. DAP Preparation/Placement: Equal parts ground 500 mg metronidazole and 500 mg ciprofloxacin mixed with distilled water to 1 mg/mL; placed with syringe. Cotton pellet and temporary seal (Cavit G) used; apical openings sealed with sticky wax. Samples stored 2 weeks at 37 °C, 100% humidity; seals removed before testing. Apical Extrusion Apparatus: Modified Myers and Montgomery setup using weighed Eppendorf tubes (initial weight W1), tooth fixed in stopper, vent needle for pressure equalization; operator blinded to apex with foil. Randomization to three groups (n=16 each): - XPF: 10 mL 1.5% NaOCl via 30G side-vented needle placed 1 mm short of WL (~5 mL/min). XPF (size 25, 0.00 taper) at 800 rpm, 1 N·cm, inserted 1 mm short of WL and operated for 60 s with gentle 7–8 mm in-and-out motion. One file per canal. - PUI: 10 mL 1.5% NaOCl via 30G needle as above; IrriSafe size 25/0.00 tip at power setting 5, inserted 1 mm short of WL; 3 cycles of 20 s activation, keeping tip centered; one tip per canal. - SVN: 10 mL 1.5% NaOCl via 30G needle, inserted 1 mm short of WL, moved up/down within apical third (~5 mL/min). Standardization: Irrigant temperature 37 °C, equal volumes/flow/activation times; rubber stoppers ensured length control. Final flush with 2 mL 17% EDTA in all groups. Debris Extrusion Measurement: After procedures, tooth assemblies removed, root apex rinsed with 1 mL distilled water into tube to collect adherent debris. Tubes incubated at 37 °C for 15 days to evaporate moisture, reweighed (mean of 3 measures) for W2. Extruded debris weight = W2 − W1. Canal Cleanliness Assessment: Teeth split longitudinally after placing shallow buccolingual grooves; stereomicroscope imaging at 10× magnification (Canon EOS 650D on Olympus BX60). Blinded image analysis with ImageJ: total canal area delineated (100%), residual DAP area measured; percent residue = (residual area/total canal area) × 100. Percentages converted to debris scores: 0 (none), 1 (≤20%), 2 (20–60%), 3 (>60%). Single operator performed procedures; blinded examiner performed measurements; intraobserver reproducibility assessed by ICCs. Statistics: Normality assessed (Kolmogorov–Smirnov, Shapiro–Wilk); non-parametric distribution found. Kruskal–Wallis for group comparisons; Dunn’s test for pairwise. Spearman’s correlation between apical extrusion and debris scores. Significance P≤0.05. Analyses in IBM SPSS v23.

- Apical extruded debris: All techniques produced measurable extrusion; no significant difference among XPF, PUI, and SVN (Kruskal–Wallis P=0.237; effect size η2=0.073). - Canal cleanliness (remaining DAP): Significant differences among techniques (P<0.001; η2=0.772). XPF and PUI removed significantly more DAP than SVN; no significant difference between XPF and PUI. Descriptives: • XP-Endo: median score 1 (range 1–1); mean 1.0 (SD 0). • PUI: median score 1 (range 0–2); mean 1.1 (SD 0.57). • SVN: median score 3 (range 2–3); mean 2.7 (SD 0.48). - Correlation: Positive but non-significant correlation between apically extruded debris and residual DAP scores (Spearman r≈0.318, P=0.087). - None of the techniques completely removed DAP from canals.

The study demonstrates that activating irrigation with either XPF or PUI significantly improves removal of DAP from simulated immature root canals compared to conventional needle irrigation, aligning with prior reports on enhanced efficacy from acoustic streaming/cavitation (PUI) and the shape-memory, expansion, and mechanical sweeping action of XPF. Despite better cleanliness, none of the methods achieved complete removal, consistent with the literature. Apical debris extrusion did not differ among techniques, indicating that activation did not increase extrusion risk under the standardized conditions used. Methodological variables such as irrigant temperature likely influence outcomes; using warmed NaOCl (37 °C) may have enabled XPF’s austenitic transformation and effectiveness. Differences from studies reporting PUI superiority over XPF may stem from cooler irrigants impeding XPF’s phase change. The standardized 1-minute activation may be insufficient for complete DAP removal; combined activation strategies (e.g., XPF plus PUI) and longer activation times could improve outcomes. Clinically, improved cleanliness without added extrusion risk is favorable for RET, potentially reducing cytotoxic effects on periapical stem cells.

XPF and PUI achieved significantly better canal cleanliness than side-vented needle irrigation during DAP removal from simulated immature roots, while all three techniques produced similar amounts of apically extruded debris. Further research should assess longer XPF activation times and combined XPF+PUI protocols to enhance intracanal medicament removal.

- Inability to simulate intracanal temperature precisely; samples were not kept in a heated bath to avoid altering DAP solubility and extrusion measurements. Irrigants were preheated to 37 °C as a compromise. - Use of an immature root model rather than natural immature teeth due to limited specimen availability. - Lack of periodontal tissue simulation (foramina suspended in air, zero back pressure), which may overestimate apical extrusion compared to clinical conditions. - The manufacturer-recommended 1-minute activation time may have been insufficient to maximize DAP removal, suggesting time-dependent effects were not fully explored.