SEM Analysis and Pulp Tissue Dissolution Following Retrograde Preparation and Irrigation in Surgical Endodontics: A Novel Approach

Objective: This study aimed to assess the efficacy of a novel retrograde irrigation protocol involving ultrasonic activation, compared with conventional techniques, using two complementary experimental models.
Methods: Experiment 1: Sixty extracted human mandibular premolars were endodontically prepared, obturated, and randomly assigned to three groups (n=20): Group 1 (saline irrigation), Group 2 (ultrasonically activated 17% EDTA gel and 5.25% NaOCl gel), and Group 3 (no irrigation). Following 1 mm apical resection and 3 mm retrograde cavity preparation, root-end cleanliness was assessed using scanning electron microscopy (SEM). Three calibrated, blinded examiners evaluated smear layer and debris scores. Experiment 2: A 3d-printed artificial canal system with lateral extensions containing bovine pulp tissue was used to simulate organic material. Groups received: Group 1 (saline), Group 2 (ultrasonically activated 5.25% NaOCl gel), Group 3 (no irrigation). Pulp dissolution was measured using a high-precision analytical microbalance.
Data were analysed using the Kruskal-Wallis test and Dunn-Bonferroni post hoc (Experiment 1), and one-way ANOVA with Tukey HSD (Experiment 2). A significance level of p<0.05 was adopted.
Results: In Experiment 1, Group 2 showed significantly lower debris and smear layer scores than Groups 1 and 3 (p<0.001). In Experiment 2, only Group 2 achieved complete pulp tissue dissolution (p<0.001).
Conclusions: Ultrasonically activated EDTA and NaOCl gel significantly enhance cleaning efficacy and organic tissue dissolution in retrograde endodontic surgery, allowing for a more conservative apical resection approach.