Effect of Pre-Endodontic Proximal Wall Restoration on Smear Layer Removal Following Different Irrigation Protocols: An in Vitro Study

Abstract

Introduction:  Effective smear layer removal is essential for root canal disinfection, particularly in anatomically challenging areas such as the apical third. Although pre-endodontic proximal wall restoration is widely recommended for operative reasons, its influence on intracanal cleanliness during different irrigation protocols has not been fully clarified.

Objectives: To evaluate the influence of pre-endodontic proximal wall restoration on intracanal smear layer removal following different irrigation protocols in mandibular first premolars.

Methods:  In this in vitro study, 210 extracted mandibular first premolars were selected after CBCT-based screening. One hundred teeth were prepared without pre-endodontic restoration (G1), and 100 teeth received mesial proximal wall reconstruction with resin composite before instrumentation (G2). Each group was subdivided into five subgroups (n = 20): conventional needle irrigation, sonic activation with EndoActivator, sonic activation with EQ-S, mechanical activation with XP-Endo Finisher, and ultrasonic activation with EndoUltra. Ten additional teeth served as controls after shaping without final irrigation. Smear layer removal at the coronal, middle, and apical thirds was assessed using scanning electron microscopy and a four-point scoring system. Interobserver agreement was assessed using Cohen’s kappa. Data normality was evaluated with the Shapiro-Wilk test, followed by Kruskal-Wallis analysis with Tukey post hoc comparison at a significance level of 0.05.

Results:  Interobserver agreement was high (Cohen’s kappa = 0.89). Data were non-normally distributed. No significant difference in smear layer removal was observed between restored and non-restored teeth at the coronal third. At the middle third, a significant difference was observed only between the control subgroups. At the apical third, teeth with pre-endodontic proximal wall restoration showed significantly better smear layer removal than non-restored teeth. In the non-restored group, EQ-S and EndoUltra produced significantly better smear layer removal at the middle and apical thirds than the other irrigation protocols. In the restored group, EQ-S and EndoUltra were the most effective protocols at the apical third.

Conclusions: Within the limitations of this in vitro study, pre-endodontic proximal wall restoration improved intracanal smear layer removal, especially in the apical third. Among the tested irrigation protocols, EQ-S sonic activation and EndoUltra ultrasonic activation demonstrated the most effective smear layer removal in deeper canal regions.