Evaluation of smear layer removal with plastic and metal tips of ultrasonic irrigation device

Aim: The aim of this study was to evaluate the removal of the smear layer under scanning electron microscopy (SEM) after activation with a metal and plastic tip ultrasonic irrigation device using 17% EDTA and 5% NaOCl washing solutions. Materials and Methods: A total of 60 mandibular premolar teeth were used in our study. The decoronization process was performed by measuring 15 mm from the entire apical. Root canal preparation was performed using Reciproc R25 and R40 nickel-titanium (NiTi) rotary instruments (Must, Istanbul, Turkey), with instrumentation ending 1 mm short of the apical foramen. Throughout the shaping process, irrigation was conducted using 15 mL of 5% sodium hypochlorite (NaOCl) followed by 3 mL of distilled water. The specimens were then randomly assigned into three experimental groups: Group 1 (Control): Conventional syringe irrigation (CSI) (n = 20); Group 2: Passive Ultrasonic Irrigation (PUI) activated with a plastic tip (n = 20); and Group 3: PUI activated with a metal tip (n = 20). In all groups, the final irrigation protocol consisted of 5 mL of 5% NaOCl and 3 mL of 17% EDTA, each followed by a 3 mL rinse with distilled water. For Groups 2 and 3, ultrasonic activation was applied for a total of 60 seconds with NaOCl and 30 seconds with EDTA. The final rinse in all groups was completed using 3 mL of distilled water. Subsequently, the roots were sectioned longitudinally into two equal halves. To assess the smear layer, scanning electron microscope (SEM) images obtained from the coronal, middle, and apical thirds of each specimen were evaluated and scored independently by two blinded clinicians. Data analysis was performed using IBM SPSS V23 (Endicott, New York, USA) software. Mean±standard deviation and median (minimum-maximum) values were presented for quantitative variables. Since qualitative variables contained more than two categories and normal distribution assumptions were not met, differences between the groups were evaluated with the Kruskal-Wallis H test. In the variables where significant differences were detected, the Mann-Whitney U test with Bonferroni correction was applied to determine which binary groups created the difference. Cronbach α coefficient was calculated to evaluate the agreement between the scores made by two independent observers. The statistical significance level was accepted as p<0.05. Results: There was a significant difference in terms of smear layer removal effectiveness between the apical, middle and coronal regions in terms of irrigation methods (p<0.05). In all irrigation methods, smear layer removal effectiveness in the coronal and middle regions was significantly higher than in the apical region (p<0.05). Significant differences were found between GSI-plastic tip and metal tip in the middle and coronal distances (p<0.001). There was no significant difference between GSI and metal tip in the apical region (p>0.001). In the middle and coronal regions, plastic and metal tip removed the smear layer better than GSI. A significant difference was found between GSI and plastic tip in the apical region (p<0.001). The plastic tip was found to be more effective than GSI in the apical region. There was a significant difference between the plastic tip and metal tip groups in terms of smear removal effectiveness only in the apical region (p<0.001). There was no difference between plastic tip and metal tip in the middle and coronal regions (p>0.001). The plastic tip in the apical region removed the smear layer better than the metal tip. Conclusion: A notable difference in smear layer removal efficiency was observed between the plastic and metal tips of the PUI device in the apical third. This finding highlights the need for further investigation into the performance and clinical implications of using different tip materials in passive ultrasonic irrigation, a commonly employed root canal irrigation activation technique. Keywords: Passive ultrasonic irrigation, metal tip, plastic tip, smear layer removal, intermittent activation, scanning electron microscope