Smear layer removal efficacy of irrigating solutions applied distinct needle designs: a scanning electron microscopy study

This research aimed to assess the efficacy of different irrigants applied with different types of needle tips on smear layer removal (SLR) in primary incisors. This study was carried out with 35 freshly extracted upper primary incisors. The samples were randomly distributed to five study groups (n = 7) (1 to 4: experimental, 5: control). These included Group 1: 5% Ethylenediaminetetraacetic Acid (EDTA) + 1% Sodium Hypochlorite (NaOCl) applied with open-ended needle (OEN), Group 2: 6% Citric Acid (CA) + 1% NaOCl applied with OEN, Group 3: 5% EDTA + 1% NaOCl applied with double side-vented needle (DSVN), Group 4: 6% CA + 1% NaOCl applied with DSVN and Group 5: 1% NaOCl applied with OEN. Accordingly, the inner root surfaces were examined using scanning electron microscopy (SEM). The differences between the groups were analyzed using Kruskal-Wallis, Friedman and Siegel-Castellan tests (p < 0.05). In the coronal third, all the experimental groups (groups 1, 2, 3 and 4) were superior to the control group (p = 0.002, p = 0.002, p < 0.001 and p < 0.001, respectively). Groups 2, 3 and 4 showed superior SLR to the control group (p = 0.024, p = 0.001 and p = 0.004, respectively) in the middle third. DSVN groups of EDTA and CA showed superior SLR efficacy than the control (p < 0.001 and p = 0.002, respectively) in the apical third. The SLR efficacy was higher in the coronal third compared to the apical third in the experimental groups (groups 1, 2, 3 and 4) (p = 0.015, p = 0.048, p = 0.048 and p = 0.048, respectively). In addition, 3 samples of EDTA showed erosion (2 in the coronal with OEN, 1 in the middle with DSVN). It was possible to conclude that the SLR efficacy of DSVNs and OENs was similar. CA could be recommended since it did not cause erosive damage compared to EDTA in primary incisors.