Quality of Single-Cone Obturation Using Different Sizes of Matching Gutta-Percha Points of Two Reciprocating Single-File Systems in Curved and Straight Root Canals

<i>Background and Objectives:</i> Endodontic success depends on eliminating infection and creating a durable seal to prevent recontamination. The goal of this study was to assess the impact of different ISO sizes on the obturation quality using two reciprocating single-file systems, WaveOne^® Gold and Procodile^®, in two different canal morphologies. <i>Material and Methods:</i> Overall, 140 root canals from human permanent teeth were randomly assigned to 14 groups based on selected ISO sizes and straight and curved canal curvatures, and the two file systems, WaveOne^® Gold files in ISO sizes 20, 25, and 45, and Procodile^® files in ISO sizes 20, 25, 40, and 45, were employed for canal preparation. These 140 canals were obturated using corresponding gutta-percha points and AH-Plus sealer and the quality of the obturation was assessed after sectioning the roots (apical, middle, coronal third) by evaluating the resulting 420 sections under a digital fluorescence microscope with regard to the proportion of gutta-percha, sealer, and unfilled areas. The results were analyzed using nonparametric tests. <i>Results:</i> For both systems, there was a significant difference in the percentage of gutta-percha-filled areas (PGFA, <i>p</i> < 0.001) and sealer-filled areas (PSFA, <i>p</i> < 0.001 among the different ISO sizes). However, no significant difference was observed in the percentage of unfilled areas (PUA, <i>p</i> = 0.354). ISO 40 demonstrated the best results, with the highest percentage of gutta-percha-filled areas (87%) and the lowest percentages of sealer-filled areas (13%) and voids (0.5%). In contrast, the lowest percentages of gutta-percha filled areas were observed in root canal fillings with ISO 20 (81%) and ISO 25 (81%). Regarding both reciprocating file system sizes, ISO 45 in WaveOne^® Gold and ISO 40 in Procodile^® demonstrated significantly improved (<i>p</i> < 0.05) filling quality, with PGFA of 85% and 87%, respectively. The differences between both systems were not significant. <i>Conclusions:</i> The results presented suggest that larger sizes provide better filling results, especially in the apical region. These results underline the importance of selecting appropriate preparation sizes adjusted to the initial anatomical specifications to optimize root canal obturation and ensure a high quality and durable seal.