Structure Model Index Parameter for Shaping Effectiveness Difference Between Expanded and Reduced Taper Design Files: An in Vitro Study

Background and objectives: To prepare root canal systems, the complex endodontic space must be shaped, enlarged, and disinfected. The taper design significantly influences the shaping efficacy of the instruments. This study attempts to assess the performance of decreased taper endodontic instrument systems (Bassi Logic .03 taper) compared to expandable heat-treated systems (XP-endo Shaper) in shaping simulated canal resin blocks in both straight and curved canals. Materials and methods: Sixty simulated canal resin blocks have been used, comprising thirty blocks with straight canals and thirty blocks with curved canals featuring a 30° curvature. Each group was divided into three subgroups and pre-instrumentation photographs were obtained. Afterwards the resin blocks were prepared to an apical size of 25 utilizing various file systems: 1- reduced taper design (Bassi Logic .03 taper), 2- enlarged taper design (XP-endo Shaper), and 3- ProTaper Next (control group). Following instrumentation with the specified files, post-instrumentation photos were generated, and surface area and volume fluctuations were assessed utilizing AutoCAD software to determine the Structure Model Index (SMI). Statistical analysis was performed using non-parametric tests (Mann-Whitney Test and Kruskal-Wallis Test) with a significance level of p<0.01. Results: The results of these investigations indicated that the ProTaper Next group exhibited the highest mean SMI, succeeded by the Bassi Logic. 03 taper group, whilst the XP-endo Shaper group demonstrated the lowest mean SMI relative to the other groups. In terms of the canal configuration, there is a statistically significant difference between straight canals and curved canals. In comparison to the curved group, the straight group displayed higher mean SMI, which suggests that the shaping effect in the straight group results in a more structured and possibly more conical canal morphology. On the other hand, the curved group demonstrates a more conservative shaping approach with less pronounced structural modification during the shaping process. Conclusion: XP-endo Shaper group were more conservative and specific in reshaping the simulated root canals than other systems. The three systems used were respecting the internal anatomy of simulated root canals, other than non-conservative shaping of the straight canals, even they were within acceptable limits. Keywords: ProTaper Next, Bassi logic, XP-endo Shaper, Shaping ability, Structure Model Index