Dynamic Photoelastic Analysis of Stress Distribution in Simulated Canals Using Rotary Instruments with Varied Tip and Taper Sizes: A Quasi-3D Approach

Introduction To compare the stress produced on the walls of simulated canals by rotary instruments with varied tip and taper sizes. Methods Ninety isotropic transparent blocks, each containing a 60-degree curved canal, were distributed into 18 groups (n=5) based on the instrument tip (sizes 10, 15, 20, 25, 30, 35) and taper (sizes 0.02, 0.04, 0.06). The blocks were fixed in a circular polariscope setup for dark field analysis. A digital camera was employed to capture the real-time birefringence patterns generated by each instrument. Digital image frames, corresponding to the instrument reaching the end of each canal third, were extracted and evaluated by 2 independent observers for the stress generation on canal walls. The data analysis employed a semi-quantitative scale ranging from 0 to 5. Cohen’s Kappa coefficient test was used to determine the inter-observer agreement while the results were compared using Kruskal-Wallis test followed by an all-pairwise post hoc procedure (α=5%). Results Inter-observer agreement was 0.95. A significant influence of the tip size on stress was observed across the coronal (P=0.011), middle (P=0.006), and apical (P=0.026) thirds. In contrast, taper size did not affect the stress induced at the coronal (P=0.509), middle (P=0.958), or apical (P=0.493) thirds. The variations in tip and taper sizes did not result in a significant stress differences among the thirds (P=0.181). Conclusions The stress significantly increased across all canal thirds with larger tip sizes of rotary instruments, whereas the taper sizes did not influence the stress when compared the canal thirds.