Dynamic photoelastic analysis of stress distribution in simulated canals using different heat-treated flat-side rotary instruments.

OBJECTIVES: This study aimed to compare the stress produced by three heat-treated flat-side prototype rotary instruments and a non-flat side instrument on the internal walls of simulated canals with three different curvature degrees using the photoelastic technique. MATERIALS AND METHODS: Thirty-six resin blocks with simulated canals, comprising three curvature types (45 degrees , 60 degrees , and double curvature), were used in the study, with 12 blocks allocated to each curvature type. These blocks were further divided into four experimental groups (n = 9 per group) based on the heat treatment of the instruments: gold, silver, blue, and a control group with non-flat-side gold instruments. The blocks were analyzed using a circular polariscope setup, with real-time birefringence patterns captured by a digital camera. Stress on canal walls was evaluated using a semi-quantitative scale. Supplementary tests (stereomicroscope, SEM, energy-dispersive X-ray spectroscopy, and DSC) were performed to interpret the results further. Data were analyzed using the Kruskal-Wallis test (alpha = 5%). RESULTS: Inter- and intra-observer agreements were 0.91 and 1, respectively. All instruments exhibited high stress patterns on canal walls. The highest stress was observed in the 45 degrees and 60 degrees blocks (middle third) and the double curvature blocks (apical third). The flat-side gold instrument recorded the highest stress in the coronal third, and the flat-side blue in the apical third (p < 0.05). All instruments displayed some degree of distortion after use. CONCLUSIONS: Instrument type and canal curvature significantly influenced stress distribution across root canal thirds. All flat-side instruments exhibited high stress patterns, warranting caution in curved canals due to potential distortion and performance impact. CLINICAL RELEVANCE: This study recommended caution when using newly designed flat-side instruments in curved canals due to potential stress on canal walls and greater distortion, which may affect performance and durability.