Effect of NiTi Cutting Efficiency on Generating Intra-Canal Splitting Forces During Root Canal Treatment: An In Vitro...

This study aims to measure the effect of the lateral cutting efficiency of reciprocating and rotary NiTi files on the produced intracanal splitting forces (ICSF) during root canal preparation.

Forty-eight mandibular anterior bovine teeth with straight roots were used to create 48 simulated premolar roots and 26 enamel-dentin disks. The required sample size was determined through power analysis conducted with G^*Power 3.1.9.7 software, utilizing data from preliminary studies. Based on a large effect size (0.8), significance level of 0.05, and statistical power of 80%, the analysis indicated a need for at least 21 specimens per group for splitting force evaluation and 10 specimens for cutting efficiency assessment. To maintain sufficient statistical power and accommodate possible sample attrition, the study employed 24 specimens per group for splitting force analysis and 13 specimens for cutting efficiency evaluation. The investigation examined two file systems with comparable heat treatment but distinct kinematics, geometries, and designs to assess the intracanal stress forces generated during preparation and their respective cutting abilities in dentin discs. The tested instruments were WaveOne-Gold (WOG) and Pro-Taper GOLD (PTG). Random allocation was performed using a computer-generated randomization sequence (Random.org). Specimens were numbered consecutively and assigned to groups using block randomization to ensure equal group sizes. Tests were carried out on a custom-made platform under automated conditions. The data collected by the force gauge is in newtons (N), and the cutting efficiency was calculated by measuring the depth of cut produced in dentin in mm. Data analysis was carried out with the Kolmogorov-Smirnov test and one-way Anova.

The splitting forces test was significantly higher in the PTG group (S1) file when compared to other PTG and WOG files. The force generated in WOG strokes presented an ascending manner as the file went deeper apically. The cutting efficiency of PTG (F2) was significantly higher than WOG's primary file. However, no significant correlation between splitting force and file cutting efficiency was detected.

WOG single reciprocating file produced significantly lower splitting force values with significantly less aggressive dentin cutting compared to PTG multi-sequence rotary files. File design, kinematics, depth of strokes, and the maximum diameter of each file at the coronal third in relation to canal diameter may be influencing factors in generating splitting forces.