Introduction: The purpose of the research was to use the finite element approach to examine the impact of peri- cervical dentin conservation during root canal therapy on the longitudinal development of cracks. Methods: Two mandibular teeth that were manufactured in 3D underwent a mock root canal procedure. Two test populations of teeth were created: Group 1: Rotary files from a Protaper Gold (PTG) instrument were used. Group 2 was equipped with TruNatomy. At the level of the CEJ, every entrance was repaired with composite to the occlusal surface. To build 3-D models and stereolithographic reconstructions for Finite Element Analysis, the two teeth were digitally obtained through a high-resolution micro-computed tomography scan. The distal marginal ridge was the starting point of a crack that was mimicked, and it extended horizontally to the distal occlusal cavosurface and apically 2 mm above the CEJ. A 247-newton weight was applied to each model in order to simulate the strain put on the mouth during mastication. Results: The crack began to spread in both groups at about 40,000 mastication cycles. At 60,218,000 mastication cycles, Group 1, which was equipped with a Protaper Gold equipment, experienced crack expansion of 0.5mm. Group 2 had 0.5mm of crack propagation at 10,042,000 cycles and was equipped with TruNatomy. Conclusions: Given the constraints of this investigation, it can be said that mandibular molars instrumented with PTG rather than TruNatomy experienced reduced fracture propagation. About 40,000 mastications in, the simulated crack began to spread in both PTG and TruNatomy.