Finite Element Analysis of Fracture Resistance of Mandibular Molars with Different Access Cavity Designs.

INTRODUCTION: This study aimed to assess the fracture resistance (FR) of mandibular first molars after preparation with three different access cavity designs and two rotary systems using finite element analysis (FEA).

METHODS: Six three-dimensionally printed mandibular first molars simulating natural teeth received traditional, conservative, and ultraconservative (truss) access cavity preparations. The root canals in each group were instrumented with either XP-Endo Shaper or TruNatomy rotary files. The models were individually digitized, and micro-CT scans were transferred to Mimics software to create a geometrical model of the tooth. The designed model was exported to 3-matic software, and STL files were transferred to Geomagic Design X. Point cloud data were used for surfacing and transferred to ANSYS software. A 200 N superficial force was applied vertically to the buccal cusps and central fossa, and the maximum and minimum equivalent von Mises stress values were calculated and reported.

RESULTS: The traditional and ultraconservative access cavity designs yielded the highest and the lowest von Mises stress values, respectively. In the ultraconservative cavity design, the stress values in peri-cervical dentin (PCD) were lower in canal preparation with TruNatomy, compared with XP-Endo Shaper. In the traditional and conservative cavity designs, stress was lower in the first 2 mm from the cementoenamel junction (CEJ) in the XP-Endo Shaper, and in the next 3 mm in the TruNatomy group.

CONCLUSIONS: Stress was lower in ultraconservative and conservative cavity designs, compared with the traditional design. Also, root canal preparation with TruNatomy yielded lower stress values in general, compared with XP-Endo Shaper.