Introduction The aim of this study was to compare endocrown restorations of mandibular first molars using four distinct preparation designs with different residual tooth heights by employing finite-element analysis. A butt joint marginal design was compared with three shoulder finish line preparations. Materials and methods Four three-dimensional finite-element models were developed to represent different endocrown configurations. Model 1 simulated a butt joint margin design, whereas Models 2, 3, and 4 represented shoulder finish line designs with remaining tooth structure heights of 1, 2, and 3 mm, respectively. Two restorative materials, zirconia and IPS e.max® computer-aided design, were evaluated. The geometry of a healthy mandibular first molar was obtained from computed tomography data and reconstructed using SolidWorks®. Cortical and cancellous bone were modeled as coaxial cylinders. Two loading conditions were applied, i.e., a 400 N vertical load and a 200 N oblique load at 45°, both of which were directed to the buccal cusp tips and central fossa . Results Under vertical loading, the butt joint design exhibited the lowest von Mises stress values, whereas the shoulder finish line designs showed progressively higher stresses with increasing axial wall height. The butt joint design also reduced stresses in the cortical bone by up to 15% compared with the shoulder finish line designs. The choice of restorative material had minimal influence on stress distribution; however, zirconia crowns demonstrated slightly higher stress values, suggesting greater material durability . Conclusion Endocrowns with a butt joint margin demonstrated superior biomechanical behavior by minimizing stress transfer to the underlying tooth and supporting bone. The influence of the endocrown’s design decreased toward the alveolar bone, while the restorative material only exerted a minor effect on the stress distribution.
Qahtani et al. (2026) studied this question.