Influence of Occlusal Cusp Inclination and Restoration Thickness on the Biomechanical Performance of Lithium Disilicate Molar Endocrowns: A 3D Finite Element Analysis.

Abstract

This study used finite element analysis to investigate the effect of occlusal cusp inclination and restoration thickness of endocrowns on the stress distribution and biomechanical performance.A total of six models of a mandibular first molar representing two different heights of remaining tooth structure above the cemento-enamel junction (1.5 and 3 mm), each with three different buccal cusps inclination angles (original, 10 degrees, and 20 degrees increase in cusp inclination angles) were generated. Models were designated as: 1.5/original, 1.5/10 degrees, 1.5/20 degrees, 3/original, 3/10 degrees, and 3/20 degrees. All models were subjected to an oblique load of 400 N. The maximum principal stress (MPS), maximum shear stress (MSS) at the cement interface, and factor of safety (FoS) were calculated.Increasing the cuspal inclination by 10 degrees in models with a 1.5-mm remaining tooth structure, resulted in a 20% reduction of the MPS in the dentine (27.2 MPa), in comparison with original cuspal inclines (33.9 MPa). However, increasing the cusp inclination in model 1.5/20 degrees resulted in a comparable dentinal stress reduction (17%, 28 MPa) accompanied with an increase in the MSS at the cement interfaces (26.8 MPa), in comparison with 1.5/original (18 MPa). On the other hand, increasing the cusp inclination angle in models 3/10 degrees and 3/20 degrees led to a reduction in MPS within the dentine by 1 and 2%, respectively, while causing an increase in the MSS at the cement interfaces (16.4 and 16.0 MPa, respectively), in comparison with 3/original (11 MPa). Models 1.5/original and 3/original reported the minimum FoS values (3.10 and 3.38, respectively), while model 1.5/10 degrees reported the highest FoS value (3.86).Within the limitations of the current study, cusp inclination adjustments up to 10 degrees may enhance stress distribution in endocrown-restored molars with limited coronal structure.