Effect of cement loss on stress distributions in class II inlays: a threedimensional finite element analysis of resin tooth

Purpose:The aim of this study was to evaluate, by means of 3D finite element analysis, the effect of marginal cement loss on the stress distribution of class II MOD inlays.Materials and Methods: The resin model teeth scanned with optical 3D digitizing system (Comet 5, Steinbichler optotechnik).The 3D images were processed by SolidWorks (Dassault Systmes SolidWorks Corp., Concord).ANSYS workbench V13 (ANSYS Inc., Canonsburg) was used to mesh and analyze 3D FE model.Class II MOD inlay cavities were filled with Lava TM zirconia ceramic inlay (3M ESPE), IPS Empress II (Ivoclar Vivadent) and Tescera TM (Bisco).As for the resin cement, Variolink II (Ivoclar vivadent) was used.After restoration, an oblique load of 400 N and a vertical load of 400 N were applied to the five areas.von Mises stress on the restorative materials, cement layer and bonding layer were evaluated separately.Results: Oblique loading generated higher von Mises stress than vertical loading.The intact cement layer showed lower stress distribution than both marginal and base cement loss models, with stress concentrated at the edges of the cement defects.Inlay materials with lower elastic modulus transmitted more stress to the cement layer.Under oblique loading, the composite resin inlay showed the highest stress, while in the base cement loss group, stress followed the order of material stiffness: zirconia > lithium disilicate > composite resin.Conclusion: Within the limitations of this study, it was concluded that areas with cement loss showed stress concentration, which could further lead to the destruction of the cement layer and consequently affect the longevity of the restoration.(