3D modelling and finite element analysis of molars restored with ceramic inlays

For patients requiring aesthetic restorations, ceramic inlays provide durable alternatives to posterior composite resins. It is important to ensure optimal performance in selection of the adequate preparation design to reduce stresses and their susceptibility to fracture. Purpose: The aim of the study was to develop 3D finite element models of molars with different preparations, restored with inlays, in order to evaluate and compare stress distributions under occlusal loads. Material and Methods: Thirteen 3-D models of first upper molars of the same shape and size were created: an intact tooth; six unrestored teeth with class II cavity preparations with different tapers (between 0 and 10Ί); the same six teeth restored with ceramic inlays. The geometries of the teeth were constructed by 3D scaning using a manufactured device. These were exported in Ansys finite element analysis software (Ansys Inc., Philadelphia, USA), to be used for structural simulations. In making the finite element models, the characteristics of the materials used for the restorations were entered into the computer program. Each model was subjected to a force of 200 N directed to the occlusal surface. Stresses were calculated in the tested inlays, and tooth tissues. Results: In the teeth restored with ceramic inlays, the von Mises equivalent stress values were higher than in the intact tooth. High stresses were located at the junction of the butt joint margin inlay and enamel. The values depend on the preparation shape and decrease with the increase of the taper. Conclusion: The study provides a biomechanical explanation for inlays restored teeth. Ceramic inlays do not restore the original strength of the teeth, but the preparation shape is decisive for the stress values and distribution. Keywords: ceramic inlays, 3D models of molars, stress distribution, finite element analysis