Effect of different restorative design and materials on stress distribution in cracked teeth: a finite element analysis study.

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Abstract
Objectives To compare stress distribution and crack propagation in cracked mandibular first molar restored with onlay, overlay, and two types of occlusal veneers with two different CAD/CAM materials by Finite Element Analysis (FEA). Materials and methods A mandibular first molar was digitized using a micro-CT scanner. Three-dimensional dynamic scan data were transformed, and a 3D model of a cracked tooth was generated. Finite element models of four different models (onlay, overlay, and two types of occlusal veneer restored teeth) were designed. Two different CAD/CAM materials, including Lava Ultimate (LU) and IPS e.max CAD (EMX), were specified for both models. Each model was subjected to three different force loads on the occlusal surfaces. Stress distribution patterns and the maximum von Mises (VM) stresses were calculated and compared. Results Compared to the base model, all restorations showed high-stress concentration moved from the lower margin of the crack area towards the top of the crack area. The EMX-restored onlay, overlay, and occlusal veneer 2 had the lowest stress in the cracked area and the lowest average von Mises stress levels at the lower margin along the cracked line, especially under the 225N lateral force (P < 0.05). The occlusal veneer 1 filled with resin had a poorer stress distribution and higher stress concentration of stress at the remaining crack than the occlusal veneer 2 without resin filled inside. Conclusions The EMX restorations with onlay, overlay, and occlusal veneer 2 showed lower stress concentration at the crack surface's lower margin compared to the LU-restored models. The occlusal veneer with internal resin filler exhibited higher stress on the end of the lower margin of the crack surface. Clinical relevance Our results suggest that onlay, overlay ceramic restorations and occlusal veneer (without resin filling inside) may be a favorable method to prevent further crack propagation.

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