Stress Distribution in an All-Ceramic Crown/Tooth System: An FEA Study

Methods: A FEM of a maxillary first premolar restored with an all-ceramic crown and cemented with an adhesive lute was constructed using micro-CT. A micro-CT scan of the restored tooth was taken and incremental slices were segmented according to pixel density into its component parts using Mimics software (Materialise Co., Ltd). The various component parts were exported in STL (Standard Triangle Language) format and fed into FreeForm software. A virtual model of the periodontal ligament and the cortical and cancellous bone were generated using a PHANTOM haptic device (SensAble Technologies, Inc). Subsequently, all the STL files were imported into the ICEM software (ICEM 11, ANSYS, Inc) and modified as necessary. Two occlusal preparation designs and five different values for the Young's modulus of the resin cement were assessed in the FE analysis. FEA software (Hypermesh®, Altair Hyperworks, USA) was used to apply an occlusal load of 300 N to the occlusal surface of two models with the different Young's modulus cements.

Results: The elastic modulus of the cement and the occlusal preparation design are important determinants of the stress state in different layers. A flat, occlusal reduction demonstrated more benign stress distribution compared to an anatomic design. A low elastic modulus cement in the anatomical design and a high elastic modulus cement in the flat design, demonstrated the most benign stress states.

Conclusions: A sophisticated FEM is a further aid to establishing the optimum configuration of a tooth restored with an adhesively cemented all-ceramic crown, so that the stresses can be minimised enabling a more conservative tooth preparation.