Abstract: PURPOSE: To analyse the effect of restoration and tooth tissue stress distribution under different occlusal preparation thickness, based on three-dimensional finite element modal of the mandibular second molar with root canal therapy and endocrown restorations. METHODS: A mandibular second molar was scanned by cone-beam CT (CBCT) and a three-dimensional finite element model with endocrown restortions was established. Three kinds of endocrown restorations materials with different elastic modulus (glass ceramic, lithium disilicate ceramic and zirconia), and three types of occluscal thickness (1, 2 and 3 mm) were adopted. With a 200 N force loaded vertically and obliquely, the distribution and magnitude of stress in the tooth tissue and endocrown restorations were investigated by three-dimensional finite element analysis. RESULTS: The restoration and tooth tissue maximum stress values were increased firstly and then decreased with the increasing of occlusal thickness; the base material maximum stress values were decreased with the increasing of occlusal thickness; the maximum stress values of tooth tissue and base material were increased with the increasing of restoration material's Young's modulus. Compared to the loading in vertical direction, the maximum stress values were increased with loading in oblique direction. CONCLUSIONS: It's beneficial for tooth tissue to reduce the stress concentration under 2mm thickness. The stress on endocrown will be more concentrated with the increasing of restoration material’s Young's modulus.

Key words: Endocrown, Occlusal thickness, Glass ceramic, Lithium disilicate ceramic, Zirconia