journal of the mechanical behavior of biomedical materials 124 (2021) 104853 Available online 23 September 2021 1751-6161/© 2021 Elsevier Ltd. All rights reserved. Research Paper Biomechanical behavior of endodontically treated premolar teeth restored with novel endocrown system: 3D Finite Element and Weibull analyses Ahmed Shams a, * , Amal Abdelsamad Sakrana a, b , Shaimaa Ahmed Abo El-Farag a, b , Fatma Abdallah Elerian c , Mutlu ¨ Ozcan d a Fixed Prosthodontics Department, Faculty of Dentistry, Mansoura University, Egypt b Fixed Prosthodontics Department, Faculty of Dentistry, Horus University, Egypt c Production Engineering and Mechanical Design Department, Faculty of Engineering, Mansoura University, Egypt d University of Zürich, Division of Dental Biomaterials, Center for Dental and Oral Medicine, Clinic for Reconstructive Dentistry, Zürich, Switzerland A R T I C L E INFO Keywords: Novel endocrown Premolars PEKK IPS e.max CAD Finite element analysis Weibull analysis ABSTRACT Objective: To date, there is no clear consensus in the literature which endocrown design with which material is the most effective treatment option to restore endodontically treated maxillary premolars with extensive loss of tooth structure. The aim of this study was to evaluate the stress distribution pattern and failure probability of maxillary frst premolars restored with a novel endocrown system compared to the conventional one by means of Finite Element and Weibull analyses. Materials and methods: Two fnite element (FE) models representing two endocrown systems used for restoration of severely-destructed endodontically treated maxillary frst premolar tooth were generated: model C for the conventional monolithic IPS e.max CAD endocrown and model P for the novel bi-layered endocrown (PEKKTON ivory coping veneered with cemented IPS e.max CAD). A static occlusal compressive load was axially and centrally-applied. Modifed von Mises and maximum principal stress values on the remaining tooth structure, cement lines and restorative materials were evaluated separately. Weibull function was incorporated with FE analysis to calculate the long term failure probability. Results: Regarding stresses occurred in the remaining tooth structure (enamel and dentin), model P transmitted less stresses than model C. The individual enamel of model C showed about 5% and 40% risk of failure at normal and maximum occlusal load values, respectively, while for model P, it had no failure risk at both values. For dentin, model C showed about 13% failure risk at the normal masticatory force, while model P showed only 2%. At clenching value, model C dentin showed about 44% failure risk, while only 9% was resulted for model P. Conclusions: Compared to the conventional endocrown system, the positive impact of the studied novel endo- crown system on the stress distribution pattern and also on the survival/failure probability of the restored severely-destructed endodontically treated maxillary frst premolar teeth was refected (more tooth-friendly), not only at normal masticatory forces but also at the maximum functional loads. Clinical signifcance: The novel endocrown system using a PEKK coping veneered with cemented IPS e.max CAD can be considered a favorable option for restoration of severely-destructed endodontically treated premolar teeth, with more protection for residual tooth structure. Despite the conventional endocrown system may beneft the durability of tooth bonding, it should not be selected for restoration of clenching cases because of the too high overall failure risk. 1. Introduction The restoration of endodontically treated teeth (ETT), which are affected by a higher risk of biomechanical failure, remains a challenge (Schestatsky et al., 2019). Traditionally, a crown with a post-and-core has been used, but this procedure may interfere with the mechanical resistance of the tooth structure and increase the incidence of root fracture (Naumann et al., 2018). The requirement for using post and * Corresponding author: Fixed Prosthodontics Department, Faculty of Dentistry, Mansoura University, Egypt E-mail addresses: a.m.shams44@gmail.com (A. Shams), amal.sakrana@yahoo.com (A.A. Sakrana), Shaimaafarag@mans.edu.eg (S.A. Abo El-Farag), fatmaelerian@mans.edu.eg (F.A. Elerian), mutlu.ozcan@zzm.uzh.ch (M. ¨ Ozcan). Contents lists available at ScienceDirect Journal of the Mechanical Behavior of Biomedical Materials journal homepage: www.elsevier.com/locate/jmbbm https://doi.org/10.1016/j.jmbbm.2021.104853 Received 15 August 2021; Received in revised form 17 September 2021; Accepted 20 September 2021