Coronal restoration of endodontically-treated teeth (ETT) has been routinely done by placing full anatomic crowns in conjunction with or without post and core placement depending on the amount of the remaining tooth structure of the treated teeth [1]. Intracanal posts serve as intraradicular means of retention to a coronal foundation. However, the placements of posts can lead to root fractures and the invasive nature of this approach is irreversible and may hinder future interventions [2], [3]. The growing trend of minimally invasive dentistry with the recent advances in dental materials and adhesives has provided dentists with wider options of coronal coverage for ETT with no need for the post and core approach [4], [5].

Endocrowns are alternative more conservative restorations for ETT that were first described by Pissis in 1995 [6] as monoblock restorations consisting of porcelain crown-core without the need for a post. Bindl and Mormann in 1999 [7] expanded on this concept on severely destroyed coronal structure of posterior teeth. An endocrown restoration is a form of an onlay design for ETT with a butt joint cervical margin and an extension to fit into the pulp chamber. It gains retention to tooth structure macromechanically by extending to the axial walls of the pulp chamber of the ETT and micromechanically by luting the restoration with adhesive resin cement [8]. Endocrowns were found superior to full anatomical crowns when restoring ETT as reported by previous studies [9], [10]. They do not only conserve the tooth structure more than conventional crowns, but they are also specifically useful in restoring ETT with short anatomical crowns and insufficient retention ability for a full crown.

Endocrowns can be made of glass ceramics, polycrystalline ceramics, resin-matrix ceramics, or resin composites [11]. These materials are now available in the form of CAD-CAM blocks to be milled for chairside treatment. They are preferred to metal restorations due to their optimal esthetics, excellent mechanical properties, and biocompatibility with oral tissues [12], [13]. However, ceramic restorations are brittle in nature and are susceptible to fracture due to relatively lower modulus of elasticity and tensile strength [14]. Other factors that can lead to fracture of all ceramic restorations extend to involve restoration thickness, the elastic modulus of the abutment, preparation design, and residual stresses of the fabricated CAD-CAM material [15], [16], [17]. According to finite element and fractography analyses, during mastication, stresses are generated on the all-ceramic restorations and were reported to be higher near the cervical margin of the restoration than on the occlusal surface. Hence, the cervical design of prepared ETT for endocrowns is crucial for successful restoration [18], [19]. Shoulder finish line was found to increase the fracture resistance of endocrowns as reported by Taha et al. [20].

The mechanical behavior of endocrowns, with different cervical margin designs, can be investigated by different experimental tests [21]. However, other methods can provide more detailed information on stress distribution within each component of the tested structure with predictions of time-failure probability. Finite element analysis (FEA) can mathematically simulate the geometry and the loading conditions of the structure to be analyzed. It maps the different levels of stresses and deformations within any component of the model [22]. Weibull analysis can indicate the survival capacity of a tested specimen. It gives details on the Weibull modulus and characteristic strength of the tested component. Weibull modulus reflects the reliability of the materials so higher Weibull moduli ensure reliable use of the materials within its respective recommended indication range [23]. Characteristic strength is the strength at which 63.2% of tested specimens fail [24].

To the best of our knowledge, there is scarce or no data in the literature on how cervical margins of endocrowns can be affected by stresses generated during mastication. Therefore, this virtual study aimed to investigate the effect of different cervical margin designs and CAD-CAM materials on stress distribution and Weibull risk of fracture probability of endocrowns using finite element analysis and Weibull function. The null hypothesis tested was that neither cervical margin design nor the endocrown CAD-CAM material would affect 1- stress distribution in endocrown material and remaining tooth structure, and 2- Weibull failure probability in endocrown restorations.