## 1 Introduction  
Cuspal coverage of posterior endodontically treated teeth is recommended to minimize tooth fracture and restore function [1; 2; 3]. However, the choice of appropriate restorative treatment modality in these situations is not simply reached. The reduced dental structural integrity in such cases is brought about by extensive caries, mechanical trauma, and/or existing large defective restorations [4; 5; 6; 7]. Caries lesions and extensive defective restorations extending gingivally and proximally in posterior teeth are of particular concern with highly variable prognoses, as they lead to inadvertent deviation from classical tooth preparation designs for definitive restorations [7; 8]. This led to full coverage crowns reportedly being the restorative treatment of choice for such cases [9; 10]. In a systematic review, single crowns versus direct restoration on endodontically treated teeth showed 81% and 63% survival rates, respectively [11]. Post and core is a well-established technique to restore endodontically treated teeth with significant loss of tooth structure [12]. Metal and ceramic posts both have an elastic modulus that is much higher than that of dentin, which could ultimately lead to root fracture when the tooth is overloaded. Fiber posts have been recommended for a more conservative approach, with their tooth-similar modulus of elasticity and the utilization of adhesive luting agents that could better distribute occlusal stresses along the tooth structure [13; 14; 15]. However, prefabricated posts require the removal of tooth structure during post space preparation, risk of root perforation, additional costs, and custom post and core technique require several visits [16]. Improvement in adhesive dentistry led to more conservative tooth preparation for endodontic treatment such as endocrowns [17]. Endocrown is a monoblock crown restoration retained by the intra-coronal pulp chamber space and bonding to the remaining tooth structure [18; 19]. Endocrown was introduced in 1995 as a more conservative and convenient treatment option requiring no intra-radicular post space preparation [15]. Since then, endocrowns have continued to grow in popularity among dental practitioners [20; 21; 22]. There is limited data in the literature concerning endocrowns that established a fully detailed standardized cavity depth within the pulp chamber [18; 23]. However, the Shoulder finish line combined with a short axial wall has been reportedly advantageous to the fracture resistance of endocrowns [19]. Additionally, the addition of a ferrule in the coronal preparation of the tooth to increase fracture resistance has been argued, with studies both advocating and/or advising against further tooth structure loss associated with such preparation design [9; 10; 20; 22; 24; 25; 26]. Generally, the endocrown preparation comprises a cervical butt-joint margin, cuspal reduction, and an intra-pulp-chamber conservative cavity [23; 24; 25]. [PERSON] and [PERSON] [26] found in their systematic review that endocrown for molars is a reliable alternative to conventional post-and-core crowns. A recent meta-analysis compared endocrown with conventional post-and-core, and crowns showed no significant difference in overall survival or success estimates [27]. Many studies evaluated the influence of different modifications of the endocrown design on fracture resistance, including adding ferrule design [20; 24; 25], different pulp chamber depths [10; 23; 28], various restorative materials, and types of teeth [6; 10; 21; 29; 30; 31; 32; 33]. Perception and determination of the extent and seriousness of failures of restorations and fixed prostheses into catastrophic or restorable failures often vary between individuals depending on the background and experience of the clinician [34; 35; 36]. Unfortunately, only a few studies have reported on the variation in detecting the extent and restorability of failures and cracks associated with conventional crowns or prostheses and, more specifically, endocrowns [37; 38; 39; 40].