## 4 Discussion  
Examinations in clinical practice reveal distal teeth with outdated direct restorations, necessitating their replacement with indirect restorations that are more resilient to masticatory forces. One of the modern materials of interest in recent years is the lithium dissilicate ceramic, e.Max Press (Ivoclar AG, Liechtenstein, Schaan). This material has shown esthetic properties approaching or equal to those of leucite-reinforced glass-ceramic materials but has significantly better strength properties and provides a high level of esthetic restoration for restorations in the distal zone. Researchers have conducted numerous in vitro studies on ceramic restorations, primarily focusing on areas such as fit, marginal accuracy, gap location, cement thickness [22; 23; 24], micro-leakage [25; 26; 27], nano-leakage, fracture resistance [28], and the impact of different cements [29; 30; 31]. Hybrid composite blocks (CERASMART), as an alternative material for single indirect restoration, overcome the disadvantages of direct composite resins and the lack of polymerization defects induced during their application [32]. Composite blocks with increased filler loading have better clinical performance under intraoral loading conditions [33]. Accordingly, some researchers suggested using materials with similar elastic moduli as dentin, whatever composite blocks are, to achieve a more reasonable stress distribution [34]. However, the efficiency of machinable composites is still controversial as their mechanical properties are lower than those of ceramics [35]. Figure 1: Graphical distribution of clinical cases by different period for grades “Bravo” and “Charlie” against criteria. Some papers discussed that lithium dislocates are not biologically inert, and that many have a similar cytotoxicity dynamic regardless of small differences in composition or processing [36]. Insufficiently effective enamel bonding or material fatigue can lead to failures due to the degradation and destruction of the adhesive layer and cementum. Therefore, the best possible adaptation of the tooth structure is required for these restorations, including the restoration margins and cavity shape [21; 37]. The results of this study clearly demonstrate that the main problem is the boundary between restoration and tooth structure. According to [PERSON] et al., every clinical study evaluating ceramic restorations reported some deterioration in the marginal zone's quality. Insufficient bonding to the enamel, degradation of the cementing agent, or fatigue of the materials may cause this [38]. The negative results observed for marginal adaptation occurred in the first few months. This fact clearly shows that the main concern in this type of restoration should be the initial adaptation of the ceramic material at the time of cementation and the first months of use, as well as the material and technique used to cement these restorations [39; 40; 41]. Scientific research and clinical experience confirm the use of adhesively fixed restorations to meet tooth esthetic demands, and we may have entered the so-called \"post-amalgam era\" described by [42]. Regarding the preparation of distal ceramic restorations, some authors have demonstrated that occlusal reduction leads to a reduced chance of restoration failure, thereby increasing the durability of the restoration [43; 44]. Fracture resistance tests are used to determine the forces that can induce fracture (cohesive or adhesive) in such restorations, thus enabling a proposed preparation design that can provide the greatest resistance. [PERSON] et al., in a controlled clinical trial, evaluated the clinical performance of ceramic inlays and onalys made with two systems: sintered (Duceram, Dentsply-Degussa = D) and pressed (IPS Empress, lvoclar = IPS) after two years. Eighty-six restorations (\(n\) = 86), forty-four IPS and forty-two D, were cemented in the mouths of 35 patients. A total of 27 premolars and 59 molars were prepared for Class II, for a total of 33 onalys and 53 inlays.