## 4 Discussion  
The survival and stability of implant restorations are directly related to the biomechanical characteristics of the materials used, such as the precision between the individual components, resistance, aesthetics, etc. [27; 28]. We are in agreement with [PERSON] et al. [3], in that implant suprastructure components prevent the implant and peri-implant tissue from overloading and severe implant complications. All samples successfully passed the fatigue test without any of the listed complications. This confirms the good mechanical behavior in laboratory settings from the data provided by [PERSON] et al. [29], who obtained identical results. After conducting compressive strength tests, it was found that there was a statistically significant difference between the test groups. The analysis of variance differentiated Group A as the one with the highest statistical difference, followed by Group B and Group C. This showed that the monolithic zirconium dioxide implant restorations on a titanium base demonstrated the highest mechanical resistance compared with the other study groups. As a probable reason, the greater thickness of the zirconia monolithic crown, which has also been stated by [PERSON] and [PERSON] [30], compared with the other restoration groups, can be considered. The standardized size of the titanium base required a greater thickness of the restoration material, whereas the customized titanium abutments in the other study groups had greater volumes at the expense of the reduced thickness of the implant restorations. All samples were defragmented into two halves, with Subgroup A1's fracture being in the neck area, circumferentially and horizontally. The reason for this may be the narrower cone-shaped transmucosal part of the implant restoration in the frontal area, supported by the cylindrical titanium base. This results from the narrow and high mucogingival profile of the implants, which is determined by the specific aesthetic requirements in the visible part of the oral cavity, namely, the sufficient gingival volume, which characterizes the concept of \"pink aesthetics\". In the other subgroups, we observed a longitudinal fracture that separated the monolithic restoration into two parts. The high twisting forces that act in the cervical region can also be a prerequisite for fracture of the restorations in the anterior segments of the mouth. In none of the cases was the implant abutment or connecting screw deformed, which is contrary to the study data provided by [PERSON] et al. [13] and [PERSON] and [PERSON] [31]. Consequently, the applied force broke the adhesive bond between the two components of the implant suprastructure. \begin{table}
\begin{tabular}{c c c c c c} \hline  & \multicolumn{2}{c}{**Group A**} & \multicolumn{2}{c}{**Group B**} & \multicolumn{2}{c}{**Group C**} \\ \cline{2-6}  & **Incisors** & **Molars** & **Incisors** & **Molars** & **Incisors** & **Molars** \\ \hline Mean value & 4790.2 & 6548.2 & 2217.4 & 4035.6 & 1734.4 & 1966.8 \\ \hline \(p\)-value & \multicolumn{2}{c}{0.002} & \multicolumn{2}{c}{0.009} & \multicolumn{2}{c}{0.602} \\ \hline \end{tabular}
\end{table} 
Table 4: Comparison of the compressive strengths of implant superstructures of incisors and upper maxillary molars in each of the study groups. It is important to analyze not only the mechanical resistance of the crown--abutment complex but its components as well. Groups B and C have the same size and material of custom abutments, but the crowns are made of different materials. The received data revealed higher values in both subgroups in the tests, 2217.4 for Group B for incisors (Subgroup B1) and 4035.6 for molars (Subgroup B2). It can be concluded that the different resistance, in that case, comes from the application of different crown materials. This is why we think zirconia prosthetic constructions over individual abutments could be considered more durable in compressive strength than lithium disilicate crowns.