## 4 Discussion  
The survival (100%) and success (93.7%) rates determined in the present study were similar to previous investigations examining multi-unit FDPs [3, 4]. For single crowns, slightly lower survival rates (92.8-98.5%) were reported after three years of intraoral use [8, 9]. In general, differences of survival rates for monolithic zirconia restorations might be explained by variations in the manufacturing process--particularly during occlusal adjustments [9]. Regarding complications, the extensive wear of zirconia or antagonists against zirconia has been described and discussed but might be neglectable when premising a properly polished zirconia surface [10, 11].  
Therefore, these considerations emphasize that monolithic occlusal surfaces fabricated from zirconia could be an interesting option for patients with bruxism. In these clinical scenarios, short-term clinical use was positively evaluated in several clinical trials [5, 12, 13]. In the present study, bruxism was not assessed according to the current international guidelines but was not explicitly excluded [14]. Another shortcoming of this study is the limited sample size, which was due to the long-lasting recruiting process of patients. Nevertheless, the results of this study suggest that the short-term clinical use of multi-unit FDPs fabricated from monolithic zirconia in the posterior region can be recommended.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Event**} & **Units/Facial** & \multirow{2}{*}{**Material**} & \multirow{2}{*}{**Cementation**} & \multirow{2}{*}{**Type of Event**} & **Time of Event** \\  & **Veneering** & & & & **(Months)** \\ \hline \multirow{2}{*}{**I complication**} & \multirow{2}{*}{3/yes} & Zenostar ZR translucent & \multirow{2}{*}{glass ionomer} & \multirow{2}{*}{technical, debonding} & \multirow{2}{*}{12} \\  & & (Wieland, Pforzheim, Germany) & & & \\ \hline \multirow{2}{*}{**II complication**} & \multirow{2}{*}{4/no} & Zenostar ZR translucent & \multirow{2}{*}{glass ionomer} & \multirow{2}{*}{biological, symptomatic} & \multirow{2}{*}{12} \\  & & (Wieland, Pforzheim, Germany) & & & \\ \hline \multirow{2}{*}{**III complication**} & \multirow{2}{*}{4/yes} & Lava Plus (3M, Saint Paul, MN, USA) & glass ionomer & \multirow{2}{*}{
\begin{tabular}{} \end{tabular} } & \multirow{2}{*}{14} \\  & & Paul, MN, USA) & & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Overview of the events.  
Figure 1: Kaplan–Meier curves for the survival and success of multi-unit fixed partial dentures with monolithic occlusal surfaces fabricated from zirconia (insertion \(n=50\); 2-year follow-up \(n=43\)).  
**Author Contributions:** E.P. data curation, investigation, formal analysis, software, visualization, and writing original draft; S.H. project administration, resources, supervision, validation, and writing review & editing; O.S. conceptualization, methodology, supervision, and writing review & editing; M.B.S. investigation, validation, and writing review & editing; A.S. investigation, validation, and writing review & editing; A.R. conceptualization, formal analysis, methodology, software, visualization, and writing review & editing. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Institutional Review Board of University of Leipzig (#298-14-25082018).  
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.  
Data Availability Statement: Data can be requested from the authors upon reasonable request.  
The authors acknowledge support from Leipzig University for Open Access Publishing.  
The authors declare no conflict of interest.