## 4 Discussion  
The results of the present retrospective study are in line with the current literature, confirming that the use of zirconia for ISFCDPs showed good clinical outcomes, with high survival rates (88-100%). The major prosthetic complication (superficial chipping) was easily and directly restorable by the clinician with no necessity for laboratory repair [10]. Technical complications are more commonly reported in implant-supported prostheses than in those supported by natural teeth. Therefore, the design, material choice and production processes of ISFCDPs represent critical factors influencing the prosthesis' success over time [16]. The prosthetic design should allow for optimal load distribution and the minimization of implant micromovements; in particular, when immediate loading is considered, a rigid structure provides an optimal distribution of occlusal load, which prevents stress on the peri-implant bone, thus reducing osteointegration impairment [17]. It should be noted that most of the tissue-related complications (high probing depth, BoP, recessions) were reported on a single smoker patient who did not follow through with re-education in order to stop the smoking habit. Regarding tissue-related complications, a statistical comparison between different prosthetic designs could not be performed due to the low incidence rate: through the simple observation of available data, however, it appears that different prosthetic designs do not influence the incidence of tissue-related complications; smoking, on the other hand, can represent a factor influencing soft-tissue complications. Regarding prosthetic complications, only one incidence of the chipping of the pink gingiva on a zinc-on-zirc ISFCDP was reported for one patient: this may be due to the fact that pink gingiva is stratified and sintered upon the zirconia framework. \begin{table}
\begin{tabular}{c c} \hline \hline
**Satisfaction** & **Percentage** \\ \hline Completely satisfied & 78.57\% \\ Very satisfied & 14.53\% \\ Satisfied & 7.14\% \\ Not satisfied & 0\% \\ Would recommend treatment with ISFCDPs & 100\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: PROMS results. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Complications** & **Zirc-on-Zirc** & **Progressive** & **Zirconia-on-** \\
**ISFCDPs** & **Zirconia ISFCDPs** & **Titanium ISFCDPs** \\ \hline Presence of purulent discharge & \multirow{2}{*}{\(1/5\)} & \multirow{2}{*}{\(0/3\)} & \multirow{2}{*}{\(0/6\)} \\ (over total n\({}^{\circ}\) of ISFCDPs) & & & \\ \hline Presence of sites with PPD \textgreater{}3 mm but \textless{}5 mm & \multirow{2}{*}{\(2/5\)} & \multirow{2}{*}{\(2/3\)} & \multirow{2}{*}{\(0/6\)} \\ (over total n\({}^{\circ}\) of ISFCDPs) & & & \\ \hline Presence of sites with swelling and redness & \multirow{2}{*}{\(2/5\)} & \multirow{2}{*}{\(2/3\)} & \multirow{2}{*}{\(0/6\)} \\ (over total n\({}^{\circ}\) of ISFCDPs) & & & \\ \hline Sites with bleeding on probing & \multirow{2}{*}{\(2/5\)} & \multirow{2}{*}{\(2/3\)} & \multirow{2}{*}{\(0/6\)} \\ (over total n\({}^{\circ}\) of ISFCDPs) & & & \\ \hline Chipping & \multirow{2}{*}{\(1/5\)} & \multirow{2}{*}{\(0/3\)} & \multirow{2}{*}{\(0/3\)} \\ (over total n\({}^{\circ}\) of ISFCDPs) & & & \\ \hline Presence of at least one implant spire exposure & \multirow{2}{*}{\(2/5\)} & \multirow{2}{*}{\(2/3\)} & \multirow{2}{*}{\(2/6\)} \\ (over total n\({}^{\circ}\) of ISFCDPs) & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Complications stratified considering prosthetic design. It has been observed that zirconia frameworks show higher strain concentration compared to titanium frameworks, which may translate into a higher incidence of framework fracture over time [18]. Additionally, titanium is biocompatible and possesses high resistance to mechanical stresses and corrosion [18].