## 4 Discussion  
The aim of the present retrospective single cohort study was to assess the clinical outcomes of immediately loaded maxillary and/or mandibular cross-arch metal-resin screw-retained fixed prostheses on four-to-five immediately placed dental implants without bone augmentation in totally edentulous maxillary and/or mandibular jaws with a 7-year follow-up, in order to evaluate whether four-to-five immediately loaded implants supporting fixed cross-arch prostheses could be a reliable treatment option to rehabilitate edentulous patients  
The choice to evaluate all clinical outcomes is aimed to analyze the average performance of this type of rehabilitation in a medium-to-long-term follow-up. The findings of the present study are encouraging since only 14 patients lost in total 21 implants up to 7 years after loading and all patients have their implant-supported fixed prostheses in function. Of the 549 implants inserted, 21 failed and 18 dropped out, showing an implant survival rate at seven years of 96%. More specifically, 3 patients out of 14 lost three implants each, while 1 patient lost 2 implants, and the remaining 10 patients lost 1 implant each. One-hundred-and-two prostheses were remade, which is a high number. However only 2 prostheses were remade because of implant failures, the other 33 prostheses had to be remade because of mechanical failures of the prostheses themselves. In particular, 25 of the original metal-resin prostheses constructed adding commercially available denture teeth had to be remade versus only 8 of the replacement monolithic metal-resin prostheses. This clearly indicates an insufficient robustness of the original delivered metal-resin prostheses. This type of prosthetic design should be considered as a provisional and not as a definitive prosthesis. Therefore, it was decided to start a free-of-charge recall program to replace the original metal-resin prostheses with a new and more robust design. A similar problem was described in a 5-year post-loading prospective study including 80 patients rehabilitated with immediately loaded screw-retained prostheses supported by only two mandibular implants [33]. Two different types of frameworks were used: titanium laser-welded rods \begin{table}
\begin{tabular}{c l} \hline \hline
**Patient Number** & **Type of Complication** \\ \hline
69 & Maximly prosthesis fractured once; mandibular prosthesis fractured once; prosthesis chipping \\
70 & Prosthesis chipping \\
71 & Prosthesis chipping \\
81 & Mandibular prosthesis fractured twice \\
86 & Prosthesis chipping \\
93 & Prosthesis chipping \\
94 & Monolithic mandibular prosthesis fractured twice \\
96 & Prosthesis chipping \\
98 & Prosthesis chipping \\
99 & Prosthesis chipping \\
100 & Prosthesis chipping \\
101 & Monolithic maxillary prosthesis fractured once \\
103 & Maximly prosthesis fractured once; mandibular prosthesis fractured once \\ \hline
**Total** & **86 complications in 42 patients** \\ \hline \hline \end{tabular}
\end{table} 
Table 7: _Cont._and cast silver-palladium alloy frameworks. Significantly, more mechanical complications occurred at laser-welded prostheses (19 patients out of 46 versus 6 patients out of 34; \(p=0.032\)). In particular, nine laser-welded prostheses versus only one cast prostheses had to be remade. Only those implants that achieved an insertion torque superior to 35 Ncm were immediately loaded. This appears to be a clinically sound decision. In fact, a randomized controlled split-mouth trial, evaluating the clinical outcome of immediately loaded implants placed with an insertion torque between 25 and 35 Ncm versus implants placed with a torque superior to 80 Ncm, showed statistically scarcer failure using insertion torque above 80 Ncm [34]. In addition, no implant inserted with a torque above 30 Ncm failed either.