Suarez studied the outcome 3 years after the placement of ZrO2-ceramic restorations on 18 teeth. Only one tooth had failed after the experimental period because of radicular
fracture. According to this study, it is possible to consider zirconium oxide restorations as reliable for clinical use.74 Raigrodski et al. studied the durability of three-unit zirconia FPDs and asserted that these also showed a good outcome after 3 years.75 This result is in agreement with a study by Sailer et al., in which a similar outcome was found for restorations of this kind.76 A systematic review of the literature evaluated all-ceramic restorations survival rate in comparison with porcelain fused to metal and, inside all ceramic group, with zirconia ceramic restorations.77,78 5-years survival rate of all-ceramic restorations resulted 93.3%, whereas metal-ceramic restorations have a 5-years survival rate of 95.6%. In particular, all ceramic restorations on posterior teeth resulted to have the worst 5-year survival percentage (84.4%). These results did not considered zirconia restorations. On the other hand, when comparing Zr-ceramic restorations with other all-ceramic systems, zirconia frameworks resulted as the most reliable. The weakest point of these restorations resulted veneering chipping or cracking whereas other all-ceramic restorations showed a percentage of framework fracture. These results are in accordance with clinical indication for all ceramic restorations that indicates that all ceramic systems can be used preferably on anterior teeth; only zirconia showed adequate mechanical resistance for both anterior both posterior restorations.28 More clinical long term evaluation must be performed to understand behavior and reliability of zirconia compared with porcelain fused to metal restorations that are, nowadays, the most reliable system for FPD restorations.