Behavior of Porcelain-Veneered Zirconium Oxide Restorations after Static Load

Objective: To study the behavior of three types of porcelain-veneered crowns with zirconia cores when subjected to static compressive loading. Methods: 80 individual full coverage crowns were studied. Crowns were divided in to four groups: Group I: Ivoclar IPS e.max Zir-CAD crowns (Core: IPS e.max ZirCAD; Porcelain Veneer: IPS e.max Ceram); Group II: Ivoclar IPS e.max ZirPress crowns (Core: IPS e.max ZirCAD; Porcelain Veneer: IPS e.max ZirPress); Group III: 3M ESPE Lava™ crowns (Core: Lava ™ Frame Zirconia ®; Porcelain Veneer: Lava ™ Ceram); Group IV (Control Group): metal-ceramic crowns with porcelain stratification layering technique (Core: Rexillium V nickel chrome alloy; Porcelain Veneer: IPS d.SIGN ceramic). The compression test was carried out using an Instron 4202 testing machine. The load applicator descended onto the sample exercising continuous vertical force with a crosshead speed of 0.5 mm per second, moving vertically downwards perpendicular to the occlusal zone. Results: In the porcelain veneer compressive test, Group IV, the control group, achieved the highest values (2310.49 N), closely followed by Group III (2210.95 N). Group II (1818.01 N) and Group I (1773.92 N) came in third and fourth place respectively. The different groups were compared to the control group applying Mann-Whitney non-parametric tests (ZirPress vs Control, p-value: 0.000; ZirCAD vs Control, p-value: 0.000; Lava™ vs Control, p-value: 0.565), taking a significance level of 5% (p-value=0.05). When the resistance of different porcelains is compared, excepting the control group (Lava™ vs ZirPress, p-value: 0.002; Lava™ vs ZirCAD, p-value: 0.001; ZirPress vs ZirCAD, p-value: 0.553). Conclusions: Resistance to compressive loading for the metal-ceramic and Lava™ samples obtained an average surface fracture value that was significantly greater in comparison with the ceramic coatings of ZirCAD and Zir-Press. All the porcelain veneers analyzed far surpassed average compression loads subjected during mastication as established by ISO 6872.