Fracture Strength of Implant Crowns after Different Zirconia Abutment Preparations

Zirconia implant abutments offer enhanced esthetics and promote biological sealing; however, the effect of mechanical processing due to preparation has not been investigated under chewing simulation. Objectives: The purpose of this study was to evaluate the fracture strength of single implant all-ceramic crown restorations luted to zirconia ceramic abutments with three different preparation designs under quasi-static and dynamic loading. Methods: 42 zirconia abutments (ZirDesign™, Astra Tech) were connected to corresponding implants (OsseoSpeed™ D: 4.5mm. L: 15 mm, Astra Tech) and received a 0.5 mm [Group A], a 0.7 mm [Group B] or a 0.9 mm [Group C] deep circumferential chamfer preparation in 14 specimens each. Lithium disilicate all-ceramic crowns (IPS e.max Press Ivoclar Vivadent) were adhesively cemented using a self-etching luting composite system (Multilink Automix, Ivoclar Vivadent) in order to restore a right maxillary central incisor. Subgroups of seven specimens each were subjected to quasi-static loading (S) at 135 degrees (0.5mm/min, Z010/TN2S, Zwick). Additional subgroups were subjected to dynamic-cyclic loading (C) at 135 degrees with 100N in a thermomechanical chewing simulator (Kausimulator, Willytech) up to 1.250.000 loading cycles followed by quasi-static loading until fracture. Results: All single implant all-ceramic crown restorations subjected to dynamic loading survived 1.250.000 loading cycles without abutment or crown fracture and without loss of retention. The mean fracture strengths under quasi-static loading in N were: Group SA: 384±84; Group SB: 294±95; Group SC: 332±52; Group CA: 403±67; Group CB: 374±75; Group CC: 373±105. Differences between groups and subgroups were not statistically significant (two-way ANOVA). Conclusion: This study showed that regardless the abutment preparation depth, single implant lithium disilicate crowns adhesively luted to zirconia abutments have the potential to withstand physiological maximal biting forces in the anterior area and to successfully serve for more than 5 years of simulated fatigue. (Supported by AstraTec Dental and Ivoclar Vivadent)