In vitro performance of two-piece zirconia implant systems for anterior application

Objectives. To investigate the influence of the implant-abutment connection on the long-term in vitro performance and fracture resistance of two-piece zirconia implant systems for anterior application. Methods. Six groups of two-piece zirconia implant systems (n = 10/group) with screw-retained (5x) or bonded (1x) connections were restored with full-contour zirconia crowns. A two-piece screw-retained titanium system served as reference. For simulating anterior loading the specimens (n = 8/group) were mounted at an angle of 135 degrees in the chewing simulator, and subjected to thermal cycling (TC: 2 x 9000 x 5 degrees/55 degrees C) and mechanical loading (ML: 3.6 x 10(6) x 100 N). Failed restorations were examined (scanning electron microscopy). Fracture resistance and maximum bending stress of surviving restorations were determined. 2 specimens per group were loaded to fracture after 24h water storage without TCML. Data were statistically analyzed (ANOVA; Bonferroni; Kaplan-Meier-Log-Rank; alpha = 0.05). Results. The bonded zirconia system and the titanium reference survived TCML without any failures. Screw-retained zirconia systems showed fractures of abutments and/or implants, partly combined with screw fracture/loosening. Failure frequency (F) varied between the groups (F = 8 x : 3 groups, F= 3 x: 1 group, F =1 x : 1 group). The Log-Rank test showed significant (p = 0.000) differences. Fracture forces and maximum bending stresses (mean +/- standard deviation) differed significantly (ANOVA: p = 0.000) between 233.4 +/- 31.4 N/317.1 +/- 42.6 N/mm(2) and 404.3 +/- 15.1 N/549.2 +/- 20.5 N/mm(2). Fracture forces after TCML were similar to 24 h fracture forces. Significance. Screw-retained two-piece zirconia implant systems showed higher failure rates and lower fracture resistance than a screw-retained titanium system, and may be appropriate for clinical anterior requirements with limitations. Failures involved the abutment/implant region around the screw, indicating that the connecting design is crucial for clinical success. (C) 2016 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved