Influence of Cementation-Mode on Reliability of Zirconia Implant-Abutment-Crown-Systems

Objectives: To investigate the reliability of zirconia implant-abutments* and zirconia-crowns* using mouth-motion step-stress fatigue and to determine the influence of cementation mode on fatigue resistance. Methods: Zirconia-abutments*(n=40) indicated for maxillary central incisors were CAD/CAM fabricated. All abutments were scanned and Y-TZP-Procera*-copings were produced. Zirconia-crowns (NobelRondo*-veneered) were either cemented conventionally (KetacCem, 3M-ESPE)(GIZ) (n=20) or adhesively luted (PanaviaF2.0, Kuraray Medical Inc.)(PAN) (n=20) on abutments screwed to Replace-Select-Tapered* implants (RP4.3x16mm) (*NobelBiocare). Step-Stress Accelerated Life Test (SSALT) with three stress-time-varying profiles was performed based on preliminary load to failure data (1.5-2Hz)(ELF-3300, Bose). Ultimate failure was defined by abutment or screw fracture. Specimens were inspected (polarized-specular-reflection-light-microscopy) at regular intervals to visualize crack propagation and failure mode. Reliability software (Alta Pro 7, Reliasoft) was employed. Results: Off-axis single-load-test resulted in porcelain chipping and abutment fracture. Radial crack propagation in the veneering porcelain was observed during fatigue while ultimate failure occurred by abutment or screw fracture. Weibull-stress-level-probability-curves were calculated and the reliability (2-sided at 90.0 % confidence bounds) for 50K cycles and a 350N load indicated a value of 0.44(0.67/0.19) for GIZ cemented crowns and 0.40(0.56/0.24) for PAN bonded restorations. Confidence bounds for the two test groups overlapped and therefore, did not demonstrate a significant difference. Conclusions: Based on current data, implant-supported zirconia crowns and abutments exhibit appropriate fatigue resistance independent of the cementation mode. Supported by Nobel Biocare, Goteborg, Sweden. christian.stappert@nyu.edu