Retentive strength of implant-supported CAD/CAM lithium disilicate crowns on zirconia custom abutments using six different cements

Objectives: Zirconia implant abutments and lithium disilicate (IPS e.max) crowns have been fabricated extensively for restoring dental implants but there has not been research published in the area of bond strength. The purpose of this study was to evaluate the retentive strength of implant-supported IPS e.max CAD/CAM crowns bonded to custom zirconia implant abutments using six cements. Materials and Methods: An optical scan of a zirconia custom abutment and a full coverage modified crown was designed using an E4D intraoral camera. 120 IPS e-max crowns were milled and bonded to 120 Zirconia abutment replicas using 6 cements: Panavia 21, Multilink Hybrid Abutment, RelyX Unicem 2, RelyX Luting Plus, Ketac Cem, and Premier Implant. The specimens were stored at 37°C in 100% humidity for 24 hours. Half of the specimens were thermocycled for 500 cycles according to ISO/TS11405 intermediate aging protocol. The retentive force was measured using a pull-out test with a universal testing machine, set at 0.5mm/min crosshead speed. Mean retentive strengths (MRS) were calculated using 2-way ANOVA. Fisher's PLSD test was performed to evaluate if there were statistically significant differences. Failure mode of cement was also recorded. Results: MRS after 24-hour storage were: Panavia 21 (3.1 MPa) > Multilink Hybrid Abutment (2.5 MPa) = Unicem 2 (2.5 MPa) > RelyX Luting (1.3 MPa) > Ketac Cem (0.9 MPa) > Premier Implant (0.5 MPa). MRS after thermocycling were: Multilink Hybrid Abutment (2.5 MPa) > Panavia 21 (2.2 MPa) > RelyX Luting (1.8 MPa) > Ketac Cem (1.4 MPa) > Unicem 2 (1.1 MPa) > Premier Implant (0.3 MPa). Panavia 21 had the highest MRS after 24-hour storage (p<0.0001), but after thermocycling Multilink Hybrid Abutment showed the highest MRS (p<0.0001). Unicem 2 showed a significant decrease after thermocycling (p<0.05). Most cement residues retained on the zirconia abutments for Panavia 21 while the others were on the IPS e.max crowns. Conclusions: Of the six cements tested, Multilink hybrid Abutment was the most retentive after thermocycling. The most retrievable restorations were cemented with Premier Implant temporary cement. Thermocycling simulates the oral environment, and Unicem 2 lost the most retention.