STATEMENT OF PROBLEMThe bonding of implant-supported prostheses is determined by abutment material, convergence angle, height, surface treatment, and luting agents. However, studies evaluating the bonding of luting agents to titanium base abutments with different heights under fatigue conditions are scarce.PURPOSEThe purpose of this in vitro study was to evaluate the retention of zirconia crowns bonded with different luting agents to titanium base abutments of different heights before and after fatigue testing.MATERIAL AND METHODSZirconia crowns were designed, milled, and distributed into 4 experimental groups according to the luting agents (G-Multi Primer/G-Cem LinkForce MP/GC and Scotchbond Universal/RelyX Ultimate SU/RU) and titanium base abutment heights (2.5 mm and 4 mm) (n=10). Pull-out testing was performed in a universal testing machine at a crosshead speed of 1 mm/min until crown displacement. Fatigue testing was performed by an electric precision fatigue simulator (1×106 cycles; 100 N; and 15 Hz), followed by pull-out testing of fatigued specimens. Collected data were statistically evaluated by using a linear mixed model after post hoc comparisons by the least significant difference test (α=.05).RESULTSLuting agents, abutment heights, and fatigue influenced the bonding retention of zirconia crowns to titanium base abutments. SU/RU agents promoted higher pull-out compared with MP/GC for both abutment heights before and after fatigue. Higher abutment height increased pull-out regarding lower abutment height for SU/RU materials before and after fatigue testing. Although fatigue had no significant effect on the pull-out of MP/GC, lower bond retention was observed for SU/RU after fatigue, regardless of abutment height.CONCLUSIONSLuting agent composition and the interaction with abutment height and fatigue influenced the retention of zirconia crowns to titanium base abutments.