The purpose of this study was to test the bacterial penetration of screw access holes in monolithic zirconia implant crowns sealed using different methods. Twenty-four monolithic premolar zirconia crowns (IPS e.max ZirCAD) were divided into 4 groups (n = 6) according to the screw access hole filling method: unbonded composite (UBC), bonded composite (BC), airborne-particle abrasion and bonded composite (ABR-BC), and control without a screw access hole. Polytetrafluoroethylene tapes were placed inside the apical parts of the crowns. Crowns were fixed in plastic upper chambers with the occlusal part of the crown being inside the chamber and the apical part outside. A Streptococcus mutans bacterial suspension was poured into the upper chambers. The lower chambers were filled with bacterial culture media up to the apical parts of the crowns. Bacterial penetration through the screw access hole was assessed by visual inspection for turbidity in the lower chamber. The bacterial identity was confirmed on an agar plate culture. The statistical analysis was performed using the Fisher-Freeman-Halton exact test and pairwise comparisons with a z-test. In all test groups, bacterial penetration was observed by the eighth day (/6 specimens in BC, 3/6 in ABR-BC, and 6/6 in the UBC group). The control group stayed bacteria-free. Bacteria penetrated through the screw access hole of all specimens in the UBC group within 24 hours, which was significantly faster than in other groups (p = .011). Within the limitations of this study, it can be concluded that the sealing method of the screw access hole affects the penetration of S. mutans.