Purpose: Bacterial colonization of the inner part of dental implants has been reported in numerous studies. The aim of this in vitro study was to analyze the bacterial colonization of the implant lumen of two implant systems that were partly subjected to a thermal cycling regimen after three different approaches to reducing bacterial load: filling of the hollow parts with either a disinfectant agent, a setting sealing compound, or a nonsetting sealing compound. Materials and Methods: Two implant systems with internal connections (the Bego Semados RI implant, Bego, and the Xive S Plus Screw Implant, Dentsply) were used in this study. Before the corresponding abutments were fixed, the internal cavities were pretreated in four different ways (application of a 0.2% chlorhexidine gel, a special silicone, or a sealing grease, or no pretreatment). Half of the specimens were subjected to thermocycling. After incubation of the assemblies in a bacterial suspension of Escherichia coli for 1 week, the abutments were removed, and microbial samples of the internal aspects were collected; contamination was evaluated with quantitative realtime polymerase chain reaction (PCR). Results: No pretreatment could hinder bacterial leakage in all cases, but all applied agents could reduce bacterial burden significantly (P .05). There was less bacterial colonization after thermocycling (P .05), and the Xive implants showed better resistance against microbial contamination (P .05). Conclusion: The application of products to reduce bacterial invasion can help reduce bacterial load to a minimum and therefore can be helpful in minimizing the cofactors that contribute to the development of peri-implantitis. Keywords: bacterial contamination, bacterial leakage, implant-abutment connection, implant-abutment interface, in vitro, real-time PCR