Influence of implant-abutment connection design on bacterial microleakage and interfacial sealing: an in vitro and finite element study

This study assessed the sealing performance and microgap formation in hybrid and conical implant-abutment connections via integrated in vitro and finite element analyses. Three implant–abutment connection designs from a single manufacturer were evaluated: a hybrid design (Regular Neck, RN), a 15° internal conical connection (Regular CrossFit, RC), and a 7° internal conical connection (Regular Base, RB), designated as Groups G1, G2, and G3, respectively. Microgap dimensions at the implant-abutment interface were measured on assembled models using high-resolution industrial micro-computed tomography (micro-CT). Bacterial microleakage was evaluated by incubating torque-assembled complexes, which had been inoculated with a Porphyromonas gingivalis suspension, in culture medium; leakage was assessed at 72 h and 168 h. Finite element models—developed based on product specifications and micro-CT data, and validated against experimental results—were loaded according to ISO 14801:2016 to analyze the microgap behavior under simulated masticatory loading. Layer-by-layer analysis of 2 μm-resolution industrial CT scans revealed tight apposition at the implant–abutment interface in all three groups under standard assembly conditions, with no detectable gaps. Bacterial microleakage testing showed that all groups provided good sealing initially; however, after extending incubation from 72 h to 168 h, low-level bacterial leakage was observed in the G1 and G2 groups, with the G2 group exhibiting the most pronounced leakage ( P < 0.001; 4033 CFU/mL). In contrast, the G3 group demonstrated superior sealing performance ( P < 0.001), showing no detectable bacterial infiltration at either time point. Finite element analysis (FEA) revealed distinct microgap formation patterns under load: the G2 group exhibited the largest gap (3.92 μm), whereas the G1 group—owing to its external marginal lip design—showed no visible microgap under simulated loading conditions. Implant–abutment interface configuration significantly influences microgap formation and microleakage, with low-taper internal connections appearing to offer superior sealing performance.