Clinical evidence and Science 19 Seal of the implant-abutment connections Existence of microgaps with every implant-abutment connection Microgaps between the implant and abutment favor microbial colonization of the implant-abutment interface. As a result, endotoxins may penetrate the surrounding tissue and may induce inflammatory processes leading to bone resorption and implant loss. Contrary to earlier publications with limited test possibilities several studies by e.g., Zipprich, Zabler and Rack (3–6) showed microgap formation evident in all implant-abutment connections regardless of their design. Visualizing and proving of the existence of microgaps in the internal conical implant-abutment connections for the first time was achieved by Rack et al. (2010) using synchrotron-based radiography (5). High resolution radiographic images were taken under varying static mechanical loads of up to 100 N on the systems Friadent Ankylos C/X, Ankylos Plus, and Straumann Bone Level. The images showed that the microgap size varied between 1 and 22 µm depending on the applied mechanical load. A subsequent study investigating the microgaps after fatigue loading revealed extended gaps with the possibility of micromovement of the implant-abutment complex (Rack et al., 2013) (6). Seal of the CAMLOG® implant-abutment connection The seal of CAMLOG® implants mounted with abutments was first measured by Steinebrunner et al. (2005) using dynamic loading in a chewing simulation test set-up including alternating load with 2 mm lateral movement on a 30° cusp slope with a force of 120N (7). Within five different implant-abutment connections, the Brånemark, FRIALIT-2, the Replace Select, CAMLOG® and the Screw-Vent, they checked migration of test microbes from the internal area of the connection in a sterile external culture medium during cyclic loading. The CAMLOG® Implant System reached a significantly higher number of chewing cycles than the FRIALIT-2 and Screw-Vent implant systems before microbial leakage was noticed (Fig. 14). A follow-up study by Zipprich et al. (2016) examined the bacterial microleakage from outside into the implant interior during dynamic loading (3). The study team developed a new experimental design to eliminate some limitations of the Steinebrunner test setup and to better simulate the clinical situation. Fourteen different implant systems, one half with conical the other with butt-joint connections, were loaded in a chewing simulator with gradually increased load (0 to 200N with steps of 25N). With the help of a channel drilled into the implant wall the lumen below the implant-abutment connection could be rinsed and analyzed for bacterial contamination after each loading step. The team concluded that in general conical implant-abutment connections showed better seal properties than butt-joint implant-abutment connections. However, the CAMLOG® SCREW-LINE implants tested (one group with Platform-Switching abutments, one group with platform matching abutments) did not show any microleakage in this study setup. SCIENCE BEHIND THE IMPLANT-ABUTMENT CONNECTIONS
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