CAMLOG and Science

CAMLOG&Science – Chapter 3 16 | 17 SEAL AND MICROLEAKAGE In the mid-90ies, several groups studied leakage at the implant-abutment interface. Jansen et al. (1995 and 1997) analyzed in vitro bacterial penetration from the bore of the implant-abutment connection to the external surroun- ding. Gross et al. (1999) used for a similar in vitro approach the dye gentian violet. Both research groups noticed that leakage was always a measurable phenomenon with differences in systems, samples and starting torques. Rack et al. (2010) used synchrotron-based radiography to visualize for the first time microgaps in internal conical implant-abutment connections and thereby proof their existence in vitro. High resolution radiographic images were taken under varying static mechanical loads of up to 100N. The images showed that the microgap size varied between 1 and 22 μm depending on the applied mechanical load. This finding indicates that also conical implant- abutment connections bear the risk of bacterial infiltrates, that may be responsible for inflammatory reactions at the implant-abutment interface as the measured microgap clearly exceeds the size of endotoxins and oral pathogens. The same research group (Rack et al., 2013) compared in a sub- sequent study the abutment stability during loading in three different new and fatigue-loaded conical implants (Dentsply Friadent Ankylos C and Ankylos Plus, Straumann ® Bone Level). They again used synchrotron-based radio- graphy in a test set-up very similar to the one described above. Before radiographic measurements were performed, fatigue-loaded implants had been generated by applying a force of up to 120N for 5 million cycles. In all three tested conical implant-abutment systems, microgaps were detected regardless of the amount of static mechanical load applied. After fatigue loading, the gap had even been increased and facilitated micromovement of the implant-abutment complex. Finally, the cone angle of the connection seemed to have an effect on abutment stability, i.e., flatter cones were more stable. Microgap enlargement due to fatigue loading was also demonstrated by Zabler et al. (in press). They tested four commercially available implant systems (Astra Tech, Straumann ® Bone Level, Dentsply Friadent Ankylos and Ankylos c/x) using x-ray phase contrast microtomography before and after cyclic extra- axial load of 120 N. Before loading, all implants with the exception of Ankylos c/x showed high tightness of the implant-abutment connection with only small gaps ranging from0.1 to 1.0 μm. However, loading resulted in an increase of the gap width. In addition, all systems showed plastic deformation at the implant-abutment connection, which was accompanied by the formation of broad and wide gaps around the pivotal point of the force vector. Harder et al. (2012) investigated the leakage of bacterial endotoxins from conical implant-abutment connections in two implant systems (Straumann ® Bone Level, CONELOG ® ) in vitro. The test specimens were inoculated with endotoxin and submerged in human whole blood. Endotoxin leakage was assessed in terms of changes in gene and protein expression involved in inflammatory processes in the blood cells. With both implant systems, leakage could be demonstrated even under unloaded conditions. The authors concluded that the good sealing capacity of conical implant-abutment connections should be reconsidered.