22 Clinical evidence and Science Steinebrunner et al. (2008) tested the influence of long-term dynamic loading on the fracture strengths of five different implant systems, one with external connection (Brånemark) and four with internal connections (FRIALIT-2, Replace Select, CAMLOG® and Screw-Vent) (11). The test specimens (molar) were subjected to dynamic alternating loading for a maximum of 1.2 million cycles in a dual axis chewing simulator before maximum loading was applied for fracture strength determination. The results demonstrated that the CAMLOG® and the Replace Select implant systems with deep internal tube-intube connections with cam-slot fixations had the highest fracture strength score (Tab. 2 and Fig. 16). During chewing, grinding and/or clenching not only axial forces occur on the crowns but also rotational torque which can lead to fractures. Using a torsion testing device Watanabe et al. (2015) investigated the torsional strength of CAMLOG® implant-abutment connections (12). Six specimens of each diameter (3.3, 3.8, 4.3, 5.0, 6.0) were tested with a rotational speed of 3.6°/min until deformation or fracture occurred. The device registered the maximal torque and the torsional yield strength, and each specimen was examined by scanning electron microscope after being tested. The implant diameters 3.3, 3.8, and 4.3 had comparable mean fracture torques. However, these were statistically lower than the ones of the diameters 5.0 and 6.0. The implant diameter and thickness of the implant wall seem to have a direct influence. The microscopic evaluations additionally revealed that the implants including indexing grooves remained intact while the notches of all the abutments were destroyed meaning that in the event of excessive torque the implant remained intact and most probably would not need to be explanted. Dynamic resistance (fatigue resistance) of Tube-in-Tube® connection Torsional resistance of Tube-in-Tube® connection Sc dynB Sc contrB Ca dynB Ca contrB Re dynB Re contrB Fr dynB Fr contrB Br dynB Br contrB 2000 1750 1500 1250 1000 750 500 250 0 Subgroups Fracture loads (N) ** ** Fig. 16_Box plot diagram of the quasistatic fracture strengths of the five tested implant systems: Br – Brånemark, Fr – Frialit-2, Re – Replace Select, Ca – CAMLOG®, Sc – Screw-Vent. dyn = after chewing simulation using dynamic loading; contr = without dynamic loading (adapted from Steinebrunner et al. 2008) Tab. 2_Survival rates of eight implants from each group in the dynamic, alternating loading test. The test was ended after 1 200 000 cycles (adapted from Steinebrunner et al. 2008) survival rates loading cycles failure [n] Replace Select 1.200.000 ± 0 0 Camlog® 1.200.000 ± 0 0 Branemark 954.300 ± 121.014 3 Compress 922.800 ± 102.242 3 Screw-Vent 913.200 ± 102.242 6 Frialit-2 627.300 ± 164.097 6 SCIENCE BEHIND THE IMPLANT-ABUTMENT CONNECTIONS
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