Clinical evidence and Science 17 A B C Fig. 11 A–C_(A) Rotational deviations, (B) vertical deviations, and (C) canting discrepancies after repeated detachment and re-attachment procedures. Median values. Pe1, Pe2, Pe3 test persons performing the test procedures. S1 Straumann Tissue Level, S2 Steri-Oss, S3 CAMLOG®, S4 Astra Tech, S5 Replace Select. (Semper et al. 2010, reproduced with kind permission of Quintessence Publishing co, Inc, USA) The mathematical considerations of Semper et al. 2009 described above can be directly transferred to the rotational fit of the CONELOG® connection as the positional index is ensured with the same concept of a cam-groove design. Low manufacturing tolerances combined with the geometric design lead to a high positional stability. Both, the theoretical considerations and the established experimental set-up developed by Semper et al. were used to investigate the positional stability of different implant systems with hand-tightened conical implant-abutment connections, i.e., NobelActive, Bone Level, Ankylos C/X, and CONELOG® (Semper-Hogg et al., 2013) (17). Although malposition of the abutment was found to be possible in all tested implant systems, the values for rotational displacement of the CONELOG® Implant System were significantly lower than the ones of the other three implant systems. The median rotation was 0.25°, and the maximum range was 2.14° in the CONELOG® implants. Since the analytical and experimental results for CONELOG® were in very good agreement, the authors concluded high-precision manufacturing for this implant system. The same experimental setup was used for a subsequent study investigating the influence of torque tightening on the positional stability of different conical implant-abutment connections (Semper et al. 2015) (18). The authors aimed to reveal if tightening of the abutment with a predefined torque during all laboratory and clinical procedures leads to more accurate positioning. The hypothesis had to be refuted since torque tightening caused similar displacements than with hand-tightening. In detail the range of the vertical displacement was higher compared to the hand-tightened implant-abutment complexes evaluated by Semper et al. 2013 (17) and was increased for implant systems with a cone angle >10°. The CONELOG® connection with its cam-groove indexing once more confirmed the lowest rotational freedom supporting the accuracy of fit of the prosthetic restoration (Fig. 12). Superior positional stability of the CONELOG® conical connection SCIENCE BEHIND THE IMPLANT-ABUTMENT CONNECTIONS
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