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SCIENCE / CLINICAL RESEARCH 6 How does repeatedly tightening the abutment screw using a system-specific torque after repositioning of the abutment affect the positional stability of the implant-abutment connection? A new study investigated this question using six different implant systems. THE INFLUENCE OF THE TIGHTENING TORQUE OF CONICAL IMPLANT-ABUTMENT CONNECTIONS ON THE POSITIONAL STABILITY OF THE ABUTMENT Introduction When implant components are repeatedly tightened hand-tight, this produces posi- tional changes in the abutment [1, 2]. These changes should be as small as possible for implants with a conical inner connection if the abutment screw is tightened with a system-specific torque during all interme- diate prosthetic steps before insertion of the final suprastructure [3, 4]. The research group headed by Katja Nelson evaluated how repeatedly repositioning the abut- ment and tightening the abutment screw using a system-specific torque affected the rotation, vertical displacement, and cant- ing of the abutment using an established experimental setup [1, 2]. Materials and method Six commercial dental implant systems with conical implant-abutment con- nections and different cone angles (S1: Conelog 7.5°, S2: Nobel Active 12°, S3: Ankylos C/X 5.7°, S4: Astra Tech 11°, S5: Straumann Bone Level 15°, S6: Strau- mann Tissue Level 8°) were fixed in a pre- fabricated metal block at different angles to the longitudinal axis. Two testers disas- sembled and reassembled the abutment test body complexes twenty times each. After tightening with a system-specific torque and system-specific torque wrench, the position of the test body was meas- ured after each test using a coordinate measuring machine and the change in the height, the rotation, and the canting of the abutment were determined. Results A change in the abutment position was identified for all three parameters meas- ured (Fig. 1 to 3, Tab. 1) . The implant sys- tem evaluated had a significant effect on the results (p=0.001, p<0.001, p=0.006). The values for the vertical displacement ranged as far as 144 µm (S5). Rotation- al deviations of up to 6.02° (S4) were observed. The smallest deviations were seen for S1, S5, and S6. The canting mo- ments of S4 had the largest spread. Conclusion It is also not possible to achieve positional stability of the abutment by repeatedly tightening the abutment screw with a sys- tem-specific torque. Changes in the positi- on of the abutment during the restoration process lead to the prosthetic suprastruc- ture not fitting. Semper Hogg W, Zulauf K, Mehrhof J, Nelson K. (from the original publication in English) Fig. 1: Spread of the vertical displacement (image taken from Semper Hogg et al. (2015)). CONELOG Nobel Ankylos C/X Astra Tech Straumann Straumann Active Bone Level Tissue Level Vertical shift in µm 160 140 120 100 80 60 40 20 0 Fig. 2: Spread of the rotation (image taken from Semper Hogg et al. (2015)). CONELOG Nobel Ankylos C/X Astra Tech Straumann Straumann Active Bone Level Tissue Level Rotation in º 7 6 5 4 3 2 1 0